The fracturing models of hard roofs and spatiotemporal law of mining-induced stress in a top coal caving face with an ex
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ORIGINAL ARTICLE
The fracturing models of hard roofs and spatiotemporal law of mining-induced stress in a top coal caving face with an extra-thick coal seam Zhiqiang He . Heping Xie . Mingzhong Gao Gaoyou Peng . Cong Li
. Guangdi Deng .
Received: 22 July 2020 / Accepted: 17 November 2020 Ó Springer Nature Switzerland AG 2020
Abstract Hard roof fracturing characteristics and mining-induced stress behaviors can be studied to ensure production safety in top coal caving face. Field tests were conducted at top coal caving face No. 8309 in the Tongxin mine of the Datong Coal Mining Group in China. The monitoring results indicated two modes of periodic weighting: short weighting steps with low intensity and long weighting steps with high intensity. According to three periodic weighting phenomena, three models of hard roof fracturing were proposed based on the cantilever-voussoir beam compound structure. And the equations of the working resistance for long/high periodic weighting were derived. Furthermore, a difference in the pressure changes among the front leg, back leg and front beam of the supports
Z. He H. Xie M. Gao (&) G. Peng C. Li State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource and Hydropower, Sichuan University, Chengdu 610065, China e-mail: [email protected] Z. He H. Xie M. Gao C. Li Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Institute of Deep Earth Sciences and Green Energy, College of Civil and Transportation Engineering, Shenzhen University, Shenzhen 518060, China G. Deng College of Architecture and Environment, Sichuan University, Chengdu 610065, China
was observed, and the back leg pressure significantly increased during periodic weighting. The change in the single prop pressure was divided into a slow growth stage and a rapid growth stage. And the front abutment pressure fluctuated with the periodic instability of the roof compound structure. Moreover, the fracturing of the roof above the stope resulted in roadway deformation. The instability of the cantilever-voussoir beam structure also intensified the roadway deformation. Finally, a support-surrounding rock mechanical model was established considering the behavior of an elastic cantilever beam. The required work resistance considering the bearing capacity of top coal were discussed, providing a basis for reasonable support selection. These research results can provide references for mining pressure and stratum movement control. Keywords Top coal caving Hard roof Cantilevervoussoir beam compound structure Mining-induced stress List of symbols Fj Pressure on the support, [kN] u Friction angle between rock blocks, [°] h Thickness of the block, [m] Q0 Total weight of the fractured block itself and its controlled overlying strata, [kN/m] hm Thickness of the coal, [m] kp Fracturing coefficient of the top coal
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