Geotechnical Investigation for Estimation of Liquefaction Hazard for the Capital City of Gujarat State, Western India

Abstract

Gandhinagar, the capital city of Gujarat state (Western India), is situated in the middle of the moderately active Cambay rift. The region lies under the seismic zone III of the seismic zoning map of India. The city rests on 250–300 m thick flood plain deposits consisting of coarse sand, silt and clay. In this work, liquefaction hazard is assessed using geotechnical investigations. A total of 14 boreholes of 35 to 50 m depth were drilled with sampling at every 1.5 m depth interval (till termination depth) covering entire Gandhinagar city. A standard penetration test (SPT N-value) was conducted at an interval of 3 m depth in every borehole. We used 400 samples for the estimation of index properties of the soil in the study area. The lithological distribution in the city is also mapped based on the soil classification. The liquefaction hazard is estimated by standard methodologies using density, plasticity index, groundwater level, Peak Ground Acceleration (PGA), fine content and Standard penetration test (SPT) N value. The site-specific PGA values at the surface are estimated by carrying out ground response analysis. The study shows that the area comprises of alternate layers of argillaceous and arenaceous soil. We found that in general the area has low liquefaction potential but in case of heavy rainfall the chances of liquefaction may increase as the soils are conducive of liquefaction.