Site-Specific GRA to Quantify Ground Motion Amplification for Bettiah Site: A Case Study

Abstract

In the present study, one-dimensional nonlinear seismic ground response analysis (GRA) was carried out for the Bettiah site of Bihar, India, which comes under the seismic zone IV. The nonlinear seismic GRA was performed using the DEEPSOIL computer programme with the consideration of excess pore water pressure variations. Total 18 boreholes up to the depth of 40 m were considered for the analysis. The water table location at the sites was varying from 0.8 to 1.6 m below the ground surface. The shear wave velocity (Vs) at different depths was estimated from the empirical correlations between Vs and SPT-N values. Three acceleration time histories obtained from the 2011-Sikkim earthquake (Mw = 6.9) of PGA 0.16 g (recorded motion), 0.286 g (scaled motion), and 0.43 g (scaled motion) are chosen to represent low, moderate high, and very high seismic hazards. The results obtained from GRA have been presented in terms of variations of acceleration, shear strain, shear stress ratio, and pore water pressure (PWP) along with depth. The variations in acceleration from the bottom layer to the surface layer indicate the amplification of seismic waves. The high shear strains (up to 5%) development may cause permanent deformation in the ground. An increment in shear stress near the ground surface, i.e. from 0.18 to 0.42, indicates the tendency of soil liquefaction with an increase in seismic energy. Further, the increase of PWP ratio up to 0.93 with increasing seismic energy or higher PGA input motion indicates the initiation of soil liquefaction at most of the boreholes at the Bettiah site. Hence, it is recommended to perform GRA before the construction of any soil-supported structures in the Bettiah region.KeywordsSite-specificNonlinear GRAGround motion amplification