Interaction Mechanism of the Upper and Lower Main Roofs with Different Properties in Close Coal Seams: A Case Study

Shengrong Xie, Yiyi Wu, Fangfang Guo, Dongdong Chen, En Wang, Xiao Zhang, Hang Zou, Ruipeng Liu, Xiang Ma and Shijun Li
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Shengrong Xie: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Yiyi Wu: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Fangfang Guo: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Dongdong Chen: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
En Wang: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Xiao Zhang: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Hang Zou: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Ruipeng Liu: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Xiang Ma: School of Energy and Mining Engineering, China University of Mining & Technology, Beijing 100083, China
Shijun Li: State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China

Energies, 2022, vol. 15, issue 15, 1-21

Abstract: Close-distance coal seams are widely distributed in China, and the mining of overlying coal seams leads to floor damage. To grasp the properties and the fracture spans of the damaged main roof in the underlying coal seam, combining the calculation of the floor damage depth with rock damage theory and the formulas for calculating the first and periodic weighting intervals of the damaged main roof and the instability conditions of the damaged key blocks are obtained. Three interaction stability mechanics models are proposed for key blocks with different properties of the upper and lower main roof, and the instability conditions of the lower damaged key blocks are obtained when the fracture lines overlap. When combined with a specific example, the field monitoring verified the calculation results. The research results are as follows: (1) The first and periodic weighting intervals, horizontal thrust between blocks, and critical load of instability of the damaged main roof are significantly reduced. Still, there are differences in its reduction under different loads, rotation angles, and lumpiness. (2) When the fracture lines of the upper and lower main roofs overlap, the stability of the damaged key blocks is the lowest. There are three linkage stability regions in the critical load curves of the two key blocks. (3) In this case, the damage equivalent of the main roof is 0.397, which belongs to the local damage type. Its first and periodic weighting intervals are 40 m and 16 m, which is 22% and 24% less than when there is no damage. (4) A supporting load of 0.489 MPa is required to maintain the stability of the upper key block, and the lower damaged key block is prone to rotary and sliding instability during the first and periodic weighting, respectively. Thus, the supports need to bear a total of 0.988 MPa and 0.761 MPa to maintain the stability of the two key blocks simultaneously. The ground pressure data monitored on-site is in accord with the calculation results.

Keywords: multi-coal seam mining; depth of floor damage; ultimate span of fracture; instability condition; linkage of key blocks; support bearing capacity (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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