Analysis of Cushion Effects in Unconnected Piled Raft Foundation

Abstract

The piled raft foundations are an economical solution as well as a settlement reducer in the construction of high-rise buildings. Unconnected piled raft foundation is an innovative technique where a cushion separates the pile and raft. The cushion takes the load transferred from the raft and safely distributes over the piles beneath. This article analyses the seismic behaviour of connected and unconnected piled raft foundation of a multistorey building using ANSYS software based on the finite element method. An 8 m × 8 m × 1 m raft and 0.4 m × 0.4 m square concrete piles with depth of 12 m resting on a very soft clay stratum were modelled. The soil block of 16 m × 16 m plan dimension with a depth of 16 m was provided with transmitting boundaries at all lateral edges with properties corresponding to shear wave velocity of clay (150 m/s) and was analysed for the response under the ground motion corresponding to El Centro 1940 earthquake. The building load acting on the raft was considered as a uniformly distributed load of 0.2 MPa. The vertical and lateral displacements at the top of the raft were analysed with cushions having different elastic modulus and thickness. An increase in the elastic modulus of cushion tends to reduce the settlement considerably whereas, a positive correlation was observed between the depth of cushion layer and corresponding settlement. It is evident from the results of the numerical analysis that the stiffness of cushion layer and thickness are two important aspects which determine the displacements of unconnected piled raft systems. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.