Research on the spatiotemporal evolution of deformation and unloading mechanical effects of underlying coal-rock under upper protective layer mining

Wulin Lei ^1* Jing Chai ² Chao Zheng ¹ Jian Zhao ¹ Siyang Wang ¹ Guixian Liu ¹ Jufeng Zhang ¹ Rili Yang ¹

• ¹ Longdong University, Qingyang, China
• ² Xi'an University of Science and Technology, Xi'an, Shaanxi, China

The spatiotemporal rule of pressure release of rock-coal strata in the mining zone is the theoretical basis for the prevention and control of dynamic disasters during the mining of the stress-concentration stratum. Taking the mining of the upper protective layer of Hulusu Coal Mine located in Ordos City, Inner Mongolia Autonomous Region, China as the engineering background, based on the theory of elastic-plastic mechanics, the pressure relief law of the underlying coal and rock under the upper protective layer mining was studied from different scales through rock mechanics experiments, numerical simulation calculations, and on-site industrial experiments. The stress field and displacement field spatiotemporal evolution law of the underlying coal and rock under the upper protective layer mining were simulated and calculated using the 3 Dimension Distinction Element Code. The Brillouin Optical Time Domain Analysis distributed fiber optic sensing technology was used to monitor the deformation and unloading dynamic process of different rock-coal strata under the mining floor in real-time. The results indicate that the stress changes in the underlying rock-coal strata during the mining of the upper stress-concentration stratum can be divided into 4 phases: in-situ stress, stress-concentration, stress release, and stress restoration. Due to the uneven distribution of the waste rock collapse in the mined-out area, the stress in the mined-out area is alternately distributed in the unloading stable zone, unloading recovery zone, and boosting zone. The mining-induced stress distribution curve in the protected coal seam changes from a U-shape to a W-shape, and then to a "WWW" shape. The stress-relieving effect of the upper stress-concentration stratum mining is significant, but the stress-relieving parameters vary due to time and spatial factors. The research results have important theoretical and practical significance for guiding the layout and key parameter design of stress-concentration stratum mining.