Site Response Analysis for a Site with the Dipping Bedrock and Liquefiable Layers Using FLAC 3D

Abstract

To get the precise input motion for seismic analysis of important structures located in liquefiable soil layers, this study demonstrates site response analysis using FLAC 3D [. Based on the previous earthquake diaster experiences and regulatory requirements for nuclear power plants (NPP), the seismic wave propagation in the site having dipping bedrock surface was modeled, also the excess pore water pressure during excitation process was added into the soil elements. The free-field site response model is used to generate the response spectra at different ground surface locations, and to predict the influence range of soil liquefaction. The analysis results show that soil liquefaction could reduce site amplification effect, and might have different degree of impact depending on natural frequency and soil pressure resistance of structures. The 3D model also can capture the soil unceratinties and reflect the real topographic effect in one computer run, so the current multiple one-dimensional equivalent linear analysis process could be improved. Therefore, the FLAC 3D model can fulfill nuclear regulatory requirement, and provide suitable ground-motion prediction for liquefiable soil sites and complex bedrock surface sites for the need of seismic evaluations of existing NPPs after Fukushima Dai-ichi Tragedy.