Pile-clayey soil interaction analysis by boundary element method

Abstract

This paper is an attempt to solve the soil-pile interaction problems using the boundary element method (BEM). A computer package called PGroupN, which deals mainly with the analysis of the pile group problem, is employed in this study. Parametric studies are carried out to assess the impacts of the pile diameter, pile length, ratio of spacing to diameter and the thickness of soil stratum. The external load is applied incrementally and, at each increment, a check is made that the stress state at the pile-soil interfaces does not violate the yield criteria. This is achieved by specifying the limited stresses of the soil for the axial pile shaft capacity and end-bearing resistance. The elements of the pile-soil interface yielded can take no additional load, and any increase in load is therefore redistributed between the remaining elements until all elements have failed. Thus, by successive application of loading increments, the entire load-displacement relationship for the pile group is determined. It is found that as the applied load reaches the ultimate bearing capacity of the pile group, all the piles will share the same amount of load. An exception to this case is for the center pile in a group of 9 piles embedded in clay, which is not consistent with the behaviors of the other piles in the group even if the load reaches the ultimate state. For the 4 piles group embedded in clay, the maximum load carried by the base does not exceed 8% of the load carried by each pile with different diameters. This low percentage ascertains that the piles embedded in cohesive soils carry most of the load throughout their shafts.