Temporal and spatial evolution law of microseisms and induced impact mechanism in complex spatial structure area of steep and extremely thick coal seam

The occurrence of coal mine rock burst disasters is closely related to the spatial structure, especially in the complex spatial structure area. It is of great significance to master the law of coal and rock catastrophe and reveal its mechanism in the complex spatial structure area of coal seam mining for the prevention and control of rock burst. Taking the Wudong Coal Mine as the research background, using numerical simulation, micro-seismic monitoring, theoretical analysis and other methods, the abnormal size effect of rock pillar stress is studied, the temporal and spatial evolution law of microseisms in the complex spatial structure area is analyzed, the mechanism of rock burst under the complex spatial structure is revealed, and the impact risk in the different areas of coal mining is evaluated. The research results show that: ① The steeply inclined rock pillar with narrower thickness and higher exposed height has stronger prying effect, and the abnormal stress of rock thickness variation forms five divisions. ② The area with narrower rock pillar thickness has more micro-seismic frequency, higher energy, stronger spatio-temporal activity and higher dispersion. The high stress region, the stress gradient region and the stress plateau region show the micro-seismic response characteristics of “low frequency-high energy”, “high frequency-high energy” and “low frequency-low energy” in turn. ③ The micro-seismic events in special spatial structure area are clustered and the energy level increases, and the temporal and spatial activity and dispersion increase sharply. This feature is more obvious especially at the edge of the structure, the energy accumulation and release rate increases, and the probability and intensity of rock burst are higher. The micro-seismic activity of special spatial structures located in the narrower area of rock pillars is more acute. ④ The narrower the thickness of rock pillar (the greater the height of coal pillar), the faster the growth rate of bending moment and energy in the depth of rock pillar, and the higher the impact risk. According to the strength effect of structural plane, it is inferred that the fault zone has slip and dislocation, and fault zone is the dominant area for energy accumulation and release. It is revealed that the mechanism of rock burst is the joint action of high static load and low critical load. The impact risk in the different areas of coal mining is evaluated based on stress concentration characteristics

Stress distribution and evolution characteristics in horizontal layered mining of steeply inclined coal seams

In order to reveal the stress distribution and dynamic evolution characteristics of the surrounding rock under the conditions of horizontal layered mining of steeply inclined coal seams, the stress distribution and dynamic evolution characteristics of the alternate mining of two working faces at the same level were studied by using theoretical analysis and numerical simulation with B1+2 and B3+6 working faces in the south mining area of Wudong Coal Mine as the engineering background. The results show that: with the increase of mining depth, the overall peak pressure of coal body support in the two working faces increases and the peak point keeps moving downwards; the peak stress concentration in the coal body shows a “serration” fluctuation growth and the downward distance of the peak stress point shows a “step” growth. The B3+6 coal body stress peak is always greater than that of B1+2 coal body, and the stress peak position is always lower than that of B1+2 coal body; the linear correlation between the stress concentration peak and stress peak position and the mining depth of the two working faces is obtained by function fitting; the idea of impact ground pressure prevention and control scheme is proposed with the increase of mining depth

Microseismic temporal-spatial precursory characteristics and early warning method of rockburst in steeply inclined and extremely thick coal seam

Early warning of a potential rockburst risk and its area of occurrence helps to take effective and targeted measures to mitigate rockburst hazards. This study investigates the microseismic (MS) spatial-temporal precursory characteristic parameters in a typical steeply inclined and extremely thick coal seam (SIETCS) with high rockburst risk and proposes three spatial/temporal quantification parameters and a spatial-temporal early warning method. Analysis results of temporal parameters show that the sharp-rise-sharp-drop variation in total daily energy and event count can be regarded as a precursor for high energy tremor. The appearance of peak values of both energy deviation (≥20) and event count deviation (≥1) can be regarded as precursors that indicate imminent rockburst danger. A laboratory acoustic emission (AE) experiment reveals that precursor characteristics obtained from the study can be feasibly used to warn the rockburst risk. The spatial evolution laws of spatial parameters show that the high energy density index of MS (EDIM), velocity, velocity anomaly regions correlate well with stress concentration and rockburst risk areas. The field application verifies that the temporal-spatial early warning method can identify the potential rockburst risk in a temporal sequence and rockburst risk areas during the temporal early warning period