Research On Seismic Effort Of Burst And Failure Of Coal-rock Mass Associated With Mining And Its Application

As the dynamic behavior of mining-induced tremor of coal-rock mass in longwall faces or roadways, rock burst is closely related to the failure of coal-rock mass associated with mining. Therefore, studies on the failure mechanisms and burst effects of mining-induced tremors are quite essential for the forecasting and prevention of rock bursts. Focusing on the seismic effects of the burst and failure of coal-rock mass associated with mining, this paper studied the failure mechanisms of typical mining-induced tremors, revealed the transmission and attenuation rules of the seismic energy radiated by tremors. Additionally, the mechanism of rock burst induced by tremor, and the influential factors of the burst effort to surrounding rock of the roadway, as well as the corresponding forecasting and control method were analyzed by theoretical analysis, laboratory physical simulation experiment, numerical simulation, field testing, and engineering practice as well.Mining-induced coal and rock fracturings or movements near the roadways or longwall faces will be generated by mining activity underground. Generally, the tremors induced by roof tensile fracturing, caving and bed separation have a typical tensile failure source characteristics, the tremors induced by roof rotation and compressive fracturing of coal pillar show a typical implosive failure characteristics, while the tremors induced by roof shear fracturing, rock block sliding, dynamic bursting of coal pillar and fault reaction are characterized by typical shear fracturing source model. Based on above, equivalent source models of mining-induced tremors were established based on the construction of the relation matrix between the equivalent force and the far-field displacement, then the characteristics of seismic displacement and radiated energy were studied, and the differences of failure mechanism of typical mining-induced tremors were revealed as well. Finally, different tremors were classified according to the differences of seismic displacement characteristics.Laboratory-scaled experiments were carried out to analyze the seismic effects and displacement field characteristics of roof, coal pillar, and fault burst and failure modes systematically. Studies indicate that the displacement fields of main shock, two aftershocks of the rock block conform to roof horizontal tensile fracturing, sliding and rotation instability, respectively, and the weak and strong burst-prone coal/rock samples under uniaxial compression approximately conform to the implosive failure and dynamic bursting of coal pillar, respectively. In addition, the seismic effects take on the evolution rules of amplitude increasing and dominant frequency decreasing with the extension of the failure radius.Moment tensor inversion method was used to quantitatively analyze the failure mechanisms of mining-induced tremors. Studies show that a satisfying inversion result of failure mechanism and fracturing characteristic deternimantion of mining-induced tremor can be achieved by least-square linear inversion of moment tensor, using the combination of P, S-wave displacement fields, especially P, SH-waves, or P, SV, SH-waves.Seismic effects during the transmission of seismic waves in coal-rock mass associated with mining process were studied by on-site testing and Siroseis monitoring. Results show that the average P-wave velocities, mean values of Comb. Max. Amplitudes and frequencies of the first arrivals were reduced greatly by roof caving, goafing expanding and intensity weakening of the overlying strata associated with mining process.Seismic energy transmission and attenuation modes radiated by mining-induced tremors were theoretically analyzed, and the mechanism of rock burst induced by residual dynamic load of tremor was revealed. Then, the influential factors of the burst effort to surrounding rock were simulated by using dynamic modules of FLAC2D and source-time function simulation of mining-induced tremors. Finally, the corresponding forecasting and control method of rock burst were proposed.Taking LW10302 in Baodian Coal Mine with strong tremor risk and LW250102 in Huating Coal Mine with high burst risk for the on-site practice. Based on SOS microseismic monitoring and the respective mining and geological conditions of the two mines, the failure mechanisms of mining-induced tremors with different energy levels and the seismic effects of strong tremors on the surrounding rocks of roadways or longwall faces were comparatively analyzed, which provides basis for the forecasting and prevention of rock burst.