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Processes 2018, 6(9), 146; https://doi.org/10.3390/pr6090146

A Numerical Study of Stress Distribution and Fracture Development above a Protective Coal Seam in Longwall Mining

1
International Engineering Company of China Coal Technology and Engineering Group, Beijing 100013, China
2
College of Resources and Safety Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
3
Department of Mining and Mineral Resources Engineering, Southern Illinois University, Carbondale, IL 62901, USA
4
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada
*
Author to whom correspondence should be addressed.
Received: 7 August 2018 / Revised: 16 August 2018 / Accepted: 17 August 2018 / Published: 1 September 2018
(This article belongs to the Special Issue Fluid Flow in Fractured Porous Media)
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Abstract

Coal and gas outbursts are serious safety concerns in the Chinese coal industry. Mining of the upper or lower protective coal seams has been widely used to minimize this problem. This paper presents new findings from longwall mining-induced fractures, stress distribution changes in roof strata, strata movement and gas flow dynamics after the lower protective coal seam is extracted in a deep underground coal mine in Jincheng, China. Two Flac3D models with varying gob loading characteristics as a function of face advance were analyzed to assess the effect of gob behavior on stress relief in the protected coal seam. The gob behavior in the models is incorporated by applying variable force to the floor and roof behind the longwall face to simulate gob loading characteristics in the field. The influence of mining height on the stress-relief in protected coal seam is also incorporated. The stress relief coefficient and relief angle were introduced as two essential parameters to evaluate the stress relief effect in different regions of protected coal seam. The results showed that the rock mass above the protective coal seam can be divided into five zones in the horizontal direction, i.e. pre-mining zone, compression zone, expansion zone, recovery zone and re-compacted zone. The volume expansion or the dilation zone with high gas concentration is the best location to drill boreholes for gas drainage in both the protected coal seam and the protective coal seam. The research results are helpful to understand the gas flow mechanism around the coal seam and guide industry people to optimize borehole layouts in order to eliminate the coal and gas outburst hazard. The gas drainage programs are provided in the final section. View Full-Text
Keywords: longwall mining; gob behaviors; stress relief; permeability; gas drainage longwall mining; gob behaviors; stress relief; permeability; gas drainage
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Zhang, C.; Yu, L.; Feng, R.; Zhang, Y.; Zhang, G. A Numerical Study of Stress Distribution and Fracture Development above a Protective Coal Seam in Longwall Mining. Processes 2018, 6, 146.

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