2D nonlinear site response analysis of shallow bedrock sites using integrated subsurface profiles

Deepu Chandran,Panjamani Anbazhagan

doi:10.4401/ag-8236

Abstract

In this study, an attempt has been made to generate the subsurface profiles using integrated geophysical approach and a site-specific 2-D nonlinear site response analysis at shallow bedrock sites in Peninsular India. The site selected for the study is Tarapur, India in which three survey lines were selected for the sub-surface mapping. The subsurface profiling of these three locations was done by an integrated geophysical approach by carrying out Multichannel Analysis of Surface Waves - 2D survey, Ground Penetrating Radar survey, and conventional drilling borehole and measurement of Standard Penetration Test N values. Thirteen intraplate recordings from all around the world are selected for the site response analysis. The subsurface profiles generated by the integrated geophysical approaches are modeled in FLAC - 2D nonlinear module and site response parameters are estimated. Further 1D site response analyses are carried out at selected points in 2- D profiles using the program DEEPSOIL and the 2D site response results are compared. Results of site response analysis are expressed in terms of short-period amplification factor (Fc) and long period amplification factor (Fs) and the results show that the 2D geometry of sub-surface is more sensitive to the higher frequency content of ground motion especially for subsurface with more heterogeneities. Also, a parametric study has been done on a synthetic 2D profile to quantitatively evaluate the effect of different ground motion characteristics like amplitude and frequency content on 2D site response analysis. The parametric study shows that underground heterogeneity is very sensitive to the ground motions with high-frequency content and low amplitude.

Highlights

Earthquakes are one of the most destructive natural events in the world which can cause tremendous damage to the structures
Site response analysis is a process of estimating the local site effects due to the ground motion propagation during an earthquake shaking and it became an important step for the geotechnical design of important structures [Roesset, 1977; Idriss, 1990; Kramer, 1996; Borja et al, 2002; Idriss and Seed 1968; Ferraro et al, 2008]
In this study subsurface profiling is done at three selected survey lines in Tarapur, India using integrated geophysical approaches by using Ground Penetrating Radar (GPR), Multi-Channel Analysis of Surface Waves (MASW) and drilled borehole data

Summary

Introduction

Earthquakes are one of the most destructive natural events in the world which can cause tremendous damage to the structures. Many researchers have noted that the seismic activity of Peninsular India has increased in recent years and cannot be considered as a stable continental region [Anbazhagan et al, 2010; Boominathan et al, 2008; Ganesha Raj and Nijagunappa, 2004] All these studies are pointing to do a site-specific ground response analysis in Peninsular India especially for the important structures. Most of the site response analyses carried out in Peninsular India are one dimensional [Boominathan et al 2008; Anbazhagan and Sitharam 2008; Jaya and Remmya 2010; Maheswari et al, 2008], in which the input parameters are obtained through SPT data or MASW 1-D data These analyses were done with the assumption that the soil layers are uniform which is not completely true due to the heterogeneous soil deposits in the region. The application of 2D or 3D site response could result in better estimation of site response which accounts the effect of spatial variability of the subsurface [Sanchez-Sesma and Luzon 1995; Heymsfield, 2000; Kamiyama and Satoh 2002; Finn et al, 2003; Semblat et al, 2003; Capilleri et al, 2018]

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