Centrifuge tests on seismic response of piled raft foundation with large spacing

Centrifuge tests are performed to study the seismic response of piled raft foundation with large spacing in saturated soft clay. By laying sand on clay surface before centrifuge consolidation under 50g, the soil layer with upper over-consolidated clay and lower normally-consolidated clay is simulated. Structural models are simplified to mass points and members. Two foundation types of connected and non-connected piled rafts are considered in tests. The responses of earthquake acceleration, displacements, pore water pressures and pile strains are investigated. The test results show that in the natural vibration frequency range of soft clay ground, the interaction of superstructure-foundation-soil is very remarkable, and the acceleration amplification factors of structure and foundation are higher than those in other frequency ranges. The earthquake induced instant settlements of the connected and non-connected piled rafts are larger than those of the surrounding ground, but a long time after the earthquake the settlement velocities of foundation and ground are almost the same. At the end of the earthquake, more than half of lateral displacement of superstructure and foundation inclination of the connected piled raft are reduced compared with those of the non-connected piled raft, but with higher acceleration amplification effects of superstructure. After the earthquake some loads transfer from pile group to raft on account of soil degradation and loss of bearing capacity of piled raft. However, there are generally few changes of load sharing ratio between piles and raft. The research has revealed the deformation control mechanisms of pile foundation under seismic subsidence in soft clay, and it may provide evidence for the design of settlement-reducing piles.