Behavior Of Pile Groups Research Articles

Experimental study of the effect of inclined pile on the seismic behavior of pile group

Seismic behavior of inclined piles has been considered detrimental for years. However, recent researches show that battered piles can have a beneficial effect. In this framework, a series of centrifuge tests on an inclined pile group is performed. The analysis is based on the comparative response of two 2×1 simplified pile groups: one with vertical piles and the other with one vertical and one inclined pile. The response of these pile groups to repeated earthquakes or sinusoidal inputs is analyzed through the response frequencies, the envelop curves of bending moment profiles, the axial loads measured in both piles and the kinematic response of the cap. Results highlight that the effect of inclined pile is highly influenced by the frequency content of the input. In addition, the inclined pile induces non-negligible residual bending moments, higher horizontal stiffness at the pile cap and larger rotation.

Effect of soil nonlinearity and liquefaction on dynamic stiffness of pile groups

<p>Determination of the behavior of pile groups under dynamic condition is a complex problem. The complexity becomes more intricate when the soil medium surrounding the piles behaves nonlinearly due to higher cyclic loading under dynamic condition. Further if the soil is saturated then the behavior of pile groups is also affected due to liquefaction. In this paper, nonlinear dynamic analyses of pile groups have been performed with and without generation of pore water pressure.</p><p>A three-dimensional finite element soil-pile model has been developed with proper radiation boundary conditions. Frequency dependent Kelvin elements have been used for simulating radiation conditions at infinity. The numerical model and the process of computation have been verified with the established literature. For soil nonlinearity, work-hardening plastic cap model has been considered for further investigation. The pore pressure generation for liquefaction has been incorporated by two-parameter volume change model reported in literature.</p><p>The effects of nonlinearity and liquefaction of soil medium on dynamic stiffness of single pile and pile groups have been investigated. Effects of frequency of excitation have been examined. It has been observed that the work-hardening soil plasticity and generation of pore water pressure has a significant influence on dynamic behavior of pile groups.</p>

Experimental Study on the Behavior of Pile Group under Cyclic Lateral Loading

Experimental Study on the Behavior of Pile Group under Cyclic Lateral Loading

Cam Elyaf Takviyeli Plastik Profilli Pasif Kazik Grup Davranişinin Deneysel Olarak İncelenmesi

Experimental Investigation of Glass Fiber Reinforced Plastic Profiled Passive Pile Group Behavior In this study, the use of glass fiber reinforced plastic (GFRP) profiled passive piles in slope stability is investigated and it is aimed to contribute to the literature as the first model study regarding this topic. A special experimental setup is designed in order to model pile groups subjected to soil movement under its own weight. Soil pressure distributions acting on instrumented GFRP pile groups are examined for various pile spacings. As a result of experiments, it is revealed that the loads acting on piles increase with decreasing pile spacing due to soil arching. Experimentally determined soil pressure distributions are compared with the soil pressure values calculated by analytical methods.

Effects of Separation on the Behavior of Soil-Pile Interaction in Liquefiable Soils

Separation and sliding between soil and pile have a significant effect on the complex behavior of pile groups under dynamic condition. In addition to separation between soil and pile, the behavior of soil medium surrounding the piles is nonlinear during strong excitations. Therefore, soil is modeled using a nonlinear work-hardening plastic cap model. Because of shaking, there is an increase in pore water pressure. To simulate it, the pore-pressure generation capability is added in modeling the behavior of the soil medium. A full three-dimensional finite-element soil-pile model has been developed with approximate radiation condition at infinity simulated by frequency dependent Kelvin elements. The model and the process of computation have been verified with the established literature. The effects of separation on the dynamic stiffness and seismic response of single pile and pile groups have been examined considering work-hardening soil-plasticity without and with pore-pressure generation capability for a wide range of frequencies of excitation. Real-time earthquake motions are also applied and the effects of separation on the responses of pile groups are investigated. Significant effects of separation of the soil medium on the response of the soil-pile system have been observed and approximately quantified.

Lateral Response of Pile Group

The main objective for this study is to determine the relationship between pile spacing and p-multipliers (fm - pile-to-pile modulus multiplier) for a laterally loaded pile-group. In addition, the appropriate p-multipliers for a 3-pile group configuration at 2D, 4D, 6D and 8D pile spacing is also determined. Therefore, a three-dimensional finite element approach was used to assess the lateral pile and pile group response subjected to pure lateral load. Results of the influence of load intensities, group configuration, pile spacing are discussed in terms of response of load vs. lateral displacement, load vs. soil resistance and corresponding p-y curves. The improved plots can be used for laterally loaded pile design and also to produce the group action design p-multiplier curves and equations. As a result, design curves were developed and applied on the actual case studies and similar expected cases for assessment of pile group behavior using improved p-multiplier. A design equation was derived from predicted design curves to be used in the evaluation of the lateral pile group action. It was found that the group interaction effect led to reduced lateral resistance for the pile in the group relative to that for the single pile.

A simplified nonlinear analysis method for piled raft foundation in layered soils under vertical loading

This paper presents a simplified nonlinear solution for piled raft foundations in layered soils under vertical loading. Based on the elastic–plastic analysis of a single pile in a layered soil, the shielding effect between a receiver pile and the soil is taken into account to modify the conventional interaction factor between two piles. An approximate approach with the concept of the interaction factor is employed to study the nonlinear behavior of pile groups with a rigid cap. Considering the variation of soil properties, the solution to multilayered elastic materials is used to calculate the settlement of the soil. The interactions between pile–soil–raft are taken into account to determine the stiffness matrix of the piled raft. By solving the stiffness matrix equations, the settlement and the load shared by the piles and raft could be obtained. Compared with results of the available published literatures, the proposed solution provides reasonable results.

Discussion of “Behavior of Pile Groups Subject to Excavation-Induced Soil Movement in Very Soft Clay” by D. E. L. Ong, C. F. Leung, and Y. K. Chow

Discussion of “Behavior of Pile Groups Subject to Excavation-Induced Soil Movement in Very Soft Clay” by D. E. L. Ong, C. F. Leung, and Y. K. Chow

Closure to “Behavior of Pile Groups Subject to Excavation-Induced Soil Movement in Very Soft Clay” by D. E. L. Ong, C. F. Leung, and Y. K. Chow

Closure to “Behavior of Pile Groups Subject to Excavation-Induced Soil Movement in Very Soft Clay” by D. E. L. Ong, C. F. Leung, and Y. K. Chow

Nonlinear Coupling Analysis on Working Behaviour of Pile Group

The numerical analysis of finite element coupling infinite element is recently used to simulate the effects of unbounded foundation of stresses and displacements. In this thesis, the finite element analysis is adopted to simulate the piles and the near soil; between the pile and the soil a joint element is designed to imitate the relative settlement while the infinite element is used to imitate the distant soil. elastic analysis way for concret elements and infinite elements are used, K-G model and E-U model for near soil.Calculation results show that using Goodman contact element to simulate the interaction of pile and soil has the advantage of flexibility;and the graphic formula of the calculation curves of nonlinear model and K-G model accords with that of the measure curve while the elastic calculation curve is far from the measure curve;the skin friction and pile-tip resistance pressure of the corner pile is the largest, the side pile less, and the center pile the least.The analysis of one example shows that the analytical model adopted in the thesis is reasonable, the results are both reasonable and accurate.

An analysis method for the influence of tunneling on adjacent loaded pile groups with rigid elevated caps

AbstractTunnel excavation could influence the working performance of adjacent pile foundations. How to accurately predict the tunneling‐induced pile responses is becoming an important issue in urban areas. Previous methods tend to neglect the influence of working loads on the tunneling‐induced pile responses. In this paper, a two‐stage analysis method is proposed to study the behavior of pile groups with rigid elevated caps subjected to tunneling‐induced ground movements, in which the pile–pile interaction, coupling of longitudinal and lateral deformation, and influence of working loads are considered. This method is validated by comparing the results with those from a general pile analysis program, GEPAN, centrifuge test data and field measured data. Thereafter, a series of parametric studies is carried out. The results show that the influence of working load on tunneling‐induced pile responses is significant. Three different features of the pile responses will take place for different depth ratios. With the increase in soil stiffness, the tunneling‐induced axial force increases linearly, whereas the bending moment increases nonlinearly. For soils with high stiffness, the maximum bending moment increases linearly with the ground loss ratio within the range of 0–5%; but for soils with low stiffness, this tendency becomes obviously nonlinear. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Wave propagation in the elastic half-space due to an interior load and its application to ground vibration problems and buildings on pile foundations

A method is presented which allows to calculate the wave-field in a homogeneous or layered soil in case of a dynamic interior load. The wave propagation along the surface, the distribution of the response over the depth, the horizontal propagation at different depths and the vertical downward propagation are shown and compared with the simpler surface solution of the half-space and the interior solution of the full-space. The complete wave-field (Green's function) is applied to the dynamic behaviour of piles and pile groups by use of a boundary element formulation. The stiffness, damping and – typically for piles – mass of different groups of piles are presented. Different group effects occur for lines, circles, grids, parallels and crosses of piles, which can be regarded as oscillations around average values. Moreover, the piles and pile groups behave almost like a damper for most of the frequencies. A building on a pile group that is excited by ground vibration due to surface or interior loads shows a reduction of the wave-field due to kinematic and inertial soil–building interaction effects. The results presented lead to simplified descriptions of the wave-field due to interior loads and of the soil–pile–building interaction which can be used for the prediction of technically induced vibration.

Experimental Modeling of Large Pile Groups in Sloping Ground Subjected to Liquefaction-Induced Lateral Flow: 1-G Shaking Table Tests

ABSTRACT A series of 1-g shaking table model tests were carried out to study the behavior of pile groups embedded in sloping ground subjected to lateral flow of liquefied soil. Two different configurations of pile groups: large (6×6 and 11×11) and small (3×3), were considered. The models were subjected to the liquefaction-induced large ground deformation to investigate the effect of several parameters on the response of pile groups and mechanism of lateral flow. These parameters comprise amplitude, frequency, and direction of input motion; density and slope of ground; and the thickness of non-liquefiable layer at the surface. The outcome of this parametric study reveals the importance of above mentioned factors which should be taken into account for analysis and design purposes. In addition, the results from the experiments clearly illustrate that in sloping ground configuration, both front (in upstream) and rear (in downstream) row piles receive greater lateral forces than middle row piles. This finding is attributed to the distribution of soil motion (displacement and velocity) of the liquefied soil in the model. As a result, installation of additional pile rows in front and behind an existing pile foundation can be considered as an effective retrofitting technique. Finally, soil-pile interaction was evaluated by running experiments with different pile spacings, and reliability of the JRA 2002 design manual in estimation of liquefaction-induced lateral force on piles is evaluated.

Experimental Investigations on the Behaviour of Pile Groups in Clay Under Lateral Cyclic Loading

This paper presents the results of two-way cyclic lateral load tests carried out on model pile groups embedded in soft marine clay. The tests are conducted on 1 × 2, 2 × 2 and 3 × 3 pile groups having length to diameter ratio (L/D) of 15, 30 and 40 with the spacing to diameter ratio (S/D) of 3, 5, 7 and 9. The experimental results are presented in the form of load–deflection curves and bending moment profiles. Cyclic group efficiency, critical spacing, critical cyclic load level and cyclic p-multipliers are evaluated. It is found that the lateral capacity of the 3 × 3 group reduces by about 42% after 50 cycles of loading. The cyclic p-multipliers of 3 × 3 pile group are found to be 0.41, 0.25 and 0.29 for leading, intermediate and rear rows respectively. The test results are compared with the numerical analysis carried out by p–y method using GROUP program. The analysis carried out with experimentally evaluated p-multipliers predicts load—deflection and bending profiles of pile groups reasonably well, but underestimates the depth to maximum bending moment by about 15%.

Influence of axial load on lateral pile response in liquefiable soils. Part I: physical modelling

Current research work into the behaviour of piled foundations in liquefiable soils has concentrated on the response to lateral inertial and kinematic loads. It has recently been demonstrated in the literature, however, that an alternative mechanism exists, whereby piles carrying significant axial loads may become unstable as lateral soil restraint is lost owing to earthquake-induced soil liquefaction. In the work presented here and in a companion paper, this effect is examined in greater depth, particularly regarding the integration with and effects on the lateral response of piles such that the two effects can be treated under a unified framework. Dynamic centrifuge testing was used to investigate pile instability by examining the behaviour of pile groups with lateral deflections. Amplification of these deflections was observed to occur during liquefaction, although currently available simple idealisations of soil behaviour were found greatly to over-predict these amplifications when compared with the experimental observations. The response of the soil to such large-deformation events was determined for use in more sophisticated numerical modelling presented in the companion paper. Relative pile–soil flexibility was found to have a strong influence on amplifications occurring in the tests. Ultimately, at high axial load or amplification, unstable collapse (bifurcation) was found to occur both during earthquake shaking, and afterwards owing to excess pore pressure migration altering the strength of the supporting soil surrounding the piles.

Discussion of “Pile Spacing Effects on Lateral Pile Group Behavior: Analysis” by Kyle Rollins, Kimball Olsen, Derek Jensen, Brian Garrett, Ryan Olsen, and Jeffery Egbert

Discussion of “Pile Spacing Effects on Lateral Pile Group Behavior: Analysis” by Kyle Rollins, Kimball Olsen, Derek Jensen, Brian Garrett, Ryan Olsen, and Jeffery Egbert

Behaviour of Pile Group behind a Sheet Pile Quay Wall Subjected to Liquefaction-Induced Large Ground Deformation Observed in Shaking Test in E-Defense Project

ABSTRACT This paper aims to illustrate a large-scale test on a pile group and a sheet pile quay wall which were subjected to liquefaction-induced large ground deformation. The sheet pile quay wall was displaced laterally and the 2×3 pile group was forced by the flow of liquefied soil. This experiment was conducted in March 2006 at the National Research Institute for Earth Science and Disaster Prevention (NIED), Hyogo Earthquake Engineering Research Center, Japan. Liquefaction-induced lateral spreading was achieved, and soil moved laterally about 1.1 m behind the sheet pile quay wall. Lateral soil displacement was measured by the inclinometers, and results were in close agreement with the directly observed values. Soil lateral displacement and velocity of soil flow decreased as the distance from the quay wall increased toward the landside. Bending strain records were able to explain the damages to the piles, yielding at the top and buckling at the middle height. Lateral force of the liquefied soil exerted on the piles was obtained using earth pressure (EP) sensors and it is shown that rear row piles (close to the quay wall) received larger lateral forces than front row piles (far from the quay wall). This behaviour is explained by the distribution of displacement and velocity of the liquefied soil throughout the shaking. In addition, the lateral soil force was back calculated from strain gauge data and the results are compared with the ones directly measured by the EP sensors. Then, the limitations and advantages of the back-calculation approach are elaborated in this study. Moreover, the time history of lateral soil force showed no correlation with either soil or pile displacements, while it demonstrated a fairly close correlation with the relative velocity until a specific time. This interesting finding would confirm the rate-dependent behaviour of the liquefied soil, though more data from large scale experiments, field testing and centrifuge model tests are needed in this regard.

Nonlinear Analysis of Torsionally Loaded Pile Groups

An empirical approach is developed to analyze the nonlinear torsional behavior of free-standing pile groups with rigid pile caps. In this approach, the lateral and torsional responses of individual piles in a pile group are modeled by p-y and τ-θ curves; the interaction among lateral resistances of the individual piles is predicted through Mindlin's elastic solutions; the interactions between the torsional and lateral resistances of the individual piles are described through Randolph's solution; and the coupling effect of lateral resistance on torsional resistance of the individual piles is quantified using an empirical factor β. The proposed approach is capable of capturing the most significant aspects of pile-soil-pile interactions and coupling effect in pile groups subjected to torsion. The proposed approach is verified using results of centrifuge model tests. In general, the applied torque-twist angle response and the transfer of applied torque in pile groups can be reasonably well predicted and are sensitive to the pile group configuration.

Behavior of Pile Groups Subject to Excavation-Induced Soil Movement in Very Soft Clay

A series of centrifuge model tests was conducted to investigate the behavior of pile groups of various sizes and configurations behind a retaining wall in very soft clay. With a 1.2-m excavation in front of the wall, which may simulate the initial stage of an excavation prior to strutting, the test results reveal that the induced bending moment on an individual pile in a free-head pile group is always smaller than that on a corresponding single pile located at the same distance behind the wall. This is attributed to the shadowing and reinforcing effects of other piles within the group. The degree of shadowing experienced by a pile depends on its relative position in the pile group. With a capped-head pile group, the individual piles are forced to interact in unison though subjected to different magnitudes of soil movement. Thus, despite being subjected to a larger soil movement, the induced bending moment on the front piles is moderated by the rear piles through the pile cap. A finite element program developed at the National University of Singapore is employed to back-analyze the centrifuge test data. The program gives a reasonably good prediction of the induced pile bending moments provided an appropriate modification factor is applied for the free-field soil movement and the amount of restraint provided by the pile cap is properly accounted for. The modification factor applied to the free-field soil movement accounts the reinforcing effect of the piles on the soil movement.

EFFECTS OF NON-LINEARITY OF FOUNDATION, GIRDER, PILE AND SOIL-PILE SPRING ON DYNAMIC BEHAVIOR OF PILE-SUPPORTED STRUCTURE

Seismic behavior of pile group is different at the position of piles. It is because of not only the nonlinearity of structure, pile and soil but also axial-force fluctuation and foundation girder stiffness. There is no example of its having examined all factors at the same time though the examination of each factor is done. Authors examined the analytical study on the influence of the nonlinearity of pile, soil and foundation girder for seismic response of pile-supported structure. This report shows the influence of nonlinearity of ground, piles, and foundation girder for the seismic response of a pile-supported structure.