Study on Liquefaction Evaluation of Subsoil Strata Along Visakhapatnam Coastal Area

Abstract

Among the ramifications triggered by earthquakes, liquefaction of soils poses more challenges to civil engineering structures. Liquefaction generally occurs in poorly draining saturated loose silty sands and fine sands. Under short-term dynamic excitation, complete or partial loss of shear strength occurs in these soils due to the development of hydrodynamic pressure in excess of the existing total stress. It is difficult to accurately predict the damage potential of liquefaction owing to its dependence on a variety of factors. However, prediction of the liquefaction occurrence under the anticipated earthquakes is possible by evaluating the liquefaction potential. The seismicity associated with Visakhapatnam city (Zone II) is moderate to minimal. But the built-up of stresses over several years along the fault planes can make the city vulnerable to earthquakes in future. With an increase in the number of constructions of high-rise structures and developmental activities, particularly along the coastline, it is essential to identify the liquefaction-prone areas to safeguard the infrastructure and life against the adverse effects of liquefaction. In the present study, the liquefaction potential of the subsoil profile of selected locations along Visakhapatnam coastline is evaluated as per IS 1893 Part 1 2016 and Idriss and Boulanger (2004) methods. The factors of safety (FOS) against liquefaction are determined corresponding to various seismic zones for different magnitudes of the earthquakes based on standard penetration resistance (N) values of subsoil strata from bore logs of the study areas and liquefaction-prone areas are identified based on the evaluated factors of safety. Liquefaction potential indices (LPI) of the subsoil strata are calculated as per Iwasaki et al. (1978) method to evaluate severity of the liquefaction at the study areas. From the study, it is found that all the study areas under consideration are not prone to liquefaction under the considered magnitudes of earthquakes with respect to present seismic zoning 2. However, the subsoil profiles of study areas indicated risk against liquefaction corresponding to seismic zones 4 and 5.KeywordsLiquefaction PotentialFactor of safetySaturated fine sandEarthquakeDamage potentialSaturated silty sand