Temporal and spatial characteristics of raw coal deformation during the adsorption of CH4/N2 under triaxial stress

In order to further study the temporal and spatial characteristics of coal deformation during the interaction between loaded coal and CH4/N2. The dynamic test of adsorption capacity and adsorption deformation of raw coal adsorbing CH4/N2 and its binary mixture under triaxial stress loading were carried out. The results showed that the adsorption capacity of CH4 in raw coal was greater than that of N2 under constant triaxial stress. The adsorption capacity of binary mixed gas was between that of pure gas. There was anisotropy in the adsorption expansion deformation of raw coal under triaxial stress. Under different gas injection pressure conditions, the axial/circumferential strain of raw coal presented the same evolution law with the adsorption time. The axial strain of the gas injection end could be divided into 5 stages, and the axial/circumferential strain in the middle and exhaust ends of the coal sample could be divided into 3 stages. Under the same gas injection pressure, when raw coal adsorbed gas, the time order of axial strain changed from negative to positive in each measuring point was CH4, CH4/N2 mixed gas, N2. When the raw coal adsorbed CH4, N2 and CH4/N2 mixed gas, the axial/circumferential strain of raw coal increased with the increase of adsorption capacity in the order of exponential function, unary linear function and unary quadratic function. After triaxial stress loading, the axial/circumferential initial strain of raw coal was different, and the initial strain of the raw coal was distributed was small at both ends and large in the middle. When raw coal adsorbed CH4 under triaxial stress, the expansion deformation ability was stronger, it had large reduction of surface free energy, and obvious reduction of coal strength, which made it more prone to deformation and failure. © 2023 China University of Mining and Technology. All rights reserved.