EVALUATION OF LIQUEFACTION POTENTIAL OF KOLKATA CITY, INDIA USING LPI AND LSN APPROACHES

Abstract

Soil liquefaction is a phenomenon that occurs when soil strength and stiffness are reduced due to fast loading, such as shaking from an earthquake. Several approaches to evaluating the intention of initiating liquefaction have developed over the years. The present study aims to evaluate the Liquefaction Potential Index (LPI) for Kolkata city based on the Vs approach using IS code. The Shear Wave Velocity (Vs) of Kolkata city has been calculated through the empirical correlations between Vs and uncorrected SPT-N values. Kolkata city is situated at the border of seismic zones III and IV, which is indicative of a moderate to high seismic alert. The study involved the creation of LPI contour maps and LPI hazard maps for Kolkata city for different earthquake magnitudes with amax/g=0.24. Also, the present study aims to compare liquefaction severity for eight boreholes located around Kolkata using both Vs and CPT approaches. Furthermore, calculating of Liquefaction Severity Number (LSN) for many boreholes around Kolkata based on the CPT approach for different earthquake magnitudes. The LPI contour and hazard maps show that most of Kolkata city is in high danger of liquefaction, particularly in the central and eastern parts. Also, the study shows that Kolkata's susceptibility to liquefaction varies based on the magnitude of the earthquake Mw. As the liquefaction potential index (LPI) and the liquefaction severity number (LSN) values increase, the liquefaction potential also increases. The results of the comparison between the liquefaction severity using the Vs approach and CPT approach show good agreement. Since Kolkata is situated on the Indo-Gangetic Plain, most of the soil is thick, soft, and alluvial. The city is underlain by quaternary sediments of clay, silt, and silty sand of varying texture and grain size. Due to the presence of soft and thick deposits of alluvial soil at shallow depths, Kolkata city falls under a high seismic zone.