Composite piled raft foundation with intermediate cushion in layered soil under seismic forces



In order to mobilize shallow soil to participate in the interaction of piled raft foundation sufficiently, the concept of piled raft has been modified to new type of foundation named composite piled raft. In the system of composite piled raft, the short piles made of flexible materials is used to strengthen the shallow soft soil, while the long piles made of relatively rigid materials is used to reduce the settlements and the cushion beneath the raft is used to redistribute and adjust the stress ratio of piles to subsoil. Finite element method is applied to study the behaviour of this new type of foundation subjected to seismic forces. This paper focuses on behaviour of various components of foundation system such as long pile, short piles and subsoil under seismic force (T2-I-2(1995, HYOUGOKEN_South, EW)) in layered soil related to Surat city geological condition. A comparative study is done to understand the effect of cushion on axial stresses, shear stresses and shear forces along piles and soil beneath the raft.