Experimental study on performance of soil-pile-raft-structural system and estimation of piled-raft coefficient under seismic excitations

Piled-raft foundations are mostly being used to support structures as they considerably improve the overall performance under seismic conditions. The present paper investigates the influence of the spacing of piles and pile group action on the seismic response of the building and piled-raft foundation through scaled-down model tests. All the model tests are performed in the newly developed laminar shear box and are subjected to sine sweep tests and scaled-down input motions. The present study estimates the seismic response of the building, which is characterized by natural frequency, peak spectral acceleration, lateral displacement, and inter-storey drift of the building. The foundation responses are expressed in terms of rocking, bending moment, and lateral deflection. The load sharing between the pile and the raft in the piled-raft foundation have also been interpreted during seismic events. The test results show that the lengthening in fundamental period occurs for the soil-piled-raftstructural system in the range of 18.47-77.35 %, in comparison with fixed-base conditions. It is also observed that the fundamental period of the coupled system (H/B = 11.25) has reduced by 10.25 %, spacing between the piles increases from 2 to 6. The test results also indicate that the fundamental period of the coupled system reduces by 14.59 %, when the number of piles in the piled-raft system increases from 4 to 9. The experimental investigation also shows that the piled-raft coefficient in the piled-raft foundation varies in the range of 0.38 - 0.62 for different seismic excitations.