Study on pre-grouting reinforcement technology by multi-step coupling under static and dynamic pressure in fault structural zone of working face

When the working face of the coal mine encounters a fault zone with complex original rock stress environment affected by mining activation during the mining process, in order to solve a series of problems such as difficulties in roof and coal wall support, low mining efficiency of broken surrounding rock, high mining cost and poor safety when stopping mining and stopping face reinforcement, the UDEC numerical simulation method was used to establish a working face fault activation model.The stress distribution characteristics of the original rock in the fault structural belt, the activation process of the fault during the mining process of the working face, and the development and evolution law of the rock mass fracture during the mining process were analyzed and it was determined that the reasonable and effective distances of the two-stage pre-grouting of static and dynamic pressure were 300-400 m and 30-50 m ahead of the working face.Through the grading and progressive arrangement of parallel and fan-shaped grouting holes in the fault structure zone, the calculation and selection of high-pressure grouting equipment and pump efficiency check, and the design and strength check of “two blocks, one injection+exhaust pipe” high pressure (15-20 MPa) positioning sealing method,the combined hydrostatic and dynamic pressure multi-step coupling pre-grouting key fault zone reinforcement technology including curtain grouting (0-10 m hole), shallow hole grouting (10-30 m hole), medium and deep hole grouting (30-80 m hole) and reserved deep hole grouting (80-130 m hole) was formed.The long-distance high-pressure grouting with grouting pressure of 5-15 MPa, grouting flow of 0～6 m3/h and grouting range 0～150 m has been realized, and the goal of 30～400 m pre grouting in advance working face to strengthen the coal and rock mass in the fault fracture zone has been achieved. The technology has been successfully applied in HuainanMining Area. When the working face passes through the fault,there is no rib spalling and roof fall, the working condition of the support is stable, and the supporting condition of the gateway is good during working face passing fault. The advancing degree of the working face is about 6 m/d, and the efficiency is increased by 1-2 times, realizing the continuous and efficient recovery of the working face across the fault without breaking the face.