Rainfall seepage characteristics of open-pit high slopes with gently-inclined soft interlayers

In order to explore and study the influence of gently-inclined soft interlayers on the rainfall seepage characteristics of open-pit high slope, taking the high slope of typical limestone mine as an example which is located in the southwest China, simultaneously based on the actual engineering geological and hydrogeological conditions in the site, a rainfall seepage model of open-pit high slopes with gently-inclined soft interlayers is established. Based on the saturated-unsaturated seepage theory, the infiltration process of rainwater during rainfall and post-rainfall periods is simulated under the condition of maximum rainfall, and the dynamic variation rule of pore water pressure about open-pit high slope with gently-inclined soft interlayers is revealed. The research results show that the soft interlayer, as an isolation layer which means low permeability, changes the shape of rainwater infiltration curve and the seepage path of rainfall. The rainwater infiltration curve presents a "V"-shaped structure, and the seepage path changes from vertical slope infiltration to seepage along the upper surface of the soft interlayer. In the two periods of rainfall and after rainfall, the pore water pressure of upper fractured weathered rock increases first and then decreases, but the pore water pressure is always negative. The upper surface of soft interlayer will produce rainwater accumulation and the pore water pressure first increases to a positive value and then decreases gradually. The time of pore pressure reduction is lagging behind the rainfall time, that is to say, the pore pressure decreases after the rain stops for a period of time. The pore water pressure at the foot of the slope always increases during the two periods of rain and after-the-rain; due to the good water resistance of the soft interlayer, the pore water pressure inside the soft interlayer and that of the limestone at the bottom of the slope do not change too much. The research results can provide a useful reference for revealing the rainfall seepage laws of slopes under similar geological conditions.