Study On Rockburst Prevention Mechamism Of Coal Drillhole With Bursting Liability Reduction-Deformation Control-Energy Dissipation

Rock burst is a severe trial for the mining safety of coal resources.Coal seam drilling was regarded as a common measure for the prevention and control of rock burst due to its convenient operation,low cost.However,the current research on the anti-scouring mechanism of coal seams mainly focuses on the decompression effect of the boreholes,ignored the effect of drilling on the physical properties of the coal body.As a result,the coal seam anti-scouring drilling parameters do not match the actual engineering conditions,resulting in coal seam drilling the effectiveness of control is not well.Therefore,the thesis adopt the research method combining experimental research,theoretical analysis,numerical simulation and field application.Based on the coal rock bursting liability test,and combined rock burst disturbance response instability theory,rock energy dissipation theory,fractal theory and quantitative stereoscopic based on scientific principles.Explored the bursting liability difference,deformation failure and energy evolution characteristics of samples under various drilling layout conditions,and it as revealed that coal seam drilling has the ability to reduce the bursting liability of coal,guide and control coal deformation,and increase deformation energy consumption.Based on the theory of rock burst disturbance response instability,the influence of coal seam drilling on the critical conditions of rock burst initiation was discussed.On this basis,field practice of coal seam drilling and scour prevention was carried out.The main research work of this paper were as follows:(1)Based on the test results of bursting liability of different borehole layout samples under uniaxial loading conditions,the evolution law of bursting liability under the action of borehole was analyzed.It was found that compared to complete samples,with the increase in the number of drill rows and rows,the drilled samples showed a gradual increase in the plastic damage before the stress peak,the peak strength decreased,the accumulated elastic energy decreased,and the post-peak failure time was prolonged and energy consumption increased.The hole has a weakening effect on the impact tendency of the sample.Based on the theory of rock burst disturbance response instability and combined with the test results,analyzed the change law of critical load,critical softening zone and critical stress index under the action of drilling layout.The sensitivity of the critical conditions to uniaxial compressive strength,impact energy index,and the number of drilling rows was analyzed,and the rationality of the drilling pressure relief measures can be evaluated.(2)The digital image correlation method was used to analyze the deformation and failure of different borehole layouts and the evolution of deformation energy density.Found the layout of the destressing drillholes changed the fracture mode of the samples.The complete sample forms a strain localization area from the middle of its surface,and the final fracture occurs with this area as the weak surface.The samples with single row and multiple rows drillholes arrangement,cracks occur on the upper and lower sides of drillholes,formed a localization zone,which extend up and down to form macroscopic cracks.The samples with double rows and multiple rows drillholes arrangement were easily to crack in the rock bridge between the same row of drillholes,and then the cracks in the rock bridge between the vertical drillholes further developed,and finally formed the vertical and horizontal and oblique macroscopic cracks.Also with the increase of drillhole in sample showed the spatial effect.(3)Using the acoustic emission monitoring information and the characteristics of broken particles,the changes in acoustic emission characteristic parameters of samples with different borehole layouts,the energy-frequency evolution characteristics of acoustic emission events,the correlation betweent he fractal dimension of broken particles,the additional surface area of broken particles,and the energy input dissipation were analyzed.It was found that the fractal dimension of broken particles has a good negative correlation with the newly added surface area:the lower the degree of sample breakage,the higher the fractal dimension and the smaller the newly added surface area.And the law of post-peak energy release and dissipation was consistent with the change law of the new added surface area of broken particles.Drilling increased the activity intensity of AE events and reduced the proportion of high-energy events.(4)The comparative analysis results based on the law of energy evolution in the whole process of loading different borehole samples show that:the borehole reduced the accumulated strain energy before the peak,and reduced the energy release per unit time after the peak.Drillholes reduced the growth U_Vand peak value U_maxof deformation energy density,it also delayed the release rate U_RVof deformation energy at the moment of failure.Also with the increase of drillhole,the greater the reduction amplitude of the peak deformation energy density Umax and the release rate U_RV,making the sample less prone to dynamic damage.(5)Based on the rock burst disturbance response instability theory and combined with the test results,analyzed the critical load,critical softening zone,critical stress index and the critical condition of the sample under the effect of the physical modification of the samples.Sensitivity of critical conditions to uniaxial compressive strength,bursting energy index,and number of drill holes.The change of the number of drilling rows has a significant impact on the critical load,critical softening zone,and critical stress index,and reduced the possibility of rock burst.(6)According to the specific engineering situation of the 513 working face of a mine,based on the analysis of the coal stress and microseismic monitoring data,found that the coal stress recovered and has a rising trend with the increase of time after the implementation of a single row of drilling.The danger of rock burst has not been effectively eliminated.The numerical simulation method was used to analyze the evolution characteristics of the surrounding rock of the roadway before and after multiple rows of boreholes and the stress distribution between boreholes.Compared with the single-row drilling layout,the multi-row drilling layout expands the stress disturbance area,which in turn induced the destruction of the surrounding rock mass near the borehole,and the coal body stress gradually decreased,which lead the high stress transfer to the end of the borehole and reduced the bursting hazard of the surrounding rock mass.The optimization of drilling arrangement was realized.This paper contains 66 figures,23 tables and 128 references.