Reliability Applied To Loess Slope Stability Analysis In West Henan-Shanxi Area

The West Henan-Shanxi Area with complex landforms and intense geologic structure,located in east central the loess plateau, is one of areas where landslide disaster developwell in china. Landslide disasters caused by the slide of high loess slope has continuouslybrought enormous threat to the national economy and safety of people. Therefore, itappears especially important to carry on the stability evaluation of loess slopes in thisregion. The safety coefficient method is the mostly used method in project, but the result ofstability evaluation for loess slope have a large randomness since the variability ofparameters cannot be considered in this method. This article, combining the naturalanalogism method, the limit equilibrium method and the reliability analysis method,provides references for the design of loess slope in West Henan-Shanxi Area.According to the characters of the structure, landform, water system and engineeringgeology, the research area was divided into subregions, such as Sanmenxia-Hejin,Xingning-jixian and Xixian-Lishi, and the double logarithmic linear correlation analysismodel of length and height of limit slope sections was build. Then statistical analysis hasbeen carried on to the model in confidence of0.95,0.85and0.75．After the collecting of1938groups of sample data, physical and mechanical indexes were analyzed in statisticsaccording to the subregion and geological age and strata in research area wereapproximately divided referring to the dry density. After type inspection of probabilitydistribution of loess strength index of each stratum in subregions with the K-S inspection method,the conclusion that c and value of different stratra in each subregions conform to thenormal distribution was obtained; the Monte-carlo method was used to simulate andcalculate, useing c、 as random variables,during the establishment of limit state equationthe Morgenstern-Price method was used. The calculated results indicated:(1) The failure possibility of the low slope is higher than that of high slope, when thecoefficient of variation value of c is high; while the failure possibility of the high slopeis higher than that of low slope, when the coefficient of variation value of is high.(2) Based on an overall consideration of average level of coefficient of variation inresearch area, the failure probability Pfof limit slope is about50%, and the stabilitycoefficient is about1.0; the failure probability of slopes with the confidence of0.75isabout30%, stability coefficient is about1.1; the failure probability of slopes with theconfidence of0.85is about25%, stability coefficient mainly range from1.15to1.20; thefailure probability of slopes with the confidence of0.95is below20%, normally thestability coefficient is larger than1.25. (3)According to related standard of highway engineering and architecturalengineering in china, design safety factors of slopes in highway engineering and naturalslopes of a-grade building generally take the value1.25. If this standard is used, maximumof failure probability of loss slopes in research area is25.5%which is a greater value. Thestability coefficient need to be larger than1.35, if the failure probability falls to20%below.If the failure probability falls to10%below, the stability coefficient must achieves above1.45.