Performance of Piled Raft Foundation Subjected to Strong Seismic Motion

Abstract

This paper offers a case history of a low-rise building, located in Ibaraki Prefecture, supported by a piled raft in medium to dense sand underlain by over consolidated silty soil. To confirm the validity of the foundation design, field measurements were performed on the foundation settlement and the load sharing between the piles and the raft from the beginning of the construction to 80 months after the end of the construction. During the monitoring period, 44 months after the end of the construction, the 2011 off the Pacific coast of Tohoku Earthquake struck the site of the building. The peak horizontal ground acceleration of 3.24 m/s² was observed in the neighbourhood of the building. Although the foundation settlement near the centre of the raft increased by 4 mm from the pre-earthquake value of 21 mm to 25 mm, no significant changes in the load sharing between the piles and the raft were found after the strong seismic motion.