Prediction of elastic settlement of rectangular piled raft foundation

Abstract

A FE – BE coupling technique is used in the present study for prediction of elastic settlement of rectangular piled raft foundations. The raft is idealised as a thick plate freely resting on soil medium, which is idealised as a semi-infinite, isotropic and homogeneous elastic half -space. The plate and the half- space are two separate models in unilateral and frictional contact at the interface. Pile is idealised as a spring of equivalent stiffness, obtained from simplified approach based on elastic theory assuming it to be a shaft in the half-space. Boundary element method is employed to determine the soil stiffness matrix by inverting the soil flexibility matrix, using Mindlin’s solution for a point load in half-space as a fundamental solution. Finite element method is employed to determine the raft stiffness matrix based on Mindlin’s plate bending theory, which allows transverse shear deformation. Transformation of the boundary element matrices are carried out to make it compatible for coupling with plate stiffness matrix obtained from finite element method. Combined stiffness matrix of the soil-pile-raft system is obtained by summing up the stiffness of the soil-raft system and the stiffness contribution of the piles at selected locations. A computer programme is developed, based on the procedure describe above, in which discretisation is automatic and requires very nominal data input. Effect of pile parameter on settlement of a piled raft system subjected to uniformly distributed load is studied for different number and configuration of piles to demonstrate the efficacy of piled raft system in reducing settlement.