Failure law of floor during strip mining backfill with paste-tailings over confined aquifer: A case study in China mine

To tackle the challenge of extracting residual coal resources in Zhangzhao Coal Mine while preventing floor water inrush, a strip filling mining method has been proposed. A two-step mining approach was designed to ensure roof stability and avoid floor water inrush. The first step involves mining and filling at 15 m intervals, leaving a 20 m strip coal pillar. In the second step, a 20 m strip coal pillar is mined and filled at intervals. To meet the filling mining requirements, tailings and industrial slag are used to create the filling body, designed using a paste ratio test. The optimal ratio for silt has been determined to be 1:5, with a mass concentration of 70 %. Simulation tests were conducted to determine the dynamic failure development of the floor under different advancing footage. The self-designed pressurized water sac was used in the simulation experiment, and the results showed that maximum floor damage occurred at 130 m. Additionally, monitoring stations were installed during mining to track the failure depth of the floor. The research revealed that filling mining significantly reduces the failure depth of the floor and prevents water bursting passages, demonstrating the potential of this method for use under similar conditions. This study provides useful references and recommendations for future mining efforts.