Estimation of Liquefaction Susceptibility of a New International Airport Site in Sylhet, Bangladesh.

This study carries out a site response and liquefaction analysis of a new international airport site in Sylhet, in the northeastern part of Bangladesh. The site is situated in an area near the Himalayan thrust which is home to numerous large earthquakes, including the 1869 Cachar, the 1897 Great Indian, 1918 Srimangal, and 1923 Durgapur, and many other relatively smaller earthquakes. Hence, in view of the past seismicity and significance of the power plant site, a seismic investigation was performed in the seismic control region within a radius of 300 km from the center of the plant site. The peak ground acceleration (PGA) value at the bedrock level for a return period of 475 years for the site was estimated to be 0.30 g. For the last few decades, the coefficients of a site have generally been estimated from the mean shear-wave velocity for the top 30 m of a location. The surface PGA of a location is equal to the product of the bedrock PGA and the estimated site coefficient. If the bedrock is located more than 30 m below the ground, the site effect estimated from Vs30 cannot appropriately represent the site coefficient. For the study site, the bedrock is approximately 150 m below the ground. For loose sedimentary deposits of this site, the site coefficient based on Vs30 used to assess the PGA on the surface is not suitable. In this research, a site amplification factor based on Vs30, equivalent-linear, and nonlinear methods was used to estimate the PGA at the surface of the site. In this site, the susceptibility to liquefaction was estimated utilizing 61 boreholes having SPT-N values at intervals of 1.5 m from the surface to a depth of 20 m. Here, liquefaction susceptibility was assessed by applying Seed and Idriss' simplified method, Japanese method, and Chinese method. The estimated liquefaction potential index (LPI) contours show that 80–90% of the total area is highly susceptible to liquefaction and the rest of the area has low susceptibility. [ABSTRACT FROM AUTHOR]