Nonlinear Seismic Ground Response Analysis for Site Classes D and E of Bihar Region, India: Fid-Bau Portal

Nonlinear Seismic Ground Response Analysis for Site Classes D and E of Bihar Region, India

Kumari, Khushboo / Kumar, Prabhakar / Kumar, Shiv Shankar

According to the NEHRP (2003), the soil site classes C, D and E are more responsible for the seismic wave amplification; however, among these three site classes, the site class E is more responsible for soil liquefaction. Based on the borehole profiles and SPT-N values, collected from all 48 sites within Bihar region, it was observed that the entire Bihar region comes under the range of site classes D and E with the variations of V_s30 ranging from 180 to 360 m/s. Therefore, an attempt has been made to perform nonlinear seismic ground response analysis (GRA) of site classes D and E of Bihar region using DEEPSOIL software, since the entire Bihar region comes under the seismic zone of III, IV and V. Three acceleration time histories of different peak ground acceleration (PGA) of 0.1 g, 0.26 g and 0.45 g indicating low, moderately high and very high seismic hazard scenarios, respectively, have been chosen for this analysis. The results obtained from seismic GRA have been presented in terms of the variations of acceleration, amplification/deamplification of seismic waves, shear strain, shear stress ratio and pore water pressure along with the depth. The high shear strains (greater than 0.5%) observed within the soil deposit may cause permanent deformation in the ground resulting catastrophic damage to the existing structures. The amplification factor (i.e., ratio of output acceleration to the input acceleration) of seismic wave was found to be in the range 0.35–3.0. Further, the results obtained from nonlinear GRA also indicated that the seismic wave is amplified by 180%, but the deamplification by 50%. The increase of pore water pressure ratio up to 0.93, with increasing seismic energy or higher PGA input motion, indicates the initiation of soil liquefaction at most of the soil site. The results indicated that the seismic GRA is significantly affected by input motion and the soil variability. It can be stated that this study can be useful for the geotechnical engineers to design the earthquake-resistant structures; however, more experimental investigations are required to understand the mechanism of soil liquefaction in the entire Bihar region. Further, this study can also be utilized for the development of surface level ground motion attenuation relationship for the Bihar region. Overall, this study is one of the preliminary investigations toward seismic microzonation study of Bihar region, which can be useful for the development of disaster management plan by providing seismic microzonation map.