Research On Prevention And Treatment Mechanism Of Rock Burst By Coal Seam Drilling

The technology of coal seam drilling is an important measure to prevent rock burst in coal mine.By changing the physical and mechanical properties of the surrounding rock near the roadway and improving the hole rate(It’s the volume of the borehole divided by the coal sample volume.)of coal body in the drilled area,the energy absorption and buffering performance can be enhanced.Absorb the energy amplified by the breaking of far-field surrounding rock,thereby protecting the stability of tunnel support.At the same time,drilling is used to reduce the elastic modulus of coal body in the drilling area,reduce the stress concentration of the surrounding rock in it,transfer the peak stress area of the tunnel surrounding rock to the deep part of the coal seam,improve the stability of the tunnel surrounding rock system,and prevent deformation and damage of the tunnel support caused by high stress.Firstly,the paper studies the deformation and failure characteristics and mechanical properties such as elastic modulus,bursting liability and energy absorption of borehole coal sample under static and dynamic loading,and obtains the law of the influence of borehole on the physical and mechanical properties of coal body.Then based on the instability theory of rock burst disturbance response,this study reveals the role of coal seam drilling during the formation and occurrence of rock burst,and reveals the mechanism of coal seam drilling to prevent and control rock burst.Finally,the parameters of coal seam drilling are optimized and improved by numerical simulation.Through a single free surface coal sample quasi-static compression experiment,the changes of mechanical properties,deformation and failure characteristics,such as elastic modulus,bursting liability and so on,without boreholes,single boreholes,double boreholes and three boreholes were tested.It is found that the failure of it is mainly shear through fracture,while the fracture of drilled coal samples is the fracture between vertical boreholes,and the fracture between horizontal boreholes will be formed under many boreholes,and the fracture is relatively developed.Under the drilling condition,with the increase of the hole ratio of the coal sample,the compressive strength and elastic modulus of the coal sample gradually decrease,and the ability to accumulate elastic strain energy gradually decreases.Simultaneously,the bursting liability of coal sample decreases significantly,which changes the physical and mechanical properties of coal body and makes it different from the raw coal body medium.Through the compression experiment under the impact load of single free face coal sample,the energy absorption mechanical properties and deformation and failure characteristics of coal sample without borehole,single hole,double hole and three holes are tested.It is found that under the condition of undrilled coal sample and borehole diameter of 5mm,local large fractures are developed in the whole middling coal sample during impact.However,after the impact,the pore ratio of the it gradually increases as the borehole diameter and quantity increase.Under the same impact load,the macroscopic cracks of the coal sample are more developed,and the coal sample fragmentation is more uniform.It can be seen that with the increase of pore ratio,the surface energy of coal samples in the impact failure process is significantly improved,which has a better energy absorption effect.Based on the rock burst disturbance response instability theory,the influence of coal seam drilling measures on the critical stress of roadway surrounding rock instability is analyzed when the medium properties of roadway surrounding rock change after drilling changes the porosity rate and compressive strength of coal body.It is found that under the condition that the roadway support resistance is 1MPa and the strength of coal and rock in the drilling area is 50%of the strength of the original coal body,if the mechanical parameters of the coal body are?_c=10MPa,E/?=1,the increase of the critical instability load of the roadway shows a linear downward trend with the increase of the porosity,which can play a good anti-scour role.The energy absorption of coal body in drilling area can be increased by spacing and deepening of drilling depth.At the same time,the density of the drilling coal body is small,and the impact impedance is relatively small,which prolongs the duration and rise time of the positive pressure of the shock wave,reduces the impulse of the shock wave,reduces the impact load in the impact force of the tunnel support,avoiding the instability and damage of the tunnel support.The higher pore ratio allows the borehole area to have a good energy absorption buffer effect.But it reduces the elastic modulus of the coal body,causing it to undergo greater deformation under the same load,increasing the shrinkage of the tunnel,and increasing the pressure of the surrounding rock on the tunnel support,which can easily cause significant deformation or even failure of the tunnel support.Then the spacing at the bottom of the borehole 2?is the most suitable.Taking the on-site drilling pressure relief measures of 21404 working face in a certain mine as the research object.Through FLAC3D numerical simulation,it is found that the coal seam drilling can make the stress peak shift to the depth of the roadway wall rock.With the increase of the depth of the drilling,the peak position will be further shifted to the depth.At the same time,the stress peak in the stress concentration area is slightly reduced.Too large spacing of boreholes not only fails to play an anti-scour effect,but also too dense spacing of boreholes will lead to the decline of coal strength and further aggravate the deformation of roadway surrounding rock.Therefore,it is necessary to reasonably design the coordination relationship between coal seam drilling and tunnel support before drilling and pressure relief in the tunnel.Combined with the relevant research results of this paper,the designing scheme of pressure relief parameters of in-situ drilling in 21404 working face of a mine is given.There are 83 pictures,11 tables and 54 references in this paper.