Three-Dimensional Soil Slope Stability Analysis Under Rainfall Conditions

With global warming, the frequency of extreme rainfall is increasing in the whole world. Because of the widely distributed mountainous regions and hilly countries, landslide hazards due to rainfall accounts for more than eighty percent of geologic hazards every year. Slopes are in safe condition before raining and landslides occur during rainfall or within a certain time range after rainfall. The traditional stability analysis methods do not take the impact of soil matric suction into consideration and the stability analyses of the slopes are two-dimensional analyses, the results obtained from these methods are quite different with the real situations.In this paper, the three factors, including the rainfall intensity, the rainfall patterns and the rainfall duration, are analyzed using the Geostudio software. Based on the theory of the unsaturated-saturated soil slope, the three-dimensional rigid limit equilibrium method is proposed to analyze the stability of the unsaturated-saturated soil slopes. The MATLAB programs are written to calculate the rainfall intensity, the rainfall pattern and the rainfall duration of the soil slope.Conclusions:(1) Soil is not saturated in the natural state, in which there exists matric suction. The matric suction of soil materials can improve the stability of slopes. With the rainfall infiltrating, the soils of slope surface gradually turn form unsaturated state to saturated state, the matric suction gradually disappears, pore water pressure gradually increases, and the factors of safety of the slopes gradually decrease. Then the landslide may occur.(2) The three factors, which include rainfall intensity, rainfall patterns and rainfall duration, are the main factors affecting the factor of safety of the slopes. The factor of safety of the slopes decreases with an increase in the rainfall intensity. When the rainfall intensity keeps constant, the rainfall patterns is more uniform, the factor of safety is more decline. While the rainfall patterns is more concentrated, the factor of safety is smaller decline.(3) The saturated permeability coefficient of soil has a great influence on the rainfall infiltration, which has a great influence on the slope safety coefficient under the condition of rainfall.The innovation points of this paper:(1) This paper takes the effects of rainfall on slope safety factor into consideration. Quantitative analyses of the three factors, which include rainfall intensity, rainfall pattern and rainfall duration, affecting the slope seepage are investigated.(2) The unsaturated soil strength formula is applied to analyze the stability of slopes. The three-dimensional rigid limit equilibrium method is established to analyzing the stability of the unsaturated- saturated soil slope.(3) In this paper, the effects of the rainfall intensity, rainfall pattern and rainfall duration on slope safety factor are quantitatively investigated. It provides a theoretical basis for predicting the factor of safety of soil slopes under rainfall condition.