Abstract: The depth to seismic bedrock and the nonlinear and hysteretic model of soil under cyclic loading have essential influences on the evaluation results of the nuclear island seismic site response. Using the one-dimensional (1D) equivalent linear wave propagation analysis (ELA) and nonlinear analysis (NLA) methods based on both the Matasovic and the Davidenkov-Chen-Zhao (DCZ) hysteretic models, three borehole profiles of 470 m depth with volcanic rock interlayer for the AP1000 nuclear plant located in the coastal deposits in China are selected to numerically simulate seismic site response. Five rock and soil layers with different shear wave velocities and depths are selected as the seismic bedrocks, the effects of input ground motion characteristics, the depth to seismic bedrock and the soil nonlinear and hysteretic model on the nonlinear site response characteristics of extremely deep deposit with volcanic hard rock interlayer are investigated. The results show that regardless of taking a shallow hard rock interlayer or a deep soil layer as the seismic bedrock, the 5%-damped surface spectral accelerations (SAs) at short periods calculated by the NLA method is greater than those calculated by the ELA method. However, the surface SAs at long periods calculated by the NLA and ELA methods are almost identical. Moreover, the curve shapes of surface SAs and peak accelerations along the soil depth calculated by the NLA method based on both the Matasovic and the DCZ models are basically consistent. Finally, from the surface peak ground acceleration and the cumulative absolute velocity calculated by the NLA method, it is suitable to select a shallow hard rock interlayer with the shear wave velocity of approximately 2 500 m/s as the seismic bedrock.

Key words: extremely deep soil deposit site, nonlinear seismic site response, seismic bedrock, hard rock interlayer