Study On The Breaking And Caving Rules Of Thick And Hard Top Coal And Cracking Promotion In Shenshupan Coal Mine

The Yushen mining area is an important energy base in China.The mining area has a large thickness of coal and a simple structure,which is suitable for fully mechanized caving.However,due to the shallow depth of the coal seam and the high hardness,the mine pressure is not obvious,resulting in a large amount of coal gangue falling.Facilitate the recovery of top coal.This paper takes the 3107 working face of Shenshupan Coal Mine as the engineering background,and uses the method of laboratory experiment and numerical simulation to study the breaking and caving characteristics of thick hard top coal under shallow burial depth and the situation of hydraulic fracturing top coal The law of expansion of hydraulic cracks puts forward the technical parameters of hard top coal cracking and promotes the application,which has been applied in the field and achieved good test results.The conclusions of the thesis research are as follows:(1)According to the actual form of top coal broken movement in fully mechanized top coal caving,the characteristics of linear model and bonding model in PFC software and their applicability to top coal broken movement and fall simulation are analyzed.The analysis shows that the linear model has no bonding between the particles,and the particles slip between each other.It can simulate the flow of the top coal and the characteristics of the coal gangue interface.It is suitable for simulating the flow characteristics of loose soft coal;It has the characteristics of resisting stress and torque,and will be converted into a linear shape after the bond is destroyed.It can simulate the stress state,breaking form and transportation and dropping process of the coal body more realistically.It is suitable for the hard coal seam breaking feature Simulation analysis.(2)Using uniaxial compression and Brazilian split experiment,the mechanical parameters of the top coal were calibrated and the numerical calculation model of the mining face was established.The simulation found that the roof has a long first stride step length under thick and hard roof coal,the coal fracture line lags behind the support tail beam,and the fracture angle is less than 90 °.Poor volatility;the pressure of the mine increased when the basic roof broke down for the first time,the top coal was fully destroyed,the broken block was reduced,and the volatility was improved.Due to less top coal emission,coal gangue fills the goaf after breaking up,making the basic roof less slewing space after breaking,forming a more stable masonry beam structure.The bearing effect of the coal gangue in the goaf further leads to The pressure in the mine is not obvious,and it is difficult to top coal.(3)By constructing a fluid-structure coupling numerical model,the effects of insitu stress,natural weak surface,borehole diameter and other factors on hydraulic crack propagation were studied.The results show that under the condition of in-situ stress difference,the maximum principal stress has an induction effect on the propagation of hydraulic cracks.The larger the stress difference,the more obvious the induction effect.The minimum principal stress mainly affects the fracture pressure of the hole wall.The smaller the intrusion angle of the weak surface,the easier the hydraulic cracks propagate along the weak surface.When the intrusion angle is less than 30 °,the hydraulic cracks fully propagate along the weak surface.When the intrusion angle is 30 ° ~ 60 °,the expansion path of the hydraulic fracture is the first along It spreads along the weak surface and then spreads along the weak surface along the direction of the maximum principal stress.When the intrusion angle is greater than 60 °,the hydraulic fracture mainly spreads along the direction of the maximum principal stress.The cracking pressure of the pore wall decreases with the increase of pore size,and the decreasing gradient gradually decreases.(4)The effects of borehole arrangement parameters and water pressure on top coal fracture were simulated and analyzed,and the reasonable parameters of hydraulic cracking of thick and hard top coal were put forward.There are 35 pictures,9 tables and 69 references in this paper.