Dynamic Response Characteristics And Failure Mechanism Of Roadway Subjected To Stress Waves Radiated By Mining Tremor

Mining tremor is a common dynamic phenomenon in coal mining,which is the process of radiating vibration wave when the coal and rock mass break.The mining tremor mainly disturbances medium in the form of stress wave,when the roadway is subjected to static stress concentration,the disturbance of mining tremor may break the the stress balance state of surrounding rock and even induce rockburst.Through theoretical analysis,laboratory test,numerical simulation and field investigation,the condition,the mechanism,influencing factors,the precursor characteristics of induced faliure and the evolution of dynamic stress around roadway under mining tremor disturbance were studied through the thesis,the corresponding prevention and control measures were also proposed.Based on the actual geomechanical conditions of rockburst around roadway induced by mining tremor in field,the failure and instability mechanical model of roadway induced by stress wave incidence is established,and the dynamic stress evolution and instability conditions of roadway under the disturbance of mining tremor are deduced.The results show that the critical conditions of failure of roadway induced by mining tremor is determined by the vertical stress P,lateral pressure coefficientγ,friction angle in coal φ,shear modulus G,uniaxial compressive strength Rc,wave number of stress wave α,amplitude of stress wave φ0 and dynamic stress concentration coefficient c.With the help of Hopkinson bar impact test and biaxial loading impact test,the characteristics of failure around the roadway under the condition of the uniaxial,biaxial confining pressures are studied.The research results indicating:the failure easily occur in the parallel and vertical incident directions of roadway when it it is incident by compressive stress waves under uniaxial conditions.Under the condition of biaxial confining pressure,when the stress wave is vertically incident from directly above of the roof,the two sides and corners of the roadway are most likely to be failure,followed by the roof,and the floor is the most stable.There are obvious precursor characteristics before the failure and instability of the roadway,which manifested as a sharp increase in the count of acoustic emission ringing,the release of energy reaching peak,a sharp increase in RA value,formation of a large number of tensile cracks,and a large number of low frequency AE events occurring and values of b changing from high to low.The experiments of failure around roadway induced by stress wave incidence under uniaxial and biaxial confining pressures are reproduced based on PFC particle flow software,and the evolution characteristics of physical parameters such as velocity,stress,displacement and energy of surrounding rock are studied.The results indicating:tensile stress and shear stress concentrated at the parallel and vertical incident direction of the hole,respectively,due to the incidence of compressive stress wave under uniaxial condition.When the stress wave is incident vertically from above the roof and roadway is under biaxial confining pressure,tensile failure occurs at the roof caused by the tensile stress generated by the elastic rebound of coal.The failure of side wall of roadway occurred in stress wave incidence stage,which was shear failure caused by the concentration of compressive stress.The floor is less disturbed due to the barrier effect of the roadway,and there is no fissure.The stability of the roadway is comprehensively affected by the confining pressure and the frequency,amplitude and duration of the incident stress wave.By universal distinct element code numerical simulation software(UDEC),the whole dynamic process that from generation and propagation of mining tremor to induce rockburst is reproduced,and the evolution of physical parameters and influencing factors in the static load transfer and dynamic disturbance stages are studied.The results indicating:mining tremor generated from the shear fracture is triggered by the mutual dislocation of the broken rock mass on both sides of the fault plane.The S wave appears on both sides of the fault plane,and the P wave appears at the four corners of the fault plane.Due to the disturbance of mining tremor,the stress of surrounding rock will be redistributed.In the process of stress readjustment,failure of roadway will occur when the concentrated stress exceeds the bearing strength of surrounding rock.The risk of failure around roadway induced by mining tremor disturbance is affected by many factors,such as buried depth,width of working face,the relative spatial location of the tremor source and the roadway,and the scale of the fracture plane.Based on the "8.30" strong mining tremor occured in the 63pper06 working face of the Dongtan Coal Mine,the formation of strong mining tremor and the mechanism of the inducted failure around roadway were analyzed through microseismic monitoring,which includes stress concentration,fracture form and precursor characteristics of strong mining tremor in the source area.At the same time,the prevention and control methods of rockburst in the working face with frequent strong mining tremor were discussed through combining with the main control factors of failure around roadway induced by mining tremor,and which were verified in the the 103lower07 working face of the Baodian coal mine.There are 146 figures,12 tables and 164 references in this dissertation.