Ground fracturing of multi-strata for strong ground pressure control in extra-thick coal seams with hard roofs: Numerical simulation and case study

Abstract

Strong ground pressure in the mining field is the key factor restricting safe mining of hard-roof mining areas. A hard roof combines high strength with a large breakage step, and the large breakage area would easily cause ground pressure disasters in the working face with gradual breakage of multi-hard rock strata. The study investigated the characteristics of the dynamic hazards under multi-hard rock strata conditions. The method of graded ground fracturing of multi-hard rock strata was proposed to control the ground pressure, and the characteristics of the bending strain energy release of the rock strata breakage and instability under the condition of equivalently decreasing the thickness of the strata by ground fracturing were theoretically analyzed. A numerical simulation model of weakening in multi-strata rock formations by fracturing was established, and the structural characteristics of rock strata breakage under the ground fracturing effects were analyzed. The results showed that the breakage characteristics of the overlying hard roofs were altered by ground fracturing, the bearing properties of the fractured rock strata were drastically reduced, while the effect of the breakage and destabilization of the rock strata was subsequently weakened. The ground fracturing practice of the L1 and L2 hard rock strata in the Tashan Coal Mine, China, taken as a case study, revealed that the cracks extension length reached approximately 220 m, and the crack’s width was 30 ∼ 120 m. During the working face was mined in the area covered by the cracks, the average supports resistance was reduced by 21 %, the rate of rib spalling was reduced by 23 %, greatly alleviating the intensity of ground pressure in the working face. The application of ground fracturing technology to multi-hard rock strata effectively weakened the hard rock strata, improving the ability of ground pressure control.