Mechanism of surface subsidence and sinkhole formation in mining areas: insights from MPM

Sinkholes are a major geohazard caused by underground mining, significantly deteriorate the ecological environment. To understand deeply the formation mechanism of widespread sinkholes in mining areas, the unsaturated Material Point Method (MPM) was employed to study the mechanical and hydraulic characteristics during the sinkhole formation process in a southwestern mining area. This study explored the impacts of different mining modes and rainfall intensities on sinkhole characteristics and validated the results with 3D laser scanning data. Results show that prolonged and concentrated rainfall and subsurface mining activities are the main factors contributed to the formation of sinkholes. The initial rainfall infiltration behavior significantly elevates groundwater levels, leading to saturation of the surface moraine soil layer. Subsequent mining activities result in double funnel-shaped fracture zones. The differences in the expansion rates of various fracture zones lead to widespread subsidence on the surface first, followed by the evolution into sinkholes in the central area. The multi-channel mining mode is identified as the main factor causing the enlarging of sinkholes, while variations in rainfall intensity affect the distribution and morphologies of these sinkholes.