Abstract
Cyclic loading widely exists in coal mining activities, and it can significantly change the mechanical and seepage characteristics of coal. In this study, raw gas-bearing coal with different coal rank was mechanically tested under three stress paths: cyclic loading with stepwise increased peak stress (path 1), with step-by-step increased peak stress (path 2) and with crossed peak stress (path 3) using a tri-axial seepage testing machine. The acoustic emission (AE) signals under different loading and unloading paths indicate different mechanical properties of the coal sample. The Kaiser point is not a good indicator of the stress history of coal. The ratios of the quiet effect of the three coal samples under the three stress paths show that loading path 1 can increase defects such as micro-cracks in the coal samples (the AE quiet period decreases), while the other two paths decrease the number of defects (the AE quiet period increases). The cumulative dissipated energy of the coal shows an exponential growth with axial effective stress. The damping coefficient of coal first decreases then increases under cyclic loading. The damage variables can be used to predict the failure of coal samples, regardless of the stress path. Our results provide theoretical support and insight into the permeability increase mechanism and strengthened permeability increase mechanism of coal seams based on cyclic-loading-induced fracturing (repetitive hydraulic fracturing) under multiple protections and gas drainage engineering.
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Acknowledgments
This work is financially supported by the State Key Research Development Program of China (2017YFC0804206 and 2016YFC0801404), the National Natural Science Foundation of China (51674050 and 51704046), the National Science and Technology Major Project of China (2016ZX05043005), the Fundamental Research Funds for the Central Universities (2018CDQYZH0001 and 106112017CDJXY240001) and the Open Fund Research Project of State Key Laboratory Breeding Base for Mining Disaster Prevention and Control (MDPC201710). The authors thank the editor and anonymous reviewers very much for their valuable advices.
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Li, Q., Liang, Y., Zou, Q. et al. Acoustic Emission and Energy Dissipation Characteristics of Gas-Bearing Coal Samples Under Different Cyclic Loading Paths. Nat Resour Res 29, 1397–1412 (2020). https://doi.org/10.1007/s11053-019-09508-2
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DOI: https://doi.org/10.1007/s11053-019-09508-2