Formation and evolution law of high-intensity mining ground fissures and damage reduction method

High-intensity mining in the Shendong mining area has caused serious overburden and surface damage, which threatens the ecological security of the mining area. Scientific understanding of the evolution law of ground fissures and the conduction mechanism of mining induced overburden-surface damage is the key to realize underground safety mining, aquifer self-repair, and surface ecological environment treatment. Comprehensively adopting on-site measurement, theoretical analysis, numerical simulation, and physical simulation methods, the mining pressure law of the longwall face, the characteristics of the overburden structure, and the variation law of the width of ground fissures were first analyzed. Then, considering the magnitude of cyclic pressure and the characteristics of overburden structure, the dynamic development process of ground fissure width was explained in detail in an “M” - shaped bimodal shape, and the generation mechanism of ground fissures was revealed in depth. Finally, a reduction method for mining damage system was proposed from three aspects: working face, overlying rock, and surface. Finally, a methodology for the systematic reduction of mining damage was proposed in terms of the longwall face, overburden and surface. The result shows that there are large and small cyclic pressure in the longwall face of double key layer structure, the breakage of sub-critical layer affects the small cyclic pressure, and the instability of the main key layer controls the large cyclic pressure, the step of large cyclic pressure is 2-4 times of that in the small cyclic pressure, and the load in the large cyclic pressure is 1.07-1.13 times of that in the small cyclic pressure; The dynamic cracks in the central region exhibit a “bimodal” distribution with self-healing phenomena, while the boundary cracks exhibit a “unimodal” distribution, which is more destructive to the surface; Accelerating the advancement speed can reduce the extent of mining damage and accelerate the rate of roof subsidence; The dynamic cracks in the centre opening-closure-opening-closure evolution process was explained in terms of rotary subsidence of the key block; The instability of the pressure arch structure caused by high-intensity mining is the fundamental reason for the generation of ground cracks; A systematic damage reduction method of advancement speed optimization, grouting arch reduction damage and zoning treatment of ground cracks was proposed. The research results provide theoretical and technical support for the coordinated development of large-scale coal mining and ecological environmental protection.