Larry M. Tucker
U.S. Army Corps of Engineers
Miscellaneous Paper GL-88-28
A research program to compare the ultimate axial capacity of vibratory and impact 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.
Reed L. Mosher
U.S. Army Corps of Engineers
Waterways Experiment Station
Technical Report ITL-87-7
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.
Daniel O. Wong
University of Houston
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 proposed and a procedure to select a vibro-driver for given soil conditions Is recommended. A computer program has also been developed to model vibratory driving.
Note: this contains much of the data shown in NCHRP 316.
Michael W. O’Neilll, Cumaraswamy Vipulanandan, and Daniel O. Wong
University of Houston
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 knowledge 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
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.
Royal Institute of Technology
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 sheet pile 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.
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.
Geert Jonker and Simon Hartog, ICE
The installation and extraction of sheet piles 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 tendency to use these hammers also for permanent systems as an alternative to impact hammers. The reason for this is not only the specific 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.