Analysis On The Influence Of Rainfall To The Stability Of Expansive Soil Cutting Slope

With the development of national expressway network, there aremuch more geotechnical problems in the engineering. It is difficult tohandle with the cutting slope protection in the expansive soil zone due tothe unique mechanical properties of expansive soils. The failures ofexpansive soil cutting slopes affect largely the operation of expressway,causing heavy damage to property. It is necessary to do special research onthis field. This paper sets out from the northeast section of Nanjing bypassexpressway, one passage of Changchun-Shenzhen national expressway asthe base, using the method of fractal theory in unsaturated soil and finiteelement simulation of seepage flow and stability analysis on theunsaturated soil slope under rainfall infiltration. These research contentswere done as follows:(1) Based on the X-ray test, the clay mineral compositions of theexpansive soil in Nanjing were analyzed. Its basic physical properties wereobtained from related indoor geotechnical tests. The expansive soil inNanjing was graded as the weak expansive soil according to Likos method.(2)Filter paper method was used to measure the soil watercharacteristic curve of expansive soil in Nanjing. On the base of the fractaltheory in the unsaturated soil, the parameters of fractal model for Nanjingexpansive soil were determined. The fractal method which used to predictthe strength performance of unsaturated soil was verified by laboratorytests.(3)Unsaturated seepage model for the expansive soil slope underrainfall infiltration was established. With the method of finite elementsoftware coupled with the fractal theory, it studied the seepage process and stability analysis on the unsaturated soil slopes under rainfall and thefactors controlling instability of unsaturated soil slopes. The saturatedcoefficient of permeability and rainfall type take a greater impact on theinstability of unsaturated soil slope. A new formulation for the criticaldepth for rainfall induced slope failure was also derived.(4)The changing on pore-water pressure and volumetric water contentof unsaturated expansive soil slope under the rainfall infiltration andevaporation were simulated and analyzed. The impaction of climaticcondition on the slope stability was studied.