Considering The Influence Of Rainfall Infiltrtion On The Reliability Of Expansive Soil Slopes

The basic idea of this paper was to consider the influence of rainfallinfiltration on the expansive soil slopes stability evaluation. In this paper, based onthe saturated-unsaturated seepage theory, three methods (consisted of Nlinfit,Lsqcurvefit, Fminsearch) in MATLAB programming language and six models(included Fredlund-Xing three models and van Genuchten three models) were adoptedto fit the matric suction and volumetric water content data into Soil-WaterCharacteristic Curve (referred to as “SWCC”) of four types of soils at home andabroad, then the values of fitting parameters a, n, m could be obtained, which couldbe used for probability and statistic analysis. Through the analysis, the mean valuesof the fitting parameters could be got. The author chose the SWCC fittingparameters of Hefei expansive soils to analyze the slope stability. In the stabilityanalysis of considering the influence of rainfall infiltration, the rainfall intensitieswere7.510-3m/d,1510-3m/d and3010-3m/d respectively, and the rainfall durationwere3days for all the3cases. The changes of water pressure and moisture contentin the expansive soil slope were simulated by using GeoStudio, the factors of safetycould be obtained through the deterministic approach. In order to consider theinfluence of the variability of the fitting parameters, the reliability theory wasadopted to analyze the stability with first order reliability method through theiterative calculation, and the reliability indexes could be obtained, which wereimplemented by MATLAB. Thus, the stability of some unsaturated expansive slopeduring Jinxiu Avenue station and Ziyun Road station of Hefei rail transit Line I wasevaluated by both the deterministic approach and reliability analysis method. Themain research results were concluded as follows:It could be obtained that fitting models had a great effect on the SWCC fittingparameters when considering the impact of SWCC fitting factors. For the samenumber of data points, the three-parameter models (included FX2, FX3, VG2andVG3) were preferable than the four ones (consisted of FX1and VG1). Besides, theinfluence of fitting methods to the SWCC fitting parameters was far less than thatof fitting models, and it can be obtained that whichever fitting method was adoptedhad a little effect on the values of the mean, standard deviation and coefficient of variation of SWCC fitting parameters. According to the results of SWCC fittingparameters, it could be concluded that among the fitting parameters of the fourstudied soils, the value of parameter a was larger in the clay than that of sand, andthe value of parameter n was smaller than that of clay. Moreover, for clay, the curveinflection point was not obvious and the gradient of central curve was relativelysmall, the situation in the clay was opposite.Rainfall infiltration had a great influence on the stability of expansive soilslope. In the case of the same rainfall intensity and same rainfall duration, beforethe rainfall ceased, the values of factors of safety and reliability indexes graduallydecreased as time progressed, and their values reached the minimum after threedays of rain. During the specified simulation days after the cessation of the rain, thevalues of factors of safety and reliability indexes picked up over time, but theycould not recover to the initial highest values. In addition, it could also be obtainedthat in the same simulation time, the values of factors of safety and reliabilityindexes presented a decline trend with the rainfall intensity went up, but this trendwas gradually decreased with the increasing of rainfall intensity.