Analysis On Stability Of Unsaturated Loess Slope Under The Condition Of Rainfall

Many slopes in arid and semi-arid loess area will be subjected to rain infiltration in rainyseason, resulting in slope instability. Soil body of slope in arid and semi-arid area is mostlyunsaturated soil, matric suction of unsaturated soil will increase the shear strength ofsoil, making the slopemore stable. The rain’s infiltration will reduce the matric suction in thesoil, which affects the shear strength of soil.Rainfall infiltration will make the water content of slope increased, and the increase ofit will cause changes in pore-pressure.The rainfall intensity, rainfall duration and slopegradient also affect the distribution of moisture content of slope body.The matric suction isassociated with moisture content in unsaturated soil, besides the permeability coefficient andthe moisture content also exists certain contact. The relation between matric suction andmoisture content of unsaturated loess is highly nonlinear. There is a direct relation between drydensity and porosity, and the porosity determines the degree of saturation of unsaturated soil.Thus, soil of different dry density will be different in soil-water characteristic curve.To studythe strength of unsaturated soil slope, you should first explore the relationship among the matricsuction, permeability and moisture content.In order to study these issues, the paper make thefollowing main aspects:(1)Through the GCTS apparatus, three different dry density of loess drained soil watercharacteristic curves are measured, and fit, analyzes the effects of dry density on soil watercharacteristic curve.The significance of the fitting parameters, and the influence of parameterson the curve shape, and might be produced in the process of the experiment error are analyzed.(2)Through the basic seepage theory of saturated soil,saturated-unsaturated seepage basicdifferential equation is deduced.In the analysis of seepage field, boundary conditions andinitial conditions under the conditions of rainfall are given, andthe distribution of the slopebody moisture contentis simulated in different rainfall duration, rainfall intensity and slopeconditions. And the further analysis is variation of pore water pressure of the change ofmoisture content in the process above three cases.(3) The results of the analysis of seepage field is used for the analysis of the stress field andthe stability of the slope. It is calculated that regularity of distribution of stress field and the changing rule of the coefficient of slope stability while Rainfall and slope changes. In addition,set up the three types of dry density of soil water characteristic curve fitted out through previousexperiments in slope stability analysis, and concludethe corresponding coefficient of slopestability.Soil-water characteristic curve of loess of different dry density is studed in the paper,porosity and compaction degree of soil determines the shape of the curve. The duration andintensity of rainfall have great impact on the seepage field analysis results of slope,distribution of water content determines the distribution of pore water pressure, and directlyaffect the calculation results of stress-strain field of slope. The increase of water content willreduce the negative pore water pressure of soil, as well as the shear strength of the soil,thereby reducing the stability of slope.