Formation mechanism of karst collapse after mine closure:A case study of Enkou coal mine in central Hu’nan Province

Groundwater level has raised and the ground collapse often occurred in Enkou coal mine since the mine ceased operation 20 years ago. In order to understand the formation mechanism of the karst collapse and to conceptualize the collapse models due to the recovery of water level, in this paper, spatial and temporal distribution of the karst collapses and associated soil structure in the mine area were discussed, with focus on the analysis of the relationship between the occurrence of karst collapses and the groundwater level recovery, from which it is realized that the formation and the modes of the karst collapses have experienced two phases, i.e. during and after the mine water level rebounce. In phase 1, the main karst collapse mode is a water floating-soil softening process, in which the ground collapses occurred obviously less than that in the mine drainage process; the occurrence of the collapses was highly related to the karstic earth caves formed by the process of underground mining and drainage. In phase 2, the ground collapse were dominated by suffosion-buckling process, which was caused by the natural fluctuation of the groundwater level between rock and soil, with the hazards occurred sporadically. The study of Enkou coal mine karst collapses, can bring values to scientific, economical and viable suggestions in relation to the prevention and treatment of the geological hazards in Loudi City. Meanwhile, it provides a reference for karst collapse prediction and remediation in similar areas in central Hu’nan Province.