Quantitative Assessment of Shear Wave Velocity Correlations in the Shallow Bedrock Sites

Abstract

In this study shear wave velocity (V s ) and standard penetration test (SPT) N values up to the bedrock have been measured by multichannel analysis of surface wave and drilling of boreholes at 51 locations in shallow bedrock sites of South India, as part of the intraplate seismic region of India. Testing covers the major cities as Bangalore, Chennai, Coimbatore, and Vizag in South India. Drilling of boreholes in the above locations shows that the top surface consists of soft to very dense soil followed by very hard Granitic rock. N values are measured up to 100 and values beyond 100 were reported as rebound. Soil thickness of these locations varies from 1 m to about 20 m. The measured N and V s values are used to generate correlations between N and V s values for each city and also for the combined data by excluding and including SPT N of 100 for rebound layer. Further the applicability of the V s and N correlations developed for a particular site to other sites in the same region has been studied and it has been found that the site specific correlations are more accurate. The correlations developed for other cities display high percentages of error, even though the sites are similar in geology and soil type. Additionally, the developed empirical correlations have been compared with the existing worldwide correlations using logarithmic Euclidian distance (logED). The logED value has been estimated between the measured and calculated lower logED respectively for different cities and arrived the best suitable predictive equations for the four cities. Lower logED value between the measured and calculated V s corresponds to better empirical relationship.