The Mechanism Study Of Rainfall Induced Loose Soil Landslide

Landslide disaster has now become our primary geological disaster, it can interrupt traffic, clog rivers, bury villages and destroy factories and mines, which has been causing serious harm to people’s lives and property safety. However the rainfall, especially heavy rainfall is the most important factor induced landslide. According to statistics, landslides which induced by the rainfall are the most widely distributed, the highest frequency of occurrence in the world and can cause considerable harm. And a large number of statistics have showed that the vast majority of landslides occurred during or after the rainfall. Understanding of the mechanism of rainfall-induced landslides has always been a difficult problem in the field of Mountain Hazards research and also been the bottleneck which constraints effective disaster prevention and early warning and forecast. Therefore, the study on the mechanism of rainfall-induced landslides provides a scientific basis for the disaster prevention and mitigation work of rainfall-induced geological disasters, which has a very important practical significance. Based on the rainfall infiltration theory, laboratory soil test and model test research tools and some other research methods, the paper does a preliminary exploration and research on the formation mechanism of loose soil landslide induced by rainfall. The main contents and results completed are the following:1) This paper developed the testing device of artificial rainfall soil column infiltration and implemented the silty clay infiltration experiments under six groups of different rainfall intensity. Among which the longest duration of rainfall is105min.The experimental results show that the soil infiltration process can be divided into three stages:the pressureless infiltration, the pressure infiltration and the saturated infiltration. It also defines the soil initial infiltration front and end infiltration front under the action of rainfall, The positions of the two decreased with the increase of rainfall intensity and the amplitude between the initial infiltration front and the termination infiltration front widened with the increase of rainfall intensity. Finally, the paper puts forward the soil rainfall infiltration equation, which can characterize the process of silty clay soil infiltration in Chongqing area.2)By means of on-site sampling for loose soil landslide in Chongqing, the author has carried on the X ray spectrum analysis and the indoor sensitivity test:the tests of the soil grading, material composition, the permeability, characteristic curve of soil-water and shear strength parameters.The paper also studied the response relationship between the above parameters and the soil compactness, moisture content condition, getting the change rule of the physical mechanics strength parameters of soil under the condition of rainfall.3)Based on the influence of rainfall infiltration on landslide and combined with the changes of physical mechanical properties of landslide under the condition of rainfall, this paper analyzed the mechanism of landslides induced by rainfall, coming to a conclusion that landslides induced by rainfall mainly through the following aspects: the soil suction’s reduction, increase of pore water pressure; increases of slope body weight induced by rainfall; the degradation of shear strength parameters; fracture development, the appearance of static water pressure and the erosion effect on slope surface by rainfall.4) Based on the limit equilibrium theory and many factors during rainfall such as the surface crack, rainfall infiltration, rainfall process of dynamic and static water pressure, density and attenuation of intensity, the paper corrected the calculation formula of the stability of the landslide under the action of rainfall.5) By doing indoor rainfall-induced landslide model test, the paper studied the landslide failure modes under the action of different rainfall pattern, rainfall intensity and lasting time. Also it revealed the topography and mechanical properties of the formation and evolution process of landslide induced by rainfall and tested and verified the stability calculation by experiments.