ANALYSIS OF PILED RAFT FOUNDATION

Abstract

Piled raft foundations are adopted to reduce the total and differential settlements of foundations. In the present study, analysis of piled raft foundation is done by "Plate on Spring" approach in which the raft is represented by an elastic plate while the soil and piles are modeled as bed of equivalent spring at nodal points and intersecting spring respectively. Finite difference method is used for the analysis of the foundation system. The stiffness of pile is estimated by procedure given by Hazarika and Ramasamy (2000). For the estimation of soil stiffness a method by De-beer and Martens (1975) is employed for sand. For clays the same is estimated using immediate settlement and e-log p curve. Software for the analysis of raft using finite difference method, estimation of stiffness for soil and pile and the structural design of raft and pile is developed in MATLAB. Using this software a typical case study is analyzed and results are presented. Effect of coefficient of subgrade reaction of soil and pile stiffness on the settlement and bending moment of raft are studied. Present study show that increase in coefficient of subgrade reaction by three to four times, reduces the settlement by 55% to75% and bending moment by 9.55% to 20% respectively. Piles located at boundary corner are more susceptible to tilting of pile in comparison to interior nodes.