Subgrade Stability Under Rainfall Infiltration

With the generous construction of expressway, more and more high filled and deep cut subgrade appearing constantly. The heavy rain with certain duration can cause serious damages to the expressway, such as slope sliding. Analyzed the stability of subgrade due to rainfall infiltration with limit equilibrium method and finite element method, in this dissertation. The main content is as follows:(1) Discussed the mechanics characteristic of unsaturated soil from many aspects, such as the composes, the shear strength theory, the deformation theory, the soil-water characteristic curve, influence on shear strength and deformation due to the water content.(2) From deliberating the characteristic of rainfall infiltration, the process of the rainfall infiltration, the influence factor of the rainfall infiltration, the computational method of the infiltration depth and other many aspects, the infiltration mechanism is studied in this dissertation. In the following content, the theoretical calculation method and the numerical computational method of Green-Ampt model is also discussed.(3) Applied and developed the simplified Bishop method to the unsaturated soil. The parameter selection has been also carried on the discussion in this dissertation.(4) By the safety coefficient formula to matrix suction derivation, has analyzed the matrix suction to the safety coefficient influence. The infiltration depth has been inducted to the formula for safety coefficient by seepage force. And obtain the derivate of infiltration depth by safety coefficient. Has also analyzed the subgrade stability change which causes by the infiltration depth. Through the safety coefficient to theφ~b derivation, has analyzed theφ~b value and rains in the process theφ~b value change to the subgrade stability influence.(5) Unified the project example to analyze the subgrade stability under the condition rainfall, and discussed the influence of various factors changing to the subgrade stability.(6) Probed into the principle and method of the elasticity and plasticity finite element which used in slope. Through the project example, used the large-scale finite element procedure ANSYS to analyze different rainfall condition to the subgrade stability impact. Through analyze, draw the law of the nodal displacement, the nodal stress and the plasticity area vary with rainfall condition.(7) Applied and developed the finite element shear strength reduction method to the unsaturated soil to extract the earth and the rock ground subgrade' s safety coefficient under different rainfall condition, and carried on the contrast analysis between finite element method and limit equilibrium method.