Fracture Development and Multifield Coupling Evolution Law of Soft Overburden Rock in a Medium-Thick Coal Seam Mine

Abstract

To study the fracture development and multifield coupling evolution law of soft overburden rock for medium-thick coal seam mining, taking the first 50105 working face of the Faer coal mine as the research background, a numerical simulation, a fractal theoretical analysis, and network parallel electric method experiments were conducted; the fracture development and coupled stress field and energy field evolution law of soft overburden rock for medium-thick coal seam mining are analyzed. The results showed that the overburden collapse process could be divided into three stages: pseudo-top collapse to key layer breakage, key layer breakage to overburden bending, and overburden bending to collapse and compaction. The fractal dimensions of the overburden fracture before and after breakage of the key layer showed a rising-stable-declining trend, and the experimental analysis showed that fracture development began in the unmined area at the front end of the working face under the influence of overstress. In addition, the height of fracture development after stabilization was 53.7 m. A relationship was established between the height of the overburden fracture, peak stress, and dissipation of the energy density of the key layer, and their associated disaster mechanism induced by mining in a medium-thick coal seam progressed as follows: coal mining → stress redistribution → dissipation energy increase → fracture development → stress concentration → key stratum breaking → stress transfer → energy release → dynamic disaster. These results can be used as a reference for observing and mastering the development law of overburden fractures and preventing disasters under such conditions.