Research on Roof System of Large Dip Angle Coal Seams with Ultra-high Pressure Hydraulic Cutting

In view of the problem that it is inappropriate to use shaped charge blasting to cut roof and relieve pressure in mines of Shanxi Baoli Yufeng Coal Mine,it is proposed to adopt dense drilling combined with ultra-high pressure hydraulic roof cutting technology.Adopting a double acting supercharger to optimize water cutting hosts,and realize the isolation of liquid suction and discharge pipelines,the fluid pressure is doubled through hydraulic balance,combined with an accumulator,the ultra-high pressure water is stably output,ensuring smooth and controllable cutting surfaces.The maximum cutting pressure reaches 300 MPa,solving the problem of poor stability of traditional water cutting hosts.The ground simulation test results show that increasing the cutting pressure from 100 MPa to 280 MPa will increase the cutting efficiency from 57 mm2/s to 150 mm2/s,with an increase of 163%.As the cutting depth and area increase,although the cutting efficiency decreases from 150 mm2/s to 83 mm2/s,the decrease slows down,which is beneficial for continuous cutting operations under higher cutting pressures.The development of this system can provide technical support for on-site downhole roof cutting and pressure relief construction.