Soviet S-834 Impact-Vibration Hammer: Calculations, Part II

The introduction to this series is hereThe first installment of the calculations is here.

Calculations of Main Details (Strength
Calculations)

Strength calculations assume that the inertial forces during impact are 150 times those of the weight.

Rotor Shaft

We checked the rotor shaft strength in the optimal mode, i.e., when the impacting force direction formed a 90° angle with the direction of the blow. To simplify calculations consider that the forces act at one point. In the vertical place the shaft is loaded with impact inertia forces from the shaft weight and parts which are located on it.

where Q1 = inertial force from eccentric weight(s) and part of the shaft ahead of the eccentric.
Q2 = inertial force from the part of the shaft under the bearing.
Q3 = inertial force from the rotor weight and the middle part of the shaft.

A diagram of the shaft assembly is shown below.

Figure-1

A diagram of the beam forces in the vertical plane is shown below.

Figure-2

A diagram of the beam forces in the horizontal plane is shown below.

Figure-3

The forces which act on the shaft in the horizontal plane arise from the vibrating forces of the eccentrics.

The reactions in the vertical plane are

The reactions in the horizontal plane are

The bending moment in the vertical plane in section A-A is

In section C-C it is

In section B-B it is

The bending moment in the horizontal plane in Sections A-A and C-C is

and for Section B-B

The sum of bending moments in Section A-A is

In Section B-B they are

and in Section C-C they are

The bending tension is calculated in the same way at all points.

For Section A-A

For Section B-B,

and Section C-C,

The tension in this section will be much less because the calculations do not take into account the force from the rotor shaft. Calculation of the shaft deflection will be done in Part C.

The calculations consider that the shaft is of uniform diameter, equal to 62 mm. In the vertical plane the deflection is equal to

where kg-cm
= axial inertial moment of cross-section of the shaft

E = spring modulus of shaft material = 2,000,000 kg/cm²

The deflection in the horizontal plane is equal to

The total deflection from horizontal and vertical moments is

In reality deflections will be smaller because we did not take into account the rotor forces.

Determination of Tensions in Vibrator Casing

The casing is subjected to loading tensions when the vibrator impacts on the pile cap. As the ram is located in the centre of the casing the critical sections are two perpendicular sections which are located at the planes of symmetry of the vibrator.

Let us determine the moment of resistance of the section which is shown in the drawing of bending tensions in this section, shown below.

Figure-4

This section is weakened by a hole for the ram but this weakness is compensated for by the local boss. So we do not take into account the hole and its boss.

The moment of inertia for the section relative to axis X-X is determined as

where = sum of inertial moments of the separate elements.
= sum of multiplication of squared distances from the mass centre of element ot the axis X-X by the area of the element.

The moment of resistance for this section is

The distance between the axes of the electric motors is mm. So the bending moment is equal to

The bending tension is equal to

Let us determine the bending tensions in the section perpendicular to the axis of the rotors. The section is shown in the drawing below.

Figure-5

To simplify the calculations consider the section of the casing is symmetrical and consists of two circles and two rectangles.

The inertial moment is equal to

The moment of resistance equals to

Let us now determine the bending moment considering that the load from the weight along the axis parallel to the rotor axis is distributed uniformly.

Figure-6

The bending tension is equal to

Spring Deflection Calculation

The maximum force for which spring deflection is required is P = 1000 kgf. The number of spring N = 2. The maximum deformation of the springs is f = 200 mm. The load for each spring is

As the springs are operating in relatively easy (not hard) conditions we can consider the permissible tension equal to 5500 kgf/cm². So the permissible tension per 1 kgf of load is equal to

The necessary spring stiffness is equal to

So we choose the spring with the following specifications:

Average Diameter

Wire Diameter

Hardness of One (1) Turn

Number of Working Turns

Npad = 14.5

Total Number of Turns

N = 21.5

Tension per 1 kgf of Load

A = 11.18

Hardness of the whole spring

So the spring we have chosen meets all of the requirements.

Determination of the Geometrical Configuration of the Eccentrics

Consider that the balanced part of the eccentrics (I and II; see diagram below) cancel each other.

Figure-7

So the coordinate of the center of mass of the rest of the eccentric (in the shape of a sector of a circle) is determined by the equation

The weight of the unbalanced part of the eccentric for a 1 cm thickness is equal to 1.7 kg. The eccentric moment of this eccentric is

The dynamic force of the eccentric is

The angular speed is rad/sec. The necessary eccentric moment of the eccentric is

The necessary total thickness of the eccentrics is

As during the determination of the eccentric moment it was increased a little, consider the thickness of the eccentrics equal to 80 mm.

This configuration of the eccentrics which we have come up with gives us an increase of its weight in comparison with the weight which is necessary to provide the required eccentric moment. So decreasing the moment of the rotary parts makes it easy to operate the motors.

Sizing the Bearings

The rotor shafts are mounted to spherical, double-row roller bearings No 3614 which have a coefficient of workability C = 330,000. The rotor weight Gb = 25 kgf. The eccentric weight is Gg = 28 kgf.

For the calculation of dynamic loads consider that the accelerations during impact are equal to 150 times the free weight.

As the shaft is symmetrical, each bearing is subjected to half the dynamic load

The shaft rotates at n = 950 RPM. Consider a factor of safety Kd = 1.5 and a dynamic load coefficient Kk = 1. The durability of the bearing “h” is determined as

Therefore, for 950 RPM, h = 160 hours.

 

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Soviet S-834 Impact-Vibration Hammer: Calculations, Part I

The introduction to this series is here.

Moscow, 1963

Head of the Vibrating Machine Department L. Petrunkin
Head of Vibration Machine Construction: I. Friedman
Compiler: V. Morgailo and Krakinovskii

Specification

The impact-vibration hammer is intended for driving heavy sheet piles up to 30 cm in diameter as well as concrete piles 25 cm square up to a depth of 6 m for bridge supports and foundations.

Parameter

Value

Power N, kW

9

Blows per Minute Z

475

Revolutions per Minute

950

Ram mass

,
kg

650

Force F, kgf

5000

Determination of Velocity and Energy per Blow

Impact velocity is determined:

where = fraction of natural frequency (without limiter) to force
frequency

i = fraction of the number of revolutions to the number of impacts
R’= coefficient of velocity recovering (assume R’=0.12)

In our case

therefore

rad/sec

kgf-sec²/m

Energy of blow is determined as

Power necessary to make impacts is

Impact-Vibration Hammer Springs

So that the impact-vibration hammer operates in the optimal mode while the gap is equal to zero, the spring suspension stiffness should meet the equation

where = stiffening coefficient = 1.1 to 1.3, assume 1.2

Stiffness Distribution and Maximum Deformations
of Upper and Lower Springs

The upper springs are necessary to provide positive gaps, so their stiffness should be minimal to provide undisplaced operation the springs in the whole range of gap adjustment. Therefore

where Cb = stiffness of the upper springs
A = number of vibrations of the ram

a = maximum positive gap when the hammer is able to operate without danger of transferring into the impactless mode. When there is no limiter it is equal to the amplitude of vibrations

Assume a = 0.8.

where = coefficient which depends upon i and R’. Hammer coefficient of
velocity recovery may be increased up to R’ = 0.2. In this case = 7.1.

For calculation purposes let us assume A = 5.5. Now substitute the values into the formula

The bottom spring stiffness is then equal to

Now let us determine the maximum deformations. For upper and lower springs,

where b = negative gap. It is considered equal to “a” (maximum positive gap)

Assume .

Because of design considerations use four (4) upper and four (4) lower springs. The stiffness of one upper spring is

and the stiffness of one lower spring is

The material for the spring is “60 Sg” steel. The permissible tension in this steel is kgf/cm².

Upper Springs

Tension per kgf of load is

According to the table of S.I. Lukowsky choose the spring as follows:

The stiffness of one turn and the number of working turns is

Assume turns. For this spring,. The actual tensions in the spring are as follows:

(Units should be kgf/sq.cm.)

and the total number of turns is

The full free height of the spring is

The distance between the support surfaces while the gap is equal to zero is

Lower Springs

According to the table the closest value A = 4.24 corresponds to the spring with dimensions

The stiffness of one turn is equal to . The number of working turns is

Assume 10 turns.

The total number of turns is

The spring height in free position equals to

 

Soviet S-834 Impact-Vibration Hammer: Overview

With this we begin a series of posts on the S-834 impact-vibration hammer, which the VNIIstroidormash institute in Moscow designed and produced in the early 1960’s.  With the revived interest in Soviet and Russian technology, it’s a detailed look at how Soviet equipment designers came up with an equipment configuration.  But it’s also a close-up view of how heavy machinery in general and pile driving equipment in particular is designed.

The impact-vibration hammer was a long-time interest for Soviet construction machinery institutes from 1954 to 1970.  An overview of the history of this type of equipment in the Soviet Union is here.  Since vibratory pile driving equipment was first developed in the Soviet Union, it’s also interesting to look at the entire subject; that overview is here.

The series is in three parts:

General View of the S-834 Hammer

The specifications for the S-834 are here.  What follows is an overview of the hammer itself and its general construction.  We apologise for the poor quality of the scans.

A general view of the machine. The impacting ram (1) is driven by eccentric weights and a motor within, which both lift it and force it down to impact. The hammer frame (2) receives the pile from below through a centre hole, which makes it possible for (1) to impact the pile. The motion of (1) is governed by the upper and lower springs (3). The compression on those springs is adjusted by (4), (5) and (6).
A cutaway view of the impacting ram. Basically the centre shaft (3) is driven by the electric motor (2), which in turn rotates the eccentrics (9). The force is transmitted from the eccentrics to the body (1) via the bearings (4) and the bearing housings (5). Electrical power is fed to the motor at the electrical connections (12). Once the entire assembly reached the impact point, impact force is transmitted to the pile at the ram point (10).
The ram point’s force is transmitted through the anvil (5) to a wood cushion (1), which in turn transmits the force to the pile, whose head is inserted through the tapered receptacle (2). The size of the receptacle can be adjusted with (3). The leader guides (6) are used for the leaders, which are (in typical Soviet and European fashion) behind the hammer.
Another variation of the anvil assembly.
This shows how the pile is drawn up into the leaders. The pile is attached to the bottom of the frame using a sling. This was common practice in the Soviet Union and is also done elsewhere. The alternative is to use a separate pile line. If the equipment is configured properly, this can work well.

Design Calculations for the S-834

In the posts that follow, the design calculations for the S-834 will be presented.  In looking at the work of Soviet designers, it was tempting to revise the calculations.  For one thing, although the metric system was introduced with the Russian Revolution, their implementation of the system is not really the “SI” system taught today, especially with the use of the kilogram-force.  (That’s also true with many other Continental countries such as Germany and France.)  For another, Russian technical prose can be very cryptic.

In the end, it was decided to reproduce the calculations pretty much “as they are,” with a minimum of revision.  We apologise for the inconsistent sizing of the equations.  Most of the transcription of this information was done in the 1990’s in Microsoft Word, and its conversion to HTML (for this format) in LibreOffice made the equations graphics (a good thing) but inconsistently sized the images (a bad thing.)  This is one reason why we’ve migrated to LaTex for our newer technical productions online.

As with much of the Soviet material on vibration and impact-vibration pile driving, I am indebted to VNIIstroidormash’s L.V. Erofeev for the material itself and V.A. Nifontov for its translation.

Reciprocating Vibratory and Impact-Vibration Hammers

Virtually all vibratory pile drivers use rotating weights to produce the alternating force that mobilises and fluidises the soil. But it’s necessary to use the weights in pairs to cancel out the horizontal forces that result. What if the force could be produced using a reciprocating weight, thus eliminating the horizontal cancellation requirement? In the 1970’s Vulcan investigated this problem. We discuss here the two solutions it considered: the linear vibrator and the hydroacoustic driver.

Linear Vibrator

The linear vibrator was the brainchild of John J. Kupka, an Austrian immigrant who had done work for MKT on their “C” series hammers and the Horn Construction “HC” hammers that Vulcan had produced. Kupka designed the linear vibrator for Vulcan and it was tested at Vulcan’s West Palm Beach fabricating facility in March 1971.

The Linear Vibrator, from its U.S. Patent (3,704,651) drawing. The hammer worked by applying air through the inlet 70, which was admitted through slots 56b in the ram 56. The slots were set up so that they only admitted air to one side at a time and for a short length; the rest of the ram travel upward or downward past the slots expanded the trapped air and extracted the energy from it in that way. The two air cushions at the ram ends 56a additionally bounced the ram between its two extremes and provided for transmission of the alternating force to the body, and through the primitive clamp at the bottom to the pile.

The total assembly above was 67 5/8″ long; the small and large diameters of the piston 56 are 4 1/2″ and 7 1/2″ respectively. The outer diameter of the housing 18 was 11 1/2″.

The results of Vulcan’s March 1971 tests by Continental Testing Laboratories can be found here. The device worked as designed but Vulcan never pursued the technology. The primitive clamp has been noted; the suspension 40 at the top, with its Belleville washers, was already being made obsolete (along with the steel coil spring suspensions of earlier vibratories) by the rubber springs Vulcan was to use in the next decade. A more serious problem was the magnitude of the force. The peak force put out by the hammer was just shy of 5 U.S. Tons. The 400, the smallest rotating vibratory Vulcan put out, had a force of 17 tons, and the “small” 1150 (which competed with machines such as the MKT V-5 and ICE 216) 42 tons.

The basic problem with the force lay in the use of compressed air and the piston ring sealing technology used in the machine. Although Vulcan could have easily produced such a machine with the technology it used for the air/steam hammers, upscaling it to compete with vibratory hammers even in the early 1970’s would have resulted in a fairly large machine. The concept of a ram/valve with expansive use of the compressed air resurfaced in the Single-Compound Hammer which Vulcan developed a decade later.

One way of getting around the size and pressure problem would have been to make the device operate with hydraulic fluid and the pressures that went with that. In the late 1970’s Vulcan toyed with that idea but it was also presented with another concept, namely the hydroacoustic driver.

Hydroacoustic Driver

In 1974 the Naval Civil Engineering Laboratory issued its Technical Note N-1362, “Evaluation of a Hydroacoustic Rapid-Impacting Pile Driver”by Dr. Carter J. Ward. This report described the operation and tests on a new concept in hydraulic pile driving. Abstract for the report is as follows:

Tests to evaluate the driving capabilities of the rapid-impacting hydroacoustic pile driver on various types and sizes of vertical piles and horizontal batter piles are descjbed and discussed. The functional and operational characteristics of the driver are described, test results and output analysis are presented, and the hydroacoustic driver is compared operationally and economically with the vibratory driver and conventional diesel pile hammer.

Hydroacoustic-Driver
Hydroacoustic driver, as tested by NCEL. The device, although compared with a sinusoidal vibrator, is actually a reciprocating version of an impact-vibration hammer in that the lower end of the hammer/valve (piston) impacts an anvil rather than transmitting force alternately. Like the impact-vibration hammer, it was capable of high blow rates, if not a great deal of energy for each blow.

The concept was presented to Vulcan in 1977-8; however, the company was going through a generational change, this compounded by the demands of the existing air/steam line (the 6300 was being designed and produced at the time.) To apply this to conventional pile driving would require some conceptual changes in the transmission of energy to the pile (i.e., lower energy per blow with higher blow rate vs. high energy per blow and low rate.) Additionally the lower energy per blow may or may not be able to move the pile past the quake point of the soil and induce plastic deformation of the soil, essential in impact pile driving. The hydroacoustic driver nevertheless remains an interesting concept for generating impact, if not pure sinusoidal vibration.

Vulcan Vibratory Hammers and Vibratory Technology

By World War II, Vulcan’s air/steam hammer line dominated its production and revenue stream. Of all of the attempts Vulcan made to diversify is pile hammer line after that time, probably the most successful was its line of vibratory pile hammers.

Vibratory pile driving equipment represented a major departure for Vulcan, but it also represents an interesting technology in its own right. In addition to recounting Vulcan’s experience, we have a wide variety of items on vibratory technology in general:

Need a field service manual for your Vulcan vibratory hammer? Or other information. Much of that is contained in the Vulcanhammer.info Guide to Pile Driving Equipment, information about which is here.

Vulcan High-Frequency Vibratory Hammers

The mid-1980’s were lean years at Vulcan. The offshore market was still down, the aftermath of the collapse of oil prices earlier in the decade. Vulcan’s own diesel program had to be stopped, plagued by design and manufacturing problems and an overvalued US Dollar. The vibratory hammer program was going reasonably well but the market was competitive. Vulcan had reached the point where it had effectively closed its own manufacturing facility and farmed out what was left.

It was in this gloomy situation that Vulcan designed and produced one of the most innovative products it had ever produced, the 400 vibratory hammer, the first of Vulcan’s high-frequency machines.

High frequency (~2400 RPM, not to be confused with the ~7200 RPM resonant machines) vibratory drivers had been produced in Europe. Depending upon the soil conditions and configuration of the pile, the vibrations used to drive or extract the pile can also be transmitted to neighbouring structures. Since European contractors drove piles more frequently in close quarters with sensitive structures than their American counterparts, European vibratory manufacturers produced high frequency machines first. Their higher frequency, combined with lower amplitude for the dynamic force, reduce the transmitted vibrations through most soils.

Vulcan’s rationale for a high frequency machine, however, was somewhat different. The first impetus for the 400 was the development of aluminium sheet piling, which made development of a driver smaller than the 1150 attractive. MKT had already developed a medium-frequency small machine (the V-2) to drive aluminium sheet piling, but the machine a) weighed over a US ton and b) had a clamp suited to steel piling, which mangled the heads of aluminium sheets.

What was needed was a lighter machine whose clamp was easier on the pile. Vulcan’s interpretation of the theoretical data led it to believe that a high frequency machine would drive the piles (which was certainly the case with the lighter sheeting sections.) The result was the first 400 vibratory hammer, designed and built in the summer of 1987.

The 400 had several innovative features:

  • A one piece gear-eccentric, machined out of plate with the eccentric weight burned out. The gear teeth were a much smaller pitch than their medium frequency counterparts, a feature replicated on the “A” series machines four years later. The small pitch ran more quietly an dispensed with the need for surface hardening.
  • A clamp that was burned out of plate. The cylinder bolted to it used the flat end of the rod as the movable jaw. This only left a shallow round dent in the sheeting when clamped.
  • The “U” configuration which wrapped around the exciter case and transmitted the force from the crane to the pile during extraction. This and other features were subject to U.S. Patent 4,819,740. (This patent has been a nuisance to Vulcan’s competitors for long time, cited in several patents from inventors at HPSI, APE, J&M, ICE and MGF.)
  • It was the first Vulcan pile driving machine to completely dispense with castings.

The result was a machine that weighed only 1100 lbs.–half of the MKT V-2–and still drove the piles successfully.

 

 

Vulcan’s Medium Frequency Vibratory Hammers

In 1984 Vulcan re-entered the vibratory hammer market with the introduction of the 1150 vibratory hammer. This hammer made its debut on a project in Bangor, Maine for Cianbro Construction. More suited for the American market and adequately powered, these machines were far more successful than the Vulcor hammers had been.

The technology used was pretty typical for vibratory hammers of the era, including the large-pitch teeth gears bolted to cast steel eccentrics, 355 mm (14″) throat width for American-style sheeting installation, Volvo hydraulic piston motors (for the high pressure units; vane style motors were used on the low pressure 1150,) and a clamp with an industrial style cylinder bolted on to push the movable jaw into the fixed jaw. Both jaws had two parallel sets of teeth with a gap in between to accommodate the interlocks on the sheet piles, which enabled the hammer to drive two sheets at a time.

Vulcan produced three sizes of medium frequency hammers, the 1150, 2300 and 4600. The size designated the eccentric moment of the hammer in inch-pounds. All of the hammers rotated at 1600 RPM.

Vulcan used the HPSI power pack for its vibratory hammer throughout the 1980’s. (One of these is shown on the flatbed trailer in the 4600 photo below.) This power pack was simple and reliable, using air controls (as opposed to the electric controls used by competitors such as ICE and later APE.

Note: if you’re looking for service and other technical information on Vulcan vibratory hammers, take a look at the Vulcanhammer.info Guide to Pile Driving Equipment.

Below: a 2300 on the job driving h-beams in Portsmouth, Virginia, in 1990. The contractor was Tidewater Construction. A diesel hammer can be heard driving piles in the background for part of the video.

Below: the 2300L extracting soldier beams in Atlanta, Georgia, in December 1990. The fact that these machines can both drive and extract piling without modification is part of their appeal.

Below: a video of the installation of bearings in the 2300L, and a little “tour” of PACO’s yard.

The “A” Series Vibratories

In 1991 Vulcan introduced the “A” series of hammers (1150A, 2300A and 4600A) series of hammers. The biggest changes were a) the abandonment of the Morse shear fenders and b) the complete reconfiguration of the gear and eccentric design, inspired by information obtained from the Soviets. The first “A” series hammer was a 2300A, first used on a job by Agate Construction in New Jersey.

Vulcan also began to manufacture its own power packs, where it was able to make many technological advances.

Foster Units

One of Vulcan’s more interesting ventures in the 1990’s was the private label manufacture of a line of vibratory hammers for L.B. Foster in Pittsburgh. The first hammer to be produced was a replica of Foster’s existing 1800 unit, but it became apparent that this unit was very expensive to produce. Vulcan then designed a line of medium frequency vibratory hammers, the 1050, 2100 and 4200 hammers. With the combination of Vulcan’s and Foster’s experience in vibratory hammer design and manufacture, this was the best line of medium-frequency vibratory hammers that Vulcan ever produced.

Some general arrangements of the Foster hammers are here.

After the Acquisition

After it was acquired by Cari Capital, the company continued to support the line; however, it was left behind when Vulcan Foundation Equipment acquired the air/steam hammer line in 2001. It was ultimately sold at auction the following year.  Current service and support for these units is furnished by Pile Hammer Equipment.

Uraga/Vulcor Vibratory Hammer

Vulcan’s first venture into the vibratory market took place in the 1960’s with the introduction of the Uraga electric vibratory hammer from Japan, which Vulcan marketed as the Vulcor Vibratory Hammer.

Vibratory pile driving technology had been developed in the Soviet Union. One of the first countries to pick up the technology was Japan. With its volcanic soils, it is an ideal place for a vibratory hammer to be used.

Most early Japanese vibratory hammers (which are described some here) followed the Soviet pattern of electric motor(s) driving eccentrics through a chain drive system. (An example of this kind of design is shown here.) This unimaginative application of the technology prompted one Soviet trade official to describe the Japanese as “not very good students.”

The Uraga/Vulcor machine was a departure in that Uraga reversed the rotor and stator on the electric motors and positioned one motor inside of each eccentric. This resulted in a vibrator with a more direct drive than has been seen before or since, making for an efficient construction and operation.

uraga-vh1
Uraga VHD-1 model, with only one “stack” of eccentrics.

Unfortunately the width of the machine clashed with the normal American practice of setting the sheets before driving, which requires either that the vibratory hammer be narrow enough (less than 355 mm) at the throat or use an extension (which adds to both the vibrating mass and hanging weight of the hammer.) Some Uraga machines also suffered from misalignment of the eccentric bearings, a function in part of the “modular” construction of the machines (to increase the number of eccentrics, it was simply necessary to add another “stack” to the unit.

All of these difficuties, combined with American contractors’ aversion to electrics on the job, put the Vulcor at a disdavantage to other vibratories coming into the U.S. By the time Vulcan moved to West Palm Beach, the Vulcor programme was pretty much over and it would be another twenty years before Vulcan would attempt a vibratory hammer again.

Vulcor-VHD2-California
The Uraga VHD-2 (with two eccentric stacks) at a power plant project in California. The hydraulic clamp, although primitive by modern standards, was an advance over the “lever-style” clamps use by many other Soviet and Japanese units. Even Foster was still using lever-type clamps in their units in the early 1990’s.

More on the Uraga/Vulcor Hammer:

Vertical Drains: Sand and Wick

One of the more interesting applications of vibratory hammers is the installation of wick drains, a type of vertical drain. But vertical drains are of interest far beyond vibratory technology.

Overview

Soils are a composite of solid soil particles, water and air. When soils reside below the water table (phreatic surface,) there is no air, and the soils are referred to as saturated. The soils dealt with in vertical drainage are generally saturated.

Soil particle sizes vary, and with that variation come many of the variations in soil properties. Soils with large particles (sand and gravels) are referred to as cohesionless soils. Soils with smaller particles are usually silt or clay soils and are referred to as cohesive soils.

In either case, water not only fills the space (voids) between the soil particles, but it is capable of flowing through the soils as well. Flow in rivers and streams is due to the fact that the water is flowing “downhill” due to gravity, and the same phenomenon can take place in the soil voids. The property of soils relating to their allowance of water flow in the voids is referred to as permeability. As a general rule, the smaller the particle size, the lower the permeability of the soils.

One action that can result in water flow in a soil is the placement of a new load on top of the soil, which in turn exerts downward pressure on the soil. Unless the soil particles are in their most compact arrangement (which is unlikely,) water will be forced out of the soil voids under the new load. If this water is forced out, the structure on top will settle, sometimes significantly.

In the case of cohesionless soils, the large particle size enables relatively rapid water flow out from under the load, and the settlement can be very rapid. But if the soil is cohesive with small particles, the water movement (and thus the settlement of the structure) can be very slow, sometimes months or years. Structures built on top of this kind of soil can be fine to start with but over time settle significantly, creating serious structural damage and requiring expensive repair or demolition of the structure.

Although there are several ways of dealing with the problem, one of them is to drain water out of the cohesive soils before placing a structure on top of them, thus getting the settlement out of the way and enabling a stable structure to be built. The method used to do this is referred to as vertical drainage, and specifically two types of vertical drains and their installation will be described here: sand drains and wick drains.

Sand Drains

dm7_01267
Theory and Methods of Sand Drains
140C-Sand-Drain-Closeup
A Vulcan 140C hammer installing sand drains.

A sand drain is basically a hole drilled in a cohesive soil and filled with sand. Since the sand has larger particle size, its permeability is much higher, thus water will flow through it much more easily. As shown above, an array (it’s actually a two-dimensional array) of sand drains is installed, and a load is applied on top of the drains. The load shown above is an embankment, such as is used on a highway, and an additional, or surcharge, load is used to speed up the drainage process. The excess water is collected at the top and directed away from the jobsite.

The tricky part comes in getting the sand drains in the ground. The obvious solution is to simply drill the holes and fill them with sand, but if the soil is soft (which is frequently the case,) the holes will collapse. Although sand drains were first used in California in the 1930’s, the sand drain projects that were of special interest to pile hammer equipment manufacturers took place in the late 1950’s and early 1960’s during the development of the Meadowlands area of northern New Jersey.

Both Vulcan and McKiernan-Terry (MKT) developed equipment to install sand drains. Vulcan developed a special series of differential-acting hammers referred to as sand drain hammers. The major difference between the sand drain and conventional hammers was in the cylinder head at the top of the hammer. Instead of using sheaves for the hammer lifting cables, a bar which interfaced with a retractable hook was used. Vulcan developed a special hook block which was patented (U.S. Patent 3,171,552.)

Basically, the hammer would first drive a mandrel (a piece of pipe) into the ground. After this, the sand drain door (the large piece just below the hammer) would be opened, and sand would be dumped into the mandrel. Compressed air is then applied to the sand, the hammer is hooked to the crane with the hook block, and the mandrel is pulled out of the ground, leaving the sand column in the earth to do its job.

A detailed description of the process is given in MKT Bulletin 71 (why Vulcan didn’t develop a piece of literature like this is beyond me.) Below is another view of a Vulcan hammer over a sand drain dump tube.

SandDrainwithHammerandDumpTube
Another view of a Vulcan hammer over a sand drain dump tube.

Wick Drains

A cursory examination of the procedure for sand drains shows that the procedure is fairly involved. It invites simplification, at least for some applications. A popular simplification is that of wick drains.

A wick drain is just what the name implies: a geosynthetic “rope,” usually about 100 mm wide and 5mm thick, which acts as a high-permeability conduit for water to flow out of the soil and to the surface, in the same manner as takes places with sand drains. As is the case with sand drains, they are installed as an array, generally in 3 metre spacings.

Candle makers have the luxury of melting the medium into which their wicks are places. Since things aren’t so simple for the contractor, he or she has to use a mandrel to insert the wicks. The simplest way to do this is to push the mandrel/wick combination into the ground, but some soils are too stiff for this, so the mandrel is frequently vibrated.

Vulcan vibratory hammers have been used in some cases to install wick drains. Since many drains are installed, this is a fairly demanding application for a vibratory hammer, but it is another example of the versatility of vibratory pile drivers.

4600-Wick-Drain-6
Vulcan 4600 sporting bias weights and a caisson beam installing a pipe mandrel for a wick drain project, 1997. Vibratory hammers are best in cohesionless soils; since vertical drains are used in cohesive ones, this places yet another demand on the performance of the machine.

Further Information

A much more detailed explanation of the theory and installation of vertical drains–and especially of wick drains–can be found in the FHWA document RD/86/186, Prefabricated Vertical Drains, August 1986, which can be found by clicking here.

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.