Researches on floor stratum fracturing induced by antiprocedure mining underneath close-distance goaf

Comprehensive methods of numerical simulation, borehole inspection as well as the real-time floor bedding separation monitoring are employed to research the floor strata fractured zone and stress distribution affected by two fold mining action of pre-mining underneath in the Muchengjian Mine in China. By the experimental results obtained, there is the limit work-face length capable to maintain the floor strata stable. The floor strata can be divided into weakly fissured zone, slightly fissured zone, strongly fissured zone and a collapsed zone from upper to down layers. With advance in seam extraction, new separations can arise within the floor strata, thereto the strata collapse and abutment pressure distribution are symmetric. The experimental results are verified by the practical data on extraction of two mine faces.