Microzonation of Rangpur city corporation area based on site amplification using nonlinear technique and liquefaction

Abstract

The Rangpur City Corporation in Bangladesh has been taken into account in this investigation. In this research, microzonation of the Rangpur City Corporation area has been developed based on site amplification employing a nonlinear approach and liquefaction. The site coefficients have been determined using the average shear wave velocity for the top 30 m of a place. The peak ground acceleration (PGA) at the surface is generally estimated by multiplying the bedrock peak ground acceleration (PGA) by a calculated site coefficient. The site effect computed from the top 30 m average shear wave velocity will be inaccurate as a representation of the site coefficient if bedrock is deeper than 30 m below the surface. In this study, one-dimensional (1-D) site response analysis has been performed using DEEPSOIL software for the purpose of analyzing site effects. The analysis has been performed using equivalent linear and nonlinear methods in the DEEPSOIL software. The nonlinear PGA has been obtained to be 0.3238 g by averaging the surface PGA values (using DEEPSOIL software) of 16 boreholes. It has been found that the PGA value for the equivalent linear method is greater than the nonlinear method. At a depth of 160 m, the shear wave velocity is approximately 800 m/sec. The bedrock is assumed to be about 160 meters below the surface of the ground at the study site. Considering the total number of boreholes in the Rangpur area, the site class of the soil is classified as an SD site class (according to BNBC-2020) by averaging the SPT-N values of all boreholes. 24 borehole data have been collected (8 borehole data have been collected from a previous study conducted by BUET) for the assessment of the liquefaction potential of the study site. Standard penetration tests (SPTs) were conducted at 1.5-meter intervals throughout each boring, and the N values (the total number of blows in each SPT) were recorded up to a depth of 20 m. To evaluate the liquefaction potential of the surface, values of the PGA acquired by the nonlinear technique have been utilized for the Seed and Idriss simplified method, the Japanese method, and the Chinese method. The liquefaction potential index value increases as the magnitude of the earthquake increase from 6.5 to 8.5. According to the estimated liquefaction potential index (LPI) contours, virtually all of the boreholes have soil that is very sensitive to liquefaction up to a depth of 20 m, which is the case for almost all of the boreholes. The predicted LPI contours show that almost the entire area is at risk of liquefaction.