Hydraulic Roof Cutting And Pressure Relief Technology And Its Application On Thick Hard Roof Of Large Mining Face

Large mining height integrated mining is a common mining method for thick Jurassic coal seams in northern Shaanxi Province,and mines with thick hardtop geological conditions are widely distributed in Jurassic coal seam mines in northern Shaanxi Province.The so-called thick hard tops often have dense rock structure and undeveloped joints,and the layer thickness reaches 10 m.In the process of mining thick hard top coal seams with large mining heights,the thick hard tops are difficult to fall with mining,and it is very easy to form fan-shaped overhanging roofs in the workings of large mining heights,which results in a high concentration of supporting stresses in the workings and their lateral mining areas,causing serious damage and deformation of the surrounding rocks of the roadway around the mining site.To this end,this paper takes the thick hard roof hydraulic fracture unloading project of Xiaobodang 7m large mining height comprehensive mining face as the background,and adopts the research method combining theoretical analysis,laboratory test,numerical simulation and field test to systematically study the mechanism of thick hard roof fracture unloading of large mining height comprehensive mining,and gives the key parameters of lateral coal column cutting roof unloading pressure protection lane at the working face,and verifies the reasonableness of the parameters through field industrial test.The main conclusions obtained in the paper are as follows.(1)The rock distribution characteristics of the test working face were identified through field drilling and rock coring;the physical and mechanical properties of the roof rock were studied through drill core laboratory processing.Based on the key layer identification,the locations of three key layers of the overburden rock of the test workface and their distribution characteristics were given.The initial pressure step of the roof under the condition of thick hard roof of large mining face is 65.78 m,and the periodic pressure step is 45.42 m.(2)Theoretical analysis of the impact of hydraulic roof cutting and pressure removal on the overhanging roof of thick hard roof,pre-cut cracks lead to the overlying rock is difficult to form the cantilever structure of thick hard roof,reducing the length of the overhanging roof in the mining area;at the same time,the timely collapse of the lower roof gangue and play the role of timely support of the high roof,moderate the concentration of load on the coal column of the working face of the thick hard roof,thus ensuring the stability of the working face side coal column-roadway system surrounding rock.(3)Through the numerical simulation of hydraulic fracture unloading on the thick hard roof of the coal pillar side of 112201 large mining face,the influence law of hydraulic fracture top cutting and unloading parameters on the movement of overburden rock was analyzed.Based on the control variable method,the influence law of different top cutting height and different top cutting angle changes on the change of coal pillar stress and the change of roadway surrounding rock displacement is given.The parameters of hydraulic roof cutting drilling at 112201 working face were determined: 25 m and 10° on the mining side and 35 m and 15° on the coal pillar side.(4)Combined with the test on 112201 working face,the cantilever length on the mining side of 112201 working face was reduced after hydraulic fracturing and roof cutting,the stress of coal pillar decreased by 57%,the top and bottom slab shift of coal pillar-roadway system surrounding rock was reduced by 51.25%,and the shift of two gangs was reduced by 51.28%.The test parameters effectively improve the stress environment of the lateral coal pillar roadway system at the working face and reduce the support cost.