Development of correlation between SPT-N value and shear wave velocity and estimation of non-linear seismic site effects for soft deposits in Kolkata city

ABSTRACT

In the present paper, the site-specific response spectra at bedrock level are generated by deterministic seismic hazard analysis and soil amplification study for Kolkata (India) is performed. The site-specific bedrock spectra are obtained by enveloping 10 response spectra corresponding to 10 attenuation relationships with pga 0.104 g. Eighteen seismic downhole test data upto 50 m depth are collected from various sites in Kolkata, along with the SPT-N value profile. An empirical relationship between shear wave velocity and SPT-N value is proposed considering nonlinear power law for soft soil. The results of this study can be used for site response study of Kolkata. The average $(V_s^{30})$ of Kolkata soil varies from 146 to 295 m/sec. As per NEHRP classification, the sites are classified as Class D and E. Nonlinear soil amplification study is conducted in all borehole locations and uncertainty of soil parameters, like shear wave velocity with plasticity of soil, are considered. A total of 1170 soil profiles are analyzed, and site-specific response spectrum is proposed. A maximum surface PGA of 0.18 g is obtained corresponding to 3.8 times amplification in peak spectrum. The proposed acceleration time history and the response spectra may be used for design and safety evaluation of infrastructures in Kolkata.

KEYWORDS:

• Soil amplification
• design response spectra
• Shearwave velocity
• Kolkata city

Acknowledgments

The authors gratefully acknowledge Dr. Suman Ray, Chief Executive Officer and Mr. Sudip Nath, Chief Engineer of C.E. Testing, West Bengal, India, for their support and help to obtain soil data of Kolkata region.

Disclosure statement

No potential conflict of interest was reported by the authors.