Evaluation of Liquefaction Potential of Kolkata City, India: A Deterministic Approach

Liquefaction damage has been observed in several moderate to large earthquakes. Intensive efforts have been made to understand the liquefaction mechanism and develop procedures for analyzing the liquefaction potential at a particular site. In the present study, we aimed to evaluate liquefaction potential of Kolkata City, located between latitudes 22 degrees 20' N-23 degrees 00' N and longitudes 88 degrees 04' E-88 degrees 33' E, based on Standard Penetration Test (SPT) N values. The deterministic approaches as per Idriss and Boulanger [Soil liquefaction during earthquakes, Monograph (MNO)-12, Earthquake Engineering Research Institute, 2008] and IS 1893: Part 1 (Criteria for earthquake resistant design of structures & mdash;part 1: General provisions and buildings, Bureau of Indian Standards, 1893) have been used to determine the liquefaction potential of the city. The detailed soil data from 500 boreholes located across 75 locations of the city are analyzed at various depths below the ground surface for varying earthquake moment magnitudes (M-w) of 6.5, 7, 7.5 and 8 at peak horizontal ground surface acceleration (a(max)) of 0.24 g. The evaluation is carried out in terms of factor of safety against liquefaction (FSL). Hazard zonation maps and contour maps are also developed in the present study using ArcGIS 10.5 (ArcGIS Desktop Release 10. Environmental Systems Research Institute, California, 2016). It is observed that with the increase in depth, liquefaction potential decreases but increases with the increase in the magnitude of the earthquake. Conclusively, the two approaches yielded different factor of safety (FSL) values for the same soil data with the IS 1893: Part 1 (IS: Part 1, Criteria for earthquake resistant design of structures & mdash;part 1: General provisions and buildings, Bureau of Indian Standards, 1893) method giving higher values of FSL compared to the Idriss and Boulanger [Soil liquefaction during earthquakes, Monograph (MNO)-12, Earthquake Engineering Research Institute, 2008] method, indicating less risk of liquefaction.