Evaluation of Empirical SPT N-Vs Correlations Using 1D Site Response Analysis for Shallow Bedrock Sites in Islamabad, Pakistan

Abstract

The use of standard penetration test blow count (SPT- N) to obtain shear wave velocity (Vs) profiles in the absence of geophysical field test data is a common practice. This study uses a set of SPT-N profiles from Islamabad, Pakistan, to develop Vs profiles using empirical SPT-N and Vs empirical correlations. A set of SPT-N and Vs correlations based on the frequency of their use for seismic site response studies in the region were selected. A suite of one-dimensional site response analyses is then performed on the generated Vs profiles. The 13 input ground motions were chosen to be compatible with the site class B of the newly enacted building code of Pakistan (BCP 2021). A set of 546 1D nonlinear site response analyses were carried out and site response outputs were compared with the corresponding design spectra of the building code of Pakistan. The site-specific comparisons revealed that the calculations of region-specific empirical correlations are more compatible with the code design spectrum for site class C, whereas the outputs using empirical correlations of other regions are more compatible with the code design spectrum for site class D. Based on a comparative analysis, suitable empirical correlations for engineering practices in Islamabad, Pakistan are recommended.