https://orcid.org/0000-0001-8409-0661
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ABSTRACT
To evaluate the coal deformation characteristics and explore the evolution law of coal permeability under different conditions, the MTS815 and PCI-2 acoustic emission (AE) test systems were applied to conduct the triaxial percolation test under other thermo-mechanical coupling conditions, and the fractal model of coal fractal with integrated stress and temperature was established. The results indicated that the peak stress, strength and deformation parameters of the samples were positively correlated with the confining pressure. The temperature can promote the crack propagation, derivation and new cracks of coal samples. The macrocracks and percolation channels space inside the samples increased with the increase of the thermal-mechanical coupling condition. The AE signal was mainly released in the plastic and peak phases; the growth of confining pressure intensified the aggravation of the internal damage to the coal sample and caused the frequent occurrence of AE signals. The compressive coefficient Cf of coal fracture decreased with the addition of average effective stress, and the ruptured coal had the same trend with the increase in pore pressure; the calculated values of the new thermally sensitive model were consistent with the measured values. The applicability of the theoretical mechanism and the data matching were of high credibility.
Nomenclature
Symbols
| D | = | Fractal dimension (%) |
| C | = | Matrix compressibility (%) |
| H | = | Height of the coal sample (cm) |
| K | = | Coal matrix rigidity modulus (MPa) |
| T | = | Temperature (K) |
| V | = | Volume (μm3) |
| P | = | Pressure (MPa) |
| K | = | Knudsen coefficient (%) |
| l | = | Mean molecular free path (μm) |
| L | = | Side length of the matrix unit (μm) |
| A | = | Total area of the pores (μm2) |
| K | = | Permeability (μm2) |
| c | = | Width of the coal matrix (μm) |
| d | = | Crack width (μm) |
| r | = | Radius of the coal sample (cm) |
| α | = | Thermal expansion coefficient (K–1) |
| ϕ | = | Diameter of the coal sample (cm) |
| η | = | Temperature sensitivity coefficient of fractal dimension (%) |
| σ | = | Stress (MPa) |
| λ | = | Pore diameter (μm) |
| μ | = | Dynamic viscosity coefficient (%) |
| γ | = | The average absolute deviation ratio (%) |
| ε | = | Strain (%) |
| φ | = | Porosity (%) |
Abbreviations
| AE | = | Acoustic emission |
| CSC | = | Coal spontaneous combustion |
Subscripts and superscripts
| t | = | Thermal |
| 0 | = | Initial or minimum value of the relevant parameter |
| f | = | Fracture |
| e | = | Effective |
| m | = | Matrix |
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
Notes on contributors
Xin Yi
Xin Yi was Born in Wuhan, Hubei, China, in 1978. She received a bachelor’s degree in ventilation engineering in 2006. In 2009, she received a master’s in safety engineering from Xi’an University of Science and Technology, specializing in thermal damage/coal spontaneous combustion; in 2014, she got a doctorate degree from Xi’an University of Architecture and Technology, specializing in ventilation and air-conditioning engineering. Since then, she has been an associate professor in the Department of Safety Engineering of Xi’an University of Science and Technology. Her research interests are mine thermal hazard management and coal spontaneous combustion prevention.
Yao Ren
Yao Ren was a graduate of Xi’an University of Science and Technology, where she studied Safety Engineering. For the last 3 years, her research has focused on the performance improvement of coal spontaneous combustion prevention.
Yang Xiao
Yang Xiao was born in July 1979, in Meitan, Guizhou, China. Ph.D., professor-level senior engineer, doctoral supervisor, visiting scholar at De Montfort University in the UK, visiting scholar at Yunlin University of Science and Technology in Taiwan. Winner of the International Mannan Prize, member of the National Science and Technology Experts Bank, Fellow of the Royal Society of Chemistry (FRSC), Fellow of the British Engineering and Technology Society (FIET). Mainly engaged in the research and application of coal fire disaster mechanism and prevention technology.
Lei Ren
Lei Ren was a graduate of Gansu University of Chinese Medicine, her research has focused on the health hazards of air pollution and its prevention and treatment.
Mengfan Zhang
Mengfan Zhang was a graduate of Xi’an University of Science and Technology, and her current research interests include building fire prevention and the performance improvement of coal spontaneous combustion prevention.
Linchun Yang
Linchun Yang was a graduate of the Northwestern Polytechnical University, where he studied Automation. In his college years, his research has focused on the superpixel segmentation.