Indian Journal of Science and Technology

Abstract

Background: Seismic site response analyses are routinely performed for shallow soil deposits. In the seismic site response studies, depth of input motion which is also called as the depth of half-space or bedrock and is one of the important parameters which influence the amplification and attenuation characteristics of any particular site. Objectives: Finding the exact location of bedrock for deep soil deposits is difficult and uneconomical. Hence, there is a need to identify the effective depth of soil column for deep soil sites to get representative site response parameters. Statistical Analysis: In the present study, recorded bedrock and surface earthquake data with soil profiles is used to identify the matching modulus and damping curves for widely available deep soil types and investigated the depth of half-space for site response study of deep soil sites. Eleven deep soil profiles having minimum depth of 100m and maximum depth of 800 m with different sets of recorded earthquake time histories from Kiban Kyoshin network are used for the study. Nonlinear site response analyses were carried out using the program DEEPSOIL. Suitable shear modulus and damping curves are identified by a parametric study of varying shear modulus and damping curves for a matching computed response spectrum with the measured response spectrum. Soil properties and model curves are frozen for each profile, which are further used to identify the depth of half space. Findings: Perfect matching layer having shear wave velocity and depth has been analysed, the study indicated that location of half-space is independent of depth factor. However, it is noticed in the study that computed response spectrum is close to the measured response spectrum when input is given for layer having shear wave velocity of 760 m/s±100.This layer represents a depth of half space for site response analysis of the deep soil column. Application: We can utilize the finding to perform for better accuracy and consistent results based on current findings and same can be used for site response studies.

Keywords: Earthquake, Effective Depth of Soil Column, Input Motion, Response Spectrum, Site Response