FORMATION MECHANISM OF LANDSLIDE ABOVE THE MINED OUT AREA IN GENTLY INCLINED COAL BEDS

Mining-out area in slope with gently inclined coal beds always can induce some engineering geological problems including subsidence and cracking of the surface, partial collapse, landslide. They are due to the difference of the goaf size and the slope structure characteristics. They can cause large-scale geological disasters. The Madaling landslide was generated in the slope with gently inclined strata dipping inward with soft rock sandwich and coal mining-out area. The landslide was caused by the mining-out area and the storm. Its volume is up to 190104m3.According to the engineering geological survey and analysis, the weak geologic structure and the damage of the goaf under the slope mainly caused the landslide. The concentrated regional rainfall accelerated the occurrence of the landslide. The formation mechanism of the Madaling landslide is the type of collapse-rip-shear slip.The mechanism and process of the landslide can be divided into three stages as follows: (1)tension cracking of trailing edge of the slope,(2)sliding surface developing and interconnect, and (3)integral failure of the landslide. The sliding mass flowed downstream after disintegration, and formed 1.5km long debris flow accumulation area. Large area farmland was submerged by the debris.