Effects of Gas Pressure on the Failure Characteristics of Coal

• Published in: Rock mechanics and rock engineering Vol. 50; no. 7; pp. 1711 - 1723
• Main Authors: Xie, Guangxiang, Yin, Zhiqiang, Wang, Lei, Hu, Zuxiang, Zhu, Chuanqi
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.07.2017; Springer Nature B.V
• Subjects: Acoustic emission; Civil Engineering; Coal; Compression; Compressive strength; Containers; Crack propagation; Crack tips; Cracks; Damage; Deformation; Deformation mechanisms; Dilatancy; Dissipation; Earth and Environmental Science; Earth Sciences; Electrons; Energy; Failure analysis; Failure modes; Fractals; Fracture mechanics; Fragmentation; Fragments; Gas pressure; Gases; Gauges; Geophysics/Geodesy; Mechanical properties; Mechanics; Original Paper; Pressure; Strain; Strain gauges; Stress-strain relationships; Stresses; Testing; Tips; Acoustic emission; Gas-containing coal; Stress intensity factor; Mass fractal; Digital image correlation; Strength
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-017-1194-2

Several experiments were conducted using self-developed equipment for visual gas–solid coupling mechanics. The raw coal specimens were stored in a container filled with gas (99% CH4) under different initial gas pressure conditions (0.0, 0.5, 1.0, and 1.5 MPa) for 24 h prior to testing. Then, the specimens were tested in a rock-testing machine, and the mechanical properties, surface deformation and failure modes were recorded using strain gauges, an acoustic emission (AE) system and a camera. An analysis of the fractals of fragments and dissipated energy was performed to understand the changes observed in the stress–strain and crack propagation behaviour of the gas-containing coal specimens. The results demonstrate that increased gas pressure leads to a reduction in the uniaxial compression strength (UCS) of gas-containing coal and the critical dilatancy stress. The AE, surface deformation and fractal analysis results show that the failure mode changes during the gas state. Interestingly, a higher initial gas pressure will cause the damaged cracks and failure of the gas-containing coal samples to become severe. The dissipated energy characteristic in the failure process of a gas-containing coal sample is analysed using a combination of fractal theory and energy principles. Using the theory of fracture mechanics, based on theoretical analyses and calculations, the stress intensity factor of crack tips increases as the gas pressure increases, which is the main cause of the reduction in the UCS and critical dilatancy stress and explains the influence of gas in coal failure. More serious failure is created in gas-containing coal under a high gas pressure and low exterior load.