Development of Nonlinear Site Amplification Model Based on Average Shear-wave Velocity of Soil Layer and Bedrock Depth

Abstract

Ground classification refers to the process of categorizing the ground into different grades based on how soil properties impact ground motion. With the introduction of the National Standard of Seismic Design General (KDS 17 00 00) in South Korea, ground classification is now based on the average shear wave velocity of the soil layer (VSSO) and the depth to bedrock (BRDP). To consider the specific characteristics of the ground classification, this study develops a site amplification model based on a suite of nonlinear ground response analyses that utilize VSSO and BRDP as model variables. We collected borehole data from the National Geotechnical Information DB System and obtained V_S profiles through geophysical surveys. In cases where no survey record was available, the N-V_S relationship was used to estimate the profiles, or representative shear wave velocity profiles for each soil layer were obtained. The collected 93,486 profiles were then classified into 36 clusters based on VSSO and BRDP. 3,271 shear wave velocity profiles were randomly selected from each group and used for the site response analysis. This study utilized 34 observation records of horizontal components of ground motion from domestic and international earthquakes as input seismic waves. Then, each motion was scaled to 1, 1.5, and 2 times, resulting in 81 seismic waves with PGAs ranging from 0.1g to 1g. Nonlinear site response analyses were then performed using the NL_HH(Nonlinear Hybrid Hyperbolic) module using a Python-based site response analysis module, PySeismoSoil. This module requires shear wave velocity profiles and input seismic waves as input parameters. The NL_HH module uses the HH model, which employs an empirical dynamic curve (Darendeli, 2001)[1] to estimate the damping ratio. A nonlinear site response analysis of 81 input seismic waves was performed at 3,271 boreholes using the NL_HH module, and the response spectrum and site amplification ratio were determined. Based on these, this study develops a nonlinear site amplification model with the ground classification parameters, VSSO, BRDP, and input PGA level at the depth to bedrock as model variables.