A Formula for Calculating Liquefaction Probability Based on Chinese Seismic Code

Abstract eng:
The method of liquefaction prediction is very important to seismic design of foundations and engineering structures. The liquefaction prediction method in Chinese seismic code has formed more than 30 years and has been applied in engineering comprehensively. As the rapid development of engineering construction in China, more demand for liquefaction evaluation is raised. There are two questions should be answered. One is the reliability of liquefaction prediction results and only the simple answer of “yes” or “no” liquefaction is not enough. The other is that when the liquefaction prediction result is close to the critical state of discriminant the engineers often feel confusion. They want to know the conservation extent of the discriminant. However, the existing method is deterministic and can not answer the questions. The purpose of this paper is promoting the deterministic method of Chinese code discriminant to the probability method of liquefaction evaluation. Firstly, the liquefaction limit state is established according to the Chinese code discriminant, and the variable parameters are determined considering the influence factor of liquefaction, and then a probability formula is formed using first order and second moment principle. In addition, the safety factor of liquefied cases and non-liquefied cases is calculated using Chinese code discriminant and its distribution is statistically analyzed, respectively, the cure of liquefaction probability versus SPT ratio (namely safety factor) is proposed according to Bayesian theory. The extent of the conservation of Chinese code discriminant is attained from this cure. Finally, the two results deriving from these two theories are discussed and the discrepancy, merit and demerit of the new formula are pointed out.

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