Article Preview
TopIntroduction
Soil- liquefaction is one of the most significant issues of earthquake engineering. Liquefaction is a phenomenon in which soil transform to liquefied condition due to pore water pressure in soil increases and effective stress reduces. Several damages and problems are created as a result of liquefaction (i.e., destroying the bearing capacity of structure, settlement of soil, boil-sand condition and deformation or lateral displacement. Originally, Seed and Idriss (1971) proposed Simplified procedures to determine the liquefaction potential of soils. In many projects, for assessing seismic liquefaction potential based on Standard Penetration Test (SPT) obtained by seed and Idriss, is commonly used. In this article, a revised and updated semi-empirical approach developed by Idriss and Boulanger (2006) is used for determination of seismic potential of soil.
A number of studies are reported in literatures for the estimation of liquefaction susceptibility (Seed and Idriss, 1971; Seed, 1979; Seed et al.1983; Iwasaki, 1984; Kramer, 1996; and Idriss et al., 2004). Cetin et al. (2004) were developed the probabilistic approach which is based on the statistical study of liquefaction as well as non-liquefaction case histories.
Juang et al. (2008) carried out reliability analysis for liquefaction potential of soils using SPT-test. Jha and Suzuki (2009) applied the reliability method to evaluate probability of failure against soil liquefaction phenomenon and established a modified factor of safety by means of the reliability techniques. Probability of liquefaction has been determined by applying the Monte Carlo simulation (MCS) (Juang et al. 2012; Bhattacharya and Goda, 2013; Ayad et al. 2013). Das and Muduli (2011) evaluated the liquefaction potential of soil using genetic programming. Asskar et al. (2015) performed reliability study of soil liquefaction based on SPT. There are many deterministic and probabilistic liquefaction evaluation measures in order to access whether liquefaction condition will occur or not. There are major uncertainties in the different variables used in this deterministic approach. Various methods give different factors of safety (FS) and probabilities of liquefaction (PL) for the same set of input parameters. To account for the different measurement and model uncertainties, reliability analysis is needed.
In the present paper, an effort has been made to measure reliability index and probability of soil liquefaction at few locations of Bihar state. Since Bihar state is densely populated, a number of earthquakes of high magnitude before and after that were noticed. So, it is required to find out the liquefaction susceptibility of the region. The study areas are Samastipur, Darbhanga, West-Champaran and Araria district. About 234 borehole data along with their soil laboratory results from many locations of Bihar state are considered. The locations of boreholes site are scattered in the state as shown in Figure 1. Figure 2 corresponds to the box-plot of data-set, representing SPT value (N), cohesion(c), angle of internal friction (ϕ) and field-density (γ). The box plot is a standardized system of showing the allocation of data based on the five-number outline: smallest value, first quartile, mean, third quartile, and highest value.
Figure 1. Sites location of borehole in Bihar State