Applied Research Of Unsaturated Soil Mechanics In Expansive Soil Slope Stability Analysis

The main channel of South-North water transfer project goes through large areasof expansive soil. The channel slope stability is directly related to the benefits of theproject, the realization of high guarantee ratio and the project investment benefit.Expansive soil is a difficult problem in engineering field with its unique engineeringproperties, especially in the slope stability analysis. Two main factors, the fissure andexpand-shrink characteristics of expansive soil, are thought to be the dominant factorsfor causing the expansive slope, and the rainfall and infiltration were treated as luringfactors. Based on these essential features, this paper analyzed the the instabilitymechanism of expansive soil slope, provided technical support for the geologicalexploration, and further provided some suggestions in the design and construction ofchannel in the expansive soil areas.This paper has contributed to the following issues:1. By reviewing large numbers of relevant literature, it summarized thedevelopment and the current situation of the unsaturated soil theory, as well as theactual engineering application. Moreover, it elaborated on the features of unsaturatedsoils, the constitutive relationships and the shear strength theory, which leaded tobetter understanding of the methods used to analyze the unsaturated soil slopestability.2. By collecting and analyzing a large amount of failure cases in expansive soilslope, some critical features of instability of expansive soil slope were obtained,including the shallow and flat characteristics of the oil, the impact from continuousrainfall, etc..3. Based on the experience in the geological engineering investigation for landarea expanded channels and related investigation results, this paper analyzed themineral chemical composition of expansive soil, soil structure, action of soil andgroundwater, and further summarized the reasons for soil cracks, the processes ofexpansion produced by contraction cycle, and influence from the rain waterinfiltration and water pressure.4. Combined with the theory of unsaturated soils, this paper revised the physicaland mechanical properties of the expansive soil area which were reported from thegeological exploration, and attempted to make sure the test parameters used in theprojects reflecting the actual situation of engineering as much as possible, aiming tofit the calculation analysis results with the actual situation. 5. Based on of geo-slope/w module, using the Morgenstern-price method,Ordinary method, Bishop method and Janbu method, the stability of the slope, thelocation of slip surface and sliding characteristics were simulated under threecircumstances: the expansive soil without cracks at the initial time, swell-shrink cyclecracks and rainwater infiltration from the fissure. Moreover, this paper analyzed thecharacteristics and security of these four algorithms. The results demonstrated that theexpansive soil fissure is the key factor in controlling the slope stability. The results ofsimulating rain infiltration from the fissure are in accordance with the instabilitycharacteristics of expansive soil slope.