Mechanical analysis and application of floor failure mechanism under repeated mining in close-distance coal seams

The stress state of primary rocks is redistributed during coal mining, which leads to deformation and failure of the floor strata. Coal seam floor experiences repeated additional stress from the mining of two overlying seams in close-distance mining. An assessment of floor stability is required in the presence of a confined aquifer within the floor strata. The failure characteristics of floor rock strata are crucial for analyzing water inrush from floor. This mechanical response of floor deformation and failure becomes particularly pronounced when the roof is treated using the full caving method. Floor strata were analyzed for the 220,105 working face at Xinji 2^# Coal Mine, with an elastic half‑plane theory established. The stress distribution characteristics of the floor were investigated using software MATLAB. The width of the plastic zone and the maximum failure depth of floor were determined based on the slip line field theory of floor rock mass. A reference was provided for water damage control during repeated mining of the 1^# coal seam. Continuous field observation of floor failure was performed through drilling combined with the network parallel electrical method. Apparent resistivity at the depth of 19.6 m below floor was approximately twice the background resistivity of the corresponding stratum. The apparent resistivity of rock strata below 19.6 m remained constant, indicating a protective zone. These results confirm the reliability of the theoretical analysis and provide a technical foundation for safe mining in the working face.