Impact of Ground Response Analysis on Seismic Behavior and Design of Piles in Kolkata City

Abstract

Kolkata city is a major metro city of eastern India and spread in a north–south direction along the east bank of the Hoogly river with the soil being predominantly soft, thick and alluvial in origin. According to seismic code of India, Kolkata city is located along the boundary of seismic zone III and IV which indicates moderate to high seismic hazard. In this paper, using derived empirical correlations between shear wave velocity Vs and SPT N values, soil site classification is carried out and it indicated CLASS E category, highlighting the seismic hazard of Kolkata city. The alluvial nature of soil located in Kolkata city is prone to soil amplification when subjected to different earthquake motions at the bedrock level and amplification factor for bedrock level acceleration varying between 1.7 and 2.5 is obtained in the present study. The spectral acceleration at 5% damping ratio is observed to be 1.94 g, when subjected to 1995 Kobe earthquake motion. The results obtained from ground response analysis is used for seismic design of pile foundations passing through liquefiable and non-liquefiable soil strata by considering both kinematic and inertial loading. The maximum bending moment is observed to occur at the interface of liquefiable and non-liquefiable soil layers. Both bending moment and pile head deflection showed a substantial increase in magnitude when inertial loads are considered in the analysis in addition to kinematic loading. Hence the present study illustrates the significance of deflection and bending response of pile foundations in liquefiable soil as important parameters for seismic design of pile foundations in Kolkata city. © 2017, Indian Geotechnical Society.