Vibratory and Impact-Vibration Hammer Technology

Vulcan was involved in a great deal of research on vibratory technology. Most of this is presented on this page. It can be broken down into three parts:

  • Articles and Monographs written by Vulcan personnel, during and after Vulcan’s existence
  • Material from the Soviet Union and Russia, the home of vibratory and impact-vibration technology
  • Other material, including research projects

Unless otherwise noted, the links below are to pdf files.

Articles and Monographs Written by Vulcan Personnel

Development of a Parameter Selection Method for Vibratory Pile Driver Design with Hammer Suspension

This paper details the mathematical modelling of vibratory pile driving systems using a linear model with the objective of obtaining a closed form solution to estimate either the power requirement of the machine, the torque requirement of the motor driving the eccentrics, or both. It begins by reviewing the system model for the system without a suspension, which is used to enable connection of the vibrating machine with a crane, a mast of a dedicated machine, or an excavator. It proceeds to solve the equations of motion for a system with a suspension, using Laplace transforms and solving the inverse transform using residues and complex integration. The model indicates that, under certain conditions, both the amplitude and the power consumption of the system increase with a suspension, but the results make the practical implications of the result uncertain. Finally a simple set of equations is developed for actual vibratory design which results in the suspension being ignored and the necessary torque of the driving motor computed.

Letter to Michael O’Neill re Wave Equation Analysis Program for Vibratory Hammers

Vulcan correspondence which gives important information for wave equation analysis of vibratory hammers, along with other important information on vibratory hammer theory.Note: Dr. Michael O’Neill was one of the greats of the geotechnical industry, both as an engineer and as a person. This is the “memorial book” collected after he passed away suddenly in 2003.

Survey of Methods for Computing the Power Transmission of Vibratory Hammers

This paper is a survey of analytical methods used to calculate the power consumption and transmission of vibratory hammers used in the installation of piles. The paper discusses the parameters, derivation, and comparative usefulness of various methods of computing the power consumption of these machines. The paper also discusses the importance of torque calculations as well as power calculations. The power consumption of vibratory hammers is important because a) many of the existing methods for estimating the resistance and/or bearing capacity of the piles use power consumption as a parameter, and b) methods being developed to determine the bearing capacity and drivability of piles driven by vibration will probably use these methods. Suggestions for further research in this field, including factors to consider in modelling power transmission and consumption, are set forth.

Vibratory and Impact-Vibration Pile Driving Equipment

This article is an overview of the application and vibratory and impact-vibration pile driving equipment. It includes the history of the development of the equipment, the types of piles that can be driven with this type of equipment, a description of the safe operation of the equipment, and an extensive treatment of methods of determining drivability and capacity of piles driven by vibratory and impact-vibration hammers.

Material from the Soviet Union and Russia

Improvement of the Capacity of Vibrating Hammers for Driving Pipes Into Soils (article in English)

M.G. Tseitlin, VNIIGS
Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 6-9, May-June, 1973

It is known that vibrating hammers (impact-vibration hammers) are highly effective for driving pipes. However, their wide use is prevented by their insufficient durability and high energy consumption, which are determined mainly by the high velocity of the hammer at the moment of impact against the driven element. The results of the investigations described in this article indicate that the driving capacity of vibrating hammers in soils of medium density can be iniproved without increasing the impact velocily, by increasing the length of the path travelled jointly by the hammer and the pipe after each blow. When the vibrating hammer operates under longitudinal action, the above-mentioned effect can be obtained by adjusting the force in the springs, in case of large negative gaps. High driving capacity is possessed also by vibating hammers operating under longitudinal-rotary action, in which the path traveled jointly by the hammer and the pipe is increased. as a result of torsional vibrations of the driven pipe.

Russian Impact-Vibration Pile Driving Equipment (web page)

This article is an overview of both the development and present status of impact-vibration hammer, with special emphasis on the situation in the Russian Federation. This last point is significant because the technology was originally developed there. An appendix to explain unfamiliar aspects of the old Soviet economic system as they relate to this article is also included, as is a bibliography.

Vibratory Machines for Sinking Piles: Vibratory Pile Drivers (web page format)

An extract from a Soviet book on the subject of vibratory pile drivers, showing the types of vibratory drivers in use in the late Soviet period and also some of the other machines available (especially the Japanese units.) Also includes the Savinov and Luskin method for sizing a vibratory hammer for a particular application.

Vibro-Engineering and the Technology of Piling and Boring Work

Mikhail Grigorevich (M.G.) Tseitlin
Vladimir Vladimirovich (V.V.) Verstov
Gennady Grigorevich (G.G.) Azbel
Stroiizdat, Leningrad Otdelenie
Leningrad, 1987
(Translated from the Russian)

A comprehensive treatment of all aspects of vibratory and impact-vibratory technology and its application to the installation of piles and caissons for bored piles.

  1. General Information
  2. Foundation of the theory of vibratory driving and extraction
  3. Vibration and Impact Vibration Immersion
  4. Vibratory technology for production piling
  5. Vibratory Technology of the manufacture drilled works for contractors
  6. Vibratory technology for the production of some appearances of special construction works

The English translation covers about half of the work.

Other Materials

Axial Response of Three Vibratory and Three Impact Driven H-Piles in Sand

Jean-Louis Briaud
Larry M. Tucker
Briaud Engineers

U.S. Army Corps of Engineeers
Miscellaneous Paper GL-88-28
August 1988

A research program to compare the ultimate axial capacity of vibratory and iumpact driven H-piles in sand was conducted at a San Francisco, CA, site. The effects of time-lapse after driving was also studied. The piles were instrumented so that both pile tip loads and load transfer along the pile could be determined.

Comparison of Axial Capacity of Vibratory-Driven Piles to Impact-Driven Piles

Reed L. Mosher
U.S. Army Corps of Engineers
Waterways Experiement Station

Technical Report ITL-87-7
September 1987

This technical report documents the findings of an investigation into the effects on the axial capacity of piles driven by vibratory pile – driving hammers. The investigation stems from the concern that foundation engineers in the Lower Mississippi Valley Division of the US Army Corps of Engineers had over the unexpected low capacities found during the pile test at Red River Lock and Dam No. 1. While driving piles with a vibratory hammer increases productivity up to 10 to 20 times over the use of an impact hammer, there is a significant reduction in the axial capacity of the piles driven with a vibratory hammer. The study revealed that this reduction was a result of a loss in the load carried by the tip . The report documents a number of pile testing programs t h a t were performed to make direct comparison between vibratory-driven piles and impact-driven piles.

Driveability and Load Transfer Characteristics of Vibro-Driven Piles

Note: this contains much of the data shown in NCHRP 316.

Daniel O. Wong
University of Houston
December 1988

Piles installed by vibration have been a foundation practice since the early 1930’s. The method has not gained wide acceptance in the U.S. because of limited understanding on driveability and load transfer mechanisms. Restriking vibro-drlven piles is very often required for analysis. A large scale laboratory study on the basic behavior of displacement piles installed with vibratory drivers compared to impact hammers and the influence of various soil and driver parameters on the behavior of piles was undertaken.

In order to achieve the desired goals, a model testing system consisting of a long sand column capable of simulating deep sand deposits, instrumented 4-in.-diameter closed-ended pile, vibratory driver and impact hammer was designed and built. Among the driver parameters investigated are frequency, bias mass and dynamic force (eccentric moment) and sand parameters such as grain size, relative density (65 and 90%) and in-situ effective stress (10 and 20 psi).

The optimum frequency for the testing conditions. selected based on the maximum rate of penetration, was 20 Hz and was independent of bias mass and soil conditions. Among the variables investigated, the relative density of sand had the greatest effect on the rate of penetration during vibro-driving. Penetration rate also increased with increasing bias mass and decreasing in-situ horizontal stress. Impact-driven piles in sand with 85% relative density developed higher resistance in compression than the vibro-driven piles, but vibro-driven plies exhibited better static performance in sand with 90% relative density. Restriking of vibro-driven piles in sand does not significantly change the compression capacity.

Four design methods to predict the bearing capacity of a vibro-driven pile have been propcsed and a procedure to select a vlbro-driver for given soil conditions Is recommended. A computer program has also been developed to model vibratory driving.

Evaluation of Bearing Capacity of Vibro-Driven Piles from Laboratory Experiments

Michael W. O’Neilll, Cumaraswamy Vipulanandan, and Daniel O. Wong
University of Houston
1990

Representative methods for predicting the bearing capacity of piles driven by vibration are reviewed briefly, and a need to establish procedures based more closely on soil properties is established. In order to investigate the influence of soil properties on piles installed by vibration, a large-scale model study was conducted in which piles were driven into a pressure chamber to simulate in situ stress conditions and subjected to loading tests. The soil, vibrator and pile properties were closely controlled. Methods were developed from pile mechanics considerations and the test data (a) to predict pile capacity and (b) to select vibrator characteristics to drive piles of known target capacities. These methods are expressed in the form of simple equations that can be applied by designers having appropriate linowledge of soil, pile and vibrator conditions. While every attempt was made in the laboratory study to simulate field conditions, field verification/calibration of the capacity prediction methods are necessary before they can be applied in practice.

Modelling of Penetration Resistance and Static Capacity of Piles Driven by Vibration at the Pioneer Freezer Site, Syracuse, NY, and Laboratory Model Tests

Michael W, O’Neill, Curnaraswmy Vipulanandan, and Reda Moulai-Khatir,
University of Houston
October 1991

Vibratory driving is a technique used for driving piles into the ground by imparting to the pile a small longitudinal vibratory motion of a predetermined frequency and displacement amplitude from a driving unit. The vibrations serve to reduce the ground resistance, allowing penetration under the action of a relatively small surcharge, or “biased” load, also provided by the driving unit, or “hammer.” Vibratory driving is especially effective in cohesionless soils and is favored over impact driving from the perspective of rapid and silent operation. However, the use of vibratory drivers has been hampered by the inability of inspection agencies to verify the bearing capacity of installed piles in the manner afforded by wave equation analysis of impact-driven piles. The current accepted practice requires restriking the vibro-driven piles with an impact hammer to verify the capacity by means of wave equation analysis or by direct dynamic monitoring. This operation increases the time required to install piles with the use of vibratory drivers and makes the process less attractive economically than it would be if some straightforward procedure were available to evaluate capacity from pile and hammer properties and simple parameters, such as rate of penetration at full penetration, that can be observed by an on-site inspector. The study reported herein aims to extend the one-dimensional wave equation approach to predict the capacity of several full-scale and model piles to demonstrate that an appropriately modified wave equation program can be used in certain cases. Further research is necessary to generalize the results of this study.

Vibro-Driveability: A Field Study of Vibratory Driven Sheet Piles in Non-Cohesive Soils

Kenneth Viking
Royal Institute of Technology

Webmaster’s note: this study is, in our opinion, the most comprehensive study to date on the subject of vibro-driveability of piles. It includes a complete literature search, laboratory testing and field testing.

The most commonly used method to drive sheet piles is the vibratory driving technique; main reasons being the shorter installation time, less disturbance to the surroundings, and reduced damages to the driven sheet pile compared to impact driven sheet piles. It has become a desire to better predict the driveability, i.e. determine if it is possible to drive a certain sheet pile profile to desired penetration depth in a certain soil profile. The main problem to fulfil this desire lies in the lack of understanding of the fundamental mechanism behind the degradation of the penetrative soil resistance due to the continuous sheet pile motion.This thesis constitutes the final report in the research project Vibro-driveability and dynamic soil resistance in non-cohesive soils within the Swedish Building Contractors Foundation (SBUF). This thesis presents the results of a study of full-scale, vibratory-driven sheet piles in non-cohesive soils. The primary objective of the study has been to develop a better understanding of the different mechanism and dynamic pile-soil interaction during vibratory installation of steel sheet piles. This has been achieved by dividing the present study into the following three parts: (i) a literature review, (ii) an experimental part, and finally (iii) an analytical part, where the results of two pre-existing prediction (simulation) models were compared with the results of the experimental study. The thesis presents the results of a limited series of full-scale field tests where both the driveability and the ground vibrations generated during driving have been continuously monitored. In the light of these results, the thesis discusses how the complexity of vibro-driveability and the prediction of the induced vibration can be broken down and described in three subparts, namely: vibrator-related, sheet-pile-related, and soil-related parameters.

The fundamental mechanisms behind the shear strength reduction in cohesionless soils using the vibratory-technique to drive sheet piles have been explained. It appears as though the key phenomena behind the shear strength reduction observed during the vibratory installation of piles is not related solely to the liquefaction induced in saturated granular soils, since the shear strength reduction has also been found in laboratory tests on air-dried granular soils.

Previously neglected, vibrator-equipment-related parameters, as well as sheetpile- related parameters significantly affecting the vibro-driveability have been discussed in the light of the effects revealed during the field tests.

The vibro-driveability results from the field studies have been compared with the two vibro-driveability models, Vibdrive and Vipere, both of which were developed at University Louvain-la-Neuve, Belgium. The semi-empirical Vibdrive model has been used to study the predicted magnitude of the soil shear-strength reduction (the penetrative resistance) during vibratory driving, and how this is affected by variation in the two fundamental mechanisms. The semi-numerical Vipere model has been used to study the predicted magnitude of (i) the variation of soil resistance over time, and (ii) penetration speed versus depth during vibratory driving. These results have been correlated with the field test results.

Vibratory Pile Driving Predictions

Geert Jonker and Simon Hartog, ICE
1988

The installation and extraction of sheetpiles and foundation piles using vibratory pile driving hammers is a commonly applied technique.

In general, the choice of the size of the hammer is based on experience. In situations where experience is limited an incorrect selection may lead to premature refusal resp. nonperformance situations, unexpectedly resulting in an increase in job-site costs.

Whereas in the past vibratory hammers were used mainly for temporary foundation purposes or for horizontally loaded structures only, there is a certain tendancy to use these hammers also for permanent systems as an alternative to impact hammers. The reason for this is not only the spetific advantages of the vibratory hammer such as:

  • light in weight
  • high rate of penetration
  • low noise level
  • low ground acceleration level

but also because the techniques for soil vibrations and vibratory hammers are understood much better than a decade or two ago.

In this respect the vibratory hammer lags far behind the impact hammer where for instance the computer simulation of the pile driving system started in the early sixties by E.A.L. Smith.

It is approximately only 3 years ago that a similar model for vibratory hammers was initiated by TNO in The Netherlands and whose programme has been fully operational since a year ago. This paper will describe the simulation programme and its use in the pile driving prediction calculations in more detail in the sections to follow.

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Vibratory Machines for Sinking Piles: Vibratory Pile Drivers

Extract from
Erofeev, L.V., Smorodinov, M.I., Fedorov, B.S., Vyazovskii, V.N., and Villumsen, V.V. (1985) Machines and Equipment for the Installation of Shallow and Deep Foundations. (In Russian) Second Edition, Mashinostrenie, Moscow, pp. 95-111.

Webmaster’s Note

This article is an extract from the above referenced book, published in the Soviet Union in the mid-1980’s. It is a valuable document, containing information about vibratory hammers (Soviet and otherwise) not found anywhere else. But some explanation is necessary on the text.

The book itself was furnished by Lev V. Erofeev, the author of this section. The translation was commissioned by Vulcan Iron Works in the late 1980’s.

Although the information is valuable, the editing of the Soviet original is of poor quality, so much so that I told Mr. Erofeev that his editor must have been drinking a lot of vodka when putting the book together. In this edition I have tried to eliminate some of the more egregious howlers (such as confusing millimetres with metres) but the reader should take great care.

The Savinov and Luskin method shown at the end of the text is given in a possibly more understandable form in my monograph Vibratory and Impact-Vibration Pile Driving Equipment. Of course, it is shown by its original authors here.

Some of the equipment described in this monograph–and also some Russian diesel hammers–are shown in the video below, taken in Lyubertsy, outside of Moscow, in December 1992. The various types and models of equipment–including some impact-vibration equipment–is labelled in the video. Mr. Erofeev is in the video, in the blue tobaggan, describing the equipment.


Vibratory pile drivers and vibratory hammers are used for sinking steel sheet piles and wooden piles into the ground and, under certain soil conditions, for sinking reinforced concrete piles. The former machines operate on vibratory action, while the latter operate by vibration and impact.

In accordance with their purpose, vibratory pile drivers are divided into two groups: low-frequency machines, with a vibrator frequency of 300 to 500 per minute, and high-frequency machines, with vibrational frequencies of 700 to 1,500 per minute. The former are intended for sinking elements with a high frontal resistance and considerable mass (reinforced concrete piles and tubular piles), while the latter are for elements with a relatively low frontal resistance and low mass (steel sheet piles, pipes, etc.).

All types of vibratory pile drivers have directional vibration exciters (two- or four-shaft) and a device for rigid connection of the vibration exciter to the element being inserted into the ground—the driving cap.

The shafts are put into rotation by an electric motor (or motors)— a squirrel-cage motor or phase-wound motor—with the help of a pinion, belt, or chain transmission.

Centrifugal force created by the vibration exciter with the turning of the shafts with unbalanced loads, or eccentrics, attached to them causes the pile to vibrate. The characteristics of these vibrations depend on the static moment of the eccentrics, the frequency of the vibrations as determined by the angular velocity, the weight of the vibratory pile driver-pile system, and the properties of the soil. The amplitude of the system’s vibrations is decisive for insertion of the pile. At a low vibrational amplitude, displacement of the soil with respect to the side surface of the element being inserted does not exceed the limit of its elastic deformation and the pile is not sunk into the ground. As the amplitude of the vibrations increases, residual deformation of the soil occurs and the pile begins to slip relative to the soil, i.e. it is sunk into the ground.

The frequency of the vibrations also influences the effectiveness with which the pile is sunk. At relatively low frequencies (up to 200 vibrations per minute), at first there are weak elastic vibrations of the pile and of the ground mass around the equilibrium position. Soil layers adjacent to the surface of the element being inserted will be displaced along with the element and the element is not sunk at all. As the frequency of the vibrations increases up to a certain value, the element being inserted and the ground begin to be displaced relative to each other, i.e. the sinking process begins.

With regard to design, it is possible to distinguish a certain group of vibratory pile drivers in which, unlike others (the so-called simplest vibratory pile drivers), the electric motors are not connected rigidly to the vibration exciter, but they are connected by means of an elastic suspension. Here, the rigidity of the suspension is chosen in such a way that the natural vibrational frequency of the electric motor on springs is considerably (by at least one order of magnitude) lower that the rotational frequency of the eccentric shafts. If this condition is met, the spring-loaded part of the vibratory pile driver experiences considerably less vibration. In addition, with a setup of this type, the mass of the electric motor is excluded from the mass of the vibrating parts. This makes it possible to increase somewhat the vibrational amplitude without increasing the power of the electric motor.

Of the vibratory pile drivers currently being produced, only the high-frequency machines are constructed in this manner and they are called vibratory pile drivers with a spring-mounted overweight. Their primary purpose is to drive metallic sheet piles.

The technical characteristics of vibratory pile drivers with a spring-mounted overweight are presented in Table 4.22.

Table 4.22. Technical data on vibratory pile drivers with spring-mounted static parts and mechanical driving cap.
Characteristic VPP-2A VPP-4A VPP-5 VPP-6
Eccentric value, kg-cm 1 0.55 0.35 0.25
Frequency, Vibrations per minute 1,500 1,300-1,500 1,500 1,200-1,500
Greatest dynamic force, kN 250 140 83 62
Mass of vibrating parts, tons 0.7 0.4 0.35 0.25
Mass of static parts (with electric motor), tons 1.5 0.8 0.85 0.5
Amplitude of vibrations (without pile), mm 14.3 13.8 10 10
Power of electric motor, kW 40 28 16 11
Dimensions, mm l,270 x 800 l,000 x 960 l,250 x 680 830 x 760
Height (without driving cap), mm 2,250 1,150 1,250 1,380
Mass of pile driver, tons 2.2 1.2 1.2 0.75

The simplest type of vibratory pile driver mentioned above is characterized by a relatively high eccentric value and considerable mass. In the USSR, low-frequency vibratory pile drivers of several standard sizes are produced and used. Their technical characteristics are presented in Table 4.23.

Table 4.23. Technical data on low-frequency vibratory pile drivers.
Characteristic SP-42B VP-3M VI-722 VPM-170
Eccentric value, kg -cm 9.3 26.3 22.4/29 50
Frequency, vibrations per minute 420 408 437/ 556 475/ 550
Dynamic force, kN 250 44 480/ 620 1,250/ 1,700
Electric motors: power, kW 60 100 120 200
Number of electric motors 1 1 2 1
Amplitude of vibrations (without pile), mm 20 36 36 50
Dimensions, mm:
length 1,321 1,550 2,000 1,435
width 1,290 1,410 2,000 1,800
height 2,778 2,130 3,420 3,400
Mass of vibratory pile driver (without driving cap and control panel), kg 4,560 7,200 8,000 15,600

Notes:

  1. The VPM-170 vibratory pile driver has a mechanical driving cap, the others have hydraulic driving caps.
  2. The eccentric, vibrational frequency, and force of the VI-722 vibratory pile driver change when the direction of rotation of the electric motor’s shaft changes.
  3. When the transmission pinions of the VPM-170 are changed, the vibrational frequency and the force change.

The SP-42B vibratory pile driver is intended for driving reinforced concrete piles with cross sections of 30×30 and 35×35 cm weighing 2 tons, steel piles (I-beams Nos. 45-55), and “Larsen IV” and “Larsen V” sheet piles into weak, water-saturated soils. This machine is an improved model of the previously produced VP-1 vibratory pile driver [15]. This vibratory pile driver consists of an electric motor, a vibration exciter whose welded body contains two pairs of shafts with unbalanced weights loads (eccentrics), and a removable hydraulic driving cap. A three-phase vibration resistant VMT-6 electric motor with a wound rotor is attached to the upper plate of the vibration exciter. It transmits rotary motion to the unbalanced shafts through rack and pinion gears. Pinion gearing provides synchronization of the rotary motion.

The vibratory pile driver is outfitted with two types of hydraulic driving caps: one for driving reinforced concrete piles and one for driving the metallic elements mentioned above. The side surface of the vibratory pile driver has two pairs of grips for suspending the vibratory pile driver on pile driver masts (for masts with guides that are 625 mm wide).

The VI-722 vibratory pile driver is designed for driving reinforced concrete piles with a cross section of 40×40 cm and tubular piles up to 1 m in diameter weighing up to 20 tons into class B soil (according to the classification in ‘Edinye normy i rastsenki na stroitel’nye raboty’ [Unified Standards and Estimates in Construction Work]).

The mechanical diagram of the Vl-722 vibratory pile driver (Figure 4.16) is similar to that of the VP-3M, but it differs from the latter in that it has two VMT-6 vibration resistant electric motors that transmit rotary motion to the unbalanced shafts through a chain coupling, a reduction gear, and a system of gear wheels. The use of a reduction gear makes it possible to produce two rotational frequencies of the unbalanced shafts (437 and 556 rpm).

Figure 4.16. The VI-722 two-frequency vibratory pile driver.

The driving cap (see figure 4.17) is attached to the lower plate of the vibration exciter by means of bolts and it is actuated by a hydraulic station attached to its upper plate. The hydraulic station has two gear-type pumps (both with clockwise or both with counterclockwise rotation). The working fluid is fed into the one cavity or the other of the hydraulic cylinder when the rotation of the electric motor of the hydraulic drive is reversed (3-kW squirrel-cage induction motor).

Figure 4.17. Diagram of wedge-type driving cap of vibratory pile driver.

The driving cap for tubular piles differs from the driving cap for square piles only in the number of wedges. The former has six wedges and the latter has four. The wedges clamp the driving cap to the pile when they move downward along the slanted guides of the welded casing of the driving cap and release the pile when they move upward. Movement of the wedges (1) (figure 4.17) is accomplished by hydraulic cylinder (2) by way of lever (3) and elastic coupling (4).

The most powerful vibratory pile driver produced in the USSR and abroad is the VPM-170 vibratory pile driver (technical data presented in Table 4.23). Its vibration exciter has eight unbalanced shafts arranged in pairs in four vertical tiers (figure 4.18). The unbalanced shafts are put into rotational motion by a series-produced electric motor (the AK-113-8M) through a set of pinions and a rotational frequency switching unit that makes it possible to have two eccentric rotational frequencies and two different force values. The second (from the bottom) row of pinions in the gearing with the unbalanced shafts there are two synchronizing pinions that make it possible to connect two or more vibratory pile drivers in series and to synchronize their operation.

Figure 4.18 The VPM-170 Low-Frequency Vibratory Pile Driver

The VPM-170 vibratory pile driver is designed for driving tubular piles 1.6 meters in diameter into any type of soil (except rocky soil) without removing the soil from the cavity of the pile. The pile driver is started up from the control panel, which can change the rotational frequency from 0.5 times the rated value to the rated value (according to the name plate) and it can allow the electric motor to operate at a reduced rotational frequency for a limited amount of time.

The vibratory pile driver is connected to the pile by a special adapter, the upper part of which is attached to the bottom plate of the pile driver and the lower part of which is attached to the tubular pile by nuts and bolts. The VPM-170 is not designed for use with hydraulic driving caps or ASN-type driving caps.

Of particular interest among vibratory pile drivers is the VU-1.6 (manufactured by Mintransstroi). It is designed for driving reinforced concrete tubular piles measuring 1.6 m in diameter to depths of up to 30 m while, at the same time, working and removing the soil from the cavity of the tubular pile (figure 4.19). These joint operations, which significantly increase productivity, are possible because the body of the pile driver has a through-hole 1.4 meters in diameter, so that the soil can be removed without removing the pile driver. This vibratory pile driver has a welded steel body with a cylindrical opening in the center. Inside the body there are four symmetrically arranged shafts with eccentrics that are connected to one another by conical synchronizing pistons on the ends of the shafts. Each pair of shafts is caused to rotate by an electric motor through a reduction gear with cylindrical pistons. Opposite shafts rotate in opposite directions, as a result of which the vibratory pile driver produces vertical vibrations.

Figure 4.19. The VU-16 vibratory pile driver.
Technical characteristics of the VU-1.6 Vibratory pile driver
Eccentric value, kg-cm 34.5
Frequency, vibrations per minute 495
Dynamic force, kN 958
Power of electric motor, kW 150
Electric motors:
number 2
type AK3-315M1-893
Dimensions, mm:
length 3,068
width 2,618
height 1,931
Mass of vibratory pile driver(without driving cap and control panel), tons 11.7

The electric motors are at the top of the housing and are attached to it by bolts. A conical adapter ending in a flange is welded onto the bottom plate of the vibration exciter’s housing. For connecting the vibratory pile driver to the tubular pile, the protruding reinforcement bars must be threaded. The vibratory pile driver is mounted on the end of the pile in such a way that the ends of the rods enter the openings of the flange. The soil is worked and removed from the cavity of the tube by a special grab and hydromechanical method—washing out the soil with a hydraulic excavator and removing it with a hydraulic elevator. The vibratory pile driver has a control panel similar to that of the VPM-170.

VIBRATORY PILE DRIVERS PRODUCED ABROAD

Foreign firms produce vibratory pile drivers for metal tubes, sheet piles, and cylindrical and prismatic reinforced concrete piles. In general, the main parameters (force, power, vibrational frequency, mass) are similar to those of vibratory pile drivers manufactured in the USSR. They also differ little in design from the latter.

Foreign firms make frequent use of hydraulic driving caps with the pumping station on the ground or on the pile driver. Many designs use standardized units, making it possible to increase their power by combining several (up to four) vibratory pile drivers into a single unit. Without exception, all are mounted on the crane by means of a spring shock-absorber.

In recent years vibratory pile drivers have been put to their greatest use in Japan, where six firms produce 55 models and variations of these models. The greatest number of vibratory pile drivers (21 models) is produced by the firm Kensetsu Kikai Chosa. Their technical data is presented in Table 4.24.

Table 4.24 Technical Data for Kensetsu Kikai Chosa Vibratory Pile Drivers
Characteristic KM2-170E KM2-300E KM2-700E KM2-100E M2-1200E KM2-2000E VM2-2500E VM2-4000E VM2-5000E KM2-12000E KM2-12000A
Eccentric value, kg-cm 0.17 0.292 0.69 1 1.32 2.1 2.5 3.5 5 12 12
Frequency, vibrations per minute 1250 1300 1200 1100 1250 1100 1150 1100 1100 510 510
Dynamic force, kN 30 54 110 135 232 283 370 486 676 349 349
Vibrational amplitude (without pile), mm 4 4 6 6 7 7.5 8 9 9 21 22
Power, kW 3.7 7.5 15 22 30 40 45 60 90 90 90
Dimensions, m:
height 1.25 1.6 2 2.4 2.5 2.8 3 3.2 3.4 2.6 3.6
width 0.7 0.8 0.9 1 1.1 1.1 1.2 1.4 1.5 1.7 1.1
length 0.4 0.5 0.7 0.7 0.8 1 0.9 1 1.2 1.2 1.3
Necessary power input, kW-A 10 20 45 80 100 120 150 200 250 250 250
Mass, tons 0.4 0.8 1.3 1.9 2.4 3.3 3.8 4.7 6.6 7.2 6.4
Table 4.24 Technical Data for Kensetsu Kikai Chosa Vibratory Pile Drivers (continued)
Characteristic KM2-15000A KM2-17000A VM4-10000A VM2-25000A VM4-50000A LSV-40 LSV-60 LSV-80 LSV-120 BVJ-120H
Eccentric value, kg-cm 15 17 10 25 50 1 1.5 2.2 3 4.5
Frequency, vibrations per minute 400 560 1100 620 620 1500 1500 1500 1500 1700
Dynamic force, kN 40 60 135 107 214 25 37 55 75 145
Vibrational amplitude (without pile), mm 25 26 12 33 32 4 5 4 5 2
Power, kW 90 120 150 150 300 30 45 60 90 120
Dimensions, m:
height 4.4 4.8 6 4.5 4.5 2.7 3.1 3.5 4 3.2
width 1.2 1.3 1.3 1.7 1.7 1.2 1.3 1.4 1.6 3
length 1.2 1.2 1.2 1.4 1.4 3.2 0.9 1 1.3 2.3
Necessary power input, kW-A 250 450 600 600 1200 100 150 200 250 400
Mass, tons 7 7.8 10 8.5 17 3 4 6 8 23

Let us examine the most typical design for vibratory pile drivers manufactured by the Mitsubishi Company (Table 4.25). The VD-22 vibratory pile driver (Figure 4.20) is designed for steel sheet piles and for metallic piles and tubes measuring up to 300 mm in diameter.

Figure 4.20 The Mitsubishi VD-22 Vibratory Pile Driver (Japan)
Table 4.25. Technical data for Mitsubishi vibratory pile drivers (Japan)
Characteristic VD-22 VD-30 VD-45 VD-60
Eccentric value, kg-cm 0.878 1.314 2.308 3.183
Frequency, vibrations per minute 1150 1150 1100 1100
Dynamic force, kN 130 145 315 431
Vibrational amplitude (without pile), mm 4.6 5.6 6.4 6.9
Power, kW 22 30 45 60
Dimensions, m:
height 2.5 2.6 2.8 3.2
width 1.2 1.3 1.4 1.5
length 0.8 0.9 1 1.2
Mass, tons 1.9 2.3 3.6 4.6

The vibration exciter consists of three electric motors arranged on the same vertical axis in the steel housing. The rotor shafts have eccentrics and the eccentric value of the middle shaft is twice as great as the end eccentrics, so that when the end eccentrics rotate in one direction and the middle one in the opposite direction, vertically directed vibrations are produced. The vertical arrangement of the vibratory pile driver is convenient for driving (or extracting) piles in foundation pits or sheet piling. The VD-22 vibratory pile driver may be used with mechanical or hydraulic driving caps (a mechanical driving cap is shown in Figure 4.20).

Technical data on vibratory pile drivers manufactured by other Japanese firms is presented below (Tables 4.26, 4.27, and 4.28).

Table 4.26. Technical data for vibratory pile drivers with internal combustion engine and carburettor manufactured by Hikasa sengyo (Japan)
Characteristic MOH-8 MOH-24
Eccentric value, kg-cm 0.035 0.08
Frequency, vibrations per minute 1300 1300
Dynamic force, kN 15 40
Vibrational amplitude (without pile), mm 20 20
Power, kW 8 20
Dimensions, m:
length 0.27 0.36
width 0.67 0.52
height 0.43 1.1
Mass, tons 0.12 0.43
Table 4.27. Technical data on vibratory pile drivers manufactured by Nippon Shario Seizo Kaisha (Japan)
Characteristic VS-90 VS-100 VS-170 VS-200 VS-300 VS-400 VS-500
Eccentric value, kg-cm 0.845 1.295 1.727 2.2 2.6 3.5 4.6
Frequency, vibrations per minute 1100 1100 1100 1100 1100 1100 1100
Dynamic force, kN 114 175 234 298 352 474 622
Vibrational amplitude (without pile), mm 6.5 6.3 7 7.1 7.7 8.1 7.7
Power of electric motor, kW 15 22 30 40 50 60 90
Dimensions, m:
length 0.63 0.76 0.9 1 1 1.1 1.2
width 1.1 1.2 1.2 1.3 1.3 1.5 1.6
height 2.3 2.6 2.8 3 3 3.4 3.8
Mass, tons 1.57 2.48 2.87 3.69 4 5 6.9
Table 4.28. Technical data on vibratory pile drivers with internal combustion engines manufactured by Yamada Kikai Koge (Japan)
Characteristic CH1V-3 CH1V-6 CH1V-64 CH1V-64S CH1V-8 CH1V-S CH1V-15S CH1V-25S
Eccentric value, kg-cm 0.076 0.095 0.095 0.095 0.25 0.25 0.5 0.8
Frequency, vibrations per minute 1800 1500 1600 1600 1600 1600 1380 1380
Dynamic force, kN 13 35 35 35 56 56 110 120
Vibrational amplitude (without pile), mm 12 15 15 15 17 17 20 25
Power of electric motor, kW 3.3 4.4 4.4 4.4 5.9 5.9 10.3 16.2
Dimensions, m:
length 0.15 0.2 0.2 0.2 0.26 0.26 0.33 0.6
width 0.63 0.75 0.75 0.75 0.56 0.56 0.8 0.8
height 0.3 0.4 0.4 0.7 0.85 1.1 1.1 1.8

Beginning in 1978 the Japanese firms Mikasa Sengyo and Yamada Kikai Koyo began manufacturing vibratory pile drivers powered by internal combustion engines. Mikasa Sengyo produces two models of light vibratory pile drivers with a power of 5.9 kW that have internal combustion engines with a carburetor (see Table 4.27).

Table 4.29 shows data on vibratory pile drivers manufactured in the Federal Republic of Germany and in the United States.

Table 4.29. Technical data on vibratory pile drivers of several foreign firms.
Characteristic MVB-44-30 4DE-3VT 205P-1
Menck, FRG Foster, USA
Dynamic Force, kN 440 1,120 500
Frequency of vibrations/min 3,000 1,120 890/1,500
Mass of vibratory pile driver (without driving cap,) tons 3.9 18.1 4.13
Length of reinforced concrete pile, m 20 15
Length of metal pile, m 20 25 20
  • Data is presented for the most common models produced by these firms.

MON-type vibratory pile drivers are high-frequency machines and are designed for driving and extracting metallic tubes 150 to 300 mm in diameter. They are used together with cranes or with drivers of similar capacity.

Yamala Kikai Koyo manufactures eight models of vibratory pile drivers with 4.5 to 22 kW internal combustion engines. The most powerful of these are powered by diesel engines (see Table 4.28).

The GKN Company (England) produces a vibratory pile driver designed for driving reinforced concrete piles and metallic piles with a 368-kW diesel. The vibratory frequency of this pile driver is 60 to 130 Hz, the force is 10 MN, and the mass is 10 tons. Regulation of the vibrational frequency makes it possible to achieve optimal driving under various soil conditions.

CALCULATIONS FOR VIBRATORY PILE DRIVER

According to the method of O. A. Savinov and A. Ya. Luskin, the characteristics of a vibratory pile driver may be calculated in the following manner.

For a given maximum insertion depth, the total calculated critical resistance to failure for piles is:

for sheet piles:

where

  • S is the perimeter of the cross sectional area of the pile
  • tcr is the force of friction exerted on a unit area of surface of the inserted element (Table 4.30)
  • i is the number of the soil layer of height hi through which the pile passes during insertion
  • n is the total number of layers.
Table 4.30 Forces of friction exerted on inserted element.
Type of soil tcr, kPa tcr, kN/m
Wooden piles, steel tubes Reinforced concrete piles Reinforced concrete tubular piles, open at the bottom, inserted with excavation of soil Light profile sheet pile Heavy profile sheet pile
Water-saturated sandy and slightly plastic clayey soils 6 7 5 12 14
Same, but with layers of thick clay or gravely soils 8 10 7 17 20
Only slightly plastic clayey soils 15 18 10 20 25
Same, semi-hard and hard 25 30 20 40 50

The eccentric moment of the vibratory pile driver’s eccentric masses is:

where

  • x is a dimensionless coefficient
    • for reinforced concrete piles = 0.8
    • for all others = 1
  • Ao is the vibrational amplitude of the vibrator-pile system (the amplitude value may be obtained from Table 4.31
  • mo is the mass of the pile and of parts of the vibratory pile driver that are rigidly attached to it (approximate figure is used)
Table 4.31. Recommended vibrational amplitudes
Pile Ao, mm
Sandy soils Clayey soils
Vibration frequency, per minute
300-700 800-1000 1200-1500 400-700 800-1000 1200-1500
Steel sheet pile, steel tubes with open end, and other elements with cross-sectional area up to 150 cm2 8-10 4-6 10-12 6-8
Wooden and tubular steel (with closed end) with cross-sectional area up to 800 cm2 10-12 6-8 12-15 8-10
Reinforced concrete, square or rectangular cross section with area up to 2,000 cm2 12-15 15-20
Reinforced concrete tubular piles with large diameter, inserted with excavation of soil from tube cavity 6-10 4-6 8-12 6-10

The frequency of vibrations (angular velocity of the eccentrics on the vibration exciter) is:

The minimum mass of the vibratory pile driver is:

where

  • m is the mass of the piles and of the vibratory pile driver (and of any additional loads)
  • p0 is the required pressure on the pile, the value of which may be obtained from the data presented below
  • F is the cross sectional area of the pile; Po is the maximum driving force of the vibration exciter
  • k1 and k2 are coefficients
    • for a steel sheet pile k1 = 0.15 and k2 = 0.5
    • for light (wooden, tubular steel) piles k1 = 0.30 and k2 = 0.6
    • for heavy (reinforced concrete) piles and wells k1 = 0.40 and k2 = 1.0.

For piles inserted into water-saturated sandy and slightly clayey soils, the following values are recommended for the required pressure p0 (MPa) :

  • Small diameter steel tubes and other elements with cross sectional area up to 150 cm2 …… 0.15-0.3
  • Wooden and tubular steel (with closed end) piles with cross sectional area up to 800 cm2. . . . 0.4-0.5
  • Reinforced concrete piles with square or rectangular cross section up to 2,000 cm2. . . 0.6-0.8

After the main characteristics are obtained, the required power of the motors is determined:

where

  • htr is a coefficient indicating the energy losses in transmission from the motor to the shafts of the vibration exciter.

The power (in kw) spent on overcoming resistances in the vibration exciter mechanism is:

where

  • d is the diameter of the journals on the shafts of the vibration exciter, in cm
  • n0 is the rotational speed of the shaft, rpm
  • f is the coefficient of friction of the rolling-contact bearings relative to the diameter of the shaft journal, approximately equal to 0.01.

The power (in kW) required to overcome the resistance of the ground is:

where

  • K is the eccentric moment of the vibration exciter’s unbalanced masses
  • w is the angular velocity of the vibration exciter’s unbalanced masses.

Since the derivation of the formula did not take into account energy losses to vibration of the ground, it is recommended that, in every case, the value of Nmax obtained by this formula be increased by 10 to 20 percent.

Development of a Parameter Selection Method for Vibratory Pile Driver Design with Hammer Suspension

Don C. Warrington, P.E.
Originally presented at the Colloquium of the Department of Mathematics of the University of Tennessee at Chattanooga 26 September 2006.

Abstract

This paper details the mathematical modelling of vibratory pile driving systems using a linear model with the objective of obtaining a closed form solution to estimate either the power requirement of the machine, the torque requirement of the motor driving the eccentrics, or both.  It begins by reviewing the system model for the system without a suspension, which is used to enable connection of the vibrating machine with a crane, a mast of a dedicated machine, or an excavator.  It proceeds to solve the equations of motion for a system with a suspension, using Laplace transforms and solving the inverse transform using residues and complex integration.  The model indicates that, under certain conditions, both the amplitude and the power consumption of the system increase with a suspension, but the results make the practical implications of the result uncertain.  Finally a simple set of equations is developed for actual vibratory design which results in the suspension being ignored and the necessary torque of the driving motor computed.

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Dedication

As one remains in an industry for an extended period of time, the time comes all too often to say farewell to colleagues who depart.  Such is the present time; this paper is dedicated to the memory of Lev Vikorovitch Erofeev, Chief of the Pile Driving Equipment Design Department at VNIIstroidormash, the All-Union Amalgamation for Construction and Road Machinery in Moscow , Russia , who passed away in 2002.

Lev Erofeev (left) with V.S. Warrington, Vulcan’s Chairman of the Board (centre) and V.A. Nifontov (right) during a visit to Vulcan’s facility in the early 1990’s.

 

I first met Lev in 1988, on my first trip to the Soviet Union .  At the time it was difficult to make contact with Soviet people and institutes, especially for a small concern such as Vulcan Iron Works.  The combination of poor communications with the tendency of too many intermediaries to “get in the way” almost ended our relationship.  In 1990, while on tour in Moscow with CBN, I sent Lev a letter, which would have received an earlier response had he not been in his dacha, but which re-established contact.  With the end of the Soviet Union the following year, this led to proper relationships and the cooperation between Vulcan, VNIIstroidormash and other Russian organisations that were a bright spot in Vulcan’s last years.

With mutual visits, I found Lev to be a man of integrity, a fine engineer and a good friend.  Our contact was a voyage of mutual discovery, with such things as finding his VNIIstroidormash department room piled high with hydraulic hose, or his attentive viewing of the two-hour long Jesus video in Vulcan’s board room.  Lev retired just about the time that Vulcan passed out of the Warrington family.  For both of us the end came too soon, but for Lev it was especially difficult.  In his earlier days he had been involved in work in Siberia, downriver from one of the Soviet Union ’s nuclear sites.  Eating mutant crawfish out of the river, he developed radiation poisoning, which combined with Soviet medicine disfigured him and, in his later years, made it difficult for him to speak.

Lev told the story about the Soviet engineer who designed the minipile system for the Ostankino Tower in Moscow.  Minipiles were a novelty at the time, which meant that much of the Soviet engineering and construction establishment panned the concept.  The minipiles worked, but the engineer passed away, after which time he was honoured for his brilliance.  Lev noted that people who are trashed while they are living are frequently lionised after they are gone.

It has been my objective since our first joint article in Pile Buck in 1991 that Lev receive the recognition that he deserves for his contribution to the advancement of the technology of pile driving equipment.  Without the information he furnished, the entire effort that started with my OTC paper in 1989 would not have been possible.  Let this paper be a final tribute to Lev Viktorovitch, and beyond this let us remember the following: “Urge upon them to show kindness, to exhibit a wealth of good actions, to be open-handed and generous, storing up for themselves what in the future will prove to be a good foundation, that they may gain the only true Life.” (1 Timothy 6:18-19, Positive Infinity New Testament)

Vibro-Engineering and the Technology of Piling and Boring Work

This work is an excellent and detailed treatment of the titled subject. We will present an English translation of the parts of the work that most directly deal with vibration and impact-vibration of piles and the equipment used to perform the work. You can click on the hyperlinked chapters to view them.

Table of Contents

  1. General Information
    1. The essence of the development of vibratory immersion and extraction.
    2. Calculational models of the interaction of the immersion (extraction) of elements with the ground.
    3. Effective region of the application of the method of vibration and the classification of vibratory machines.
    4. Application of vibratory technology.
  2. Foundation of the theory of vibratory driving and extraction.
    1. Installation and extraction by longitudinal oscillations.
    2. Installation and extraction by longitudinal-rotational oscillations.
    3. Installation and extraction under action of longitudinal blows.
    4. Installation of tubular elements under action of longitudinal blows and rotational oscillation.
    5. Installation under action of alternating impact blows.
    6. Selection of the type of dynamic action and determination of the soil resistance.
  3. Vibration and Impact Vibration Drivers
    1. Characteristics of the dynamics of vibration and impact-vibration drivers.
    2. Methods for approximate calculation of the parameters of vibratory drivers and impact-vibration hammers.
    3. Vibrators and impact-vibrators.
    4. Means of protection from vibration loading of mechanisms, works, with vibroexcitation.
    5. Status of vibratory pile driving abroad.
  4. Vibratory technology for production piling.
    1. Installation and extraction of metal sheet piling.
    2. Installation of prismatic steel reinforced concrete pile.
    3. Installation of cylinder piles.
    4. Installation of pile groups by vibratory technology.
    5. Less frequent applications of piles immersed by vibrational methods and produced by vibration technology.
    6. Application of vibratory methods nearby essential buildings.
  5. Vibratory Technology of the manufacture drilled works for contractors.
    1. General information for the application of vibratory methods to drilled works.
    2. The capabilities of geotechnical engineering and other drilling technologies.
    3. Capabilities of continuous and connected types for impact-cabled drilling of water wells.
    4. Installation and extraction of casing for the procession of impact-cabled drilling.
    5. Installation of filter columns for the installation of engraving delay of filter holes for water.
    6. Restoration of hole production for water near their openings and repairs.
    7. Extraction of planted pipe near liquid holes.
  6. Vibratory technology for the production of some appearances of special construction works.
    1. Application of vibratory technology near the construction of remote projects.
    2. Construction of slender notification curtains.
    3. Application of vibratory technology near the layings of tubes.
    4. Vibratory technology of the depth compaction of sandy foundations.

Editor’s Forward

In 1988, while still at Vulcan, I made my first visit to the then Soviet Union with my brother Pem, our Executive Vice President. The visit had some interesting twists and turns along the way. One side trip from Moscow was to Leningrad (now St. Petersburg,) where we were able to view a B-402 vibrator drive sheet piles. (A contemporaneous account of the visit is given below.) Although we never really pursued further commercial discussions, one thing we were sent was the book Vibro-Engineering and the Technology of Piling and Boring Work, parts of which we reproduce here in translation.

Although it is acknowledged that vibratory (and impact-vibration hammers) were brought into practical use in the Soviet Union, there are very few details of this readily available. (Most of them are probably on this website!) The publishing of the English translation here will hopefully fill in some of the history and perhaps advance the technology in its present form.

Vulcan commissioned Language Services in Knoxville, TN, to translate the parts of the work that are presented here. Although we freely admit that some of the translation is too literal, the content is of sufficient value that it merits posting. We have edited the text some to make the nomenlcature more in line with terminology used in the U.S.

Visit to Leningrad (April 1988)

In Moscow we went to Leningrad Station about 2300 to take the train to Leningrad. We were met by Mr. A.A. Orlov, Chief Engineer of the All-Union Construction and Energy Mechanization Organization of the Ministry of Energy and Electrification of the USSR, and his assistant. We then took the train to Leningrad and arrived about 0830.

We were met there by a delegation from the Organization, which first took us to the Moscow Hotel where we got a room and prepared for the day. Included in the delegation were E.A. Narozhnitskii, (Director) and M.L. Pevzner of the Leningrad Experimental Factory of Construction Machinery. We then went to a jobsite in Leningard, where they were building a tunnel under the river. They had been working on this project for a year and had managed to drive some sheet piling. Their vibratory hammer was driving some Laarsen sections about 24m in length, which they did using their vibratory hammer. On the vibratory, an electric motor mounted in the suspension plate on top of the hammer and a chain drive system extending from the suspension to the gearbox. The clamp is able to drive only one sheet at a time. The hammer is electric, about the eccentric moment of the 1150 but with about half of the power. The power comes from the electric power grid (that is to say, they plug it in somewhere), and they have a control box to provide the necessary circuitry to start and stop the 3-phase motors. In spite of the potential to gear up or down, the electric motor and eccentrics both rotate at1500 rpm, and they have other models that are slower. It took them about 5-10 minutes through the glacial till they were driving through. The hammer is quiet though and, without the power pack, the noise was limited.

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After this, we went on and eventually had lunch back in the Moscow Hotel. After lunch, about 1530, we sat down for a conversation about the hammers. We explained the construction and operation of our equipment, but they thought that we used too much power for our eccentric moment, that we were wasting power and that our additional power could not accomplish anything. I replied that the only way to know this for sure was to run a race amongst the units and see. They also told us that they thought electric vibratory was better and planned to stick with it in their programme. Nevertheless, the door was kept open by both sides for further discussion, as they felt that there was potential for this. We also invited them to Chattanooga (our headquarters) for further discussions.

Driving Cylinder Piles

Editor’s Note: the term “cylinder piles” used in the section is a translation of a Russian term that is more exactly translated “shell piles” or “pile shells.” Since that term has an entirely different connotation in English (for one thing, it usually denotes a steel pile, while a concrete one is meant here) we use the term “cylinder pile.” It should be noted that the piles described here have significant differences from the Raymond type that is common in the U.S.

The period of rapid development and propagation of vibration technology in the driving of reinforced concrete cylinder piles was 1952-1963. In the construction of bridges over the rivers Usa and Klyazma, the vibrator VP-1 was successfully used for the first time in 1952-1953 for driving cylinder piles 1.2 and 0.9 m in diameter, in conjunction with the removal of gravelly-sandy soil with an air lift and washing.

Further development of the vibration technology was associated with the construction of the Ukhan bridge over the river Yangtze in China and then with broad application in domestic bridge construction. The foundations of more than 200 bridges over the Volga, Oka, Dnieper, Severnaya Dvina, Don, Neva, Ob and others have been constructed with the vibration technology, and mooring structures were erected in Novo-rossiisk, Tuaps, Sukhumi, Kaliningrad, Leningrad, Nakhodka, Varna and Ventspilsa.

The successful application of deep foundations of cylinder piles made it possible to dispense with the use of caisson foundations almost completely and obtain a substantial technical-economic effect. The bridge construction costs were reduced by 20-35% here (K. S. Silin, 1962), and the concrete consumption was reduced 2-4 fold. In comparison with mooring points of reinforced concrete prismatic piles, the use of cylinder piles 1.2-1.6 meters in diameter, not filled with concrete, makes it possible to save up to 45% of the foundation concrete and reduce the man-hours of labor by 25% (V. V. Kapliev, 1966).

In industrial construction, the use of foundations of cylinder piles 1.2 in in diameter in comparison with foundations of clusters of prismatic piles assures a concrete saving of 25-35%, and of the hardware by 50-60%, a reduction in labor costs of 55-65%, and a shortening of the work time by 50-70% (I. G. Vypov and L. E. Litvintsev, 1981).

In the most general form, the technological scheme for constructing foundations of cylinder piles is described as follows. The cylinder piles consisting of separate sections of factory or on-site manufacture are placed at the driving site with a crane through a preliminarily prepared guide arrangement. Then the piles are driven into the ground with a vibrodriver, employing washing and extraction of the soil or the drilling out of obstacles encountered if necessary. In order to increase the bearing capacity of the piles, a broadening, filled with concrete by the feed method, can be constructed in their base.

Foundations of cylinder piles are constructed on dry land or in water (K. S. Silin, N. M. Glotov, and V. I. Karpinskii, 1966). The work in water is more complicated. The sequence of the operations in the construction of foundations in the water can be presented in the following order:

  • The preparation of the reinforced concrete piles;
  • The preparation on shore and assembly of the guide housing on flotation means for fixing the piles in the projected position during their driving into the ground;
  • The arrangement around the guide housing of a special floating system with raising and regulating compound pulleys for installing the housing in the projected position;
  • Removal of the guide housing from the floating system to the construction site of the buttress and consolidation as an anchor;
  • Lowering the housing into the water, assembly of its successive sections and placement of the housing in the projected position in the scheme;
  • Driving several piles to the’ prescribed mark through the stages of the guide housing and suspension of the housing on them;
  • Freeing and removal of the floating system from the constructed support and driving the remaining piles into the ground;
  • Removal of the soil from the internal cavities of the piles;
  • Drilling holes in the base of the piles, cleaning them of sludge, installation of the fixture housings and the placement of concrete by the vertically movable pipe method with subsequent control drilling;
  • Installation of a tongue-and-groove enclosure of the foundation pit on the perimeter of the guide housing;
  • Removal of soil from the foundation pit and placement of a concrete mass by the feed method, joining the pillars.

There were special conditions in the construction of bridges in the building of the Baikal-Amur trunk line. In the case of the Amur the flow is rapid and the soil is rocky. Nevertheless, even under such conditions the bridge builders rejected caissons in favor of cylinder piles. In order to accomplish this proposal, it was also necessary to solve the problems of sinking reinforced concrete piles into the rock and their reliable fixation. Drilling machines with ordinary chisel bits did not furnish the proper effect at the Amur. The drilling problem was solved with the aid of an especially improved turbine drill.

The installation of the foundation of cylinder piles under the bridge supports under the conditions of the Baikal-Amur trunk line construction was accomplished in the following manner. A floating crane with a lifting capacity up to 100 tons lowers the five-section piles into the stages of the guide housing (the piles are 3 m in diameter and 30 m in height). Under the action of the vibrodrivers, the lower end of the piles cuts through the layer of bottom soil and rests in rock. After removing the soil from the pile cavity with a grab bucket, a reaction turbine aggregate is lowered in for drilling spurs in the rock. Then the inner cavity of the spurs and part of the pile are concreted. The operating site is enclosed with a tongue-and-groove wall.

The water is pumped out of the reservoir formed. The three upper sections of the pile are removed. The subsequent operations — installation of a concrete slab (grating) on top of the pile and construction of the buttress — are carried out in the dry.

When the foundations of cylinder piles are laid out on dry land, the technology of the work is substantially simplified. We shall examine the results of applying the complex of vibration equipment in the laying out of the foundation of a building for manufacturing purposes in Leningrad (M. G. Tseitlin, E. G. Godes, and V. M. Klementyev, 1976).

The complex of vibration equipment, which was used on one of the objects, consisted of a vibrator for driving cylinder piles, a vibro-grab bucket for extracting the soil from their cavity, a grooved vibrodriver for setting up the guide conductor and a depth vibrator on a tube or rod for the placement and compaction of the concrete mixture in the cylinder piles.

Cylinder piles 1.2 m in diameter were driven to the 19-meter mark. Their driving was accompanied by periodic extraction of soil from the cavity.

In order to assure the verticalness of the piles and their precise positioning in the plane, the piles were driven through the joint guide conductor for each row of piles. All the elements of the conductor were prepared from the Larsen-V pile, where the vertical pile pillars were driven to a depth of up to 4 m with the VPP-2 vibrodriver. The cutting section of the cylinder pile was lowered through “he guide conductor into the sump and centered. The vibrodriver VTJ-1.6 was fastened on the knife section of the pile prepared for driving; when it was switched on, the section was driven to the upper flange (Figure 62) of the guide conductor, after which the vibrodriver was disconnected from the pile and the soil extracted from its cavity with the vibrating grab bucket. Then the pile was built up and driven to the designated mark.

Figure 62. Driving cylinder piles with a VU-1.6 vibrodriver.

After extraction of the soil from the driven cylinder pile, the reinforcing cage was lowered into its cavity and then the pile was filled with a grade 200 concrete mixture with a settling of the cone of 4-6 cm. The concrete mixture was poured into the pile cavity with buckets through the receiving bunker and the guide tube and then the mixture was compacted with the aid of a tube fastened to the VPP-2 vibrodriver. The upper layer of concrete was compacted to a depth of 2 m with an IV-59 vibrocompacter. Then, in order to increase the degree of the concrete compaction, high-frequency IV-60 vibrators were used, which were fastened to the tubular rod with a length of 15 m.

An analysis of the results of the studies revealed that the use of the complex of vibration equipment in the construction of foundations of cylinder piles on dry land makes it possible to substantially increase the rhythm of the work due to an increase in productivity in fulfilling all the basic operations associated with driving the piles.

A successful vibrodriving of cylinder piles was accomplished in the first stage of adoption basically with the VP-1 and VP-3 low-frequency vibrators (6-7 Hz).

Adhering to the concept of the independence of the driving ability of the vibrators on the magnitude of the dynamic force, B. P. Tatarnikov developed the low-frequency vibrodriver NVP-56. Powerful vibrators — the two-frequency VP-160 and the one-frequency VP-170 — were developed at the same time. The said vibrators are similar in power, but considerably different with regard to amplitude-frequency mode of the vibrations.

The driving abilities of these machines were compared during the driving of reinforced concrete piles 1.6 m in diameter to a depth of 26 in in clay soils in the construction of a bridge over the Neva (A. D. Prokhorov, 1968).

The VP-170 vibrodriver proved to be the most efficient under the said conditions. In the vibrodrivers tested the same dynamic force was achieved in different ways. In the VP-160 vibrodriver the dynamic force of 1000 and 1250 kN was achieved due to an increased rotational speed of the eccentrics, while in the VP-170 vibrodriver, due to an increase in the moment of the eccentrics.

Due to the extreme reduction in the rotational speed of the disbalances in the NVP-56 vibrodriver, the dynamic force with values of the moment of the eccentrics identical to those of the VP-170 vibrodriver proved inadequate for driving the piles to the specified depth.

In addition, as a result of conducting this cycle of full-scale experimental studies, the following was determined:

  • the frequency of the forced vibrations in driving reinforced concrete piles into clays in the presence of soil plugs in the pile cavity should not exceed 6.6-3.3 Hz;
  • the most advantageous frequency of the vibrations changes with varying depth of driving;
  • the maximum depth and rate of driving the piles into clays are basically dependent on the frontal resistance of the soil;
  • with periodic extraction of the soil from the pile cavity the driving ability of the vibrator is sharply increased with the same parameters ;
  • the application of washing by means of a pressure of 1.5-2 MPa for breaking down the soil plugs in clays in the pile cavity is not very efficacious; therefore, soil-processing mechanisms are necessary with their forced sinking into the soil.

An analysis of the hodographs and graphs of the vibrodriving of reinforced concrete piles 1.6 m in diameter with the VP-30, VP-3 and VP-80 vibrodrivers into low-moisture sandy soils made it possible to draw rhe following conclusions (A. S. Golovachev and A. D. Prokhorov, 1968):

the driving of the piles to the specified depth is greatly facilitated with periodic advanced extraction of soil from the pile cavity to the mark below the knife;

even with advanced extraction of the soil as the sinking progresses, the amplitude of the vibrations of the vibrosystem and the power required decrease due to an increase in the frictional forces of the pile in the ground.

According to the data of A. D. Prokhorov, the mode in which an amplitude of the vibrations of 8-10 mm is assured at any driving depth must be considered a reasonable amplitude-frequency vibration mode. Driving of the piles to the projected marks, accompanied by the extraction of soil from the cavity, can be assured by vibrators with Po > 1.5 (F—m0g).

An analysis of the driving of the piles into plastic clay soils with stony inclusions with the aid of the VU-1.6, VP-160 and VP-170 vibro-drivers makes it possible to draw the following conclusions:

  • a soil plug with stony inclusions is formed in the cavity of the pile during driving;
  • The vibrodriving of piles into clay soils with stony inclusions can be effective only with periodic removal of the soil from the cavity and processing of the leading apertures under the pile with a depth of 2.5-5 m and a diameter approximately equal to the inside diameter of the pile;
  • The use of external washing (undermining) for facilitating the driving of piles under such conditions is not recommended because undermining results in an intensive washing out and accumulation of gravel inside of the pile.

Advance removal of the soil should be done carefully, due to the danger of its influx inside of the pile. Advance removal of the soil can be carried out to a depth of 4—6 m below the blade of the pile only in stiff-plastic and semihard clays.

In driving piles into compact soils with low-frequency (up to 7-5 Hz) vibrodrivers, the characteristic and most effective mode is accompanied by a rebounding of the vibrodriver from the soil.

During vibration driving into light soils, extraction of the soil from the cavity of the piles is superfluous in most cases. During the vibrations the soil rises along the internal cavity of the pile upward, sometimes 2-3 m above the level of the ground surrounding the pile.

A study of experience in the vibration driving of cylinder piles under various hydrogeological conditions permitted us to note methods and solve a number of current problems, which open up new prospects for further propagation of these progressive edifices in construction. Above all, this is an exploitation of vibrodrivers with regulatable parameters, the use of which makes it possible not only to increase the driving ability of heavy pile vibrators, but also substantially reduce the power of the electrical supply sources. Figure 63 shows the VRP-30/132 vibrodriver in the driving of a reinforced concrete pile 0.6 m in diameter.

Figure 63. Driving reinforced concrete piles 0.6 m in diameter with a VRP-30/132.

An important characteristic of the driving of cylinder piles is associated with the formation of the soil plug in their cavity, which causes a change in the vibration scheme of the cylinder piles and creates the risk of their damage (basically in driving through a layer of water). In addition, the need for extracting soil from the cylinder piles substantially reduces the rhythm of the work in constructing foundations.

The results of the studies conducted by the All-Union Scientific Research Institute of Hydraulic and Sanitation Engineering Operations (VNIIGS) on the said characteristics and the technological measures recommended are considered below.

Tubular piles and cylinder piles 0.6-1.6 m in diameter are usually driven with a low-frequency vibrator with an open lower end, without removal of the soil that penetrates into the cavity of the pile. In such piles, especially with a blade bevelled inward, a compact soil core participating flush with the wall in load transfer is formed when bearing on sands of medium density or stiff-plastic clays. A compacted zone of soil of considerable volume, which is as it were a broadening of the pile base, is created here under the bottom of the pile. When resting on a sandy or stiff-plastic clayey soil, the pile begins to operate as a pile column under conditions close to those that are possible for ordinary solid piles only when resting on rock (A. I. Prudentov, 1971).

The bearing ability of such piles with respect to the soil approaches the maximum attainable with regard to the strength of the wall material, amounting to 2000-10,000 kN or more on one pile. The specific carrying capacity of a pile with an earth core reaches 1500-2000 kN per m3 of reinforced concrete.

With appropriately selected parameters of the vibrator, the cylinder pile is driven quite easily to the determined depth and then stops with the formation of the soil plug. In many cases, the stoppage of the cylinder pile occurs at a depth considerably less than the planned mark.

This leads to the need for extracting the soil plug and continuing the vibration driving in order to create a pile with a soil core at the planned mark or to free the pile cavity of the soil in preparation for the subsequent concreting.

The tendency developing in recent years of driving metallic tubular piles, where a soil plug is also formed, should be noted. Thus, an urgent problem is the study of the formation conditions of the soil plug during the vibrational driving of a tubular element.

Experimental data demonstrate (M. G. Tseitlin and V. E. Trofimov, 1973) that the elastic component of the resistance forces can be quite large in a number of cases. In connection with this, it became necessary to study the conditions of formation of the soil plug in the elastic-plastic mechanism of soil resistance (M. G. Tseitlin and A.. A. Kosheleva, 1931).

Figure 64 shows the calculation scheme for driving a tubular element with the formation of a soil plug, taking into account the elastic-plastic nature of the soil resistance.

Figure 64. Calculation scheme of the vibrational driving of a tubular element with soil plug.

The soil core does not move relative to the tubular element if there is equilibrium between the forces acting on it:

(70)

where R* is the frontal soil resistance acting on the plug. When FBH > FKP, a slippage of the soil core takes place

(71)

where

  • sKP is the specific value of the dynamic forces required for separation during vibration driving, assigned to the area of the lateral surface of the driven part of the tube, and 1 is the height of the soil core.
  • mn is the mass of the soil plug;
  • FBH is the force acting on the side of the tubular element and holding the soil plug; and
  • xn is the coordinate corresponding to the maximum deposition achieved during the preceding cycle.
Figure 65 Dependence of the force under various conditions of slippage, characterizable by fKP.n = FKP/Po and the internal diameters of the tubular element.
  1. d = 0.2;
  2. d = 0.5;
  3. d = 0.8;
  4. d – 1.2;
  5. d = 1.6;
  6. d = 1-9;

I, II, and III — respectively at f = 0.1; f = 0.4; and f = 0.7.

According to the experimental data, the sKP value is 25-30% higher for the plug than for the external surface of the tube.

The condition of formation of the soil plug:

Slippage occurs when

(72)

In determining the maximum height of the soil plug, it is necessary to take the sign of the equality in expression (72) that reflects the equilibrium of the forces acting on the plug in the vibration driving process, substitute the FKP value found with formula (71) into the right-hand side of it, and into the left-hand side — x and R* — the parameters of the process of vibration driving the system, tubular element-soil plug as a single unit , into the ground. For determining d2x/dt2 and R*, it is necessary to solve the differential equation that reflects the process of vibration driving of the tubular element with the soil plug:

(73)

In accordance with the calculated scheme assumed, the frontal resistance to driving is

We should note that the problem of driving a pile with the elastic-plastic mechanism of soil resistance was previously solved by various methods (I. I. Blekhman, 1954; M. Ya. Kushul and A. V. Shlyakhtin, 1954; Yu. I. Neimark, 1963; and S. A. Varsanovich, 1968).

We introduce the following dimensionless parameters supplementarily to (9):

(74)

The characteristic graphs reflecting the dependence of the maximum value of the force fBH acting on the tube-soil core contact on the parameters of vibration driving of tubular elements and the soil re sistance with the dimensionless generalized characteristic x = 100w2D/g =1.2, sKP = 30 kPa and p = 2 t/m3, are given in Figure 65.

An analysis of the results obtained reveals that the force FBH is basically dependent on the frontal resistance of the soil R*. The lateral resistance and the elasticity of the soil and also the frequency of the vibrations substantially influence the variation in the mode of the vibrations during vibrodriving and in fact the acting forces of soil resistance R*. In determining the height of the soil plug, only the modes at which the driving of a tubular element is possible (R* &Mac179; R) are of interest.

As indicated above, the formation conditions of the soil plug for these modes are determined by the force FBH that acts on the tube-soil core contact, or the force FKP, at which a slippage of the soil core occurs. Figure 65 shows the graphs of variation in fKP as a function of qn.

The maximum height of the soil plug that forms for a given tube diameter is determined by its parameter qn, which is found by the points of intersection of the fKP graph with the fBH curve with the corresponding parameters of vibration driving.

The value g at which the driving of a tubular element with a soil plug is possible, is a function of the force of gravity of the system being driven, the frequency of the vibrations and the elasticity zone of the soil during vibration driving.

The case z = 0 corresponds to a purely plastic model of soil resistance, examined previously.

We should note that when the elastic-plastic soil resistance model is used, the calculated height of the soil plug is somewhat less than in the purely plastic model.

The graphs given, plotted for various z, make it possible with the specified parameters of vibration driving to determine the height of the soil plug formed. It is also possible with the aid of these dependences to select the parameters of the vibration driving of a tube, at which the height of the soil plug will be maximal.

The studies conducted revealed the superiority of the regimes characterizable by large values of dimensionless frontal resistance of the soil: the maximum height of the soil plug is achieved at the minimal dynamic forces that assure the driving of a tubular element at a given frontal resistance of the soil.

The particular difficulties in driving cylinder piles arise during the extraction of clay soils from their cavities, when the use of hydro-mechanization means or drills is impossible or of little effect. The use of jaw grippers for this purpose usually does not assure the required productivity of the work. Penetrating under the effect of its own weight, the gripper or grab bucket (even of heavy construction) does not fill the bucket in compact soils. The resistance to closing of the jaws and the conditions of cutting the soil in the closing of the grab bucket limit the height of the jaws and, consequently, the working capacity of the grab bucket at the given transverse dimensions. Besides the said shortcomings of a cable grab bucket, it should be noted that its geometric form does not match the cylindrical cavity of the tubular element. Apart from this, the small capacity of the grab bucket is also limited by the size of its open jaws, which must be less than the inside diameter of the pile. The problem of extracting compact clay soils from the cavity of the driven cylinder piles is solved by using of vibrating grab buckets with a longitudinal-rotational action.

Vibrating grab buckets have been developed at the present time, which assure extraction of the soil from cylinder piles (drive pipes) with an internal diameter of 400-1200 mm. A vibrating grab bucket with a longitudinal-rotational action (Figure 66) is a mobile driving apparatus operating on a cable with a load-lifting mechanism that assures its raising, lowering and transport to the site of unloading.

Figure 66. Overall view of the vibrating grab bucket of longitudinal-rotational action.

a – PV-530 vibrating grab bucket; b – PV-820 vibrating grab bucket; 1 – special vibration exciter; 2 – drive electric motor; 3 – shock absorbing suspension; 4- – soil sampler; 5 – interchangeable attachment.

For reducing the dynamic load on the crane construction, the vibrating grab bucket is equipped with a shock absorber. Vibrating grab buckets are easily hung on the suspension hook of any crane mechanism with an adequate lifting ability without having to remodel it, which is an important operational achievement because it permits the use of the same load-lifting crane for various operations on the construction platform.

The operation of the vibrating grab bucket of longitudinal-rotational action is carried out in the following modes:

  • Driving the vibrating grab bucket into the soil — with longitudinal vibrations, which permit an effective collection of the soil;
  • Separation and vibratory extraction of the vibrating grab bucket with the soil core filling the soil sampler — with rotational vibrations that assure the slippage of soil sampler relative to the adjacent soil and reduce the extraction effort in comparison with the static effort by 2-3 times;
  • Discharging of the vibrating grab bucket — with longitudinal vibrations.

The peculiarity of the vibrating grab bucket operation consists in the fact that its soil sampler cuts through the soil with thin walls, and then the core filling the internal cavity is extracted to the surface and discharged. This operating principle of the vibrating grab bucket makes it possible (in contrast to rotational drilling machines) to sink shafts of large diameter without a substantial increase in the power of the mechanism, its mass and dimensions.

Vibrating grab buckets with a longitudinal-rotational action assure the extraction of sandy and clayey (up to semihard consistency) soils from the cavity of the cylinder piles. The hermetically sealed construction of the vibrating grab buckets permits their use under water or with a clay suspension.

Experience has accumulated in recent years on the use of vibrating grab buckets for extracting soil from the cylinder piles on dry land (from depths up to 30 in) and under water (from depths up to 25 m). The construction of foundations of cylinder piles 1.2 m in diameter on a construction project within the boundaries of a city can serve as an example of driving cylinder piles under industrial construction conditions. The construction area was comprised of clay soils, basically of stiff-plastic to semihard consistency with the inclusion of pebbles and gravel. The cylinder piles consisted of two sections 8 m in length; they were driven with a VU-1.6 vibrator. Driving cylinder piles under the said soil conditions was possible only with the use of drills or vibrating grab buckets, the average productivity of which was 5 m3/h in the extraction of soil from the piles, i.e., 10 times higher than the productivity of drilling machines. The production factor of the operations with soil extraction by a vibrating grab bucket is shown in Figure 67.

Figure 67 Removal of the soil from a cylinder pile with a PV-500 vibrating grab bucket.

The technology of driving cylinder piles, providing for periodic removal of the soil plug, made it possible to drive the piles without a substantial exceeding of the power consumed and with a minimum level of vibrations of the surrounding soil.

In the initial stage of driving (down to a depth of 6-7 m) the soil core was not removed from the pile and had practically no effect on the driving rate, which was 0.8-0.9 m/min. In this case, the power consumed by the vibrodriver was 200-210 kW. In the interval of 9-16 m the driving was carried out with extraction of the soil from the pile cavity at an. average driving rate of the pile of 0.6-0.7 m/min.

Advance removal of the soil was effected to a depth up to 6 m below the pile blade. Without extraction of the soil from the cavity, the cylinder pile was practically not driven at all in this interval. The power consumed in the vibration driving was reduced to 120 kW with removal of the soil plug.

It was possible through the use of vibrating grab buckets to increase the productivity with regard to the extraction of cohesive soils by 3-4 times (in comparison with ordinary grab buckets) and reduce the time lost in soil removal from 85 to 50% of the total duration of the working cycle in driving the piles, and eliminate the operations with respect to reloading the soil extracted from the cylinder piles due to the possibility of discharging it from the vibrating grab bucket directly into a motor transport means.

According to the LSU data of the Gidrospetsfundamentstroi organisation, the application of the vibration technology complex for this purpose permitted the execution of the layout of foundations of cylinder piles with a total carrying capacity of 250 MN after 5 months, which is twice as fast as the existing standard periods.

Under the conditions of hydrotechnical construction, experience in conducting these operations on projects of the Gidrospetsfundament-stroi and Dalmorgidrostroi organisations, in which sandy and clayey soils with various stony inclusions were extracted from cylinder piles from 1000 to 1920 mm in diameter with vibrating grab buckets from under water from depths up to 30 m can be indicated as typical examples of driving cylinder piles employing vibrating grab buckets with a longitudinal-rotational action.

The use of vibrating grab buckets of longitudinal-rotational action in these operations permitted a 2-3 fold increase in productivity as compared with cable jaw grippers, and it was the only means in some cases that assured removal of the soil plug and the possibility of driving cylinder piles.

The characteristics of the vibrational driving of cylinder piles under deep-water construction conditions were first investigated in connection with elucidating the causes of the damage of cylinder piles in the construction of a moorage in the Tallinn ocean fishing port (M. G. Tseitlin, B, P. Shik, I. L. Krymskii, G. A. Pridchin, Yu. V. Shachkin, and A. M. Ivanov, 1966). The moorage had a stockade construction on reinforced concrete cylinder piles 1.2 m in diameter, 14-16 m in length and with a wall thickness of 10 cm (300 grade concrete). The piles were driven with a VP-5 vibrator into moraine loams covered with a thin layer of silt. The water depth was 6-9.5 m. It was established by examination that most of the piles have longitudinal cracks and chipping of the concrete that develop during vibration driving. The nature of these defects is as follows: longitudinal cracks develop in the lower sections of the piles, the length and width of which are dependent on the duration and intensity of the vibration driving; chipping and holes are found in the concrete in some piles. The cracks are formed at the level of the bottom and propagate upward, extending to the junction of the lower section. The opening width of the cracks is from several millimeters to 15-20 cm.

It should be noted that this type of damage became typical at this point in time (1963-1965), but it was usually explained by extreme longitudinal stresses in the walls of the cylinder piles, which developed during their vibrational driving.

In explaining the causes of the damage of the piles, a complex of large-scale experimental studies was conducted on the process of driving reinforced concrete cylinder piles through layers of water with measurement of the vibration and stress parameters in the walls of the piles that appear during the vibration driving. Tensometric sensors were implanted in the piles during their preparation for this purpose.

An analysis of the results obtained in the experimental studies demonstrated that the normal stretching and compression stresses in the annular sections of the tubular piles that arise during vibrational driving are not sufficiently large to be the cause of the formation of longitudinal cracks. It was established that periodic stretching stresses that reach values at which crack formation is possible in the concrete arise in the radial cross sections of the driven tubular piles.

The appearance of stretching stresses in the longitudinal sections of the pile during its upward movement can be explained by the dynamic action of the water column present inside of the pile.

In order to verify these hypotheses, a special cycle of tests was conducted, the program of which included the driving of tubular piles by both the usual technology and with the preliminary pumping out of water from the internal cavity of the tubular pile in order to eliminate the dynamic pressure.

These tests confirmed the hypothesis that the cause of damage to the tubular piles under the hydrogeological conditions of the construction of the Tallinn marine fishing port is the dynamic action of the water.

The experimental studies and large-scale observations conducted afterwards (G. A. Pridchin, L. I. Afanasyeva, et al., 1970) also revealed that the cause of damage to the reinforced concrete cylinder piles driven through a layer of water is an increase in the hydro-dynamic pressure in its cavity during the vibration driving.

It was established in examining the oscillograms of the driving process that stretching stresses arise in the longitudinal sections of the pile during its upward movement. This phenomenon can be explained if it is assumed that the soil plug moves together with the pile and it interacts with the water column present inside of the pile (M. G. Tseitlin, 1966).

During the downward movement of the pile with an acceleration roughly equal to the acceleration of the force of gravity, (this type of movement was observed during the vibratory driving of piles in the Tallinn marine fishing port inertial forces counterbalance the force of gravity and the water exerts practically no pressure on the pile walls.

During the impact of the pile on the soil and its subsequent movement upward, there is an impact of the water on the soil plug. By virtue of the fact that perturbations in the water are propagated at a finite velocity v1, at first there is a change in the velocity of the layer of water adjacent to the soil plug Dl1 = v1 Dt, which prior to impact on the soil plug had the velocity of the water column vo, and after impact it acquired the velocity v* (the velocity of the boundary between the soil plug and the water). At the same time, the soil layer adjacent to the boundary Dl2 = v2 Dt, which has the velocity v01 (velocity of pile movement), acquires the velocity v*(v2 is the propagation velocity of the perturbation in the soil).

By designating the force of interaction between the soil and the water by P and employing the theorem on the variation in the amount of movement of the layers Dl1, and Dl2, we obtain:

(75)

(76)

where r1, and r2 are the densities of the water and soil respectively and Un is the cross sectional area of the soil plug.

We find from formulas (75) and (76) that

(77)

By substituting (77) into (75) and assuming that P = DpUn (Dp is the pressure increment in the water layer D1), we obtain

(78)

During the following time interval Dt, the water and soil layers adjacent to the interacting layers change their velocities. Thus, the gradually increased pressure that arises at the boundary between the water and the soil propagates in the form of an increased pressure along the water column and the soil plug. With a subsequent movement of the pile downward, the pressure in the water column is equalized and the cycle of phenomena described is repeated.

Equation (78) does not take into account the process of wave reflection from the free surface cf the water and from the soil, and gives an assessment of the maximum possible increase in pressure with a change in velocity from vo to v01. In the meantime, it is obvious that at shallow water depths the pressure values calculated with formula (78) can be overstated.

Observance of the following inequality is a reliable criterion of the applicability of formula (78)

ty < 2 l/v1

where ty is the time cf the impact interaction between the water column and the soil plug and 1 is the height of the water column.

The physical significance cf this inequality consists in the fact that the impact is completed before the expansion wave arrives.

As the preliminary calculations revealed, a large number of cases are encountered in practice where ty > 2 l/v1 . These cases obviously take place when the water column is not large and the impact time is not very short. It all takes place as if all the layers of the column inside the pile changed their velocity simultaneously. This assumption makes it possible to consider the movement of the entire water column as an incompressible body in determining the excess pressure (the force of interaction between the soil plug and the water).

The accumulation of experimental data on the impact time (under different soil conditions) and on the nature of perturbation propagation in the water column inside of the pile makes it possible to select for calculation either the wave model given above or the model where the movement of the water column is considered as the movement of an incompressible body.

In accordance with the experimental data obtained, the impact time of a tubular pile on the soil is roughly:

for compact soils ty (0.05— 0.08) T
for soils of medium density ty (0.1— 0.4) T
for loose soils ty (0.3— 0.5) T

The propagation rate of the impulse in the water inside of the elastic reinforced concrete tube is determined with the formula of N. E. Zhukovskii

where EB, Ed and Ea are the moduli of elasticity of water, concrete and reinforcement; d is the wall thickness of the tubular pile; and a is the coefficient of reinforcement of the annular reinforcing material.

The propagation rate of perturbation in the soil v2 can be selected from the table (D. D. Barkan, 1948), which contains the results of measuring the propagation rate of longitudinal elastic waves in some types of soils.

v2 ,m/s
Wet clay 1500
Tight gravelly-sandy soil 480
Fine-grained sand 500
Medium-grained sand 550
Medium-size gravel 750

The results of experimental studies confirmed the hypothesis that with a water column height of l < v1ty/2 it is possible by assuming further simplifications in the calculation scheme to consider the movement of the water column inside of the pile as the movement of an incompressible body. In this case, the pressure of the water inside of the cylinder pile at the level of the soil plug that develops during vibrodriving can be determined with the formula

pmax = p1l1a (79)

where l1 is the height of the water column and a is the maximum acceleration.

Correspondingly, in the layer of water separated from the soil plug by the value 1*,

p1 = p (l11*) a. (80)

The maximum acceleration value a for the various soil conditions and vibration modes is determined by the results of studies on the process of driving tubular elements with the formation of a soil plug. Comparison of calculation by the above formulas with the experimental data offers a satisfactory concordance of the calculated and experimental values (G. A. Pridchin, L. I. Afanasyeva, M. F. Reut, and I. D. Bobrik, 1970).

In order to reduce the hydrodynamic loads, a specially prepared shock absorber, consisting of several automobile chambers mounted in a container with ballast, was proposed and used. The vibration driving of tubular piles, using a shock absorber, was carried out in the following manner. The shock absorber was suspended to the head of the vibrodriver on cables, the length of which somewhat exceeded the length of the tubular pile driven. In fastening the vibrator on the pile the shock absorber was lowered to the ground. After driving the pile, the vibrator together with the shock absorber fastened to it are placed on another pile. The experimental work conducted demonstrated the high efficiency of such a shock absorber.

An apparatus proposed by VNIIGS for the vibration driving of piles under conditions of deep-water construction, obviating the possibility of withdrawing the shock absorber from operation during its suction into the soil and assuring maintenance of the shock absorber in the zone of maximum water pressure during the entire period of vibration driving was used in another organisation, Baltmorgidrostroi.

The apparatus (Figure 68) consists of a shock absorber suspended on a cable to a float. The length of the cable is selected so that the shock absorber hangs on the float close to the bottom. The entire apparatus is suspended to the head of the vibrodriver on cables and is introduced inside the pile when the vibrodriver is set up [21].

Figure 68. Apparatus for preventing damage to the cylinder piles during vibration driving through a layer of water. 1 – shock absorber; 2 – cable of the shock absorber; 3 – float; 4 – vibrodriver; 5 – cable of the float.

Because the height of the water column inside the pile varies practically not at all during the vibration driving of the pile, the shock absorber always remains in the zone of the greatest water pressure.

The studies conducted on the causes of the development of cracks during the driving of cylinder piles also permitted us to conclude that the elasticity of the medium filling the cylinder pile is an important factor, on which the magnitude of dynamic pressure in the pile cavity is dependent.

Stand tests confirmed that a reduction in the modulus of elasticity of the medium filling the pile with the aid of aeration makes it possible to reduce the amount of dynamic pressure to safe values.

An air-injection arrangement was proposed and incorporated, the essential operation of which consists in saturating the water and soil in the cavity of the cylinder pile with air [22].

The water and soil in the cylinder pile cavity are saturated with air from a compressor through a steel tube, which is sunk into the soil core together with the washing tube. The use of this apparatus in the construction of piers assured a 100% integrity of the cylinder piles. VNIIGS worked out the new protective arrangement that made it possible to improve the technology of carrying out the operations [23].

Air is fed into the cavity of the driven cylinder pile through a polyethylene conduit, laid in the wall of the cylinder pile during its manufacture, and exits through an annular collector, also located in the wall of the cylinder pile at a distance of 2.5 diameters from the pile toe. The proposed protective apparatus was investigated in the projects of the organisation Baltmorgidrostroi (E. N. Perlei, G. A. Pridchin, and I. Sh. Gonikman, 1981).

The studies conducted revealed that the stresses in the concrete of the walls of the cylinder piles, caused by internal dynamic pressure, in driving without the supplying of air into the cavity of the cylinder piles exceed by 1.6 times the calculated resistance to expansion of grade 400 concrete. When a protective apparatus is used, the stretching stresses in the concrete are considerably less than the calculated stresses.

Driving Prismatic Steel Reinforced Concrete Piles

The mass vibration driving of heavy steel reinforced concrete piles was first done in the beginning of the 1950’s with the aid of vibratory drivers of the VP-1 and VP-3 types (B. P. Tatarnikov). Several tens of thousands of steel reinforced concrete piles with a cross section up to 45 x 45 cm and a length up to 14 m were driven solely in the construction of bridges.

An industrial test on driving heavy steel reinforced concrete piles indicates that the use of the vibration technique is most effective in this case in loose water-saturated soils, while the use of vibratory drivers for this purpose is not feasible in low-moisture and compact soils.

At the present time, the driving of prismatic steel reinforced concrete piles with vibratory drivers is carried out relatively rarely not only due to the limited range of the effective application of vibration during the driving of elements with a high lateral resistance, but also due to additional complications (with the use of nonspecialized vibratory drivers) with separate raising of the vibratory driver and pile and their subsequent rigid connection.

The vibrational driving of prismatic steel reinforced concrete piles is most widely used under the conditions of the construction of electric transmission lines (ETL) and the supports of the contact system of railroads, where specialized units are used for this purpose, and the piles themselves due to the construction conditions are equipped with threaded pins for subsequent fastening of the metallic support to them.

The use of specialized self-propelled units makes it possible, on the one hand, to assure a complete autonomy of these machines and, on the other hand, due to the use of part of the mass of the unit, to achieve an optimal pressure of the end of the pile on the soil.

One of such specialized units is the AVSE-U unit, designed for the vibrational driving of pile foundations for the support of a contact line (M. B. Belkind, A. N. Tarasov, and M. N. Margolin, 1983). The construction of the units was worked out by the Central Scientific Research Institute of Communications (TsNIIS), jointly with the planning and design office (PKB) of Glavstroimekhanizatsiya Mintransstroya. The AVSE-U unit is equipped with a contactless system for controlling the vibratory driver.

The driving of pile foundations with the aid of the AVSE-U unit takes place in the following manner. After it is set up around the point of driving, the crane with the vibrating driver and pile fastened to it is turned perpendicular to the axis of the path, moved to the required distance, after which the slewing guide box, together with the vibratory driver, is moved by hydraulic drive into the vertical position. Then the machine operator, paying out cable, guides the vibratory driver with the pile downward, switches on the electric motor and effects the installation. If necessary, the pile is directed with the aid of an extensible or rotary crane. When the installation is complete, the hydraulic holding clamps are loosened, the vibratory driver is raised, the guide box is moved into the horizontal position, the crane is moved and turned into position along the platform, after which the next pile, which lies on the table, is gripped.

The specialized units also include vibrating impressing units of the VVPS-20/11 (Figure 57) and VVPS-32/19 types, the characteristics of which are given below. The construction of the units was worked out by the Leningrad branch of the Orgenergostroi Institute in collaboration with the All-Union Scientific Research Institute of Hydraulic and Sanitation Engineering Operations (VNIIGS).

VVPS-20/11 VVPS-32/19
Amplitude value of the compelling force, kN 200 320
Maximum value of the crushing effort, kN 110 190
Static moment of the mass of the eccentrics, kg-cm 3500 6000
Frequency of the compelling force, Hz 12-15 11-13
Engine power of the basic machine (tractor), kW 79.4 132.4
Figure 57 The vibro-driving unit VVPS 20/11.

As is evident from Figure 57, the encompassing welded frame, to which all the basic subassemblies of the unit are fastened, is located on the tractor with an elongated travelling section. A generator is placed in the lower stage of the rear portion of the frame; it is driven by the power takeoff shaft of the tractor through a reducer. A two-drum friction winch with an electric motor is installed in the second level of the frame above the generator. The raising of the vibratory driver with pile, placement of the upper section of the crane in the transport position are accomplished with the aid of the winch and, inversely, the loading force is also created.

The vibratory drivers constructed according to the scheme of the VPP-2 (see Figure 45c) do not have any structural peculiarities, with the exception of the sets of the driving cables, located on the spring-mounted part of the driver frame.

In connection with the limited driving ability of the vibratory drivers, further development was obtained with impact-vibrational driving units, the driving force in which is applied directly to the pile (or other driven element). A representative of such machines is the UWS-60/10 unit.

For the driving of boltless or pinless piles, the impact-vibration hammer of the unit is equipped with a special head that makes it possible to grip and hold the pile that is lying on the ground, with its subsequent raising into the initial position without the aid of any additional load-lifting devices.

The pile is placed in the head of the impact-vibration hammer in the following order (Figure 58). The gripping frame is placed over the top of the pile and a pintle with a fast-acting fastener is inserted. The frame is held with a chain for longitudinal transfer during the lifting of the pile. Due to the fact that the frame is connected with two measuring cables to the head, during the raising of the impact-vibration hammer the pile passes from the horizontal position to a vertical one and gradually enters the cavity of the head. After the lower end is pulled away from the ground, it hangs in the cables in the vertical position and due to the eccentric suspension of the frame the pile is fixed into the front cavity of the head. When the impact-vibration hammer is lowered, the pile is fixed in the internal cavity of the head when it reaches the ground with its lower end.

Figure 58. Scheme of raising a bolt-less pile with the UVVS-60/10 unit.

During the driving of bolted piles, the technology of their lifting involves the following. The pile is placed on a support so that its end with the bolt was located near the point of driving. For lifting, the pile cap of the unit is connected to the pile with two cables. Then with an inclined boom of the unit, the impact-vibration hammer and the pile are raised. With the pile raised, the unit strikes the driving point, after which the vertical position is imparted with the aid of the mechanisms of longitudinal and transverse correction of the boom and pile, and the pile is lowered onto the driving point.

In some cases a 12-meter pile was driven in 5 minutes. Although the underlying soils (loams and dense clays), lying at a depth of 6-8 meters, had a substantial solidity, application of the impact-vibration hammer assured the driving of the pile to the given depth with an accuracy of ± 2 cm. The productivity of the impact-vibrational driving unit, taking into account the time for technical maintenance during the installation of a pile 12 m in length, is about 10 piles per shift.

The impact-vibrational driving apparatuses also include the AVS-1 of VNIIGS construction for the driving of enclosure posts. Its technical characteristics are given below:

Working element free springed vibrating hammer with the possibility of transition to the vibratory driver mode
Mass of the impact part, kg 450
Static moment of mass of the eccentrics of the vibration exciter, kg • cm 300
Frequency of the vibrations, Hz 25; 15.5
Driving force, kN 20
Basic machine ETU-357 excavator

The device (Figure 59) was operated in the construction of the guard rails for the Oktyabr railroad (a total of 6000 posts were driven). With the vibration mode, the post was driven in 2.5-30 minutes only to a depth of 0.7-0.8 m, and with the impact mode, to the projected depth of 1.3 m. The use of part of the mass of the pile-driving apparatus for driving the post during its vibrational-impact installation permitted a reduction in the driving time to 1-1.5 minutes. The work was performed according to the following technology:

  • The unit was moved to the site of driving the post, raising the impact-vibration hammer upward with the boom to a height of 3.2 m;
  • The post was drawn up to the apparatus and raised under the opening of the head with an auxiliary winch of the aggregate;
  • The impact-vibration hammer was lowered, the post was clamped in the head with a hydraulic cylinder and positioned over the point of driving with the aid of hydraulic cylinders of longitudinal and transverse correction;
  • The post was driven by switching on the impact-vibration hammer;
  • The impact-vibration hammer was switched off, it was raised 10-15 cm above the top of the post and the aggregate was moved to the new driving site.

A time study of the basic and auxiliary operations revealed that the post driving cycle had an average duration of 4 minutes and 28 seconds, where the driving process itself occupied about 30% of the cycle; the power required by the electric motor of the impact-vibration hammer did not exceed 2.5-3-0 kW.

Figure 59. Driving of guard rail posts on a railroad run.

The use of the AVS-1 unit made it possible to free the drilling machine, bulldozer and transport means, previously for transfer of the gravel and cement, and also to reduce the consumption of materials and the manual labor required (V. M. Klementyev, 1976).

In the calculation schemes of impact-vibrational driving the driving forces on the pile are considered constant over the entire driving cycle.

In order to assess the effect of the rigidity of the driving cables and the mass of the pile-driving apparatus on the driving ability of the impact-vibration hammer, it is necessary to consider the calculation scheme depicted in Figure 60.

Figure 60. Calculation scheme of the impact-vibrational pile driver.
Figure 61. Dependence of the dimensionless displacement of the pile on the parameter ξ5.

1.y = 4.17;

2.y = 2.38;

3.y = 1.67;

4.y = 1.28;

5.y = 1.04.

In establishing the basis of the calculation model it is necessary to introduce the following into the previous assumptions in studying impact-vibrational systems:

  • The pile-driving apparatus is an absolutely solid body that is supported through an articulation on a nondeformable base;
  • The free vibrations of the pile-driving apparatus are damped during the movement of the impact part in breaking away from the pile.

The first stage of the movement of the system examined begins at the time of the impact part of the impact-vibration hammer breaking away from the pile and ends at the moment of applying the impact. By virtue of the assumed mechanism of soil resistance, the pile is immobile during the first stage, i.e., the rigidity of the elements of extraneous driving and the mass of the pile-driving apparatus have no effect on the movement process of the impact part.

The second movement phase begins at the time of impact and joint displacement of the impact-vibration hammer and pile. It ceases with the termination of driving.

The differential equation of movement of the impact part in breaking away from the pile – the flight of the hammer (first movement stage) – has the form described in Section 7, with the same initial and final conditions.

The differential equations of movement for the second stage have the form:

where m3 is the mass of the pile-driving apparatus, QP is the driving force on the pile, c5 is the coefficient of rigidity of the connections between the pile-driving apparatus and the impact-vibration hammer, and l is the distance from the axis of turning of the pile-driving apparatus to the point of application of the driving force to the pile.

In addition to the dimensionless variables and parameters (9) and (41), we introduce the following:

The calculations by the method presented above were performed on a computer. The results of the calculations are presented in the form of the graphs of Figure 61 with the following values of the parameters: sin α = 0.5, ξ1 = 0.5, β = 1.0, and δ = 0.75.

It can be concluded from an analysis of the calculations that for

loose soils (f + γ = 3-5) in the case of elastic connections between the pile-driving apparatus and the pile (ξ52 < 12.5) the operation of the impact-vibration hammer is unstable , while for ordinary impact-vibration hammers with the assumed parameters of the hammer, it is in the zone of stable operation. It should be noted that there is an optimal value ξ5 different from zero, for such soils, at which the maximum driving ability of the impact-vibrational aggregate is attained. In this case, a shift in the optimal ξ5 values takes place toward their decrease with an increase in the forces of soil resistance, and in compact soils (f + γ > 7) the optimal value is ξ5 ≈ 0.

Having compared the results of calculation by the method that takes into account the multiple masses of the impact-vibration hammer-pile-driving apparatus system and the influence of rigidity of the connections between the impact-vibration hammer and the pile-driving apparatus, with the calculations by the simplified method, which does not take into account these specific characteristics of the impact-vibrational pile drivers, it can be concluded that the simplified method expounded in Section 7 yields excessively low values of the driving ability of the impact-vibration hammers for loose soils.

For soils of medium and high density f + γ > 7, the simplified method presents results at ξ5 ≈ 0 that are quite close to the more precise calculation scheme of impact-vibrational driving units (see Figure 60). In soils of medium and high density, an increase in rigidity of the connections between the impact-vibration hammer and the pile-driving apparatus significantly reduces the driving ability of the impact-vibration hammer.

For loose soils there is an optimal value of the mass of the pile-driving apparatus (v ≈ 1.67). At the same time, for compact soils the driving ability of impact-vibrational driving units increases with an increase in the mass of the pile-driving apparatus, which is manifested particularly clearly as the rigidity of the connections between the impact-vibration hammer and the pile-driving apparatus increases.

Installation and Extraction of Metal Sheet Piling

Editors note: from a practical, equipment standpoint, this is one of the most interesting sections of the book. It describes the first use of vibratory hammers on an actual project, and an interesting description of driving sheet piles and problems that can arise during that installation.

The vibratory method of installation and extracting piles began to be used on the industrial scale in 1949. This method was first used in the construction of the Gorki (Nizhny-Novgorod) hydroelectric power plant, where the pile was driven into water-saturated sands with a vibrating driver of the BT-5 type (D. D. Barkan and V. N. Tupikov).

The high technical and economic indices of vibratory driving attained at the Gorki power plant facilitated acceptance of the new method. Vibratory pile driving enjoyed broad dissemination as a result of the studies at the All-Union Scientific Research Institute of Hydraulic and Sanitation Engineering Operations (VNIIGS) with the use of the VPP-2 vibratory driver developed by this Institute (O. A. Savinov, A. Ya. Luskin, and M. G. Tseitlin,) which was used in the construction of many power plants and other large facilities.

In the construction of the Stalingrad power plant with the VPP-2, more than 24,000 tons of piles of the ShP-1, ShK-1 and Larsen-V types was driven to a depth of up to 12-14 meters, primarily into saturated sands with gravel and pebbles, interspersed with sand-silt or clay soils. Vibratory driving of a pile into the underlying rock was difficult; therefore, the pile was driven with hammers. However, the application of VPP-2 furnished a substantial effect, especially due to the rapid setting of piles in porous dikes.

On the basis of accumulated experience:

  • Vibratory pile driving technology was acknowledged to be the most effective, especially in driving into saturated sand and plastic clay soils.
  • In driving piles by vibration, the productivity is almost 2 times higher than conventional impact driving.
  • Extraction of a pile for its reuse can be reliably accomplished by the vibratory method in those cases when the pile was driven by vibration.
  • It was found that a pile pounded in with impact hammers is not always amenable to extraction due to deformation of the interlocks.

The technical-economic advantages of the vibration method are defined not only by the increase in the driving rate and the possibility of extracting the pile, but also a more efficient technology of the auxiliary operations performed by using self-propelled load-lifting devices.

Despite the advantages indicated, the use of the vibratory method in pile driving has been limited to date, as a rule, by its length of no more than 12-15 m, and vibro-extraction, by a depth of no more than 8-10 m (VPP-2, V-401) and up to 15 m (MSh-2M). In this case, the range of efficient utilization of the method was limited by saturated sandy and plastic clayey soils.

A series of research efforts directed toward creating a vibrating device for the driving and extraction of piles with a length up to 20 m was carried out in recent years for the purpose of expanding the range of application of the vibratory method in pile driving and also for a comparison of the efficiency of the means of vibration techniques with pile driving equipment when driving piles into difficult soils.

The results of studies on the processes of vibration and impact-vibration driving and extraction of various elements with a predominant lateral resistance were used in solving these problems.

The fundamental results of these studies are summarized in the following:

  • During hammering or ramming into saturated sands and plastic clays, the rate of driving and extraction of the elements in the vibration and impact-vibration modes differs little, but the power consumption is considerably less in the vibration mode;
  • During hammering or ramming into low-moisture sands and into stiff-plastic clays, impact-vibration driving or extraction is more effective than mere vibration; with regard to the power required, it can be higher in the vibration or impact-vibration modes, depending on the rate of driving;
  • The efficiency of impact-vibration driving and extraction can be substantially increased in the two-impact mode of impact-vibration hammer operation (one impact upward and the second downward in each cycle).

The short-term two-impact action on the pile during its extraction is also useful for the initial oscillation buildup (pulling from the site) in the case of substantial resistance in the deformed interlocks of the pile being extracted.

An analysis of the results obtained and the characteristics of vibration driving and extraction of a pile determined the choice of the type of vibrating device, which could operate effectively as a function of the soil conditions and the mass of the pile in vibration, single-impact and two-impact modes of operation.

In order to assure the longest service life, the basic operating mode of the vibrating device should be vibratory. If necessary, the pile should be driven in the impact-vibration mode with impacts downward.

The pile can also be extracted in single-impact (impacts upward) or two-impact modes.

The VSh-1 vibrating device developed by VNIIGS (Figure 56) meets the indicated requirements; it is designed for driving and extracting a Larsen-type pile with a length of 20 m.

Figure56
Figure 56 Vsh-1 Vibrating Device

The parameters of the vibrating device, calculated by using the results of the studies conducted, assure a substantially greater efficiency in comparison with the VPP-2 (V-401) vibrator used at the present time, with the same adjusted power of the electric drive.

After conducting production tests for several years, the VSh-1 vibrating devices have been successfully used on projects of the trusts Gidrospetsstroi and Ukrgidrospetsfundamentstroi (M. G. Tseitlin, V. V. Verstov, and Ya. K. Baitinger, 1984).

The VSh-1 vibrating device was used by the Volgograd administration of the trust Gidrospetsstroi, with the aid of which a pile with a length of 17 m and of the Larsen-IV and Larsen-V types was extracted from a pile wall that had been driven in the 1950’s into clay soils with steam-air hammers. Attempts prior to this to extract the pile with a V-401 vibrator were not successful.

Extraction of the pile with the VSh-1 vibrating device was done with the aid of a Yubegai floating pile driver with a lifting capacity of 30 tons with piles in three pieces. The middle sheet pile, on which the vibrating device was fastened, was strengthened by the welding on of cover plates, and the interlocks of the side sheet piles were cut to the water level (1.5-2 m) in order to facilitate breakaway of the pile package in the interlocks. The pile was successfully extracted with the passage of the vibrating device to the two-impact mode at an exciter vibration frequency of 13.3 Hz. The vibration mode was also tested at a 20 Hz frequency, yielding, positive results.

In the Ulyanov construction administration of the same trust, the problem of driving a pile 19 m in length into clay soils with seams of pebbles to a depth of 7-8 m was one of the objects. An attempt was initially made to solve this problem with the aid of the V-401 vibrating driver and Diesel hammer with a mass of the impact part of 1.8 tons. The driving ability of the V-401 vibrating driver was inadequate for driving the pile to the specified mark. During driving with a the Diesel hammer the upper part of the pile was deformed and consequently the driving was ineffective. The VSh-1 vibrating device, tuned to the vibration mode at a frequency of 13-3 Hz, made it possible to drive the Larsen-V pile to a depth of 19 m. The results of operating the VSh-1 vibrating device on many objects revealed that its driving and extracting ability is considerably greater with the same power consumption than in the VPP-2 (V-401) vibrator.

In addition, during the mass production of the VPP-2 (V-401) vibrator, its refinement for increasing the service life due to some change in its parameters, reinforcement of the electric motor windings, increasing the efficiency of the suspension during operation with load-lifting means, and also the use of a hydraulic head, excluding the need for cutting an hole in the head of the sheet pile and the possibility of collision, observed when a wedged head is used. Such a modification of the VPP-2 (V-401B) vibrator was worked out by VNIIGS and the trust Gidrospetsfundamentstroi.

An experimental comparison of the effectiveness of the various pile driving means in driving piles into difficult soils was conducted by the Leningrad administration of the trust Gidrospetsfundamentstroi on an area whose geological structure is represented by the following stratifications (m):

Fill sand 0-2, 2.0
Fine sand with grains of gravel 2.2—3.0
moraine loam of hard and semihard consistency with gravel, pebbles and boulders (up to 20%) 3 and lower

A pile with the following profiles was used in conducting the experimental studies: Larsen-IV, Larsen-V, ShK-1 and the flat ShP-1.

The following were used as the driving means:

  • Drop hammers with a mass of 3.5 and 5.65 tons and a frequency of the impacts of 15-20 per minute;
  • Tubular S-858 diesel hammer with a mass of the impact part of 1.8 tons and a frequency of the impacts of around 50 per minute;
  • V-401 vibrating driver with a mass of 2.2 tons, operating at a frequency of 16.6 Hz;
  • VP-1 vibrating driver with a mass of 4.5 tons, tuned to operating in the mode of a free impact-vibration hammer with a frequency of 420 impacts per minute.

The maximum driving depth of a pile of the Larsen-IV, Larsen-V and ShK-1 type with a suspended mechanical hammer was 5-5-6.0 m, including into moraine loam up to 2.5-3 m. In this case an increase in the hammer mass resulted in a substantial deformation of the upper part of the pile and did not increase the driving depth. In a series of tests with a hammer mass of 5-65 tons and a relatively small drop height (0.3-0.5 m) the deformations of the upper part of the sheet pile were so great at the end of the driving that it was necessary to cut off the deformed part in order to continue the work.

During the driving of a pile of the Larsen-IV, Larsen-V and ShK-1 types with a diesel hammer, the maximum installation of the pile into the ground reached 7.5 m, including 4.5 m into moraine loam with substantial deformation of the top of the pile. The ShP-1 pile was driven with a diesel hammer only to the top of the moraine loams, and then lost its longitudinal stability, and its further installation became impossible. In the driving of piles of all profiles with a V-401 vibrating driver, their complete preservation was assured. However, the pile driving stopped when the roof of the moraine loams was reached.

Impact-vibration pile driving was done with a VP-1 vibrating driver, equipped with a forked guide for the pile and attuned to the mode of a free impact-vibration hammer (without being fastened on the pile.) An effective and stable operation of such a VP-1y impact-vibration hammer was achieved with an increase in its mass to 6-7 tons.

With such an adaptation, the impact-vibration hammer drove successfully without a deformation of the upper part of a Larsen-V pile with the required depth into moraine loam to 2.5-3 m. As a result, the VP-1y impact-vibration hammer-driver was used by the Leningrad administration of the trust Gidrospetsfundamentstroi in the driving of a Larsen-IV pile with a length of 11.5-12 m to a depth of 9 m in the installation of a single-row protection dike.

VP-1y drove three to four sheet piles per shift without their deformation and with a driving depth into moraine loam of 2-2.5 m. The productivity of the suspended mechanical hammer was only half as much under these conditions and the driving was accompanied by deformation of the upper part of the sheet pile.

The results of a cycle of tests in which the driving ability of various types of pile driving means in clay soils with a semihard and hard consistency was compared (V. V. Verstov, M. G. Tseitlin, Ya. K. Baitinger, and G. F. Olshevskii, 1984) indicate the greater efficiency of impact-vibration installation with a comparatively low power of the single impact and a high frequency under the condition of a free impact-vibration hammer and a ratio of the total mass of the impact part to the magnitude of the compelling force that assures a stable operation of the impact-vibration hammer. Under such conditions (in contrast to other pile driving means) no deformation of the driven pile occurs during effective driving.

The studies conducted and analysis of the industrial test on the use of the means of the vibration technology of elevated efficiency in the installation and extraction of a pile indicate the need for driving the pile primarily with vibrators or impact-vibration hammers in order to assure its vibro-extraction and reuse along with a high productivity.

The driving or ramming of a pile with hammers can be expediently used in exceptional cases, in particular difficult soil conditions, in conjunction with supplementary measures that facilitate the driving.

Installation of Sheet Piles

One of the important characteristics of the vibratory technology of pile driving in contrast to the impact method consists in the fact that, in most cases, it is necessary to fasten the sheet pile rigidly with the vibrating driver, and this operation is carried out in the horizontal position at ground level or on special supports with subsequent raising of the vibrating driver with the pile.

The choice of vibrator or impact-vibration hammer for pile driving or extraction is made as a function of the geological conditions, the type of pile, its length, the depth of installation, and also the technological scheme used for effecting the operations. The pile should be driven using self-propelled cranes or pile drivers.

The cranes or pile drivers should satisfy the following requirements:

  • The height of the crane boom should permit the lifting of the sheet pile arrangement with the vibrating driver fastened to it into the interlock of the sheet pile previously driven;
  • The outreach of the crane boom should be sufficient to bring the vibrating driver to the sheet pile and permit placement of the raised sheet pile with vibrating driver on the site of installation without moving the crane;
  • The load-lifting capacity of the crane or pile driver should be sufficient to lift the sheet pile to be driven with the vibrating driver fastened to it.

The preparatory work, performed prior to beginning the pile driving, includes levelling of the land, the layout of the plan of the pile structure, establishment of the guides (templates) for pile driving (if necessary,) and delivery of the piles to the site and their preparation for driving.

The driving of a pile with vibrating drivers is divided into the following basic operations:

  • Servicing and fastening of the sheet pile in the head of the vibrating driver;
  • Raising and placement of the sheet pile at the driving site;
  • Driving the sheet pile;
  • Detachment of the vibrating driver from the driven sheet pile.

During the vibratory driving of the sheet pile, its connection with the vibrating driver should have an assured immobility; this is accomplished with the aid of a hydraulic head or wedge clamp.

During servicing, the sheet pile is placed near the site of the operations on a support (cross beam) with a height of 1—1.5 m so that the upper end projects 1—1.2 m beyond the cross beam.

During the driving of the sheet pile, it is necessary to keep track of the state of the cable and the hook of the crane, to which the vibrating driver is suspended.

The rate of lowering of the crane hook should be such that the crane does not inhibit the installation of the sheet pile; in addition, there should not be excessive free cable because with a great length of the sheet pile it is possible that it could buckle under the weight of the vibrating driver fastened on it. The cable is fully slackened in the final stage of the driving.

The following deviations from the planned position are possible during the driving of the pile:

  • Deviation of the pile from the vertical in the plane of the alignment;
  • Deviation of the pile perpendicular to the alignment;
  • Installation of the sheet pile below the planned mark due to its withdrawal with the adjacent driven sheet pile;
  • Not driving the sheet pile to the planned elevation.

Elimination of fanning in the case of a slight deviation is achieved by drawing out the pile during installation in a direction opposite the deviation, and with a substantial deviation and the impossibility of its correction by drawing out, by the installation of wedge-like sheet piles. Deviation of the pile from the line of direction is eliminated by drawing out the sheet pile in the opposite direction.

If the drawing out of the sheet pile does not straighten its position, the sheet pile is pulled out and again driven in, using the necessary measures for maintenance of its projected position. Passage of the sheet pile below the projected mark is corrected by its building up or plating.

Incomplete installation of the pile to the projected mark is eliminated by one-two-fold raising of the sheet pile by 0.5-0.8 m and its subsequent reinstallation. Extraction of the pile with the application of vibration is usually effected with cranes.

In a tentative selection of the load-lifting capacity of the crane for the vibro-extraction of a pile that has been in the ground for a short time (less than one month), it is necessary that the force at its hook exceed the weight of the system (the vibrating driver and pile) driven into the ground by at least 2 times.

When the pile has been in the ground for a prolonged period, the force at the crane hook should exceed the weight of the system driven by vibration by 3-4 times. To reduce the force transfered to the crane boom, it is permissible to use vertical props (outriggers,) joined to the crane boom in an articulated manner and based on the ground with the aid of a plate or slab. Prior to vibro-extraction, the vibrator should be rigidly fastened on the sheet pile with the aid of a wedge or hydraulic head. The rigid connection should be assured during the entire process of vibro-extraction.

If the pile has been in the ground for a long time, a preliminary vibration (prior to lifting) is indispensable, the time of which is determined by testing on each object. The crane cable should not be taut in this case. In the following stage it is necessary with the force of the crane to tension the springs until the coils almost touch and continue the vibration up to the beginning of the vibro-extraction under the action of the force of the opening springs.

Further vibro-extraction is effected with the minimum lifting rate of the crane hook, not allowing the complete compression of the shock absorber springs here. In the final stage the extraction of the pile is carried out without vibration.

Vibrating Drivers and Impact-Vibration Hammers

It was previously noted that vibration machines are classified with respect to dynamic action on the element to be driven (extracted) into vibrating drivers, impact-vibrating drivers-impact-vibration hammers, and also combined ones, in which both vibration and impact-vibration modes or their combinations can be realized. In most vibrating drivers and impact-vibration hammers the power of the engine is converted into the energy of mechanical vibrations by means of a centrifugal mechanism with eccentrics.

The arrangement of the shafts in the body of the mechanism, the eccentrics on them and also the specific direction of rotation of the shafts make it possible to obtain a different interaction of the centrifugal forces of the individual shafts with the eccentrics and, consequently, to generate various types of vibrations of the vibration exciter.

As a function of the requirements imposed on the construction of the vibrating machine, determined by its technological purpose, form, dimensions and mass, the shafts of the eccentric mechanism can be horizontal and vertical, coaxial, parallel or mutually perpendicular. The specific direction and synchronism of rotation of the shafts with eccentrics are generally achieved with gears, cylindrical or conical.

With respect to the longitudinal axis of the element to be driven (extracted), the vibration exciters used in pile-driving and drilling vibration technology are capable of exciting circular, longitudinal, rotational, longitudinal-rotational, transverse and helical vibrations. Various kinematic schemes of eccentric vibration exciters that generate the said forms of vibrations and their combinations are shown in Figure 41. These schemes assume a perpendicular disposition of the longitudinal axis of the element to be driven (extracted) to the plane of the drawing.

Figure 41. Examples of the principal schemes of the vibration exciters, which facilitate the generation of various types of vibrations with a parallel (a) and mutually perpendicular (b) arrangement of the shafts.
  1. body;
  2. shaft;
  3. gear;
  4. eccentric;
  5. bearing support

As a function of the purpose of the vibrating machine and the type of element to be driven (extracted), the vibration exciter is constructed with the possibility of generating one or more types of vibrations. In the latter case, each type of vibration is used to perform a specific technological operation, for which it is most effective. During the course of the work the vibration exciter can be adjusted to one or the other type of vibration by rearranging the eccentrics by hand on the shafts into the required position or by remote control. Remote readjustment is achieved by changing the original position of the eccentrics on a certain part of the shafts of the vibration exciter through their relative rotation by an angle of 180° /2/.

This apparatus consists of two coaxial interacting elements, one of which is an eccentric carrier and the second has two eccentric stops or supports arranged at an angle of 180°. The carrier and the stops can be on separate disks or in the composition of the shaft, eccentric or gear. The transfer arrangement is placed between the eccentric and the guide link of the kinematic chain (Figure 42) or on the intermediate transmission shaft (Figure 43). Switchover from one type of vibration to the other and vice versa is effected by reversing the drive motor. Part of the eccentrics begins to rotate here only after turning the carriers or stops by 180°; thus, the relative position of all the eccentrics of the vibration exciter and the direction of the resulting compelling forces are changed.

Figure 42. Scheme of operation of the remote transfer apparatus in its placement on the shaft of the eccentrics.
  1. longitudinal vibrations;
  2. rotational vibrations;
  3. disk;
  4. disk;
  5. stops;
  6. carrier
Figure 43. Scheme of operation of the remote transfer apparatus in its placement on an intermediate transmission shaft.
  1. longitudinal vibrations;
  2. rotational vibrations;
  • disk with carrier;
  • disk with stops

In the vibrating drivers and impact-vibration hammers the eccentric mechanism of the vibration exciter is usually driven by electric motors, less frequently by hydraulic motors. Structural solutions of the vibration exciters in which the eccentric shafts are connected with the driving motor by means of a transmission (chain, gear or V-belt transfer). Transmissionless vibration exciters (the eccentrics are mounted directly on the shafts of the drive motor) are basically used for high-frequency impact-vibration hammers (16 Hz or more).

In such vibration exciters of impact-vibration hammers, synchronizing gears are not placed on the shafts of the eccentrics, their synchronous and cophasal rotation is achieved by self-synchronization during the blows of the body of the vibration exciter on the anvil.

In general form, the structural scheme of the vibrating driver for piles, channels, tubes and other analogous elements contains an electric drive motor or hydraulic motor, a vibration exciter of the eccentric type, suspension and cap. Besides, impact-vibration hammers have special collision nodes (limiters) in the form of a block on the body of the vibration exciter, which in this case is called the impact part, and the anvil located on the frame that goes into the composition of the head. In most structural solutions of impact-vibration hammers, springs are placed between the vibration exciter — the impact part and the frame with the anvil by one method or another; the springs serve to regulate the operating node of the impact-vibration hammer in order to increase the stability and effectiveness of the impacts. In a number of cases (the driving of reinforced concrete piles, long casing pipes) devices for transferring a static load (additional load) simultaneously with the vibration or impact-vibration load are provided for increasing the operating effectiveness of the construction of both vibrating drivers and impact-vibration hammers. The series of vibrating machines also contain an electric or hydraulic starting and regulating apparatus.

Both short-circuited electric motors and motors with phase rotor are used as the electric drive motors. The former are used for all types of impact-vibration hammers and also vibrating drivers with relatively low static moments of the eccentric masses. The latter are basically used for heavy-duty low-frequency vibrating drivers with large static moments of the eccentric masses.

In order to increase the service life of vibrating machines (especially impact-vibration hammers) preference should be given to vibration-proof and impact-proof electric motors of the AOPVV type, built into the body of the vibration exciter, in the construction of the drive mechanism with a short-circuited electric motor.

These motors have the evolute parts of the stator windings coated with a special compound and a radial gap between rotor and stator that is enlarged as compared with the standard one. In addition, when they are employed the vibration exciter car be produced in the form of a rigid and reliably operating monoblock and reinforced rotor shaft used in the motor, which in this case is expediently installed on more durable spherical roller bearings.

When a drive with electric motors having a phase rotor is used, it is necessary to employ their type VMT modification, if possible. Such motors have a steel cast body with reinforced brush mechanism and bearings.

Experience in the use of vibrotechnological means revealed that in low-power vibrating drivers (up to 10-15 kW), during the operation of which the generation of impact modes is excluded, the installation of short-circuited electric motors of the usual construction is justified. In this case, if the evolute parts of the stator windings are reinforced in such an electric motor, they can also be successfully used in impact-vibration hammers with a low power (up to 5-7 kW), operating at a frequency of not more than 15 Hz. A classification of the structural solutions of vibration exciters with a eccentric centrifugal mechanism is given in Figure 44.

 

Figure 44. Classification of the applicable structural solutions for vibration exciters with a eccentric centrifugal mechanism.

Key:

  • vibration exciters with eccentric centrifugal mechanism;
  • transmissionless;
  • with a transmission;
  • motors mounted in the body of the vibration exciter;
  • motors placed on the body of the vibration exciter;
  • motors placed on a plate fastened to the body of the vibration exciter by springs;
  • moment of the mass of the eccentrics is not realized;
  • moment of the mass of the eccentrics is regulated during shutdowns;
  • the moment of mass of the eccentrics is regulated during operation by remote control;
  • the frequency of the vibrations is not regulated;
  • the frequency is regulated by degrees;
  • the frequency of the vibrations is regulated continuously;
  • body without opening passing through;
  • body with opening passing through;
  • generates one type of vibrations;
  • generates several types of vibrations with manual readjustment;
  • generates several types of vibrations with remote readjustment

During the driving of reinforced concrete casings to substantial depths, good results in increasing the effectiveness of the process are furnished by the use of TsNIIS vibrating drivers of the VRP type, which assure a regulation of the static moment of the eccentric mass and the frequency of the vibrations during operation.

The technical means for modifying the static moment of mass of the eccentrics are different. In some cases when regulation of the moment by remounting the eccentrics manually during stoppages of the vibration exciter is admissible, the eccentrics are in the form of detachable plates positioned on the arms of the eccentric shafts (for small vibration exciters). In other cases the eccentrics consist of two parts, one of which is fastened rigidly to the shaft, and the other is mounted moveably with the possibility of relative rotation on the shaft with stepped fixation with pins or other method.

In vibration exciters with substantial static moments of the eccentric masses, regulation is effected by shifting the entire eccentric or a part of it in a plane perpendicular to the axis of the eccentric shaft. This shift, which makes it possible to increase or decrease the eccentricity, is accomplished with a screw jack installed in the eccentric, or with the aid of a hydraulic drive. When the latter is used, the static moment of the eccentric mass can be regulated by remote control with the vibration exciter operating.

A stepped regulation of the frequency of the vibrations of vibration exciters mechanically by varying the transmission ratio is rarely used at the present time.

A greater spread is obtained by electrical methods of regulating the drive mechanisms with electric motors, not only with a phase rotor, but also with short-circuiting. This became possible with the introduction of thyristor transducers into practice.

The body of the vibration exciters is either welded or cast. For a number of operations (driving steel pipe or drilling wells, reinforced concrete pile-shells with an open end) it is technologically advantageous to have a central passage opening in the body of the vibration exciter. In such a structural solution of the body it is important to make it sufficiently rigid. When electric motors that are not built in are used, their rigid fastening to the vibration exciter body must be assured. For this, it is necessary to use not only bolt fastening with reliable means against loosening, but also additional snap-on collars that make it possible to avoid breakdowns of the lugs of the electric motor. Two-row spherical roller bearings that are capable of absorbing large radial loads and operating under elastic deflections of the shafts should be used as supports of the eccentric shafts.

Long-term reliable operation of the eccentric mechanism and transmission of the vibration exciter is achieved by an appropriate taking into account of the acting forces and moments from both the drive and the dynamic loads, caused by the nature of the vibration or impact-vibration modes, during the construction stage (see Section 11).

Figure 45 depicts some structural schemes of vibrating drivers used in pile driving and drilling operations. The possible variants of making up the vibration exciters and also the solutions for the suspension of the vibrating machines are evident from the scheme. The greatest spread in practice was obtained with vibrating drivers of the transmission type. As a rule, drivers with a vibration frequency of more than 16 Hz are constructed according to the scheme of a vibrating driver with a spring-mounted load, proposed by 0. A, Savinov and A. Ya. Luskin /3/.

Figure 45 Structural schemes of the vibrating drivers used in pile driving and drilling operations.
  1. transmissionless vibrating driver with separate shock absorber and rigid load-absorbing element;
  2. vibrating driver with transmission and built-in electric drive motor and shock absorber with rigid load-absorbing element;
  3. vibrating driver with spring-mounted load, ordinary electric drive motor and a rigid load-absorbing element;
  4. vibrating driver with built-in electric drive motors, central passage opening and flexible load-absorbing element.

The advantages of this scheme should include the possibility due to the additional non-inertial load of assuring an optimal specific pressure on the soil under the end of the driven element and, as a . result, an increase in the efficiency of its operation, and also the mounting of the electric drive motor on a spring-mounted base.

Impact-vibration hammers constructed according to the schemes shown in Figure 46 were used in pile driving and drilling operations. Free springless impact-vibration hammers /4/ (Figure 46a) are currently made low-frequency, primarily heavy-duty ones; they are constructed on the basis of vibration exciters with transmissions. During the operation of these impact-vibration hammers it is difficult to assure a stable operating regime over the entire range of driving the element into the soil. The principal advantage of such impact-vibration hammers resides in the technological simplicity of their use, since they do not require a rigid fastening to the element to be driven. Impact-vibration hammers with springs, set up according to the scheme of Figure 46b /5/ and also impact-vibration hammers for impact-vibrational of piles and tubes from the soil (scheme of Figure 46c) are produced with a vibration frequency of 16 Hz or higher in both transmission and transmissionless types with heads that basically assure a rigid fastening of the impact-vibration hammer frame to the element to be driven.

 

Figure 46. Structural schemes of the basic types of impact-vibration hammers for pile driving and drilling operations.

(a) free impact-vibration hammer without springs; (b) impact-vibration hammer with springs, with hammers directed downward; (c) the same, directed upward

The peculiarity of impact-vibration hammers with springs in comparison with springless one consists in the fact that they make it possible through regulation of the degree of spring tensioning to obtain a broader range of stable operation and also to vary the operating regime — to change the frequency of the impacts and the impact velocity, An important parameter for adjusting a impact-vibration hammer with springs to one operating mode or the other is also the gap between the hammer head and the anvil. In impact-vibration hammers with a double-deck system of spring installation (see Figure 46b) the mass of the impact part is absorbed by the springs. Therefore, there is the possibility of installing the impact part relative to the frame in such a way that in the position of static equilibrium between the hammer head and the anvil it is possible to achieve a positive gap (distance between the hammer head and anvil less than the amplitude of the forced vibrations), a zero gap (hammer head and anvil come in contact without clearance) or a negative gap (some clearance is produced upon contact of the hammer head with the anvil).

In the double-deck system of impact-vibration hammer springs according to Figure 46b, a rigid fastening to the element to be driven is required, which leads not only to technological difficulties, but also to the need for producing structurally complex and heavy-duty heads, the mass of which seriously worsens the ratio of the masses of the impact part and the element to be driven (extracted) with the head and, as a result, leads to a decrease in the impact efficiency.

Free spring-mounted impact-vibration hammers, the schemes of which are given in Figure 47, are devoid of the said shortcomings. The difference in the impact-vibration hammers according to the schemes of Figure 46b and 47, a consists in the fact that the second, proposed in VNIIstroidormash, having the advantages of springed impact-vibration hammers, does not require a rigid fastening to the driven element. This is achieved by providing the impact-vibration hammer with a heavy-duty head in the form-of a steel casting, inside of which a reducer with anvil and guide socket for the pile is moveably installed. The mass of the steel casting is determined from the conditions of its lack of movement under the reaction of the springs during the upward movement of the vibration exciter. However, such a free springed impact-vibration hammer has substantial dimensions and total mass, nor does it permit regulating the mode of its operation by varying the tension of the springs during the driving of the pile or tube into the ground.

 

Figure 47 Structural schemes of free springed impact-vibration hammers.
  • free springed impact-vibration hammer without regulation of the spring tensioning during its operation; free springed impact-vibration hammers with regulation of their operating mode by varying the tension of the springs with a static load;
  • force of the load applied to the vibration exciter and is transfered to the driven element during the impact;
  • the force of the load is applied to the vibration exciter and is transfered to the driven element initially only during the impact, and in the concluding stage of the driving—additionally to it in the form of a constant-acting driving force;
  • the force of the load is constantly applied to the driven element and the vibration exciter, as the element goes deeper there is the possibility of increasing its driving force with a simultaneous decrease in the load on the vibration exciter and an increase in its impact velocity.

The free springed impact-vibration hammers developed at VNIIGS, the schemes of which are presented in Figure 47b-d, do not have such shortcomings. The first of these schemes (Figure 47b) was proposed in Ref. 6 for driving piles with the aid of a movable apparatus; the construction elements of the latter were used for applying the load and absorbing the reactive forces. This scheme, in which the force of the load is applied to the vibration exciter and transfered to the driven element during the impact, was developed and actualized in a free springed impact-vibration hammer for driving pipes in drilling operations /7/. In the latter case the tensioning of the springs during the driving of tube is accomplished by the block and tackle system of the drilling frame and is regulated within the specified limits by a traction windlass, adjusted to operation in an automatic “switching in/switching out” mode. During operation, such a impact-vibration hammer initially has a small negative gap (clearance), which is increased by tensioning the springs with an increase in resistance to driving, which in the necessary cases makes it possible during the driving of tube to preserve a stable regime of impacts of the impact-vibration hammer with periods of “an impact per revolution”.

A further improvement in impact-vibration hammers constructed according to Figure 47b was the scheme depicted in Figure 47c /8/. In the latter, the compression force of the springs in the initial stage of tube driving is realized and regulated just as in Figure 47b, and in the final stage, due to the presence of an additional support frame and stops on the cables in the construction, it facilitates a static pressing in of the tube in conjunction with its driving with the impact-vibration hammer, adjusted during driving to operating in a stable regime with a sufficiently deep negative gap. Such a joint action is quite effective in driving tube to substantial depths.

The block and tackle system of the free springed impact-vibration hammer, constructed according to Figure 47d, /9/ assures the application of the load to both the vibration exciter and to the driven element. It is possible with such a block and tackle system, as the element goes deeper and the resistance to driving increases, to increase the force of its static sinking (the compression force of the lower springs increases) with a simultaneous decrease in the load on the vibration exciter (the compression force of the upper springs decreases). Thus, with an increase in the force of static driving of the element into the soil an increase in the impact velocity of the hammer head of the vibration exciter on the anvil is assured arid, consequently, the energy of ~he impacts. The most rational area of application of the scheme of Figure 47d is the impact-vibrational machines of devices designed for the driving of tubes with a closed lower end during the production of some types of special construction work (trenchless pipe laying, installation of anchors in the ground).

The structural schemes of vibrational and impact-vibrational machines of combined action have specific properties that make it possible to use these machines in such a way that in order to execute a specific technological operation it is possible to establish the most rational type of dynamic action for the specific case. One of the combined vibration machines is the vibrating driver /4/, the basic scheme of which is depicted in Figure 41b; with an appropriate rearrangement of the eccentrics it generates longitudinal, rotational, longitudinal-rotational and helical vibrations. Such a vibration exciter scheme, based on four intersecting shafts with eccentrics, joined at the center with synchronizing gears, is used in the construction of the vibrating gripper with a longitudinal-rotational action /2/ (Figure 48). The distinguishing characteristic of this immersion instrument, designed for processing the soil and the sinking of wells for construction purposes, using mobile load-lifting means, consists in the fact that it permits the sinking of a soil sampler into the ground and unload it with the involvement of longitudinal vibrations most effective for it, and effect the stripping of the core relative to the solid mass of the soil ana the extraction of the soil sampler with the involvement of rotational vibrations. Passage of the vibrations of the vibrating gripper from one type to another is effected remotely by the device mounted in it, as described above (see Figure 42). The constructions of some modifications of vibrating grippers with a longitudinal-rotational action were worked, out at VNIIGS, the vibration exciter of which has shafts with eccentrics arranged parallel in pairs in a vertical plane, and a transfer mechanism for varying the vibration mode is installed on the vertical transmission shaft /10/ (see Figure 43).

Figure 48 Structural scheme of vibrating gripper with a longitudinal-rotational action
  • body of the vibration exciter
  • soil sampler
  • partition wall
  • electric drive motor
  • synchronous conical gears
  • shaft
  • eccentric
  • transfer mechanism

In order to broaden the range of utilization of the vibrating gripper with a longitudinal-rotational action toward more compact soils, a construction of it was worked out in which the soil sampler is sunk into the ground under an impact-vibrational regime and is extracted under rotational vibrations /11/. A special feature of such a vibrating gripper consists in the coupling of the vibration exciter and the driven element by means of sleeves and guide rods, the fitting of which is with a small clearance, and also in the set of springs that are capable under compression of creating clearance at the hammer head-anvil contact.

In this solution, the vibration exciter during adjustment to longitudinal vibrations operates in the mode of a springed impact-vibration hammer with a negative gap, and under rotational vibrations imparts vibrational-torsional movements to the soil sampler in the horizontal plane.

In this case, if the vibration exciter adjusted to operating in the mode of longitudinal-rotational vibrations by a method analogous to that described is coupled with the tubular element to be driven, it is possible to obtain a combined dynamic action, in which longitudinal impacts in conjunction with rotational vibrations will be transfered to the tube. A special transfer mechanism /12/ that assures its adjustment to the mode of longitudinal-rotational vibrations or longitudinal impacts in conjunction with rotational vibrations is proposed for remote control of the operating modes of such a combined impact-vibration machine.

Other examples of impact-vibration machines with a combined action can be the structural schemes of mechanisms given in Figures 49 and 50. The first of them is a springless impact-vibration hammer with a multi-impact action, in which several differently oriented impact pulses in the longitudinal and rotational directions are imparted to the element to be driven (extracted) during one revolution of the shafts with eccentrics /13/. The vibration exciter of such a impact-vibration hammer operates in the mode of longitudinal-rotational vibrations, during which its hammer heads effect consecutive impacts on the anvils of the frame after each 90° of revolution of the eccentrics: a longitudinal impact downward, a rotational impact clockwise, a longitudinal impact upward, a rotational impact counterclockwise, etc. With an increase in the gaps between the hammer heads and the anvils to values that assure an impactless operating mode of the mechanism in specific directions, it is also possible to obtain a single-impact operating mode in the downward direction, two-impact in the downward and upward directions and three-impact in the downward direction, rotational clockwise and counterclockwise.

Figure 49 Structural scheme of a springless impact-vibration hammer with a multi-impact action in the longitudinal and rotational directions.
  • vibration exciter with electric drive motor;
  • enveloping frame;
  • hammer head of longitudinal impacts;
  • hammer head of longitudinal impacts;
  • hammer head of rotational impacts;
  • hammer head of rotational impacts;
  • anvil of rotational impacts;
  • anvil of rotational impacts;
  • anvil of longitudinal impacts;
  • anvil of longitudinal impacts;
  • guide rod (rigidly fastened with the vibration exciter and installed with a sliding fit in the enveloping frame).

The second scheme (Figure 50) assures the operation of the impact-vibrational machine, designed primarily for extracting tubes and piles from the ground /14/. A special feature of such a vibrating machine consists in the fact that impacts directed upward or alternately upward and downward (after 180° revolution of the shafts with eccentrics) can be imparted to the element to be extracted as a function of the degree of prior compression of the springs. A stable and effective operation of the impact-vibration hammer during the extraction of elements from the soil in the regime of two impacts per revolution of the shafts with eccentrics is assured in this case if the pressure of the springs is set so that there is a zero or negative gap between the hammer head and anvils that transfer upward-directed impacts to the tube or pile, and a positive gap, the size of which is 50-70% the amplitude of the vibrations of the vibration exciter, is obtained between the hammer head and anvils for the downward impact.

Figure 50. Structural scheme of a springed impact-vibration hammer with a multi-impact action in the longitudinal direction.

A common important characteristic of the said structural solutions of the impact-vibration hammers of multi-impact action is that they have a high stability in preserving the established impact-vibrational mode with a significant frequency of the vibrations. This is achieved in that an additional impact (in the direction opposite the performance of “useful” work) assures the stability of movement of the impact part, in which case the stability effect of the “two impacts per revolution of the shaft of eccentrics” mode increases with an increase in the frequency of the vibrations of the vibration exciter.

On the whole, vibration and impact-vibration machines with a combined action broaden the ranges of rational application of the means of vibration technology in pile driving and drilling operations, making it possible to create efficient vibration technologies.

The suspension or support of vibrating drivers and impact-vibration hammers (see Figures 45 and 50) assures their gripping and holding by load-lifting means. Besides load-gripping elements, shock-absorbing elements are a component part of the suspension, usually compression springs that assure the insulation from vibration of the arms and masts of the load-lifting mechanisms during operation of the vibrating machines.

Special technical means developed in recent years serve to increase the operating efficiency of the spring-mounted shock absorbers. They include the system of dynamic braking of the electric drive motor of the vibrating machines, which assures a shortening of the running down time of the eccentric mechanism of the vibration exciter during shutdowns and eliminates the resonant oscillation on the springs of the shock absorber of the body of the vibrating machine (VNIIGS),and also the system of dynamic extinction of the vibrations (DISI). These systems permit a safer application of vibrating machines during the extraction of piles and tubes from the ground with the aid of boom cranes (for more details, see Section 14). An increase in operating safety is also obtained with the signalization and safety devices built into the springed shock absorbers that record the propagation in them and operate when the springs of the shock absorber are compressed to a boundary value.

An important component of vibrating drivers and impact-vibration hammers is the head, which serves to fasten the vibrating machine to the element to be driven (extracted). The structural solution of the head should satisfy two basic conditions: reliably joining the vibrating machine with the element to be driven (extracted) in all its modes of operation and requiring the shortest possible time in performing the fastening and detaching operations with a minimum of labor, while observing the safety regulations required in these cases In some types of pile driving and drilling operations the efficiency of construction of the head and the simplicity of its application frequently predetermine the effectiveness of application of vibration technology.

As a function of the type of operation and the type of element being driven, the heads can be free or assure a rigid coupling of the vibrating machine. In the latter case, the heads can interact during the fastening process with the pile or tube through wedge pairs, special fixing components, passing through the body of the element to be driven (extracted) or by means of friction (adhesion) of the jaws with the surface of this element. The drive of the head mechanism can be manual, with the cable of a load-lifting device, hydraulic and, more rarely, electric.

The oil reservoir of the hydraulic drive can be mounted directly on the vibration machine, or can also be separate, connected to the vibrating machine by hoses. A classification of the heads used in pile driving and drilling vibration technology is given in Figure 51 and examples of the structural designs of heads of various types and different purposes are given in Figures 52-54.

Figure 51. Classification of the structural designs of the heads of vibrating drivers and impact-vibration hammers.

Key:

  1. heads of vibrating drivers and impact-vibration hammers;
  2. they assure fastening on the upper end of the driven element;
  3. they assure fastening on the outer surface of the driven element;
  4. flange heads with bolt fastening;
  5. with free guide heads without fastening (only for impact-vibration hammers);
  6. conical heads with stock component fastened to the driven element;
  7. with fixing components, moving in a transverse plane through the driven element;
  8. with jaws interacting by friction (adhesion) with the driven element;
  9. without a drive;
  10. with a drive;
  11. manually;
  12. from the cable of a load-lifting device;
  13. hydraulically;
  14. electrically.
Figure 52. Structural designs of conical heads with a stock component, previously fastened to the element to be driven (extracted)

a – head for driving reinforced concrete piles and pile shells:

b:- head for extracting casing pipes;

c – head for driving and extracting casing pipes.

Figure 53. Structural designs of heads with fixing components that move in a transverse plane through slots in the driven (extracted) element or recesses formed in it,
  1. wedge head for a pile;
  2. hydraulic head for a pile, steel pipes and shells;
  3. wedge head of vibrating gripper with a longitudinal-rotational action (the wedge pairs are conditionally shown, in the scheme turned by 90°).
Figure54
Figure 54. Types of clamps that grip the pile using friction. a) clamp for steel pipe and reinforced concrete shells, b) direct-action clamp using a hydraulic cylinder for sheeting and similar piles; c) lever-type clamp for piles and pipes.

The conical heads (Figure 52) consist of two basic components -conical seat and shaft, one of which is rigidly joined to the bottom of the vibrating driver and the other is also rigidly joined to the element to be driven by some method or other prior to beginning the operation. Heads of this type are used for driving reinforced concrete piles, shell .piles and the driving and extraction of casing pipes. The head (Figure 52a) /15/ was developed for heavy-duty low-frequency vibrating drivers of reinforced concrete piles and shell piles and has self-braking conical pairs that wedge up under the action of the mass of the vibrating driver. For unwedging the head after the completion of driving, the driving transverse wedge or hydraulic drive pi-ton-plunger shown in the Figure is used. The disadvantage of this head consists in the considerable difficulty involved in the preliminary connection of the conical shaft to the reinforced concrete element, usually done by bolt fastening.

The conical heads do not have a marked shortcoming in the driving and extraction of threaded casing pipes with a coupling on one of the ends, because in this case the connection of the conical seat or shaft with the element to be driven is easily done by screwing them into the coupling of the tube.

The conical heads for casing pipes have two variants. In one of them (Figure 52b) /16, 17/ the conical seat with longitudinal grooves is screwed into the coupling of the pipe to be extracted and then the shaft of the vibration exciter, in the form of conical and cylindrical sections, is lowered into it. After the integration of the interacting conical segments of the two components during the raising of the vibration exciter and tensioning the system of extracting static force, the head is wedged. With the completion of of the extraction cycle during operation of the vibration exciter due to the action of inertial forces, an unwedging of the head takes place and it automatically returns to the position in which the shaft freely moves cut of the seat during the following raising of the vibration exciter.

The second variant of the head of this type (Figure 52c) /18/ assures not only extraction, but also driving of casing pipes. This is achieved due to a forced locking of the wedged position of the head by means of eccentric sleeves, which are placed on the axes of the sh&ft that is screwed into the sleeve of the tube and interact with the support surfaces of the conical seat joined with the vibration exciter. Not only a fixation of the head, but also its forced unwedging are achieved by turning the sleeves in a specific direction, The cables of a load-lifting device are used to rotate the sleeves in one direction or the other; they are hooked to levers connected with the sleeves. An important feature of the head examined is the possibility of its use with vibration exciters, in the body of which there is an opening that passes through.

The wedge head for a pile (Figure 53a) is one of the first solutions of a rapid-acting unit for connecting the vibrating driver with the element to be driven. A head of this type was developed by D. D. Barkan and V. K. Typikov in 194-9 and then improved by 0. A. Savinov and A. Ya. Luskin. This construction was quite successful and has been widely used in pile driving operations by the vibration technology with the aid of high-frequency, relatively light-weight vibrating drivers. The need for effecting a notch or groove in the pile and also the involuntary weakening of the connection during vibration and the possibility of the development of undesirable impacts at wedge-pile or vibration exciter-pile contact should be considered the disadvantages of the wedge head of this type.

The head for a pile, developed at TsNIIS /19/ and depicted in Figure 53b, is equipped with a punch-die pair and a hydraulic drive. The pile is clamped with local deformation of its wall. This is a reliable gripping system; in the construction of the he.ad, however, it is necessary to have sturdy plates and jaws, capable of absorbing reactive forces from the deformation of the pile wall. The head shown schematically in Figure 53c is used in VNIIGS for joining the body of the vibration exciter of a vibrating gripper with a longitudinal-rotational action with the soil sampler. It consists of four tangentially arranged lugs belonging to the soil sampler, into which wedges are driven in pairs to meet each other. Such a connection permits a reliable transfer to the soil sampler of not only longitudinal vibrations, bu~, also a torsional moment of the compelling force during rotational vibrations.

In the heads with clamping jaws the basic condition of their reliable operation is that the frictional force created at the jaw-driven element contact point have a value that would exceed at least the lateral resistance of the pile or tube in all the stages of its sinking into the soil and, in the best case, the amplitude of the compelling force of the vibration exciter. VNIIG3, TsNIIS, VNIIstroidormash, TsNIISK and a number of other organizations worked on the development of heads in which the pile or pipe is clamped by several jaws moved by movable wedges. A. bolt-nut pair (Figure 54a), the cables of a load-lifting device, reducer with electric drive and hydraulic drive were used for moving the wedges. Such heads were designated as a rule for the vibration driving of reinforced concrete piles and pile shells and also steel pipes, i.e., elements having developed outer surfaces. Multi-jaw heads of various construction are complex in working principle, have substantial masses and dimensions, and do not have a high operational reliability, therefore, they have enjoyed limited application in pile driving and drilling practice. On the basis of experience accumulated on their development and use. effective heads with a hydraulic drive were developed. They are depicted in Figure 54b and c, and clamp the wall of the driven element (pile, steel pipe or shell) between two jaws, one of which is connected to the drive and the other is a stop.

The advantage of the structural solution of the head (Figure 54b) as compared with other clamping devices cf the jaw type consists in the fact that it is equipped with a hydraulic accumulator that prevents weakening of the grip during the operation.

Depending on their technological purpose, vibrating drivers and impact-vibration hammers used in Soviet pile driving and drilling practice can be divided into several groups. The names and technical characteristics of the vibrating machines contained in each of them are given in Tables 9-16. Table 16 contains a list and brief technical characteristics of power-operated vibration apparatuses specialized for certain types of work and used in the Soviet Union.

The vibrating drivers of various reinforced concrete elements (Table 9) are multi-shaft vibration exciters driven by electric motors with a phase rotor and with heads of the flange, conical or multi-jaw types.

Table 9 Vibrating machines for driving reinforced concrete piles and shell piles
indices LIIZhT TsNIIS
VP-1 , SP-42A VP-3, VP-3M VPM-170 VP-80 VU-1.6 VRP-15/60 VRP-30/132 VRP-70/200
Type of pile to be driven and its maximum dimensions in a plane, m Piles, 0.4 x 0.4; Pile shells, 1.0 dia. Piles, 0.45 x 0.45; Pile shells, 1.2 dia. Pile Shells, 2.0 dia. Pile Shells, 1.6 dia. Pile Shells, 1.6 dia. Piles, 0.45 x 0.45; Pile shells, 1.2 dia. Tubular piles, 0.6 dia.; pile shells, 1.2 dia.; 1.6 Pile shells 1.6 dia. and 3 in paired operation
Depth, m
Diameter of the straight through opening, mm
15 20 25 15 25
1360
15 25 40
Rated power of the electric drive motor, kW 60 100 160 100 150 (75 x 2) 63 132 200
Static moment of the mass of eccentrics, kg . cm 9300 23,600 51,000 27,500 34,500 0-15,000 0-30,000 23,000-70,000
Frequency of the vibrations, Hz 7 6.8 6.8; 7.7; 9.1 6.8; 7.7; 9 8.3 0-7.8 0-8.7 0-8.3
Maximum amplitude of the compelling force, kN 180 442 1700 900 958 342 889 1900
Total mass, kg 4500 7500 12,300 9,000 11,600 5000 7,250 13,000
Overall dimensions, mm; in a plane;
height
1300 x 1240
2100
1560 x 1540
2500
1260 x 1860
3400
1950 x 1450
2430
2618 x 3350
1910
1240 x 1000
2040
1440 x 1440
2240
1700 x 1600
3500

Vibrating drivers of various reinforced concrete elements (Table 9) are multi-shaft vibration exciters with a drive by electric motors with a phase rotor and with heads of the flange, conical or multi-jaw type.

The impact-vibrational machines of VNIIstroidormash and TsNIIS for driving and extracting piles (Table 10) are spring-mounted impact-vibration hammers. The impact-vibration hammer VI-601 and its modifications are free, spring-mounted according to the scheme of Figure 47a. The schemes of Figure 46b or 46c pertain to the other impact-vibration hammers of these organizations that require rigid coupling of the impact-vibration hammer with the pile, which is accomplished in the case of SP-58 with a wedged head, and hydraulically for MSh-2M, designed according to the scheme of Figure 53b.

Table 10. Vibrating machines for driving and extracting metal piles of the ShP, ShK and Larsen types.
indices VNIIstroidormash TsNIIS VNIIGS
VI-601
VI-633
VI-644
SP-58 VRP-3/44 MSh-2
MSh-2M
VPP-2A
V-401
V-401A
V-401B VSh-1
VSh-1M
VP-1U
Operation performed Driving Extraction Driving Driving and Extraction Driving
Maximum length of the pile, m 15 10 15 15 12 12 20 20
Rated power of the electric drive motor, kW 44 (2 x 22) 15 (7.5 x 2) 44 (2 x 22) 44 (2 x 22) 55 45 44 (2 x 22) 60
Static moment of the mass of the eccentrics, kg . cm 2000 420 2500, 3000, 3500 920, 1130 1000 1100 2500 9300
Frequency of the vibrations (impacts), Hz 8 8 0-16 16 16, 25 22 13, 16, 20 7
Maximum amplitude of the compelling force, kN 218 100 360 96, 134 250 220 400 180
Force of the total compression of the shock absorber springs, kN 250 120 120 290
Type of head Free Wedge Hydraulic Wedge Hydraulic Hydraulic Wedge Hydraulic Free
Mass of the impact part, kg 2100 700 2000 3000 7000
Total mass, kg 7300 1500 3000 4200 2300 2200 5000 7000
Overall dimensions, mm: in a plane, height; 1470 x 1130
3000
1030 x 720
2700
1600 x 9201
1800
1210 x 1175
2290
1270 x 800
2250
1550 x 1160
2590
1280 x 1250
2740
1300 x 1240
2600

Remarks:

  1. VPP-2A, V-401, V-401A, V-401B and V5P-3/44— vibration machines; VSh-1 and VSh-1M — vibration machines with readjustment to the impact-vibration mode when required; other machines — impact-vibration machines.
  2. V-401B is equipped with a dynamic braking system for the electric motors.

The VPP-2A vibrating drivers and their modifications are designed according to the scheme of Figure 45c with spring-mounted load, the VSh-1 vibrating apparatus is a vibrating machine with a combined action and is capable of operating in the vibration and in various impact-vibration modes (single-impact and dual-impact, as in pile driving and in its extraction) /45/. These vibrating machines are supplemented with heads according to the schemes of Figure 53a or Figure 54b.

The vibration apparatuses FVN-1, PYK-2 and PVN-2B are vibration machines with a combined action, generating the types of dynamic action shown in Table 11. A vibration exciter of longitudinal-rotational vibrations, coupled with the plate of a flanged head, is used in the PVN-1 vibration apparatus for the transition from the mode of longitudinal-rotational vibrations to the mode of longitudinal impacts in conjunction with rotational vibrations there is a special apparatus, which is a worm-screw mechanism with manual or electric drive. The vibration apparatuses PVN-2 and PVN-2B are designed for driving large-diameter pipes open at the bottom, and their extraction. They include four vibration exciters with circular vibrations, installed on a common frame and interconnected by a system of mechanical synchronization. The first of these machines has a straight-through opening and a wedged head, similar to that depicted in Figure 53c; the second is without a straight-through opening and is equipped with a head having two hydraulic holding devices, according to the scheme of Figure 54b.

Table 11. Vibration machines of VNIIGS construction for droving and extracting tubes in the preparation of lining piles.
Indices PVN-1 PVN-2 PVN-2B
Maximum depth, m 18 20 14-18
Diameter of the tubes, mm 377, 426 720, 1020 720, 820
Type of action during driving longitudinal-rotational vibrations or longitudinal impacts in conjunction with rotational vibrations longitudinal-rotational vibrations longitudinal vibrations
type of action during extraction longitudinal-rotational vibrations longitudinal-rotational vibrations rotational vibrations
Diameter of the straight through opening, mm 920
Rated power of the electric drive motor, kW 60 68 (17 x 4) 68 (17 x 4)
Static moment of the mass of the eccentrics, kg . cm 6000 10,000 6500
Frequency of the vibrations, Hz 8.7 8.3; 10 12
Maximum amplitude of the compelling force, kN 180 400 375
Maximum amplitude of the torsional moment or torque of the compelling force, kN . m 40 200 190
Force of the total compression of the shock absorber springs, kN 190 190 190
Type of head Flange Wedge Hydraulic
Total mass, kg 5000 5500 6000
Overall dimensions, mm: in a plane, height 1650 x 1300
3100
1990 x 1950
1660
2140 x 2100
3700

All the vibrating grippers are vibration machines with a combined longitudinal-rotational (PV-530, PV-820) or longitudinal-transverse (PV-380, TV-1D) action and have the characteristics given in Table 12.

Table 12. Vibrating grippers of VNIIGS construction for processing the soil and sinking of wells for construction purposes.
Indices PV-380 PV-530 PV-820 TV-1D UVB-1
Capacity of the soil sampler, m3 0.16 0.35-0.6 0.75-1.1 1.5 1.0
Transverse dimension of the soil sampler, mm 380 dia. 530-720 dia. 820-1020 dia. 600 x 1600 920-1220 dia.
Mean rate of driving into the soil, m/min 0.8 1.0 1.0 1.0 0.5
Rated power of the electric drive motor, kW 11 22 22 22 22
Static moment of mass of the eccentrics, kg . cm 600 1000 2400 3250 2000
Frequency of the vibrations, Hz 15.2 16.6 13 11.3 10
Amplitude of the compelling force, kN 60 110 160 165 80
Amplitude of the torque of the compelling force, kN/m 16 28
Force of the total compression of the shock absorber springs, kN 62 90 190 180 100
Mass without soil, kg 1000 1300 3000 4750 3090
Overall dimensions, mm: in a plane 380 530 820 600 x 1600 920
Height with soil sampler, mm 3950 2950 3100 3750 3000

Remarks:

  • PV-530 and PV-820 — longitudinal-rotational devices of vertical design
  • PV-380 and TV-1D — longitudinal-transverse devices of vertical design
  • UVB-1 — impact-vibrational devices of horizontal design, with the possibility of self-propulsion to the end face with a rate of approximately 15 m/min.

The impact-vibration apparatuses, the characteristics of which are contained in Table 13, are spring-mounted impact-vibration hammers. UWGP-400 and UVA-1 are constructed according to the scheme of Figure 47d; UVVGP and UVG-1 operate in a horizontal plane in the laying of pipelines, and UVA-1 in the inclined plane in the laying of ground anchors.

Table 13 Impact-vibrational devices for the trenchless laying of pipelines and ground anchor arrangements.
Indices VNIIGS MINKh and GP
UVVGP-400 UVA-1 UVG-51
Maximum length of pipe driving, m 50 20
Angle of inclination of the pipes to the horizon, deg. 0 0-45 0
Maximum diameter of the pipes, mm 426 89 529
Length of the pipe sections, m 8 2
Rated power of the electric drive motor, kW 22 15 (7.5 x 2) 75
Static moment of the mass of the eccentrics, kg . cm 2500 800
Frequency of the impacts, Hz 10 13.3 10
Amplitude of the compelling force, kN 100 57
Pressing-in force, kN 300 40
Mass of the impact part, kg 2240 650 2500
Total mass of the apparatus, kg 10,000 6000 6300
Overall dimensions of the apparatus, mm:
Length 14,700 7700 4000
Width 3200 1930 2000
Height 1260 4500 1630

NOTE:

  • UVVGP-400 and UVG-51 — for the laying of pipelines.
  • UVA-1 — for ground anchor arrangements.

The structural feature of the vibrating machines, the characteristics of which are given in Table 14, consists in the fact that all of them, with the exception of V-108 and BVS-1, have a central straight-through opening. The impact-vibration hammer S-835 is constructed according to Figure 46b, and BVS-1 according to the schemes of Figure 47b and c. The vibrating driver VO-10 and the impact-vibration hammer S-835 have heads according to the scheme of Figure 54a; the impact-vibration hammer BVS-1 for driving pipe is equipped with a head of the free type, and for their extraction in the vibration mode, with a head according to Figure 52b. The vibrators VPF-1 and VPF-2 have heads according to the scheme of Figure 52c.

Table 14 Vibrating machines for the driving and extraction of casing pipes during the drilling of wells.
Indices NIIOSP Gidroproyekt VNIIstroidormash VNIIGS
V-108 VO-10 S-835 BVS-1 VPF-1 VPF-2
Maximum depth of the wells, m 60 50 60 100 40 60
Diameter of the pipes, mm 219 – 426 168 – 273 168 – 273 273- 630 168 – 325 219 – 426
Diameter of the straight through opening, mm 305 300 250 350
Rated power of the electric drive motor, kW 28 20 (10 x 2) 15 (7.5 x 2) 22 15 (7.5 x 2) 24 (12 x 2)
Static moment of the mass of the eccentrics, kg . cm 3000 570 420 2500 800 1300
Frequency of the vibrations (impacts), Hz 13.3 20 12 (i = 2)
8 (i = 3)
10; 11.7; 13.3 13.3 13.3
Maximum amplitude of the compelling force, kN 210 92 100 178 57 93
Force of the total compression of the spring-mounted shock absorber, kN 100 216 120 200
Type of head flanged wedge wedge free, wedge wedge wedge
Mass of the impact part, kg 700 2400
Total mass, kg 1600 1700 1100 2400 880 1500
Overall dimensions, mm: in a plane 960 x 920 1710 x 1100 880 x 720 880 x 870 960 x 600 1230 x 690
Overall dimensions, mm: height 1470 1940 1120 1640 1400 1570

Remarks:

  1. S-835 and BVS-1 — impact-vibration machines, the others — vibration machines.
  2. BVS-1 in driving can operate in the mode of a free impact-vibration hammer or free spring-mounted impact-vibration hammer with a maximum tensioning force of 96 kN; in extraction, in a vibration mode.

The vibration exciters of the vibrating devices VUR-2 and VUE-3, the technical characteristics of which are given in Table 15, are mounted by means of shock-absorbing springs on rigid frames with flanged heads, designed for their rigid connection with the filter column of the well. In the VUB-2 the electric drive motor is mounted on the vibration exciter, and in the VUR-3 it is located on the frame and connected with the shaft of the eccentrics by a chain horizontal transmission.

Table 15. Vibration devices of VNIIGS construction for vibrational hydrodynamic preparation of water wells during their use or repair.
Indices VUR-2 VUR-3 VUR-4
Maximum depth of the well processed, m 120 250 800
Minimum diameter of the working column of the wells,mm 168 168 219
Maximum mass of the working element, kg 1000 2000 400
Rated power of the electric drive motor, kW 7.5 13 5.5
Static moment of mass of the eccentrics, kg . cm 800 1500
Amplitude of the vibrations of the working element at its maximum mass, mm 6 5 7
Frequency of the vibrations, Hz 11.7 11.7 13.3
Maximum amplitude of the compelling force, kN 435 820 180
Mass of the vibration exciter, kg 450 600 240
Mass of the apparatus without working element, kg 800 1300 240
Overall dimensions, mm:
in a plane
height without working element
780 x 510
1300
1400 x 680
1200
188 dia.
3260

NOTE:

  • VUR-2 and VUR-3 — surface devices with eccentric vibration exciter.
  • VUR-4 — driving device with vibration exciter of the kinematic type.

The special feature of the vibrating apparatuses of the VUR type is that after they are mounted on the well they operate in a stationary manner and are dismounted after vibrational hydrodynamic processing of the well and its pumping out. In this connection the shock absorbing springs of the apparatuses should be minimally rigid if possible in order to prevent the transfer of vibrations to the structural elements of the well.

The data of Table 16 illustrate specific examples of the aggregation variants of some types of vibration and impact-vibration mechanisms with basic self-propelled machines, as contained in Figure 2. A more detailed description of the vibrational self-propelled units is given in Sections 17 and 27.

Table 16. Vibration self-propelled apparatuses for pile driving and drilling operations.
Indices Orgenergostroi TsNIIS Glavtonnelmetrostroi PNIIS VNIIGS
VVPS-20/11M UVVS-60/10 AVSE-U OIT-1 AVB-2m AVO-2, AVR-1 AVS-1
Purpose Driving reinfoirced concrete piles 30 x 30 cm, length 8 m; loosening of frozen soil Driving reinforced concrete piles 40 x 40 cm, length 12 m Establishment of leader wells 426 mm dia., depth of 6 m under the pile; driving reinforced concrete pile 30 x 30 cm, length of 7.5 m Driving of pile foundations with a mass up to 2500 kg under the poles of a contact network Extraction of casing pipes 114-630 mm dia. from water-lowering wells with a depth up to 50 m; driving of pipe 114 mm dia. with a closed end up to a depth of 25 m Drilling of engineering-geological wells 200 mm dia. up to a depth of 20 m Utilisation and repair of water wells with a depth up to 120 m Driving of reinforced concrete posts for enclosures 18 x 18 cm, with a length of 4 m
Base Tractor T-100M Tractor T-100MB Tractor D-804 Tetraxial railroad platform Caterpillar truck Automobile GAZ-66 Excavator ETU-354
Load-lifting apparatus Collapsible three-dimensional stand Swivelling three-dimensional stand Collapsible frame with brace Extensible boom Swivelling tubular stand Swivelling tubular stand with extending boom Rigid stand
Electric power supply DVS-electric generator Rolling electric power plant with DVS and electric generator Power supply system DVS-electric genrator DVS electric generator; power supply system DVS-electric generator
Vibration Equipment Special vibrating driver Special impact-vibration hammer VMS-1 impact-vibration hammer VP-1 vibrating driver Impact-vibration hammer BVS-7 Impact-vibration hammer VB-7 Vibration apparatuses VUR-2 and VUR-4 Special impact-vibration hammer
Operation conducted with vibro-technology Driving of the pile and loosening the frozen soil Driving of the pile Driving and extraction of leader pipe, driving of the pile Driving of piles Driving and extraction of pipes Processing and extraction of the soil Hydrodynamic processing of the filter and the near-driving zone of the wells Driving the posts of an enclosure

 

Methods for Approximate Calculation of the Parameters of Vibratory Drivers and Impact-Vibration Hammers

Calculation of the parameters of longitudinal-action vibrational pile drivers.

The initial data for calculation are: the mass of the element to be driven mo, in kg; the geometric dimensions of the element to be driven;the depth of sinking l, in m; and the soil conditions.

1. The resistance of the soil is determined. The calculated value FCR of the critical separation resistance at a given maximum sinking depth (kN) is determined on the basis of the original data characterizing the soil conditions:

where i is the ordinal number of the soil layer of thickness li passed through during the sinking, k is the total number of layers and Z is the perimeter of the cross section. The values of the specific separation resistance σ are assumed according to the data of Table 5.

2. After determination of the tentative mass value mo, in kg, of the element to be driven and the parts of the vibratory pile driver rigidly connected with it, the approximate value of the static moment of the mass of the eccentrics, in kg • m, is calculated:

where ψ = 0.8 for reinforced concrete piles and ψ = 1 for the other elements sunk.

Table 5 Dependence of the specific separation resistance the soil type.
Type of soil For a pile, kPa For a sheet pile, kN/m
Steel tubes Reinforced concrete piles Tubular piles open on the bottom Light sections Heavy sections
Water-soaked sandy and fluid-plastic clay soils 6 7 5 12 14
The same, soils with interlayers of compact clay or gravelly soils 8 10 7 17 20
Stiff plastic clay soils 15 18 10 20 25
Semihard and hard clay soils 25 30 20 40 50

The recommended vibrational amplitude Ao required for an effective sinking is determined with the data of Table 6.

Table 6. Dependence of the vibration amplitude Ao, in mm, on the types of elements to be driven
Type of elements to be driven Ao, mm
Sandy soils Clayey soils
Vibration frequency, Hz
5-12 13-17 18-25 5-12 13-17 18-25
Steel sheet pile, steel tubes with open end, and other elements with cross-sectional area up to 150 cm2 8-10 4-6 10-12 6-8
Tubular piles (with closed end) with cross-sectional area up to 800 cm2 10-12 6-8 12-15 8-10
Reinforced concrete, square or rectangular cross section with area up to 2,000 cm2 12-15 15-20
Reinforced concrete tubular piles with large diameter, inserted with excavation of soil from tube cavity 6-10 4-6 8-12 6-10

3. The frequency of the vibrations of the vibratory pile driver, Hz, is calculated as follows:

When the set of parameters of the vibratory pile driver is derived with a previously undetermined interval of change in the θ value, it must be determined from the condition

The amplitude of the vibration velocity vo for a successful sinking should be within the interval of 0.5-0.8 m/s ; is a coefficient that takes the resilience of the soil into account: = 0.6-0.8 for low-frequency vibratory pile drivers (5-10 Hz) and = 1 for the others. If the value θ is determined by this method, the static moment of mass of the eccentrics is calculated with the formula, in kg • m:

4. The required minimum mass of the vibratory pile drive and driven element, in kg, is determined as follows:

where Uc is the cross sectional surface, in cm2; po are the recommended pressure values required; the dependence of the pressure po, in MPa, on the type and dimensions of elements driven into water-soaked sandy and loose clayey soils is given below:

steel tubes of small diameter and other elements with a cross sectional surface up to 150 cm2 0.15 – 0.3
tubular steel (with closed end) piles with a cross sectional surface up to 800 cm2 0.4 – 0.5
reinforced concrete piles of square and rectangular section with an area up to 2000 cm2 0.6 – 0.8

5. The value of the ratio of the force of gravity to the amplitude of the compelling force Pθ is verified:

v1 v2
for a steel sheet pile 0.15 0.5
for light piles 0.3 0.6
for heavy piles and tubular ones 0.4 1.0

In performing the calculations with respect to this point, either the mass mo or the amplitude of the compelling force (due to an increase in K or θ) is increased if necessary.

6. Finally, the values K, θ and mo are precisely defined, after which these parameters are verified with the formulas:

In addition, the precisely defined parameters are verified with the formulas of paragraphs 4 and 5.

7. The power of the driving motor is determined by:

where D is the diameter of the journals of the shafts of a vibration exciter, in cm.

The efficiency of transfer from the motor to vibration exciter (equal to 0.9), the coefficient of rolling friction in the bearings of the vibration exciter (equal to 10-3), and the additional consumption of power in the vibration of the soil mass, assumed to be 15% of the power expended to overcome the resistance of the soil, were studied here.

Calculation of the parameters of longitudinal-action impact-vibration hammers.

The original data for the calculation are the same parameters as for the vibratory pile drivers.

1. On the basis of the original data on the element driven, the mass of the impact part of the vibratory hammer is determined, in kg:

m1 =(0.7 — 1.2)m2.

2. The amplitude value of the compelling force, kN, is determined:

Po = dm1 x 10-2.

The lower limit of the parameter d (d = 2-6) is designated for impact-vibration hammers that drive elements with a relatively small cross sectional surface (up to 50 cm2). The parameter d also increases with an increase in cross sectional surface.

3. The preliminary depression force of the working springs is calculated, in kN:

The parameter sin α = 0.3 – 0.5. An attempt must be made to assure the value sin α = 0.4 in designing the hammers.

4. The static moment of mass of the eccentrics is determined, in kg • m:

K = 25.3 Po/θ2.

The frequency of the compelling force of the hammer θ lies within the interval of 6-10 Hz.

5. The optimal stiffness of the working springs of the vibratory hammer is, in N/cm:

c1 = (3.5 – 10) x 10-2 m1 θ2

In designing the hammers it is desirable to obtain the minimum c1, value from the recommended optimal range.

6. The ratio γ1 between the frequency of the natural vibrations of the impact part and the frequency of the compelling force:

7. The dimensionless resistance of the soil f and γ is calculated with the F and R values (9). The existence of an impact-vibrational mode is verified in terms of the parameters, sin α, γ1, and f + γ (see Figure 22).

8. The dimensionless impact velocity is calculated (correlation formula):

9. The velocity of the impact part at the moment of impact is determined, in m/s:

ximp = 6.28 x K θ/m1 y1

With respect to the durability of the hammer, the impact velocity should not exceed 2 m/s. If the value ximp » 2 m/s with the parameters chosen, it is necessary to select other parameters that assure a value ximp ≤ 2 m/s

10. The dimensionless sinking per impact (correlation formula)

11. The possibility of driving under the given soil conditions is checked:

The value ΔL is adopted according to the data (Yu. R. Perkov, V. N. Shaevich, 1974) given below:

water-soaked sands of medium coarseness and compactness 0.16
low-moisture sands of medium coarseness and compactness 0.46
wet sands of medium coarseness and compactness 0.22
loams of stiff-plastic consistency 0.32
macroporous sandy loams of a hard consistency 0.28

If it turns out that xPL < ΔL, it is necessary to reduce the parameter sin α to 0.2-0.3 and repeat the calculation. When xPL again proves to be less than ΔL, it can be assumed that the impact vibrational driving is ineffective under the given soil conditions.

12. The dimensionless rising height of the impact part is calculated:

13. The maximum rise value of the impact part is determined, in cm:

14. The maximum reaction of the vibratory hammer springs is calculated, in kN:

15. The drive engine power required is calculated, in kW:

The transfer efficiency from the vibration exciter to the motor (equal to 0.9) and the friction coefficient in the supports of the shafts (equal to 10-3) are taken into account in this formula.

The selection of the parameters of the the impact-vibrational machines for extracting the elements from the soil is done by the same method, but in this case, in kN,

Calculation of the parameters of longitudinal-rotatory-action vibratory pile drivers.

The initial data for the calculation are the same characteristics as for longitudinal-action vibratory pile drivers.

1. The basic calculation characteristics of the driving system are determined:

where σP,V is the specific resistance on the lateral surface of the shell being driven with longitudinal-rotational vibrations; the σP,V values are given in Table 7, compiled according to the results of experimental studies:

where Ut is the area of the end surface of the shell, in m2 ; R is the calculated resistance of the soil under the end of the shell, in kPa (undertaken according to the data of SNip 11-02 — 03.85).

Table 7 Specific resistance of the soil σ, in kPa on the lateral surface of the driven shell under the effect of longitudinal-rotational vibrations.
soils tubular piles with closed lower end shells driven with removal of the soil
water-soaked and soft -plastic clayey soils 4.0 2.5
the same, with interlayers of compact or gravelly soils 6.0 3.5
clayey stiff -plastic soils 10.0 5.0

2. The required dimensionless velocity values of the vibrations are determined:

where vn is the projected driving velocity in m/min (recommended value: vn = 0.2 -1.0 m/min) ; vn = vo/a2 ; θ is the frequency (recommended value: θ = 6-7 Hz).

3. The amplitudes of the compelling force and the static moment of mass of the eccentrics are determined, in kg – m:

4. The separation conditions of the shell relative to the adjacent soil are verified:

The Amin values are given in Table 8.

Table 8. Minimum separation amplitudes Amin, in mm, under the effect of longitudinal-rotational vibrations
element driven sandy soils clayey soils
6-9 Hz 13-16 Hz 6-9 Hz 13-16 Hz
tubular pile with closed lower end 3.0 1.0 4.0 1.5
shells, driven with removal of the soil 2.4 1.2 3.0 2.0

5. The magnitude of eccentricity of application of the compelling force is determined:

The δ value is selected as a function of the ratio of vibrator mass m1 and the mass of the driven shell m2;

6. The drive power of the vibratory longitudinal-rotational action pile driver is calculated, in kW:

where D is the diameter of the support of the eccentric shaft, in mm; ηver is the coefficient that takes into account the losses in transfer from the engine to the eccentric shafts.

7. It is recommended that the effort in extracting the tubular element from the soil under the action of longitudinal-rotational vibrations be determined with the formula

S = 10 mo + FH3

where FH3 is the mean force required to overcome the lateral resistance of the soil during vibratory extraction: FH3 = ζFe; Fe is the separation resistance along the lateral surface of a tubular element; and ζ is the coefficient of decrease in the lateral resistance as a function of the vibratory mode.

The ζ value is determined by the graphs plotted with Equation (35) and given in Figure 19, as a function of the ratio of the extraction velocity (vH3) to the amplitude of the velocity of the longitudinal component of the vibrations (). The rate of rise in the tube should not exceed 0.5-1.0 m/min in the first extraction stage.

Characteristics of the Dynamics of Vibration and Impact- Vibration Drivers

As indicated above, the questions of nonuniformity in the rotation of eccentrics and the limited drive power are as a rule considered in studying dynamic loads in the drive of the vibrodriver and vibrating hammer, and also in determining the power required.

Nonuniformity in the rotation of the eccentrics is caused by:

  • variation in the moment of gravitational force of the eccentric relative to its axis of rotation;
  • variable acceleration of the axis of rotation of the eccentric;
  • inconstancy in the moment of the drive engine and its limited power;
  • variation in the rotational resistance of the eccentric.

I. I. Bykhovskii investigated the variations in the angular speed of rotation of the eccentrics as a result of impacts with an immoveable limiter and a limited driving power. M. A. Gurin studied the influence of the limited power on the working regime parameters of an impact-vibrational earth-preparing machine and the moment developed by the drive, and also optimized the parameters of the vibrating hammer in order to obtain the maximum impact speed.

The dependences of the sinking depth of the element for one impact on the basic parameters of the vibrating hammer and the characteristics of the drive engine are revealed in the present section and the power consumption in driving piles are also determined (G. G. Azbel and B. B. Rubin, 1980).

The stable periodic movement of a system with a period T = 2π/αav, where αav is the mean value of the angular velocity of rotation of the eccentrics for a period, is examined. Just as in Section 7, it is assumed that the element to be driven is immobile during the flight of the hammer and the soil resistance during the movement of the pile has a purely plastic nature.

The calculation model of the system is shown in Figure 36.

Figure 36. Calculation scheme of impact-vibrational driving, using an absolute dynamic model.

The limiter of the impact part is modelled by a high-rigidity spring, which is selected from the conditions of correspondence with the experimental data on the duration of the impact (A. S. Golovachev and V. P. Ivanov, 1968).

The working section of the static characteristic of the engine can be described by the equation (V. S. Shevchenko, 1960)

(55)

where a and b are constant coefficients, dependent only on the characteristics of the engine.

For the calculation scheme shown in Figure 36, the first movement stage, flight of the impact part, is described by the equations:

(56)

The conditions of the beginning of the raising of the impact portion at t = 0 are determined by the relation:

(57)

The flight of the vibrating hammer ends at the moment t = t1, of contact of the impacter and limiter. Compression of the limiter takes place in the second stage up to the beginning of movement of the element to be driven:

(58)

In the system of equations (58) c2 » c1 and therefore c1 can be disregarded in performing the calculations. The boundary conditions at t = t1 for Eqs. (56) and (58) have the form:

(59)

In the third stage (t2tt3) the speeds of the vibrating hammer and pile are equalized:

(60)

At the boundary t = t2 of the second and third stages:

(61)

The fourth stage (t3tt4) is characterized by the joint movement of the vibrating hammer and pile with a compressed limiter:

(62)

At the boundary t = t, we have:

.

The movement is completed at the time t = t4 , stoppage of the system, where

During the stoppage of the system there is only rotation of the eccentrics, described by the equation

(63)

The final conditions for Equation 63 are:

(64)

The mathematical model of the calculation scheme of Figure 36 should be solved by using the method of successive approximations because at the beginning of the calculation the values of ao and αo are unknown. More precisely, one of these values is not known since the other is independent, is specified by Eq. (57) and should be calculated. Which of these values to set and which to determine with Eq. (57) makes no difference in general. However, the approximate value of ao is known: ao = aH. With regard to the approximate value for a it can be obtained only from the solution of the problem on impact-vibrational driving with α = const.

Therefore, it is logical to set the value αo, assuming the value (αo)init. = αH as a first approximation for it, and to calculate the value αo from the transcendental equation (57).

It follows from the above that solution of the problem should begin with calculation of the value ao according to the set αo value. After this, an integration of the corresponding differential equations can be carried out in accordance with the sequence of movement phases indicated above. After the calculations are completed, it is necessary to verify the value αfin with Eq. (64) and, if it does not meet the precision specified, continue the calculations; it is known from the preceding cycle of calculations here that αo = afin.

After finding ao, and αo by the method of successive approximations of the initial conditions in solving the differential equations by the Runge-Kutta method, the mean quadratic values are determined in each step of the integration

and the mean value of the angular velocity of rotation of the eccentrics per cycle

In this case the power of the engine is N = MDB mean.

In solving the differential equations of the corresponding movement phases on a computer, the following dimensionless variables and parameters are introduced:

(65)

It is established with the calculations performed that the displacement Y of the pile for one impact and the power N required by the vibrating hammer are nonlinearly dependent on the parameter ξ2, which characterizes the rigidity of the limiter; when ξ2 > 50, the driving ability and power of the vibrating hammer are practically independent of the value ξ2. This result is obtained for various degrees of soil resistance.

Figure 37,a a plots the dependences of the driving ability of the vibrating hammer on the parameter h at α = const, and a variable rotation speed of the eccentrics during the period. In the zone of parameters at rthich vibrating hammers usually operate (h = 0.2-0.5, the relative difference in the results with both methods is small and amounts to approximately 10% and with an increase in h this difference increases and reaches 37% at h = 0.7 (s = — 8, d = 4, λo = 0.01).

Figure 37 Dependence of the displacement of the element to be driven per impact when d = 4-, λo = 0.01, ξ2 = 80, ξ1 = 0.5 and s = — 8.
specific energy capacity of the angular velocity (1 — constant angular velocity; 2 — variable angular velocity)
nonuniformity of the angular velocity
on the prior compression of the working springs

The variation in the ratio of power required by the electric motor of the vibrating hammer to the sinking depth per cycle is plotted in Figure 37,b. This value, which is one of the criteria for efficient operation of the vibrating hammer, has minimal significance at h = 0.4. The nonuniformity of the angular velocity per cycle Δa = (amax – amin)/ amin is stabilized at h ≈ 0.5 (Figure 37,c) and is 3% for a vibrating hammer with the parameters d = 4, ξ1 = 0.5 and λo = 0.01 when s = -8.

One of the components of the value h is the parameter d, which is the ratio of the amplitude value of the compelling force (with a = anom or in the dirnensionless form a = 1) to the force of gravity of the impact part of the vibrating hammer and has a substantial influence on all the characteristics of the process. A decrease in the parameter d increases the sinking depth with a simultaneous decrease in the power required. Calculations indicate the need for bringing the value 1/d closer to the parameter h due to a decrease in the prior compression of the working springs of the vibrating hammer.

The parameter λo has an insignificant influence on the basic technological characteristics of the process: the sinking depth, the power required, etc., but it does determine the dynamic stability of the process.

The dependence of the sinking ability of the vibrating hammer on the dimensionless rigidity of the springs ξ1 is analogous to the dependences obtained without taking the nonuniformity of rotation of the eccentrics into account. The relative deviations in the results of calculating Δy in both models are a function of the parameter 1/d. When 1/dh, these deviations are not great and range from -1 to +5% for various ξ1 values when s = —8. These deviations increase with decreasing resistance of the soil and attain 10% when s = —4 and ξ1 = 0.6.

In selecting the optimal values of the parameters d, ξ1, and λo, the nature of the dependence of the sinking ability of the impact-vibration machine on the dimensionless resistance of the soil is in accordance with the results obtained in examining the dynamics of the process of impact-vibrational sinking, disregarding the nonuniformity of rotation of the eccentrics and the rigidity of the limiter (Figure 38). The deviations in the calculation results obtained for the various models have an essentially nonlinear nature and a maximum at s = -4.

Figure 38. Dependence of the displacement of the element to be driven (y) and the deviation in the results of calculations with the various models (Δy) on the soil resistance when h = 0.4, ξ1 = 0.5, ξ2 = 80, d = 4, and λo = 0.01.

The investigations reveal that with the calculation scheme assumed and the assumptions on it, in spite of some increase in the impact velocities of the vibrating hammer with an increase in the resistance of the soil, the useful work of the. vibrating hammer (s x y) decreases with an increase in resistance due to a decrease in the sinking depth Y and, accordingly, the power required decreases.

All these results, obtained with one specific characteristic of the motor, a variation in which influences not only the power required, but also the sinking depth of the pile per cycle and the specific energy capacity of the process (Figure 39). Thus, with an increase in the maximum moment MDB.MAX of the motor of 2.2-fold, the power required increases by 1.18-fold and the sinking depth by 1.1-fold. The variation in the angular velocity of rotation of the eccentrics during the impact reaches 10% when h = 0.5, ξ1 = 0.5, d = 12 and λo = 0.01.

Figure 39. Dependence of the displacement of the element to be driven (y) and the specific energy capacity of impact vibrational sinking (N/y) on the maximum moment of the electric motor.

The study of the vibration extraction process, using an absolute dynamic model, is carried out by a method analogous to that described above.

It was established by calculations that qualitatively the basic regularities of the impact-vibration extraction process correspond to the analogous regularities of impact-vibrational sinking (the dependences of y, N, N/y on ξ1, ξ2, λo, d and on the characteristics of the motor). At the same time, some quantitative differences are manifested between the data obtained in studying the processes of impact-vibrational sinking and extraction (Figure 40). In impact-vibrational extraction (in comparison with sinking) the displacement per impact is somewhat greater and the power required and the specific energy capacity of the process are less. At the same time, with a practically identical mean rotational speed of the eccentrics per cycle (0.9864 αH for sinking and 0.987 αH for extraction) the fluctuations in the angular velocity during sinking are greater than during extraction (amin = 0.9465 and amax = 1.024 during sinking, and αmin = 0.955 and αmax = 1.017 during extraction).

Figure 40. Comparison of the basic characteristics of impact-vibrational sinking and extraction when h = 0.2, ξ1 = 0.5, ξ2 = 80, d = 4 and λo = 0.01.

The area of existence of the “one impact for one revolution” regime for impact -vibrational sinking and extraction coincides completely for the calculation models, both those that take into account the nonuniformity of rotation of the eccentrics, and disregarding this characteristic.

The most economical mode of impact-vibrational driving and extraction, characterized by the parameters h = 0.4, ξ1 = 0.3 – 0.5, exists in practice only beginning with s = —2; at lesser resistances with respect to absolute value the regime becomes unstable, which leads to a sharp increase in the power required, an increase in the specific; energy capacity and a decrease in the efficiency of the process.

An analysis of the results of the calculations performed shows that some of the parameters of the vibrating hammer do not have a substantial influence on the power required. Thus, in the formulas for calculating the power it is possible to disregard the change in the ratio of the nominal moment of the motor imparted to the shaft of the eccentrics, and the static moment of the mass of the eccentrics.

The influence of the latter parameters is taken into account in the correlation formula below, presented in dimensionless form (G. G. Azbel and B. B. Rubin, 1983):

( 66 )

whence

(67)

The power losses in overcoming friction in the bearings , movement of the oil, etc. can be calculated with the familiar formula

(68)

where n is the nominal number of rotations of the eccentric shafts.

The power of the electric motor of the vibrating hammer NDB should be equal to the sum of two powers — the useful power M, expended in the driving or extraction of the elements, and that expended in overcoming resistance in the vibrating mechanism Npot.

Table 4. The results of comparing the power calculations with the data of the experimental studies

Original Data Source Calculated Data Experimental data, Nexp , kW
h s ξ1 d _
N
K, kg-cm ω, 1/sec N, kW Npot, kW NDB, kW
M. G. Tseitlin 0.66
0.45
2
2
0.3
0.23
2.89
4.86
0.647
1.793
230
230
62.8
87.78
0.916
3.39
0.28
0.66
1.196
4.05
1.2
4.0
V. V. Verstov and V. M. Lukin 0.24 10 0.3 4.11 2.044 2500 62.8 31.5 5.9 37.4 37.1
V. I. Chernyaev 0.36 8 0.26 9.28 3.27 259 150.8 12.5 6.3 18.8 17.9

Table 4 compares the results of power calculations with formulas (65) and (67) with the data of experimental studies. as is evident from Table 4, formula (67) for determining the power of the electric motor of the vibrating hammer, expended in driving and extracting the elements, does not require preliminary calculations of the velocity at the time of impact and offers the possibility of calculating the motor power sufficiently precisely, which permits avoiding its overloading.

In performing the calculations with formulas (56), (58), (60), (62) and (63) the moment of the motor MDB and the acceleration xi (i = 1, 2) are calculated in each step of the integration, which provides the basis for plotting within the limits of period T the loading diagram of the moments and the diagram of the inertial forces acting in the direction of the x-axis.

The loading diagram of the moments makes it possible to perform the calculation on the stability and durability of the transmission elements of the vibrating hammer, and taking into account the variation in the value of the moment from the maximum to the minimum, the values of the inertial forces and a calculation of the durability of the shafts of the vibration exciter.

An equivalent load for selecting and verifying the service life of the oscillation bearings of the eccentric shafts can be determined from the diagram of the moments and the inertial forces, taking into account the action of the compelling force Po.

The body elements of the vibrating hammer construction can be calculated for stability and durability under the action of the inertial forces.