Study On The Weakening Mechanism Of Surrounding Rock Strength Of Pressure Relief Boreholes In Deep Roadway And The Method Of Reaming Pressure Relief

With the depletion of resources in shallow ground,coal mining has gradually shifted vertically towards deep ground.Affected by the geological structure of deep ground,the frequency,intensity and damage degree of rock burst disasters are increasing day by day.At present,pressure relief and rock burst prevention methods mainly include coal seam water injection,deep hole blasting pressure relief,directional hydraulic fracturing and coal seam drilling.Among them,coal seam drilling has been widely applied to most rock burst mines for its advantages such as mild disturbance,convenient construction and highly controllable pressure relief range.However,the research remains insufficient concerning the problems of the failure and instability of coal bodies around deep roadway side boreholes and the weakening of surrounding rock strength during pressure relief drilling.Consequently,mutual restriction exists between traditional pressure relief and rock burst prevention and roadway surrounding rock control,leading to either insufficient pressure relief（occurrence of rock burst after pressure relief）or excessive pressure relief（excessive deformation of surrounding rock）.In this study,on the basis of analyzing the instability mechanism and energy release of deep roadway coal bodies,in-depth research was conducted from the perspectives of deformation laws of coal bodies around deep and shallow roadway boreholes,crack expansion characteristics and damage evolution by means of laboratory tests,theoretical analysis,numerical simulation and on-site monitoring.Furthermore,the weakening mechanism of surrounding rock strength in deep roadway pressure relief drilling was revealed,and the concept and method of deep roadway reaming and pressure relief（RPR）was proposed.Besides,a self-defined constitutive model of deep roadway side coal considering the effect of crack damage was established.With the aid of this model,the drilling parameters of deep roadway RPR were designed,and the method of deep roadway RPR was applied in the field.The main research contents and innovative achievements are as follows:（1）Triaxial loading tests were performed on three types of samples,i.e.,coal-rock combinations on the roadway side,shallow roadway side coal bodies and deep roadway side coal bodies by using the self-developed true triaxial electro-hydraulic servo loading test system.On this basis,the stress-strain laws and failure characteristics of these samples were obtained.In addition,combined with the results of acoustic emission monitoring,the main failure modes of shallow and deep roadway side coal bodies were analyzed,and the instability mechanism of deep roadway side coal bodies was analyzed.Finally,the energy criterion for judging whether deep roadway side coal bodies undergo impact instability was deduced.（2）Loading tests were carried out on shallow and deep roadway side coal samples with different drilling shapes through the self-developed real-time CT scanning true triaxial loading test system.Based on the test results,the mechanical properties and internal crack propagation evolution characteristics of these samples during deformation and failure were researched.Then,the crack damage variable of coal bodies around roadway boreholes was defined by using the ratio of the cumulative crack volume to the final total crack volume,which intuitively characterized the damage behavior caused by crack propagation inside the coal mass.Eventually,the function expression of the crack damage variable was obtained,and the weakening mechanism of surrounding rock strength in deep roadway pressure relief drilling was revealed,laying a theoretical foundation for proposing the concept and method of deep roadway RPR.（3）Cyclic loading and unloading tests were conducted on shallow and deep roadway side coal samples around boreholes with different diameters.By this means,the basic mechanical properties and crack propagation evolution characteristics of coal bodies around roadway side boreholes under the condition of cyclic loading and unloading were obtained.Moreover,the difference in shallow and deep roadway side coal samples around boreholes with different diameters was analyzed under the condition of cyclic loading and unloading and the condition of loading,respectively.Meanwhile,the function expressions of the crack damage variables of shallow and deep roadway side coal samples around boreholes under the condition of cyclic loading and unloading were concluded.Finally,the concept and method of deep roadway RPR were proposed on the basis of the traditional roadway drilling pressure relief method.（4）A self-defined constitutive model of deep roadway coal bodies considering the effect of crack damage was established by introducing the above-mentioned crack damage variables into the Mogi-Coulomb constitutive model,and the asynchronous change law of cohesion force and internal friction angle was predicted.At the same time,the calling of the established constitutive model in FLAC^3Dsoftware was realized through the secondary development user interface in FLAC^3D.According to the numerical simulation results,a method of designing drilling parameters of deep roadway RPR was proposed and then applied to the track roadway of 6307 working face in Tangkou Coal Mine.The field engineering application shows that the designed RPR drilling parameters succeed in weakening the impact on the stability of roadway surrounding rock and easing the stress concentration of coal bodies,thus achieving a remarkable effect in preventing rock burst.The method of deep roadway RPR is superior to the traditional roadway drilling pressure relief method in terms of pressure relief effect,maintenance of the original support system,influence on surrounding rock deformation and construction efficiency.The dissertation has 114 figures,18 tables,and 217 references.