Relationship between Low Strain Shear Modulus and Standard Penetration Test N Values

A low strain shear modulus plays a fundamental role in the estimation of site response parameters. In this study an attempt has been made to develop the relationships between standard penetration test (SPT) N values with the low strain shear modulus (Gmax). For this purpose, field experiments SPT and multichannel analysis of surface wave data from 38 locations in Bangalore, India, have been used, which were also used for seismic microzonation project. The in situ density of soil layer was evaluated using undisturbed soil samples from the boreholes. Shear wave velocity (Vs) profiles with depth were obtained for the same locations or close to the boreholes. The values for low strain shear modulus have been calculated using measured Vs and soil density. About 215 pairs of SPT N and Gmax values are used for regression analysis. The differences between fitted regression relations using measured and corrected values were analyzed. It is found that an uncorrected value of N and modulus gives the best fit with a high regression coefficient when compared to corrected N and corrected modulus values. This study shows better correlation between measured values of N and Gmax when compared to overburden stress corrected values of N and Gmax.