The Action of Soft Clay Along Friction Piles: Bay Mud Revisited

Lymon C. Reese
1983

Research at Berkeley more than three decades ago gave new insight into the behavior of axially-loaded piles in clay. Numerous experiments and analytical studies performed since, many of which have been supported by the oil industry with respect to offshore platforms, have added significantly to a better understanding of the problem. Yet, the prediction of the "real" behavior of such piles with effective-stress methods remains far beyond the present capabilities of geotechnical engineers.

A brief discussion is presented to elucidate the factors involved in the interaction between a pile and the clay with a view of establishing fundamental concepts. Models are described that serve as guidance to further research. Some results of studies at Berkeley and elsewhere are presented that are relevant to an improved understanding.

The thrust of the paper is to lay out the kinds of experiments that must be performed if the problem of an axially-loaded pile in clay is to be solved rationally. Further development of methods to predict the load versus settlement of a pile in soft clay must await the collection of a body of reliable data from field measurements. The discussion that is presented is built around the behavior of a single pile for simplicity but the concepts presented apply to a group of closely-spaced piles. Also, for simplicity only the load transfer in side resistance is considered. End bearing is important, of course, but for a pile in soft clay the load carried in end bearing is frequently a small fraction of the load carried in side resistance.

Applications for New Research for Pile Supported Machine Foundations

W.E. Saul and T.W. Wolf

The use of piling for machine foundations can add flexiblity for the designer, help solve special problems, and possibly reduce costs . A very complete method of analysis is presented with great flexibility in options available as well as a catalogue of very accurate pile models. A design for a power plant using the method is related as an example.

Note: another paper in a similar vein is Dr. Saul's "Pile Foundation Analysis," which is also available.

Axial Capacity of Piles Supported on Intermediate Geomaterials

Robert Mokwa and Heather Brooks
FHWA/MT-08008/8117-32
September 2008

The natural variability of intermediate geomaterials (IGM's) exacerbates uncertainties in deep foundation design and may ultimately increase construction costs. This study was undertaken to investigate the suitability of conventional pile capacity formulations to predict the axial capacity of piles driven into IGM formations. Data from nine Montana Department of Transportation bridge projects were collected, compiled and analysed. Axial pile analyses were conducted using a variety of existing method and computer programs, including: DRIVEN, GRLWEAP, FHWA Gates driving formula, WSDOT Gates driving formula, and an empirical method used by the Colorado Department of Transportation. The results of the analyses were compared to pile capacities conducted using the CAPWAP program.

The capacity comparisons clearly demonstrated the inherent variability of pile resistance in IGM's. Most of the projects exhibited considerable variation between predicted capacities calculated using DRIVEN and measured CAPWAP capacities. For example, five of the six restrike analysis were overpredicted using DRIVEN, one by as much as 580%! The majority of shaft capacity predictions for cohesionless IGM's were less than the measured CAPWAP capacities; the worst case was a 400% under prediction (a factor of 5.) Toe capacity predictions were also quite variable and random, with no discernable trends. This study indicates that the traditional semiempirical methods developed for soil by yield unreliable predictions for piles driven in to IGM deposits. The computed results may have little to no correlation with CAPWAP capacityes measured during pile installation. Currently, CAPWAP capacity determinations duirng pile driving or static load tests represent the only reliable method for determining the capacity of piles driven into IGM formations.

The Bearing Capacity Of Rigid Piles Under Inclined Loads In Sand. II: Batter Piles

G.G. Meyerhof and G. Ranjan

Following the previous investigation reported in the first part on vertical piles, this second part of the paper presents an analysis of the results of loading tests on rigid batter piles under inclined load in sand. The bearing capacity of axially loaded batter piles is discussed by comparing experimental results and theoretical estimates. The theory for ultimate resistance of rigid vertical piles under horizontal loads is extended to that of laterally loaded batter piles. Model test results are compared with those of theoretical estimates and good agreement is found. Methods of analysis of vertical piles under inclined loads are extended to those of rigid batter piles under inclined loads in sand and the analysis is compared with some test results.

Centrifugal Modelling of the Dynamic Response of Piles

J.H. Prevost and A.M. Abdel-Ghaffar

The dynamic response to laterally loaded single piles and pile groups (each consisting of four evenly-spaced piles, and spaced at different distances in each group) embedded in loose, dense, dry and saturated sands, is studied using centrigfugal modelling techniques. The response of single piles and pile groups to forced vibrations was found to depend strongtly on the magnitude and frequency of loading as well as the density of the soils. The results indicate that, as the level of force increased, 1) nonlinear softening behaviour was evidenced by a decrease in the resonant frequency of the soil-pile system, 2) there was an increase in internal soil-pile damping, and 3) the maximum bending moment moved progressively deeper below the soil surface and increased substantially in magnitude. Also, significant interaction effects were observed with close pile spacing. Finally, the experimental stiffness and damping results were compared with theoretical values as predicted by Novak's work.

Comparative Modeling of Vertical Pile Groups

M.W. O'Neill and HoBoo Ha

The recent development of mathematical models for synthesizing load deformation behavior of pile groups suggests the need for calibrating such models to field behavior. Two generic models described herein are used t o model vertical load-deformation characteristics of five full - scale compression tests of pile groups in a variety of clay soils. Values of input parameters necessary to achieve reasonable compatibility with measurements are different in the two models. Those differences are explainable in terms of model mechanics. An extension of compression behavior to load-uplift behavior is described.

Cyclic Tensile Testing of Pile in Glacial Till

R.P.L. McAnoy, A.C. Cashman, and D. Purvis
Taylor Woodrow Research Laboratories

For offshore structures in deep water, piles are being designed to withstand cyclic tension, due to uplift and wave loading, throughout their design life. However there is a scarcity of data concerning the load levels which can be safely applied in this manner. This paper reports tensile tests on a heavily instrumented 10 metre long pile jacked into glacial till. Previous work had shown satisfactory pile behaviour under cyclic tensile loads peaking at up to 48% of the ultimate tensile capacity, and so this work was aimed at investigating pile response to more severe load levels, approaching failure. Cyclic tests were performed with varying peak loads up to 80% of the initial static capacity, and up to 13,500 cycles were applied depending on pile response. The pile sustained encouragingly high loads without serious deformation, but failure did occur during the most severe test, when the peak load was nominally 80% of the ultimate tensile capacity. Pile response analysis provided insight into compression pile design methods when applied to tension piles. Alpha and Lambda methods, but not the Beta method, estimated i ultimate tensile capacity well, whilst stiffness was greater than implied by published T-Z curves.

Design and Installation of Piles in Chalk

V.N. Vijayvergiya, Fugro
A.P. Cheng, Amoco
H.J. Kolk, Fugro Gulf

As a pile is driven into semi-cohesive soils such as chalk, the soil around the pile is remolded and undergoes temporary reduction in shear strength. Thus, the soil resistance during driving can be considerably less than the static resistance that will develop after pile drhing is interrupted or terminated due to set up around the pile. This characteristic of increass in soil strength, i.e., soil set up, is one of the most important considerations in planning a successful offshore pile installation. An underestimate of the true effect on the soil set up might result in unanticipated pile driving refusal. On the other hand, when easy driving is experienced near the design penetration because of the loss of soil strength due to remolding being greater than expected, it might mislead the installation engineer to erroneously decide to drive the piles deeper than the original design penetration until high blow counts are achieved. Both cases of ill judgment would result in additional expensive offshore operations such as jetting or drilling for the former and mobilization of additional pile materials and redriving for the latter.

Driven Piles in Clay--the effects of installation and subsequent consolidation

M.F. Randolph, J.P. Carter and C.P. Wroth

This paper describes the results of numerical analysis of the effects of installing a driven pile. The geometry of the problem has been simplified by the assumption of plane strain conditions in addition to axial symmetry. Pile installation has been modelled as the undrained expansion of a cylindrical cavity. The excess pore pressures generated in this process have subsequently been assumed to dissipate by means of outward radial flow of pore water. The consolidation of the soil has been studied using a work-hardening elasto-plastic soil model which has the unique feature of allowing the strength of the soil to change as the water content changes. Thus it is possible to calculate the new intrinsic soil strength at any stage during consolidation. In particular the long-term shaft capacity of a driven pile may be estimated from the final effective stress state and intrinsic strength of the soil adjacent to the pile. A parametric study has been made of the effect of the past consolidation history of the soil on the stress changes due to installation of the pile. The results indicate that for any initial value of overconsolidation ratio, the final stress state adjacent to the’pile is similar to that in a normally onedimensionally consolidated soil except that the radial stress is the major principal stress. A method is described whereby the model of pile installation and subsequent consolidation may be extended to clays which are sensitive. The method is used to predict changes in the strength and water content of soil adjacent to a driven pile which compare well with measurements from two field tests on driven piles. It is also shown that the rate of increase of bearing capacity of a driven pile may be estimated with reasonable accuracy from the rate of increase in shear strength of the soil predicted from the analysis.

Dynamic Response of Piles and Pile Groups

M. Novak and M. Sheta
The University of Western Ontario

The paper reviews the results of theoretical and experimental reasearch into dynamic behaviour of piles and pile groups conducted at The University of Western Ontario, The importance of soil layering is experimentally demonstrated and an approximate theory to account for it is outlined. Basic features of dynamic behaviour of pile groups are discussed.

Dynamic Stiffness and Damping of Piles

Mitwally Novak

Dynamic response of footings and structures supported by piles can be predicted if dynamic stiffness and dampening generated by soil-pile interaction can be defined. An approximate analytical approach based on linear elasticity is presented, which makes it possible to establish the: dimensionless parameters of the problem and to obtain closed-form formulas for pile stiffnesss and damping. All components of the motion in a vertical plane are considered; that is horizontal as well as vertical translations and rotation of the pile head. The stiffness and damping of piles are defined in such a way that the design analysis of footings and structures resting on piles can be conducted in the same way as is applied in the case of shallow foundations.

Dynamic Prediction of Pile Static Bearing Capacity

R.H. Scanlan and J.J. Tomko, Princeton University

This paper undertakes, through use of a continuous elastic theoretical pile model, to predict the static bearing capacity of example piles from dynamic measurements taken while driving the piles. The field measurements referred to, made on both reduced-scale and full-scale piles, consist of the force and acceleration measured as functions of time at the top of the piles during driving. The prediction scheme employes an four-parameter model of elastic and rigid body pile response to the measured hammer input. When this scheme is employed to match analytically the time-varying pile velocity and displacement derived from the acceleration measurements, it then also yields an estimate of the pile ultimate static bearing capacity valid just after driving. This bearing capacity is verified by direct comparison with field static tests. For cases where a "set-up" time after initial driving has occured, reuse of the method reveals the change in bearing capacity realised by the pile. For this, at least one blow of redriving is required. Finally, a simplified approximation to the given scheme is presented for engineering use, suggesting, among other things, that a routine dynamic test may be employed to determine pile static bearing capacity.

Empirical Damping Constant for Sands and Clays

H.M. Coyle and G.C. Gibson
ASCE Journal of Geotechnical Engineering, May 1970

The objectives of this investigation were: (1) To determine soil damping constants for sands and clays by conducting laboratory impact tests on these soils; and (2) to correlate these soil damping constants with common soil properties such as void ratio and angle of internal shearing resistance in sands, and liquidity index and moisture content in clays.

Estimate Damping and Quake by Using Traditional Soil Testing

M.C. McVay and C.L. Kuo
Florida DOT Report WPI0510838
November 1999

Impact pile driving greatly alters the behavior of the soil surrounding the pile. The changes of soil responses make it is very difficult to estlmate Sinith soil parameters even by means of Pile Driving Analyzer (PDA) monitoring and CAPWAP Analysis. Although GRL, Inc. had recommended typical values of the Smith damping and quake parameters for different types of soils and pile sizes, many researches indicated that the Smith parameters were not only depended on the soil types and pile sizes, also the pile driving conditions. The ranges of the Smith soil quake and damping from published data were so widely scattered that it was very difficult to select reasonable values for Wave Equation Analysis.

The objectives of this research is to explore the meanings of the Smith soil model in Wave Equation Analysis and identlfy the key variables affecting the determination of the Smith soil parameters. Using the UF pile database for regression analysis, semiempirical equations for estimating the Smith soil parameters were developed based on conventional soil properties.

Estimating the flexibility of offshore pile groups

M.F. Randolph and H.G. Poulos

The overriding criterion in designing piles to support offshore structures is usually the required axial capacity of the pile. The number of piles, and frequently the diameter of'each pile, may be fixed at an early stage of the design, while the final length of each pile is only settled after detailed site investigation and the application of a variety of design procedures for estimating the profile of ultimate skin friction. Tne stiffness of the final foundation must also be estimated accurately in order that the dynamic performance of the structure may be assessed. Modern methods of calculating the stiffness of a piled foundation involve first estimating the axial and lateral stiffness of a single, isolated, pile, and then using appropriate interaction factors and frame analysis techniques to arrive at a stiffness matrix for the complete pile group.

Estimating Friction Pile Lengths from Boring Data

A.A. Seymour-Jones
Howard Needles Tammen & Bergendoff

A difficult task for engineers and contractors is estimating the lengths of friction piles. A theoretical equation has not been developed that results in accurate pile length estilnates. Empirical methods, rules of thumb and judgement based on experience are used.

This paper presents analytical guides for estimating the lengths of friction piles that the author has found useful. There is no claim of originality for these guides since they were developed frorn methods proposed by others. The use of these guides requires a critical review of the results obtained to insure that they are reasonable.

Estimating length of friction piles is used primarily by, foundation engineers to assure that adequate pile-friction capacity is achieved and by engineers and contractors to estimate pile contract quantities. The guides presented herein meet both of .these needs. The writer judges these guides to be applicable for driven piles up to 150 ton design load. The basic data requred to utilize these guides are boring logs containing the Standard Penetration Test (SPT) data, soil descriptions, and information on the proposed type of piling to be used such as type, design load and shape. It is not the intent of the author to imply that these guides should replace pile load tests. Rather, they can be used as a means to estimate the length of load test piles, to supplernent he load test results where soil conditions are quite variable and to provide an estimate of pile quantities prior to the making of pile load tests. These guides are not intended to be used to evaluate potential pile settlement or pile group effects. Additional studies, which are beyond the scope of this paper, are required for such evaluations.

Evaluation of Bearing Capacity of Piles from Cone Penetration Test Data

H.H. Titi and M.Y. Abu-Farsach
Louisiana Transportation Research Centre
LTRC Project No. 98-3GT
November 1999

This study presents an evaluation of the performance of eight cone penetration test (CPT) methods in predicting the ultimate load carrying capacity of square precast prestressed concrete (PPC) piles driven into Louisiana soils. A search in the DOTD files was conducted to identify pile load test reports with cone penetration soundings adjacent to test piles. Sixty piles were identified, collected, and analyzed. The measured ultimate load carrying capacity for each pile was interpreted from the pile load test using Butler-Hoy method, which is the primary method used by DOTD. The following methods were used to predict the load carrying capacity of the collected piles using the CPT data: Schmertmann, Bustamante and Gianeselli (LCPC/LCP), de Ruiter and Beringen, Tumay and Fakhroo, Price and Wardle, Philipponnat, Aoki and De Alencar, and the penpile method.

The ultimate load carrying capacity for each pile was also predicted using the static method, which is used by DOTD for pile design and analysis. Prediction of pile capacity was performed on sixty piles, however, the statistical analyses and evaluation of the prediction methods were conducted based on the results of thirty five friction piles plunged (failed) during the pile load tests. End-bearing piles and piles that did not fail during the load tests were excluded from the statistical analyses.

An evaluation scheme was executed to evaluate the CPT methods based on their ability to predict the measured ultimate pile capacity. Four different criteria were selected to evaluate the ratio of the predicted to measured pile capacities. These criteria are: the best-fit line, the arithmetic mean and standard deviation, the cumulative probability, and the Log Normal distribution. Each criterion was used to rank the prediction methods based on its performance. The final rank of each method was obtained by averaging the ranks of the method from the four criteria. Based on this evaluation, the de Ruiter and Beringen and Bustamante and Gianeselli (LCPC/LCP) methods showed the best performance in predicting the load carrying capacity of square precast prestressed concrete (PPC) piles driven into Louisiana soils. The worst prediction method was the penpile, which is very conservative (underpredicted pile capacities).

Flexural Analysis of Offshore Pile Foundations

G. Ramamany, G. Ranjan and N. Rumarjain

A rigourous flexural analysis for partially embedded piles subjected to axial and lateral loads is presented. The soil reaction in the embedded portion of the pile is obtained using both modulus of subgrade reaction theory. Piles embedded in both cohesive and cohesionless soils have been considered. The results of the analysis show that the vertical load can increase the lateral deflection to an extent of about 7-16% depending upon the degree of fixity if the vertical load is of the order of 10% of the buckling load. A comparison of the results of the analysis with those obtained using "equivalent cantilever method" has been made. The comparison suggests that the "equivalent cantilever method" needs modifications even when used to analyse a pile subjected to lateral loads only.

Ground vibrations caused by pile installation

A.R. Selby, University of Durham

The installation of steel sheet or bearing piles by impact hammer or by vibrodriver transmits energy into the ground which can be observed at the surrounding ground surface as transient or periodic vibration. The vibrations may be disturbing to neighbours, and may pose a risk of damage to nearby structures and buried services.

Within an extensive programme, ground vibrations have been measured on a large number of piling sites throughout England and Scotland. Vibration components in the radial, transverse and vertical directions at five stations were recorded simultaneously to allow time-based (true) vector resolution, and detailed study of attenuation.

Several observations have been deduced directly from the data, but because of the large quantity of data covering different types of hammer, pile and ground, a data base has been constructed. Estimation of probable vibrations in a given situation can be made by reference to similar case studies extracted from the data base. An expert system for estimation of vibrations has also been developed.

From the many records, covering a range of combinations of soil types, hammers and pile sections, it is shown that vibrations attenuate fairly rapidly to below levels at which minor structural damage is likely. However, the human frame is so sensitive to vibration that annoyance may be caused by pile driving at distances of more than 30m. A specific test to measure dynamic strains in brickwork induced by pile driving is also reported. Despite severe vibration, no damage occurred.

Heave and Lateral Movements due to Pile Driving

D.J. Hagerty and Ralph B. Peck

Whenever piles are driven, soil is displaced. The movements induced in the soil itself may have several undesirable consequences, including the lift or lateral displacement of those piles that have already been driven. This study uses data from a number of sources to analyze the heave and lateral movement of the soil during pile driving.

Influence of Cyclic Loading on Axial Pile Response

H.G. Poulos

This paper reviews reviews existing data on the effects of cyclic degradation and loading rate on skin friction and soil modulus for axially loaded piles. Some of these data are used in a theoretical analysis of cyclic axial response, and the effects of such factors as cyclic load level, number of cycles, loading rate and group effects are investigated. Group effects are shown to have a very significant influence on both the ultimate load capacity and cycle pile stiffness. Finally, a procedure is described whereby the behaviour of a pile subjected to variable cyclic loading can be estimated.

Measurement and Prediction of Vibrations Generated by Drop Hammer Piling in the Bangkok Subsoils

R.P. Brenner and S. Viranuvut

A large number of vibration measurements on the ground surface and on an adjacent building were performed in connection with the pile driving activities on a site north of Bangkok. Vibration intensity was expressed in terms of peak particle velocity. A statistical comparison with previously collected data from other sites in the Bangkok area revealed that vibrations generated by driving a pile into one of the bearing strata commonly used for foundation piles in this region, i.e., stiff clay or the underlying sand, are not of significantly different magnitude. A previously recommended upper bound for vibrations to be expected could be confirmed. A multiple correlation with penetration data obtained from Dutch cone tests at the site and pile driving records was also attempted but the only variable giving significant contribution was the cone resistance. The correlation, however, was rather weak.

Relationships between wall friction, displacement velocity and horizontal stress in clay and in sand, for pile driveability analysis

E.P. Heerema

Shaft Resistance of Driven Piles in Clay

D.M. Potts and J.M. Martins, Imperial College, London

In recent years much research effort has been devoted to the deveiopnent of an effective stress aproach to pile desiqn in clays. Although the objectives of such research are simple, the problem has proved to be of such complexity that only limited proqress has been made to date. The major problems arise in the prediction of the chanqes in effective stresses which occur as a result of both installation and the subsequent loading. Much recent work has concentrated on predictinq stress changes arising from the installation of, and subsequent consolidation around, driven piles in clay. Much progress has been made in this respect. However the same attention has not been given to the effects of loadinq such piies after installation.

In this paper the results of a numerical investigation into the mobilisation of shear resistance along the shaft of a full displacement pile are presented. The analysis has considered the behaviour of the soil around a short segment of a very long pile, well away from the influences of both the pile toe and the ground surface. The pile is assumed to have been installed by driving and only loaded after any excess pore pressures have dissipated.

Static Measurements of Pile Behaviour

M.T. Davisson

An overview of the subject from the developer of the Davisson Method for interpreting axial pile capacity from static load tests.

A survey of numerical methods in offshore piling

I.M. Smith
1980

Numerical methods have been widely used in the offshore piling industry for the past 25 years or so. This paper cannot attempt to be a literature review, but merely sets out the current state of achievement and tries to point the way to future developments. Topics include four main subjcct areas; quasi-static behaviour of piles and groups, drivability, pore pressure considerations and dynamics.

Tension Capacity in Silty Clays--Beta Pile Test

J.H. Pelletier and E.H. Doyle, Shell Oil

A summary of a pile test and its results performed in conjunction with the Cognac platform in the Gulf of Mexico.

Testing of drivability of concrete piles and distrbance to sensitive clay

Bengt Fellenius and Laval Samson

The results are reported of an investigation of a group of thirteen 12-inch diameter precast concrete piles driven through 60 ft (18 m) of sensitive marine clay followed by 10 ft (3 m) of silt and sand and 13 ft (4 m) of very dense silt to end bearing in glacial till. The purpose of the test is to study the drivability of the piles through very dense soil and to measure the disturbance caused to the sensitive clay by the driving of displacement piles. The paper presents the soil conditions at the site and the testing program. The test results are discussed and experience gained from the follow-up of the driving of 520 piles at the site is presented. Pile loading tests showed the piles to have an ultimate bearing capacity exceeding 450 tons. It was established that the shaft resistance in the clay during test loading exceeded by 25% the undrained shear strength of the clay as measured by field vane testing. In comparison, an uplift test to failure showed that the uplift shaft resistance along the pile was only 60% of the undrained shear strength of the clay. The pile driving developed large pore pressures in the clay which exceeded the effective overburden stresses. The excess pore pressures dissipated over a period of slightly more than 3 months. Vane testing within the pile group immediately after driving showed that a shear strength reduction of about 15% was caused by the piles..