Mechanical properties and permeability evolution of gas-bearing coal under phased variable speed loading and unloading
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ORIGINAL PAPER
Mechanical properties and permeability evolution of gas-bearing coal under phased variable speed loading and unloading Chengpeng Xin 1,2,3 & Kai Wang 1,2,4 & Feng Du 1,2 & Xiang Zhang 1,2 & Gongda Wang 5 & Yilei Liu 3 Received: 8 February 2018 / Accepted: 23 November 2018 # Saudi Society for Geosciences 2018
Abstract It is of great significance for the analysis and prediction of coal-gas outburst disasters to understand the mechanical properties and permeability evolution of coal and rock under conditions of stope stress evolution. In this study, mechanical tests were conducted on gas-bearing coal under four stress paths, including conventional triaxial compression (CTC), phased variable speed triaxial compression (PVSTC), unloading confining pressure (UCP), and phased variable speed unloading confining pressure (PVSUCP), simultaneously measuring the permeability in mechanical tests. The mechanical properties and permeability evolutions in gas-bearing coal under four different stress paths were compared. The obtained results show that the deviatoric stressstrain curves of gas-bearing coal under four stress paths could be divided into five stages: compaction, linear elasticity, plastic deformation, stress drop, and residual stress stage. The permeability-strain curves under four stress paths could also be divided into five stages: fast drop, slow decrease, slow increase, sharp increase, and slowed growth. Compared to the CTC conditions, the peak strain and strength of coal under PVSTC conditions increased. Furthermore, the stress drop and energy release under PVSTC were more intense at the moment of instability failure. Compared to both loading paths, the coal was damaged more rapidly under unloading paths and the damage was stronger. Additionally, among both unloading paths, the time required for the failure of coal under PVSUCP was shorter than that under UCP, while the damage under PVSUCP was stronger. The strength characteristics of the gas-bearing coal under PVSTC and PVSUCP still met the Mohr–Coulomb criterion. This preliminary study has guiding significance for the understanding of the co-occurrence mechanisms of coal-gas outburst disasters. Keywords Gas-bearing coal . Triaxial compression . Unloading confining . Phased variable speed . Mechanical properties . Permeability
* Kai Wang [email protected]
Abbreviations CTC Conventional triaxial compression PVSTC Phased variable speed triaxial compression UCP Unloading confining pressure PVSUCP Phased variable speed unloading confining pressure
Feng Du [email protected]; [email protected] 1
Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining and Technology (Beijing), Beijing 100083, China
2
School of Resource & Safety Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China
3
School of Mining Engineering, Guizhou University of Engineering Science, Bijie 551700, China
4
Hebei State Key Laboratory of Mine Disaster Prevention, North China Institute of S
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