Longwall Top Coal Caving Mechanisms in the Fractured Thick Coal Seam
Publication: International Journal of Geomechanics
Volume 20, Issue 8
Abstract
In this study, the finite difference method (FDM) coupled with a discrete fracture network (DFN) was utilized to analyze longwall top coal caving (LTCC) behaviors. The integrated FDM–DFN model enabled the influence of the preexisting fracture, stress redistribution, stress rotation, caving material compaction, and periodic rupture of roof strata to be superimposed on the failure process of top coal. It was revealed the LTCC influenced both magnitude and orientation of the principal stress within top coal. The minor and major principal stresses experienced successive peak points as top coal approached the LTCC face, and the corresponding principal axes rotated toward horizontal and vertical directions, respectively. The concentration of the major principal stress and the release of the minor principal stress resulted in the shear failure of top coal ahead of the LTCC face. The failure mode transferred from shear to tension at the rear of the face line. The principal stress rotation led to continuous variation in internal cohesion of top coal and brittle fracturing of the main roof resulted in dynamic load at the LTCC face. The stress rotation and roof rupture greatly promoted the failure process of top coal. This type of promotion was also provided by the preexisting fractures and adjacent goaf.
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Acknowledgments
This study is sponsored by the National Key Research and Development Program of China (Grant No. 2017YFC0603002) and the National Natural Science Foundation of China (No. 51674264). The authors are grateful for their support.
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Published In
International Journal of Geomechanics
Volume 20 • Issue 8 • August 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Mar 17, 2019
Accepted: Jan 16, 2020
Published online: May 20, 2020
Published in print: Aug 1, 2020
Discussion open until: Oct 20, 2020
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