Research On Pressure Relief Mechanism Of Diamond Beaded Wire Saw In Coal Seam Cutting

Coal is the main energy produced and consumed in my country.However,in some areas of China,coal seams have complex occurrence conditions,gas content is large,and mine gas disasters are relatively serious,which restricts the safe production of coal mines and the guarantee of coal energy.Gas drainage is an important means of mine gas disaster prevention and control.However,in many mining areas in my country,the permeability of coal seams is low,and gas drainage is difficult.It is necessary to reduce the stress of coal seams and improve the permeability of coal seams by cutting seams,thereby improving the efficiency of gas drainage.Preliminary engineering practice shows that diamond beaded wire saw cutting coal seam is an effective means of large-scale pressure relief,but the relevant pressure relief mechanism research is still insufficient.In this paper,through theoretical analysis,similarity simulation,numerical simulation and other means,the mechanical analysis model of wire saw cutting coal seam was established,and the stress change and deformation characteristics of coal rock mass after wire saw cutting coal seam were studied,and the effect of wire saw cutting coal seam was revealed.Pressure relief mechanism of coal formation.The main findings of the paper are as follows:(1)The mechanical analysis model of diamond beaded wire saw cutting coal seam was established,and the motion form of bottoming of the top plate above the slot after the wire saw cutting the coal seam was analyzed,and two forms of bottoming of the slot roof by bending and bottoming were revealed.Propose their corresponding conditional discriminants.(2)The similar simulation test method was used to analyze the mining stress field and deformation of the coal seam cut by the diamond beaded wire saw under different coal seam hardness and different beaded wire diameters.The pressure relief conditions of the overlying rock under different kerf factors are obtained from the strike and vertical directions,respectively.In the process of cutting the coal seam with the wire saw,the coal and rock mass around the slot goes through the following stages:compression,expansion,and recompression.Correspondingly,the vertical stress in the coal and rock on the roof of the slot can be divided into an obvious increase area,a sharp decrease area and a slow decrease area along the advancing direction of the cutting face.Viewed from the vertical direction,the stress reduction range of the top coal-rock layer near the slot is greater than that of the roof coal-rock layer far away from the slot,that is,the closer to the slot,the greater the degree of pressure relief.The hardness of the coal body and the diameter of the beaded rope have obvious effects on the stress of the overlying strata in the slot,which are mainly reflected in the degree of pressure relief and the range of pressure relief.When the coal hardness is small and the diameter of the beaded rope is large,the pressure relief degree and pressure relief range of the coal formation around the slot is larger.In the experiment of cutting the coal seam with the wire saw,the influence of the diameter of the beaded rope on the displacement and settlement of the overlying rock layer in the slot is much greater than that of the coal strength.(3)Through the UDEC numerical simulation,the deformation,damage and stress changes of the coal and rock layers around the slot under the action of wire saw cutting are analyzed.The pressure relief degree and range of the overlying rock after the wire saw cut the coal seam were obtained.After the coal seam was cut by the wire saw,the overlying strata can be divided into the following three areas from the perspective of stress change: stress increase area,sufficient pressure relief area,and stress recovery area,which are basically the same as the results of similar experiments.In the process of slotting,the pressure relief range and degree of pressure relief of the overlying rock layer in the slot will gradually expand with the increase of the cutting distance of the coal seam;in the middle of the slot,the stress in some areas is significantly reduced,and the shape is elliptical.The slot roof has not bottomed out(or not completely);the slot roof has bottomed out in some areas,resulting in a recovery of stress.The stress concentration appears in a certain range in front of the working face and behind the incision eye.There is also a certain degree of stress concentration at the cutting point of segmented cutting,and the range of stress concentration changes regularly with the continuous advancement of the cutting face.The above research results show that the diamond beaded wire saw cutting coal seam,as a new type of cutting pressure relief and permeability enhancement technology,can effectively reduce the in-situ stress and increase the coal seam permeability,which is of great significance to improving the safety of the mine.