Research On Stress Wave Formation And Its Influence Mechanism On Rockburst

Rockburst is characterized by significant dynamic behavior, and usually accompanied by stress waves induced by various mining activities, such as mining, roof break, fault slip, blasting, and earthquake. Researches have been found mainly on the destructing effects of stress wave, and few literature focus on the influence of stress wave formation and propagation on rockburst. In order to achieve the influencing mechanism of stress wave on rockburst, we conducted an investigation from three aspects, including stress wave generation, stress wave propagation and attenuation, stress wave destructing effects, by the means of modeling, experiments, and theoretical analysis.The roof break and coal fracture model were established based on the dislocation source theory, dynamic fracture mechanics and quantitative seismology. A 3D numerical code was written for stress wave generation by coal and rock break in mining space, and the code was utilized to calculate the dynamic velocity of stress wave induced by roof break and coal fracture, respectively. The numerical results indicate that the dominant factor for stress wave magnitude is fracture length and the strength of rock and coal. Larger fracture length and greater strength leads to higher amplitude of stress wave.The stress wave propagation and attenuation were experimentally investigated by split Hopkinson pressure bar system(SHPB), and the influencing mechanism of microstructure on stress wave propagation within coal has been studied. The dominant factor influencing the stress wave propagation during the crack closure and opening is friction between the crack surface and fracture energy dissipation, which could be quantitatively described by the crack closure model and brittle damage model, respectively. The numerical results agrees well with the filed data of blasting wave propagation in coal seam, which indicates that the brittle damage model is applicable for numerical study of field stress wave propagation. The dominant factor for stress wave propagation within intact coal includes friction, fluid flow, and scattering.The destructing effects of stress wave were experimentally studied using SHPB system, and the micro fractography was studied to reveal the crack initiation, propagation, converge and brittle fracture mechanism, the failure criteria was also proposed for coal under stress wave impact. The failure mode of coal under stress wave impact includes lateral tensile fracture and axial tensile fracture, the failure process is mainly characterized by tensile crack propagation. The fractography of both lateral tensile failure and axial tensile failure includes river pattern, branch pattern, and step pattern, which proves that the dynamic failure of coal under stress wave is brittle fracture, and the brittle fracture is resulted by type I crack transferring to type III crack through crack propagating and coalescence. Two crack array model were established according to both lateral tensile failure and axial tensile failure, the failure criteria was also proposed based on the critical damage associated with the crack length.Based on the aforementioned stress wave generation, propagation and attenuation, and destructing effects, a numerical method for stress wave disasters simulation is proposed, and it considers the influence of fracture length and material strength on stress wave amplitude, as well as the damage of crack propagation on stress wave propagation, which meet the real condition of coal microstructure. The influence of geostress, source stress wave amplitude and propagation distance on rockburst is investigated by the proposed method. The results indicate that the seismic energy in roadway increases with the increased geostress, source stress wave amplitude and decreased distance between source and the roadway. Based on the influencing mechanism of stress wave on rockburst, we analyzed the dynamic phenomenon occurred in the panel 92201 of the Sanhejian coal mine, including the stress wave generation and the hazard evolution process.The research results obtained in this study is of theoretical value for revealing the dynamic behavior and evolution mechanism of rockburst, and also provide theoretical and scientific basis for prevention of rockburst caused by stress wave in underground mining space.