Instability Mechanism And Application Analysis Of Partially Saturated Clay Slope Under Sustained Rainfall Infiltration

The rainfall infiltration is an important factor inducing the natural and engineering slopes failure. It is very serious of slope disaster induced by the sustained rainfall into unsaturated clay slope in rainy areas. The sustained rainfall accelerated the failure of slope which was stable at first. Therefore, it is an important significance with studying the infiltration law and the instability mechanism under sustained rainfall infiltration into clay slope, which is helpful for landslide prevention. Based on the combination of the limit equilibrium theory and the theory of soil-water seepage of partially saturated and saturated clay slope, the slope stability was analyzed by the strength reduction combining with relevant engineering and related model test. The research was done mainly in the following aspects:First of all, combining with the instability characteristics of engineering slope induced by rainfall, the engineering characteristics of clay slope and the mechanics theory due to the influence of rainfall were discussed. The shear strength parameters of clay under different moisture content were obtained through the related experiment of clay. According to the experimental results of testing matric suction, the SWCC of clay fitted as exponential curve was more reasonable.Secondly, The infiltration depth and infiltration mode were analyzed under rainfall infiltration into clay slope. Combining with the saturated infiltration theory and the Green-Ampt infiltration model, the ponding time on the slope’s surface and the ponded infiltration depth and infiltration rate could be calculated for saturated and unsaturated infiltration respectively, when the initial moisture content of clay was the same or changeable regularly.Thirdly, making full use of the limit equilibrium theory and strength reduction method based on finite difference, the calculation formula of limit equilibrium slice algorithm or strength reduction was rebuilt under sustained rainfall infiltration. After the sustained rainfall infiltration into clay slope, the moisture content and the bulk density of clay would increase with the decreasing of the cohesion and internal friction angle of clay. Therefore, the slope safety coefficient would decrease rapidly which leaded to slope instability eventually. The related theoretical analysis of influence parameters were derived comprehensively through analyzing the related factors influencing the slope stability. Through calculating the safety coefficient and the maximum horizontal displacement influenced by parameters, we could obtain the parameters sensitivity of the moisture content, cohesion, angle of friction, matric suction, slope height and slope angle. The sequence of sensitivity could be listed. Through the related transformation of various types of clay yield criterion, we could obtain the critical point of choosing or adjusting different soil yield criterion by calculating the internal frictional angle of clay, φ=16.5°, under sustained rainfall.Then, there was an intuitive test model of clay slope which showed the deformation and failure process of the slope model under the sustained rainfall infiltration. The test result showed that there was an unsaturated infiltration process in clay slope under sustained rainfall. The matric suction of soil could be obtained in the different depth of slope top and middle slope and slope toe under sustained rainfall. The safety coefficient based on potential slip surface could be calculated according to determining the depth of slope top or middle slope respectively. The safety factor was the least with the potential slip surface listed at about15cm of infiltration depth at middle slope.Finally, Combining with the engineering slope, the advantage of platform and slope height and slope ratio was discussed under sustained rainfall. Application of the idea and methods into engineering slope, the slope safety coefficient and the failure time of slope could be obtained under the different infiltration depth. And, the stability of engineering slope was analyzed under sustained rainfall.