Effect of Seismic Action on Settlement and Load Sharing of Piled Rafts Based on Field Monitoring

This paper offers three case histories of piled rafts combined with deep mixing wall grids, in which long-term monitoring on settlement and load sharing between the piles and the raft was performed. The buildings are located on soft ground consisting of liquefiable sand and soft clayey soil. The buildings experienced the 2011 Tohoku Earthquake (M=9.0, about 380 km distance from the epicentre) and the seismic response during the earthquake was successfully recorded for the two buildings. Based on the static and dynamic monitoring results, the effect of seismic action on the settlement and load sharing between the piles and the raft were investigated. It was found that no significant change in foundation settlement was observed after the earthquake. However, some change in load sharing between the piles and the raft caused by the seismic action was noted for the relatively short shaft-bearing piles, while almost no change in the load sharing was observed for the toe-bearing piles or long shaft-bearing piles.