Field tests on fixed-point hydraulic fracture with extra-high pressure in coal seam for rock burst prevention

Considering the current domestic and overseas situations of lacking mature active regional technology for rock burst prevention, a kind of new technology is introduced using fixed-point hydraulic fracturing with ultra-high pressure to form regional low stress areas in coal body for facilitating rapid excavation and mining. The field tests are carried out at the mining depth of about 1000 m in Shandong Huafeng Coal Mine. In order to monitor the whole process of the tests, microseismic monitoring system, stress dynamic real-time monitoring system and pressure sensors are used to monitor coal and rock fracture, stress variation in coal and rock and line pressure, respectively. The main conclusions are as follows: (1) After the fracture pressure reaches 24 MPa and remaines for about 11 seconds, the first fracture occurs in the coal, and then the fracture radius reaches 8 m when the pressure stays at the same level for around 13 minutes; (2) The stress performance of time sequence in the whole fracture process is that: the stress of the observation point 9.5 m away from the fracture point increases significantly after the water is pressurized→fracture occurs in the coal→line pressure plunges→stress at the observation point tends to be stable; (3) The fracture process approximately cuts the coal into cuboids of 6.2 m×8.0 m×6.2 m, and reduces coal burst tendency effectively with the injection of a great deal of water; (4) The tests show that the fixed-point hydraulic fracture can achieve rock burst prevention by means of “stress transfer, coal weakening and energy storage decrease”.