Response of Pile Foundations due to Lateral Force and Soil Movements

Abstract

This research has investigated the response of pile foundations subjected to lateral force applied directly to pile head and loadings arising from lateral soil movements of the surrounding ground. The behaviour of pile foundations subjected to lateral soil movements was studied through physical modelling with a specially designed testing apparatus. Laboratory experiments have been undertaken on a single pile embedded in progressive moving sand. A triangular loading block was used in the model tests to induce a progressive soil movement profile. Apart from eight general tests, sixteen tests were conducted on a single pile to examine the effects of the distance between the source where soil movements were induced and the pile location, the magnitude of axial load applied at pile head, the variation of loading block angle, varying combination of sliding and stable layer depths, and pile diameter on the responses of piles. The results of previously conducted pile tests with a uniform soil movement profile were compared with those of the current tests to examine the effect of soil movement profiles on the pile behaviour. Simple solutions were proposed for predicting the pile responses. They provided good estimate of the development of maximum bending moment and maximum shear force in the piles with soil movement. Importantly, the maximum bending moments induced by the soil movements were found to be linearly related to the maximum shear forces (sliding thrust), independent of the magnitude and depth of soil movement and soil movement profiles. Experiments have also been conducted on pile groups in progressive moving sand, including various pile group configurations and spacing. Both free-head and cappedhead fixity conditions have been considered. The findings show that the resistances of the piles to lateral soil movements significantly rely on their locations in a group, especially for piles arranged in a line parallel to the soil movement direction. The results of the pile group tests were compared with those of the single pile tests. Group factors were defined in terms of maximum bending moment and modulus of subgrade reaction to quantify the impact of group effect. The simple solutions developed were extended for predicting the response of individual piles in a group with soil movement. The static and cyclic responses of laterally loaded piles in cohesionless soils have been investigated as well. Guideline for estimating the design parameters for laterally loaded rigid piles in cohesionless soils were provided from extensive back calculation of measured responses of fifty-one pile tests. The elastic-plastic solutions presented by Guo (2008) were used in the back calculation. Simple expressions were presented for estimating the parameters used in the solutions. The reliability of the back calculation, the effects of the ratio of loading eccentricity to pile embedded length on the nonlinear pile response and lateral load capacity were investigated. Additionally, the apparatus was modified to apply cyclic lateral loading, with which a series of model tests were conducted on piles in dry sand under static and cyclic loadings. Analyses of the test results show that the cyclic load level has a greater impact on the pile behaviour than the number of cycles. It is noted that the gradient of the limiting force profile will decrease and the modulus of subgrade reaction will increase, after a number of unloading and reloading cycles. The induced maximum bending moment can be estimated from the applied lateral load, eccentricity of the load, and the depth at which the maximum bending moment occurs.