2D nonlinear site response analysis of typical stiff and soft soil sites at shallow bedrock region with low to medium seismicity

Abstract

In this study, an attempt has been made to estimate 2D nonlinear seismic site response of a small scale basin on typical stiff and soft soil sites in Peninsular India (PI). Six survey sites were selected from three shallow bedrock regions such as Kalpakkam, Bangalore and Vizag for which subsurface profiles are generated at these locations using Multichannel Analysis of Surface Wave -2D (MASW-2D) method. The subsurface profiles generated are classified as stiff and soft sites based on average 30 m shear wave velocity and further used for the 2D nonlinear site response analysis using the commercial program FLAC -2D. Thirteen intraplate ground motions from all around the world are selected for the site response analysis based on seismicity of the region. Results of the site response analysis were expressed in terms of short-period amplification factor (Fc) and long period amplification factor (Fs) for the intraplate shallow bedrock region. The results show that the Fc gives higher values than Fs in the case of stiff soil and it is showing a reverse trend in the case of soft soil. The trend of Fc is becoming more complex than that of the Fs especially in the case of stiff soil sites. Also, the 2D site response results were compared with conventional 1D nonlinear site response results using the program DEEPSOIL and aggravation factors were generated. Further, a parametric study has been carried out to quantitatively evaluate the effect of amplitude of ground motion on 2D site response analysis. Parametric study results show that subsurface heterogeneity is very sensitive to the low amplitude of input motion, especially in the case of stiff soil sites.