Response of pile groups in clays under lateral loading based on 3-D numerical experiments

Abstract

The response of laterally loaded pile foundations may be significantly important in the design of structures for such loads. In many cases the criterion for the design of piles to resist lateral loads is not the ultimate lateral capacity but the deflection of the piles, Poulos and Davis (1980). In the case of bridges or other structures founded on piles, only a few centimetres of displacement could cause significant stress development on these structures. The load-deflection curve of a single free-head pile can be determined using numerical methods and/or results from pile load tests, while full-scale pile group tests for determining the response of a pile group are very rare due to the extremely high cost required. Furthermore, for single piles various approaches have been proposed with the aim to take into account nonlinearities arising from soil-pile interaction. Within this framework Reese (1977) proposed the well-known “p-y analysis”, according to which the soil response is described by a family of curves giving soil resistance as a function of deflection and depth below the ground surface. The simplicity of the method, in conjunction with the welldefined procedures for establishing the “p-y” curves, made the method the most widely used. Although the method is reliable for evaluating the response of a single pile under horizontal load, it is questionable if reasonably reliable simple methods could be applied to assess the response of pile groups. It is howevercommonly accepted that for the same mean load, the piles of a pile group exhibit significantly greater deflection than an identical single pile. This behaviour should be attributed to the fact that the resisting zones behind the piles overlap. Clearly the effect of the overlapping becomes larger as spacing between piles decreases. The application of three-dimensional (3D) numerical analysis on the other hand, despite its complexity and high computational demands, is the most powerful tool for pile group response evaluation under horizontal or other loading, since it is able to predict both stiffness and ultimate resistance reduction factors, particularly in the case of sensitive soils undergoing plastification for even a low level of loading.