1d Nonlinear Ground Response Analysis of Soils in Iit Guwahati and Liquefaction Potential Identification

Abstract eng:
Earthquakes are natural phenomena that have caused the loss of millions of lives and property over centuries. Thus, characterizing these strong ground motions, predicting their damage potential and suggesting measures to minimize their threat becomes essential. For any particular site, the response of the sub-soil strata under seismic excitations plays an important role in governing the safety of earth retaining structures and super-structures. For sandy layers, with a noticeable fines content and water table close to the ground surface, the excess pore water pressure (PWP) build up rapidly under repeated cyclic loading. This further lowers the effective strength of the soil increasing the chances of occurrence of liquefaction. Guwahati city, which is located on the banks of river Brahmaputra in North-East India, is a zone of high seismicity and numerous earthquakes have been recorded in and around this region in the past. Most of the earlier ground response analysis (GRA) studies that have been performed in this region have used the linear or equivalent linear approach, with very few studies focusing on nonlinear approach. However, we know that unlike linear/equivalent linear approach, nonlinear approach can account for the pore water pressure generation and degradation of soil stiffness with number of loading cycles that occurs in an actual earthquake scenario. In the present paper, 1-D nonlinear effective stress ground response analysis, incorporating non-Masing criteria, and pore water pressure dissipation are performed on three borehole sites located at IIT Guwahati region in North Guwahati. The Sikkim earthquake motion recorded at IIT Guwahati and three of its scaled-up components are used as input. Peak horizontal acceleration (PHA) profiles, amplification/attenuation characteristics of the ground motion in the soil column, amplification factor, and 5% damped surface response spectra are presented. Reduction in amplification factor with increase in peak bedrock acceleration (PBRA) value of input motion is observed. For input motions having PBRA values in the range of 0.18g to 0.36g, soils in this region will attenuate the ground motion. Liquefaction susceptibility has also been studied using cyclic stress approach. Soils in this region are found to have a tendency to liquefy under the effect of ground motions with PBRA values greater than 0.06g. The depths of liquefaction in the three soil profiles, subjected to input motions with different PBRA values, are also identified. Furthermore, a comparison is made between equivalent linear and nonlinear approach of GRA based on some response parameters.

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