Effect of uncertainty in $$V_{\mathrm{S}}{-}N$$ V S - N correlations on seismic site response analysis

Abstract

This paper studies the reliability of the calculated shear-wave velocity ( $$V_{\mathrm{S}}$$ ) from different available $$V_{\mathrm{S}}$$ and SPT-N correlations in terms of seismic site response analysis. In the present study, various $$V_{\mathrm{S}}$$ –N correlations developed for different regions around the globe have been used to calculate the bound of $$V_{\mathrm{S}}$$ variations with depth at three different sites in Kolkata city. This bound has later been used to generate the random $$V_{\mathrm{S}}$$ profiles using the Monte Carlo simulation. Equivalent linear site response analysis has been performed to study the response of those generated profiles under different input motion excitations. Strong-to-weak ground motion records have been used for this purpose. The amplification spectra of the generated $$V_{\mathrm{S}}$$ profiles using all soil types and specific soil-type $$V_{\mathrm{S}}$$ –N correlations show significant variations. The study also shows that the $$V_{\mathrm{S}}$$ –N correlation may result in quite different $$V_{\mathrm{S},30}$$ values and subsequently it may lead to the different site classes according to the NEHRP 2003 classification. So, the random choice of the $$V_{\mathrm{S}}$$ –N correlation, where the direct measurement of $$V_{\mathrm{S}}$$ is not available, may affect the outcome of seismic hazard analysis significantly. The study points out the need for accurate estimation of the $$V_{\mathrm{S}}$$ profile either from in-situ determination or using site-specific correlation.