Abstract:
The presence of multilayered thick and hard roof strata results in frequent mine tremors, significantly complicating prevention and control efforts and posing a formidable challenge to the safe and efficient operation of coal mines.Taking the multi-layer thick and hard roof working face of Hongqinghe Coal Mine as the engineering background, the occurrence risk of mine earthquakes is identified by combining the occurrence of roof strata and surface subsidence conditions. Based on the damage theory, the mechanism of ground fracturing mine earthquake prevention and control is revealed. A method for the optimization and adjustment of ground vertical well layout and fracturing layer position, suitable for multi-layer thick hard roof mine earthquake prevention and control, is proposed. Furthermore, a test on ground vertical well fracturing mine earthquake prevention and control for multi-layer thick hard roof has been conducted. Fracturing damage weakens the mechanical properties of the rock mass, increases energy dissipation, and en-hances the discontinuity of the rock mass, providing a pathway for the fracture, sliding, and shedding of the thick and hard roof. Based on the results of rock mechanics and comprehensive interpretation of anisotropic logging data, it is possible to accurately identify thick and hard rock formations, thereby optimizing and adjusting the fracturing horizons. At the same time, a well-distribution method that comprehensively considers factors such as fracture propagation size and mining-induced fractures has been developed. Introducing temporary plugging agents during the fracturing process can enhance the construction pressure and increase the complexity of the fracturing fracture network. The main fracture extension direction of the surface vertical well fracturing is approximately N38°E. The length, width, and height of the fracturing fractures are 333, 225, and 56 m, respectively, effectively achieving pre-splitting weakening of the thick and hard roof. Ground fracturing reduces the frequency of high-energy events with a magnitude of 10
4 J and above. The average advancement of the working face for high-energy events has significantly increased from 5 m per occurrence to 48 m per occurrence, and the proportion of high-energy events has decreased from 7% to 2%. After surface fracturing, the amount and rate of surface subsidence show an increasing trend, indirectly indicating that the thick roof overburden can collapse in a timely manner with the advancement of the working face, reducing the risk of mine earthquakes.