Energy Evolution During Failure of Gassy Coals Under Uniaxial Compression

To determine the energy evolution of gassy primary and tectonic coals as well as their differences in energy during the deformation and failure processes, a primary coal sample and a briquette sample with properties and structure close to those of tectonic coal were subjected to uniaxial loading/unloading and gas release tests. The elastic energy and gas expansion energy of the two types of coal samples under various uniaxial stress conditions were accurately measured. The results show the following: as the axial stress changed, the elastic energy of both the primary coal and the briquette samples first increased and then decreased, and their gas expansion energy showed a trend of accelerated growth at an increasing rate through several stages. Throughout the stress–strain process, the elastic energy of the two types of coal samples was similar, but the gas expansion energy of the briquette sample was approximately 10 times that of the primary coal sample. Based on the test results, the relationships between the elastic and gas expansion energies and the damage variable were fitted. The fitting results show the same functional relationships for the primary coal and briquette samples, demonstrating that it is feasible to mathematically describe, based on the damage variable, the energy evolution in gassy coals as the stress changes.