Executive Summary : | Liquefaction susceptibility assesses soil's capacity to undergo liquefaction during earthquakes. Typically, this assessment is based on soil characteristics and a qualitative understanding of the geological conditions. Numerous variables contribute to the potential for liquefaction during earthquakes, encompassing non-statistical uncertainties. The imprecision and vagueness in the analysis can be handled appropriately by incorporating fuzzy set theory and fuzzy logic (Elton et al., 1995; Rahman and Wang, 2002; Xue and Yang, 2014). Hence, in the current research, a hybrid fuzzy-probabilistic approach is proposed for analysing the liquefaction risk.
Liquefaction plays a crucial role in significantly enhancing the magnitude of seismic damage. The damages are evidenced by notable ground settlements, differential settlements, and lateral shifts associated with spreading phenomena. Moreover, it alters the seismic ground motion at the ground surface. Numerous methods with simplified approaches have been developed in recent times, such as by Chiaradonna et al. (2018), Millen et al. (2020), Kokusho (2021) and Quintero et al. (2023). Among these, the stress-based approach introduced by seed et al. (1975) and subsequently refined by other researchers (Boulanger and Idriss, 2016) is widely adopted. This approach involves, at a specific depth, comparing the load exerted by ground shaking and soil resistance to liquefaction. The influence of liquefaction effects is not considered in the method proposed by seed et al. (1975) since the method is based on the surface ground motions derived from the seismic codes. For a thorough assessment of liquefaction, it is essential to conduct a comprehensive analysis of surface ground motion that is specific to the site. Hence, the present study uses fuzzy variables to focus on site-specific nonlinear ground response analysis.
As part of the study, the nonlinear ground response analysis considering the liquefaction effects will be performed with the input of appropriate ground motions for the study area in the nonlinear finite element software. The liquefaction parameters, such as cyclic stress ratio (CsR) and cyclic resistance ratio (CRR), will be obtained from cyclic triaxial tests in the laboratory. The laboratory test results are useful for obtaining the appropriate constitutive model that can reproduce the liquefaction stress-strain behaviour and pore water pressure generation. The liquefaction potential from the numerical analysis and the laboratory tests will be compared to obtain the relative difference in both methods. In addition to that, the liquefaction risk map for southern India, especially for Bangalore and Chennai city regions, has to be developed using the proposed methodology. |