Strong Ground Pressure Mechanism and Control at the Longwall Top Coal Caving with a Single Key Stratum in Goaf

A strong ground pressure in the multiseam environment manifested by rib spalling and roadway deformation at the fully mechanized working face was assessed by a comprehensive combination of field measurements, physical simulations, and theoretical analysis for two coal seams in the Buertai Coal Mine in China. A structural model of overlying stratum collapse at the working face with the key stratum breaking instability was proposed, the mechanism of strong ground pressure at the longwall top coal caving working face with a single key stratum in goaf was identified, and respective control countermeasures were developed. The latter implied the directional hydraulic fracturing for supporting the key stratum-surrounding rocks, which effectively reduced the cyclic weighting intensity and weighting interval in the working face with a single key stratum in the goaf. The working face cyclic breaking interval was assessed at 30 m. After the key stratum collapse, soft rocks underwent synergistic deformation and a cutting-type failure. The goaf effect on the hydraulic support resistance in the fully mechanized working face was assessed, and cutting blocks from the overlying stratum collapse were identified as the main sources of strong ground pressure.