Study on seismic response of unconnected piled raft with rubber mixed soil

Abstract

Piled raft foundations are conveniently adopted as the feasible solution for foundations of high-rise buildings constructed across the globe. The analysis of seismic response of unconnected piled raft foundations, where the rigid connection between the raft bottom and pile top was separated by a layer of sand or aggregates, by incorporating the complex interactions between the foundation and soil is a challenge. Therefore, the focus of the current study is on the response analysis of these foundations by considering the soil-structure interactions under dynamic loading conditions. The numerical modelling is done in Opensees with the aid of STKO software, where the complex interactions between structural elements and soil can be modelled accurately. Several models were developed for a comparative analysis of conventional and unconnected piled raft foundations. Initially, a connected square piled raft with four bored piles of 9 m length was numerically modelled in a soil domain along with absorbing boundary conditions on the lateral sides. The effect of separation layer thickness on the seismic response of the foundation was studied by modelling various models of unconnected piled raft foundations. The thickness of the separation layer varied from 0.25 m, 0.5 m, 0.75 m and 1 m. The vertical settlement under static loading conditions was initially evaluated and the behaviour of the foundation under seismic excitation was analysed subsequently. The acceleration time history data of the El-Centro earthquake (1979) was given as an input motion at the base of the soil domain. The results of the numerical evaluation include the lateral displacements and accelerations that were measured at the top of the raft foundation. It was found that the variation in the thickness of the separation layer considerably affects the seismic response of the piled raft foundation.