Stability Analysis Of Expansive Soil Slope With Rainfall Infiltration

Instable failure of expansive soil slope is a significant engineering geological problem in swelling soil area. Most of the slip region is located in shallow layer and unsaturated area of expansive soil slope. Furthermore, this type of landslides often develops during or after the rainfall. Therefore, its formation mechanism is related to the rainfall infiltration. The analysis of stability of expansive soil slope involves, saturated-unsaturated seepage flow, unsaturated shear strength, the effect of moisture expansion, rainfall characteristics and other factors. The study can provide the theoretical basis for engineering construction in swelling soil area, and has very important practical meaning.Take Yanji Basin expansive soils for research object, on the basis of understanding of the physical characters, a series of experiments were performed. These testes include the measurement of soil-water characteristic curve(SWCC), seepage test, direct shear test and swelling test. These test results provide the basic data for the analysis of the saturated-unsaturated seepage flow, the shear strength of expansive soil, and the swelling property, and then provides the basic condition for the analysis of stability of expansive soil slope.Based on the SWCC and seepage test, The permeability of unsaturated expansive soil and the relationship between permeability and matric suction were deduced. Between the drying curve and the wetting curve has significant hysteresis. It’s shown that the soil is a good medium for retaining water. However, the relationships between moisture content and permeability are almost same in the process of the dehydration or adding moisture content. And it shows that the permeability of unsaturated expansive soil is a monotonic function of moisture content, saturation or effective saturation. The direct shear test shows that the shear strength of expansive soil changes with moisture content.According to the swelling test, the relationships with high coefficients are droped between the expansion ratio and time by adopting K nothe time function, and the physical meaning of the unknown parameters is analyzed in detail. The parameter a equals to the final value of expansion ratio, and the parameter b is related to the initial expansion rate. There is a strong negative correlation between the value of a and the initial moisture. But the parameter b is affected by various factors, its determination still needs further research. In order to study the impact of swelling feature to the slope stability, this paper suggests that temperature field stress field can be equivalent the humidity stress field theory, and the expansion coefficient is calculated. The theory is introduced into the finite program(ABAQUS)with Fortran language.On the basis of the years of rainfall data,four conditions is designed to simulate rainfall. According to the unsaturated infiltration theory and empirical formulae of infiltration, This paper solves the curve of the designing rainfall process. Finally, the stability of expansive soil slope is analyzed with a commercial finite element model code ABAQUS.