Meitan xuebao (Oct 2023)
Regional failure mechanism of main roof and zonal method for ground control in kilometer-deep longwall panel with large face length
Abstract
Mining depth and face length increase gradually in coal mine. The intensity of mining pressure occurrence rises quickly. In order to improve ground control in deep longwall panel with large face length, a case study is carried out by taking 121304 longwall panel in the Kouzidong Coal Mine of Xinji Energy Co., Ltd., China National Coal Group Corp as the background. Roof micro-seismicity characteristics are summarized, aiming to reveal the mechanisms of regional failure and dynamic migration in main roof. The works are conducted by using field measurement, theoretical analysis and lab test. The results show support resistance presents valley-shaped distribution, characterized by small resistance in middle region and large resistance in side regions. At different face advancement, the location of roof rupture induced micro-seismic events with large magnitude changes dynamically along face length direction, indicating regional failure and dynamic migration of main roof. The energy associated with the strong event at middle section is smaller than that at side sections. Thus, dynamic impact of middle area is weakened, consistent with valley-shaped distribution of support resistance. The region where mining induced stress is larger than initial yield strength of main roof is defined as peak point influenced zone. Large stress magnitude within the zone leads to crack initiation while release and rotation of the stress lead to crack propagation, which reveals driving effect of rotational stress on fracture development. A model is developed for regional failure and dynamic mitigation of main roof. Pre-existing and mining-induced fractures change local boundary condition of main roof, leading to regional failure. Roof load-bearing capacity decreases from middle to side section, leading to dynamic mitigation of regional failure. Rupture size of main roof is smaller in peak point influenced zone, which explains valley-shaped distribution of support resistance. According to regional failure and dynamic migration in main roof, a zonal method is proposed for ground control, realized by coordinative movement of the supports within middle peak point influenced zone. Single mode is used in other areas. Ground control is effectively strengthened after application of the new method in 121304 longwall panel.
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