Stability Evaluation Of Loess Slope Under Rainfall Infiltration

The study of rainfall infiltration mechanism,mechanical properties and slope stability evaluation of loess slope under rainfall conditions plays an important role in reducing the risk of landslide and other natural disasters,protecting the fragile ecological environment and reducing economic losses.Taking Xi’an area as the research background,the stability of loess slope is evaluated by combining theoretical analysis,laboratory test and numerical simulation.The main research results are as follows:(1)Based on the analysis of rainfall seepage characteristics of loess slope under rainfall condition,the physical model of loess slope under rainfall condition is established,and the transient water content expression considering rainfall duration,rainfall intensity,slope angle and arbitrary depth is constructed,and the infiltration law of loess slope under rainfall condition is explored.(2)The triaxial shear test of unsaturated loess is completed.In the process of increasing the moisture content of the sample,the cohesion of the soil will gradually decrease,and the internal friction angle will also decrease,but the decreasing rate is smaller than that of the cohesion.For unsaturated loess,the change of matric suction and confining pressure will cause the change of strength.the degree of internal friction angle increases slowly,which indicates that the change of matric suction has little effect on the internal friction angle of loess.By fitting the experimental results,the relationship between the change of matric suction and the change of matric suction was obtained Φb.The expression of χ of parameters in the unsaturated effective stress formula.(3)The soil water characteristics of unsaturated loess are studied through the soil water characteristic curve test with pressure plate apparatus.In the whole process of soil water characteristic curve dehumidification and humidification,the relationship between volume water content and matric suction in different processes is not completely corresponding,and there is a certain deviation.Under the same matric suction,the volume water content in the process of dehumidification will be higher than that in the process of humidification,which is related to the pore size and spatial skeleton structure of soil.The experimental data are input into origin for fitting,and the corresponding parameters of VG model are obtainedα=0.30325,q=2.0,R2=0.98823;In the process of humidification,α=0.11773,q=2.43843,R2=0.98198。(4)Based on the coupling of seepage field and stress field,through the rainfall intensity,rainfall duration,slope angle and other parameters,the slice method of slope stability analysis is adopted to obtain the calculation expression of safety factor of loess slope under rainfall conditions,establish the stability analysis model of loess slope under rainfall conditions,explore the instability mechanism of slope,and evaluate the stability of loess slope under rainfall conditions.(5)Based on GTS/NS finite element numerical simulation software,the finite element equation of slope stability is established by Galerkin method.According to the experimental data,the finite element analysis model of two-dimensional slope under rainfall condition is established.Considering the factors of slope angle,slope height,rainfall intensity and rainfall duration,different analysis conditions are established for each factor.The details are as follows:slope angle selection is 20°、30°、45°、60°、80°;The slope height is 10 m,15 m,20 m,25 m and 30 m;The rainfall intensity is 10 mm/d,35 mm/d,50 mm/d,65 mm/d and 80 mm/d,and the rainfall duration is 0.5 d,1 d,1.5 d,2 d and 3 d.For slope angle,slope height and rainfall intensity,when they all increase,the safety factor of slope decreases gradually,but the change value of safety factor caused by the change of slope angle and slope height is greater than that of rainfall intensity;For the duration of rainfall,in the whole process of rainfall,with the infiltration of rainwater,the safety factor of the slope is gradually reduced,and the decreasing range is very small.