Study on the Analysis Method of Swelling Deformation of Protected Seam During Protective Seam Mining

In view of the study on swelling deformation analysis method of protected seam during the mining process of protective seam, the analysis method of “four invariant points around area” is put forward for the first time. The method determines the swelling deformation of protected seam and analyzes it from the perspective of plane by analyzing the variability of “four invariant points around area” of protected seam before and after the mining of protective seam. Monitoring scheme and area analysis and calculation method are respectively designed applied in coal mine and laboratory; the monitor of “four invariant points around area” has been realized in the mining practice by arranging two measuring lines in the roof and floor of protected seam. The study scheme is designed to analyze the swelling deformation of the protected seam by the application of “four invariant points around area” in the engineering practice; the theoretical calculation method of irregular “four invariant points around area” after swelling deformation of the protected seam is put forward under laboratory conditions based on the Freeman boundary encode vector and measuring the length of quadrilateral side directly with the vernier caliper.; the reasonable scale of the four invariant points around area is discussed, it is suggested that different “four invariant points around area” should be established with different scale of 1 times, 1/2 times, 1/4 times and 1/8 times thickness of coal seam. The study shows that the method of “four invariant points around area” of swelling deformation is more accurate than the analysis method of “two fixed-point”; the more cells are divided at 1 times of the thickness of coal seam, the higher the accuracy of calculation is

Study of Rock Burst Risk Evolution in Front of Deep Longwall Panel Based on Passive Seismic Velocity Tomography

Monitoring and early-warning are critical for the prevention and controlling of rock burst in deep coal mining. In this study, rock burst risk assessment criterion was built based on the correlativity between seismic velocity and stress state in coal and rock body. Passive seismic velocity tomography using mining-induced seismic waves was conducted regularly and continuously. The evolution of rock burst risk and range in front of a deep longwall panel with folds and adjoining goaf was determined. The influence of pressure-relief measures on rock burst risk was analyzed. The study results indicate that burst risk level and range during panel retreating increase first and then decrease, the peak is reached when it is located at 1# syncline shaft area. When approaching the crossheading, high burst risk zones distribute along the crossheading and further intersect with those in 1# syncline shaft area. Burst risk zones in the inclination of panel show distinct zoning features. Tomography results are in good agreement with the drilling bit result, rock burst occurrence, microseismic activity, and working resistance of hydraulic supports. Pressure-relief measures and mining layout have a distinct influence on burst risk of longwall panel. For prevention and controlling of rock burst risk in deep coal mining, pressure-relief measures should be optimized based on passive tomography results

Discrimination of Microseismic Events in Coal Mine Using Multifractal Method and Moment Tensor Inversion

Discrimination of various microseismic (MS) events induced by blasting and mining in coal mines is significant for the evaluation and forecasting of rock bursts. In this paper, multifractal and moment tensor inversion methods were used to investigate the waveform characteristics and focal mechanisms of different MS events in a more quantitative way. The multifractal spectrum calculation results indicate that the three types of MS waveform have different distribution ranges in the multifractal parameters of ∆α and Δf(α). The results show that the blasting schemes also have a great influence on MS waveform characteristics. Consequently, the multifractal parameters of ∆α and Δf(α) can be used to discriminate different MS events. Further, the focal mechanisms of MS events were calculated by seismic moment tensor inversion. The results show that an explosion is not the dominant mechanism of deep-hole blasting MS events, and the CLVD and DC components account for an important proportion, indicating that some additional processes occur during blasting. Moreover, the coal-rock fracture MS events are characterized by compression implosion or compression/shear implosion mixed focal mechanisms, while the overburden movement MS events are tensile explosion or tensile/shear explosion mixed focal mechanisms. The focal mechanisms and nodal plane parameters have close relationships with the inducing factors and occurrence processes of MS events

Discrimination of Microseismic Events in Coal Mine Using Multifractal Method and Moment Tensor Inversion

Discrimination of various microseismic (MS) events induced by blasting and mining in coal mines is significant for the evaluation and forecasting of rock bursts. In this paper, multifractal and moment tensor inversion methods were used to investigate the waveform characteristics and focal mechanisms of different MS events in a more quantitative way. The multifractal spectrum calculation results indicate that the three types of MS waveform have different distribution ranges in the multifractal parameters of ∆α and Δf(α). The results show that the blasting schemes also have a great influence on MS waveform characteristics. Consequently, the multifractal parameters of ∆α and Δf(α) can be used to discriminate different MS events. Further, the focal mechanisms of MS events were calculated by seismic moment tensor inversion. The results show that an explosion is not the dominant mechanism of deep-hole blasting MS events, and the CLVD and DC components account for an important proportion, indicating that some additional processes occur during blasting. Moreover, the coal-rock fracture MS events are characterized by compression implosion or compression/shear implosion mixed focal mechanisms, while the overburden movement MS events are tensile explosion or tensile/shear explosion mixed focal mechanisms. The focal mechanisms and nodal plane parameters have close relationships with the inducing factors and occurrence processes of MS events