Loaded Pile Groups Research Articles

Reduction of pile head displacement for restrained-head single pile

The effect of pile head fixity on the displacement of laterally loaded pile groups was investigated using analytical methods. The reduction of lateral displacement by a pile cap is generalized using a reduction factor, and the effect of soil and pile properties was investigated through a parametric study using the Davies and Budhu method. It was found that the soil properties have a major influence on the reduction factor, while the pile property influence is relatively minor. These results are presented graphically and show further the decrease in the reduction factor with increasing load level. Based on these results, a design chart for the reduction factor is suggested.

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.

Effect of pile-cap connection on behavior of torsionally loaded pile groups

To evaluate the responses of fixed and pinned pile groups under torsion, a method is presented to analyze the nonlinear behavior of free-standing pile groups with rigid pile caps. The method is capable of simulating the nonlinear soil response in the near field using p-y and τ-θ curves, the far-field interactions through Mindlin’s and Randolph’s elastic solutions, and the coupling effect of lateral resistance on torsional resistance of the individual piles using an empirical factor. Based on comparisons of the solutions for fixed- and pinned-head, 1×2, 2×2, and 3×3 pile groups subjected to torsion, it was found that pile-cap connection significantly influences the torsional capacity of pile groups and the assignment of applied torques in the pile groups. In this study, the applied torques for the pinned-head pile groups are only 44%∼64% of those for the corresponding fixed-head pile groups at a twist angle of 2°. Such a difference is mainly due to the change of the lateral resistances of individual piles in the groups.

Centrifuge Modeling of Torsionally Loaded Pile Groups

This paper reports a series of centrifuge model tests on torsionally loaded 1×2, 2×2, and 3×3 pile groups in sand. The objectives of the paper are to investigate: (1) the response of the pile groups subjected to torsion; (2) the way in which the applied torque is transferred in the pile groups; (3) the internal forces mobilized in these torsionally loaded pile groups and their contributions to resist the applied torque; and (4) the influence factors that affect the load transfer, such as soil density and pile-cap connection. In these model tests, the group torsional resistances of the pile groups increased monotonically in the test range of twist angles up to 8°. Both torsional and lateral resistances of the individual piles were simultaneously mobilized to resist the applied torque. The torsional resistances were substantially mobilized at small twist angles, while the lateral resistances kept increasing in the whole range of twist angles. Thus, the contribution of the torsional resistances to the applied torque decreased at large twist angles. The piles at different locations in a pile group could develop not only different horizontal displacements, but also different pile–soil–pile interactions and load–deformation coupling effect, hence, the torsional and lateral resistances of the piles are a function of pile location. The soil density had a more significant effect on the torsional resistances than on the lateral resistances of the group piles.

A modulus‐multiplier approach for non‐linear analysis of laterally loaded pile groups

AbstractA modulus‐multiplier approach, which applies a reduction factor to the modulus of single pile p–y curves to account for the group effect, is presented for analysing the response of each individual pile in a laterally loaded pile group with any geometric arrangement based on non‐linear pile–soil–pile interaction. The pile–soil–pile interaction is conducted using a 3D non‐linear finite element approach. The interaction effect between piles under various loading directions is investigated in this paper. Group effects can be neglected at a pile spacing of 9 times the pile diameter for piles along the direction of the lateral load and at a pile spacing of 6 times the pile diameter for piles normal to the direction of loading. The modulus multipliers for a pair of piles are developed as a function of pile spacing for departure angle of 0, 90, and 180sup>/sup> with respect to the loading direction. The procedure proposed for computing the response of any individual pile within a pile group is verified using two well‐documented full‐scale pile load tests. Copyright © 2006 John Wiley & Sons, Ltd.

Behavior of Axially Loaded Pile Groups Driven in Clayey Silt

This paper presents a case history describing measurements made during the installation and load testing of groups of five, closely spaced, precast concrete piles in a soft clay-silt. The test results extend the presently limited set of reported high-quality data for pile groups at field scale and allow assessment of the reliability of existing numerical and analytical predictive approaches. Full scale maintained compression and tension load tests on groups as well as tests on single (reference) piles and an individual test on a pile within a pile group enable the effects of multiple pile installations and interaction between piles under load to be assessed. The results are compared with existing simple methods of pile group analysis and with other case histories reporting results on small pile groups. A simple expression to evaluate pile group stiffness efficiency is proposed.

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Closure to “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay,” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Closure to “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay,” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

An experimental study of the interaction of vertically loaded pile groups in sand

The interactions among closely located piles and a cap in a pile group are complex. The current design practice for vertically loaded pile groups roughly estimates their overall behavior and generally yields conservative estimations of the group capacity. For a proper pile group design, factors such as the interaction among piles, the interaction between cap and piles, and the influence of pile installation method all need to be considered. This paper presents the results of the model test, which can be used to better understand the interactions of vertically loaded pile groups in granular soil. Load tests were carried out on the following: an isolated single pile, single-loaded center piles in groups, a footing without any piling, free standing pile groups, and piled footings. The influences of pile driving and the interactions among bearing components on load–settlement and load transfer characteristics of piles and on the bearing behavior of a cap in a group are investigated separately by comparing their respective test results. The favorable interaction effects that increase pile capacities are identified.Key words: pile group, pile installation, interaction, model test, free standing, piled footing.

Analysis of pile groups under vertical harmonic vibration

In this paper, a simple method is proposed for the analysis of vertically loaded pile groups under dynamic conditions. The method makes use of the closed-form stiffness matrices derived by Kausel and Roësset [Kausel E, Roësset JM. Stiffness matrices for layered soils. Bull Seismol Soc Am 1981;71(6):1743–61] to simulate the response of layered soils. These matrices are incorporated in a calculation procedure that is essentially analytical. Further computational advantages of the procedure derive from the fact that, under the simplified assumptions of free-field soil displacements and symmetry of the pile–soil interaction forces, the analysis of a pile group may be achieved simply using the solution for the single pile. Moreover, the soil layering effect is reliably accounted for. The accuracy of the method is assessed by comparing the results with those deduced from other existing theoretical solutions. The method is also used to predict the experimental measurements from dynamic tests on pile groups documented in literature.

Interaction Factors for the Analysis of Pile Groups in Layered Soils

In this note, the interaction factors for the analysis of axially loaded pile groups are calculated using a procedure that makes use of the stiffness matrices for the study of wave propagation problems involving layered media. As a result, static as well as dynamic analysis of piles can be achieved within the same framework, and the soil layering effect is reliably accounted for. The theoretical predictions from the proposed method are compared with experimental measurements from published static and dynamic load tests on pile groups.

Lateral Behavior of Pile Groups in Layered Soils

Assessment of the response of a laterally loaded pile group based on soil–pile interaction is presented in this paper. The behavior of a pile group in uniform and layered soil (sand and/or clay) is evaluated based on the strain wedge model approach that was developed to analyze the response of a long flexible pile under lateral loading. Accordingly, the pile’s response is characterized in terms of three-dimensional soil–pile interaction which is then transformed into its one-dimensional beam on elastic foundation equivalent and the associated parameter (modulus of subgrade reaction Es) variation along pile length. The interaction among the piles in a group is determined based on the geometry and interaction of the mobilized passive wedges of soil in front of the piles in association with the pile spacing. The overlap of shear zones among the piles in the group varies along the length of the pile and changes from one soil layer to another in the soil profile. Also, the interaction among the piles grows with the increase in lateral loading, and the increasing depth and fan angles of the developing wedges. The value of Es so determined accounts for the additional strains (i.e., stresses) in the adjacent soil due to pile interaction within the group. Based on the approach presented, the p-y curve for different piles in the pile group can be determined. The reduction in the resistance of the individual piles in the group compared to the isolated pile is governed by soil and pile properties, level of loading, and pile spacing.

Centrifuge Model Study of Laterally Loaded Pile Groups in Clay

A series of centrifuge model tests has been conducted to examine the behavior of laterally loaded pile groups in normally consolidated and overconsolidated kaolin clay. The pile groups have a symmetrical plan layout consisting of 2, 2 32, 233, 333, and 434 piles with a center-to-center spacing of three or five times the pile width. The piles are connected by a solid aluminum pile cap placed just above the ground level. The pile load test results are expressed in terms of lateral load-pile head displacement response of the pile group, load experienced by individual piles in the group, and bending moment profile along individual pile shafts. It is established that the pile group efficiency reduces significantly with increasing number of piles in a group. The tests also reveal the shadowing effect phenomenon in which the front piles experience larger load and bending moment than that of the trailing piles. The shadowing effect is most significant for the lead row piles and considerably less significant for subsequent rows of trailing piles. The approach adopted by many researchers of taking the average performance of piles in the same row is found to be inappropriate for the middle rows, of piles for large pile groups as the outer piles in the row carry significantly more load and experience considerably higher bending moment than those of the inner piles.

Discussion: Analysis of laterally loaded pile groups using a variational approach

Discussion: Analysis of laterally loaded pile groups using a variational approach

Analysis of laterally loaded pile groups using a variational approach

Analysis of laterally loaded pile groups using a variational approach

Dynamic analysis of laterally loaded pile groups in sand and clay

Pile foundations supporting bridge piers, offshore platforms, and marine structures are required to resist not only static loading but also lateral dynamic loading. The static p–y curves are widely used to relate pile deflections to nonlinear soil reactions. The p-multiplier concept is used to account for the group effect by relating the load transfer curves of a pile in a group to the load transfer curves of a single pile. Some studies have examined the validity of the p-multiplier concept for the static and cyclic loading cases. However, the concept of the p-multiplier has not yet been considered for the dynamic loading case, and hence it is undertaken in the current study. An analysis of the dynamic lateral response of pile groups is described. The proposed analysis incorporates the static p–y curve approach and the plane strain assumptions to represent the soil reactions within the framework of a Winkler model. The model accounts for the nonlinear behaviour of the soil, the energy dissipation through the soil, and the pile group effect. The model was validated by analyzing the response of pile groups subjected to lateral Statnamic loading and comparing the results with field measured values. An intensive parametric study was performed employing the proposed analysis, and the results were used to establish dynamic soil reactions for single piles and pile groups for different types of sand and clay under harmonic loading with varying frequencies applied at the pile head. "Dynamic" p-multipliers were established to relate the dynamic load transfer curves of a pile in a group to the dynamic load transfer curves for a single pile. The dynamic p-multipliers were found to vary with the spacing between piles, soil type, peak amplitude of loading, and the angle between the line connecting any two piles and the direction of loading. The study indicated the effect of pile material and geometry, pile installation method, and pile head conditions on the p-multipliers. The calculated p-multipliers compared well with p-multipliers back-calculated from full scale field tests.Key words: lateral, transient loading, nonlinear, pile–soil–pile interaction, p–y curves, Statnamic.

Behavior of axially loaded pile group under lateral cyclic loading

In this paper, a hybrid boundary element technique is implemented to analyze behavior of axially loaded pile group under lateral cycling loading. Nonlinear material behavior of soil is introduced by a rational approximation to continuum with nonlinear interface springs along the piles. Linear beam column finite elements are used to model the piles. By enforcing displacement and equilibrium conditions at each increment, a system of equations is generated which yields the solution. A numerical study to verify the proposed model is performed. To investigate the cyclic behavior three groups are loaded (1×2, 2×3, and 3×3 groups) initially half of the ultimate axial load, then a lateral loading is applied for cyclic behavior of piles, is done to investigate the behavior of pile groups.

Analysis of laterally loaded pile groups using a variational approach

This paper presents a variational approach for the analysis of laterally loaded pile groups. The displacements and reaction pressures of piles in a group are represented by finite series, and no discretisation of the pile shaft is required. The principle of minimum potential energy is applied to determine the response of a group of piles. The validity of the present approach is verified through comparison with other theoretical solutions. Case studies are also presented to show the application of the present method to pile groups in the field.

Analysis of laterally loaded pile groups using a variational approach

Analysis of laterally loaded pile groups using a variational approach