THE MECHANICAL PROPERTIES AND DAMAGE MECHANISM OF GAS ADSORPTION AND DESORPTION ON WATER-SATURATED COAL SAMPLES

The work aimed to study the mechanical properties and damage mechanism of water-saturated coal samples under different gas pressures after adsorption and desorption. A Brazilian split test was conducted on water-saturated coal samples under laboratory conditions and different gas pressures during adsorption-desorption cycles. This allowed for the determination of mechanical damage parameters in coal samples subjected to varying gas pressures. Acoustic emission technology combined with digital speckles was used to explore the crack propagation and failure characteristics of coal samples. The microscopic morphology of cracks was observed by electron microscopy scanning, and the microscopic deterioration mechanism of the coal samples was clarified. As the gas adsorption-desorption pressures increased, the peak tensile strength and splitting modulus of coal samples gradually decreased. The damage parameters of coal were linearly related to the gas pressure. The failure mode of coal samples transitioned from tensile damage to shear damage. The maximum b gradually increased, while the ringing count decreased. The greater the gas pressure, the stronger the expansion stress of coal samples and the water-gas deterioration effect. The pore structures of original coal samples could be easily destroyed, which caused the development and penetration of internal cracks. The damage of coal samples showed obvious macroscopic cracks and severe fragmentation, and crack morphology was transformed from a flaky structure to a completely cracked structure. Based on the energy principle and the damaged medium concept, the deterioration model of coal samples was qualitatively analyzed to reveal the deterioration mechanism of the physical properties of coal. The research results can provide a reference for safe, efficient pressure-relief gas drainage by fracturing high-gas soft coal seams.