Experimental study on failure process of mining landslide induced by rainfall

Mining landslide is one of the most challenging problems in geotechnical engineering. Mining landslide is a main type of geological disasters in mining areas,and its hazards are more serious than other types of geological disas- ters. Coal mining will induce strong ground deformation of gentle structural slope,and the ground deformation will tend to be stable within a certain period after coal mining under natural conditions. The occurrence of mining-induced land- slide is significantly affected by rainfall,so it is of significance to study the influence of rainfall on mining-induced landslide. The Madaling landslide in Guizhou was used as a geological prototype. The Madaling landslide is a layered structure slope with gentle dip,which has the structural characteristics of upper hard and lower soft,upper steep and lower gentle,and was induced by mining and rainfall. Using the physical simulation method,the model box and similar materials were used to establish the landslide model according to the similarity ratio. The model was monitored by soil pressure monitor,pore pressure monitor and 3D laser scanner. The model was studied under mining and rainfall condi- tions. The deformation and internal stress changes and the slope deformation and failure process under the joint action of mining and rainfall reproduce the whole process of landslide from generation to occurrence,and analyze the mecha- nism of heavy rainfall induced mining landslide formation. After the formation of the goaf,the original stress balance in the slope is broken,the stress redistribution occurs,the stress in the goaf roof is unloaded,the stress at the boundary is concentrated,and the top position of the roof is first bent and then subsided,resulting in a large number of cracks. Continuously expanding to the surrounding area,a large number of vertical tensile cracks are gradually formed,and a number of oblique cracks appear at the boundary of the goaf. At the same time,the influence of mining continues to propagate upwards,and cracks occur in the goaf roof and in the overlying rock mass. The developed cracks penetrate to form large cracks. Under the action of rainfall,the cracks in the slope continue to develop,and the rainfall leads to the formation of a stable water level in the goaf and overlying rock mass,increasing the hydrostatic pressure behind the slope,increasing the crack and pushing the slope. The deformation of the air-front surface,under the action of rain and water,gradually forms a basic sliding surface along the lower “stepped” crack,goaf,and vertical tensile crack,and fi- nally cuts the locking segment under water pressure. The sliding surface that penetrates has an overall sliding. The evo- lution process of the Madaling landslide can be divided into three stages including ① the overburden-slope deformation stage of the goaf:due to the deformation and failure of the overburden strata caused by mining,a large number of fis- sures are developed on the slope and the interior of the model,which provide favorable rainfall infiltration condition; ② the rainfall induced slope overall deformation evolution stage:rainwater infiltration aggravates the development of cracks,causing the model to deform toward the vacant direction. The crack in the slope basically penetrates,and the model reaches the critical point of instability; ③ the slip surface expansion-landslide occurrence:under the action of rainfall,the rock mass is continuously softened. At the same time,the crack in the model is filled with water,so that the crack continues to develop until it penetrates,resulting in landslide. Therefore,its deformation and failure mechanism can be summarized as the overburden-slope deformation of the goaf,the overall deformation evolution of the rainfall-in- duced slope,and the slip surface expansion-slope occurrence.