Site Response Analysis and Empirical Correlations between N-Values and Shear Modulus for Sub-Himalayan District Hamirpur using ProShake

In the present work, the empirical correlations between standard penetration test (SPT) N-values  versus  shear modulus (Gmax), and Peak Ground Acceleration (PGA) amplifications for sub-Himalayan district-Hamirpur, Himachal Pradesh (India) consisting of highly variable soil/rock strata at different depths and across the terrain are evaluated. In the first stage, the N values obtained from SPTs are conducted in the field at ۱۸۴ locations covering the studied area. The shear wave velocity for each soil profile of each borehole is calculated using the best available correlation in the literature. Further, the seismic response parameters are evaluated for these values using the ProShake software. Finally, the empirical relationships between maximum shear modulus and SPT value for different soil types are determined along with the ground motion amplifications. The amplification factor for Bhoranj sub-division varies from ۱.۴۰ to ۲.۶۰ and from ۱.۲۸ to ۲.۳۰, ۱.۲۰ to ۲.۱۰, ۱.۲۲ to ۱.۸۵, and ۱.۲۲ to ۱.۷۰ for Barsar, Nadaun, Hamirpur, and Sujanpur, respectively. The studied area consists of variable soil strata including clay, silt, sand, conglomerate, sandstone, and mixture thereof. The correlation between shear modulus and N value is coherent with already reported correlations for regular soils. The amplification factor reported for the sites plays an important role in planning infrastructure in the region. The correlations between maximum shear modulus (Gmax) and SPT value for hilly terrain comprising of highly complex geological formations such as mixed soil and fractured rocks presented in the study are not available in the research work carried out earlier.

Keywords:

Shear modulus , Standard penetration test , Shear wave velocity , Peak ground acceleration , Amplification factor