Seepage and stability of the colluvial landslide on the back hill of Qingshi Town Government under rainfall

Taking the colluvial landslide of the back hill of Qingshi Town Government in Huanggang area as an example, this paper used finite element method to study the transient volumetric water content and pore water pressure of unsaturated soil based on the analysis of its engineering geological characteristics and geological structure characteristics.The Janbu method considering pore water pressure was used to calculate the effect of rainfall on the safety factor of the colluvial landslide. The results show that:①Rainfall infiltration leads to the increase of pore water pressure in the slope, and then the shear strength of the sliding surface to decrease, and so the safety factor decreases gradually. In the early stage of rainfall, the shear strength on both sides decreases faster than that in the central part. At the end of the period, the rate of decline in shear strength is significantly faster than that on both sides.②The change in safety factor shows a slow decline at the rate of 0.008/d for the first 19 d and a slow decrease at the rate of 0.03/d for 19-30 d. After 30 d, the descending speed decreases, and no change occurres after 36 d. Among them, the change of shear strength on both sides of 0-11 d contributes more to the change of overall stability than that of the central part. The contribution of shear strength change to the overall stability of 19-36 d is greater than that of the central part.③During the rainfall infiltration, groundwater flows from the surface and sides of the slope to the middle of the slope, and the negative pore water pressure area is continuously compressed to the central part. The groundwater changes in the central area are restricted by the two sides and the upper layer. The volumetric water content and the pore water pressure change are relatively lagging.④The prevention and control of the landslide is focused on the groundwater interception at the trailing edge of the slope and the groundwater discharge at the leading edge. At the same time, a good surface drainage may reduce rainfall infiltration.