Selection of Shear Modulus Correlation for SPT N Values based on Site Response Studies

摘要

Representative evaluation of soil response requires the input parameters to be close to the physical behavior of soil column in the site. Several site response studies are carried out worldwide, considering limited representative parameter of stiffness of soil column, which was arrived from? shear modulus correlation. Bore hole data with SPT (Standard Penetration Test) - N values are used in earthquake geotechnical engineering for estimating dynamic properties and there by ground response parameters. The shear stiffness of soil column is estimated considering the existing correlations between SPT and shear wave velocity or shear modulus. As per our knowledge, there is no clear cut guideline regarding the use of a suitable correlation for estimating representative shear stiffness of a specific soil column for response studies. In this study, an attempt has been made to identify a suitable correlation for estimating shear modulus (G max ) ?for different ?types of soils such as sand, clay and gravel or the mixture of all (sand, clay, gravel, sandy soil). Sites with earthquake data recorded at the surface, (soil profiles along with SPT N values and shear wave velocity) are selected from K-NET (Japanese website) data set. Collected earthquake data consists of moment magnitude (Mw) ranging from 5.0 to 9.0, which are recorded at different epicentral distances. Nonlinear site response studies have been carried out by considering earthquake data recorded at a rock site as an input ground motion to the soil profiles as published in K-NET data site. Surface ground motion and response spectrums are further obtained from different G max correlations and are compared with surface recorded time histories for the same event. This study shows that peak ground acceleration (PGA), response spectrums (RS) and amplification factor (AF) obtained from very few G max correlations are comparable with the recorded PGA, response spectrum and amplification factor.