Study Of Effects Of Rain Infiltration On Stability Of Unsaturated Slopes

Landslide is closely related to rainfall, and for unsaturated soil slope the rain infiltration is the most important one that results in landslide. It is of great significance for the precaution of landslide to make a deep study of the landslide law under rainfall and establish a quantitative model for analysis. The variation of water distribution in unsaturated slope and the slope stability due to rain infiltration is studied in this paper.Based on the knowledge of characteristic of unsaturated soils. The law of suction change with moisture content and density is got from suction experiment, which revealed that the matrix suction changes obviously with density especially in low moisture content, and with the same moisture content, if the density is gradually added, the value of matrix suction first is lowed, then added and finally lowed, this phenomenon is probed into in this paper.On the basis of the theory about water potential in soils, a partial differential equation of water movement in unsaturated soils is derived , which chose volumetric water content as the control variable. The numerical solution of the equation using finite difference method is discussed in this paper, and the modality to calculate water movement in slope considering rain infiltration.The field of water distribution is obtained by finite difference method, then it is transformed into weight field and strength field or the field of suction distribution. The safety factor of slope during the infiltration time is calculated by slice method according to the actual weigh field and strength field.Finally, an example is given and analyzed in detail.1. The program of finite element method is complied to analysis the safety of a slope after excavation, the result obtained from the program show that stress concentration occurred only at the spot near to slop foot, and there are only a few elements whose stress level has exceeded 1.0 in slop, that is to say the slope is safe after excavation.2. For a given rain, the initial condition and boundary condition is determined, then the distribution of water in the slope at difference moments is got from the result by the FDM program calculation, and variation law of water distribution during the whole course is also obtained.3. The slice method program is complied to calculate the safety factor of the slope at difference moments according to water distribution in the slope, and the change regularity of safety factors during the whole period is also obtained. The result revealed that the safety factor of the slope decreases during a long period, and reaches the lowest value at certain moment, then increases gradually. This phenomenon is due to the variation of water distribution in slope, and is given some explanation in this paper.