Kinematic and inertial effects on piled rafts in soft ground supporting isolated and non-isolated buildings observed during the 2011 Tohoku earthquake

Abstract

Based on previous studies on the seismic monitoring of isolated (IS) and non-isolated (NI) buildings supported by piled rafts with a DMW (deep mixing wall) grid, under similar soft-soil conditions during the 2011 Tohoku earthquake, the effects of kinematic and inertial forces on the piled rafts, for which the natural periods of the superstructures were significantly different, were investigated. To evaluate the degree of contribution of the kinematic and inertial forces on the maximum bending moments and incremental axial forces near the pile heads, the coefficients related to the kinematic and inertial forces were presented. The coefficients of inertial force were separated into those of the superstructure and raft inertias to consider the embedment effects. Furthermore, the mechanisms of the inelastic behavior of the settlement and the load transfer in the piled raft systems, observed during the principal motion, were discussed. Consequently, it was found that the ratio of the natural period of the soil-pile-structure system to the predominant period of the ground, T_s/T_g, plays an important role in the contribution of the kinematic and inertial forces to the maximum bending moments near the pile head. Moreover, the T_s/T_g values were seen to be closely related to the differences in the inelastic settlement and load transfer mechanisms of the piled raft systems.