An Investigation on the Impact of Unloading Rate on Coal Mechanical Properties and Energy Evolution Law

Hongjun Guo, Zhongguang Sun, Ming Ji, Yongfeng Wu and Lihui Nian
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Hongjun Guo: Jiangsu Vocational Institute of Architectural Technology, Xuzhou 221116, China
Zhongguang Sun: State Key Laboratory of The Gas Disaster Detecting, Preventing and Emergency Controlling, Chongqing 400037, China
Ming Ji: Key Laboratory of Deep Coal Resource Mining, Ministry of Education of China, School of Mines, China University of Mining & Technology, Xuzhou 221116, China
Yongfeng Wu: Jiangsu Vocational Institute of Architectural Technology, Xuzhou 221116, China
Lihui Nian: Jiangsu Vocational Institute of Architectural Technology, Xuzhou 221116, China

IJERPH, 2022, vol. 19, issue 8, 1-11

Abstract: In order to further explore the relationship between the excavation speed and the damage of surrounding rocks and dynamic manifestation, the stress paths of unloading confining pressure and loading axial pressure were designed based on the changes in the roadway surrounding rock stress in this study. Additionally, the mechanical properties and energy evolution law of the coal body were investigated under various unloading rates. As the unloading rate increased, the mechanical properties of the coal body including the failure strength, the confining pressure, the axial strain, and horizontal strain tended to decrease at the rupture stage, while the volume strain and the elastic modulus increased, indicating that the rupture form evolved from the ductile failure to brittle failure. Regarding the energy, the axial pressure did positive work while the confining pressure did negative work, with the total work and the stored elastic strain energy decreasing. In addition, with the increase of the dissipation energy, the elastic strain energy conversion rate decreased linearly, indicating that the high unloading rate increased the possibility of dynamic disasters induced by the instantaneous brittle rupture of the coal body. On the other hand, due to the low releasable elastic strain energy stored in the coal body, the strength and probability of subsequent dynamic manifestation of coal body destruction were reduced. Therefore, increasing the excavation speed in a controllable way can benefit the safety of mining.

Keywords: coal body; the loading and unloading confining pressure of the shaft; the unloading rate of the confining pressure; mechanical properties; energy characteristics; roadway excavation (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2022
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