Outburst Precursor Characteristics of Loaded Coal: Analysis of Coal Damage and Fracture Degree from the Perspective of Energy

Coal and gas outburst (referred to as “outburst”) is induced by damage and failure of loaded outburst coal under internal and external stress. To further clarify the specific role of the elastic strain energy generated by the principal stress in the process of coal damage and fracture, from the perspective of the energy relationship between uniaxial compression test and outburst test, taking the outburst coal seam of Pingmei No. 11 Coal Mine as the research object, uniaxial compression test and true triaxial outburst simulation test were carried out. The damage evolution law of outburst coal is clarified using the characteristic parameters of acoustic emission. According to the characteristic stress and in-situ stress, the energy calculation of uniaxial specimen and outburst coal is carried out, and the specific damage degree of elastic strain energy to outburst coal is clarified. The results indicate that: (1) When the stress level reaches the crack initiation stress σ_ci, the damage begins to accumulate. When the stress level reaches the damage stress σ_cd, the coal sample strength begins to deteriorate. (2) The strain in the process of outburst coal damage and fracture can be described by referring to the relationship equation between strain and gas pressure and the variation of test gas pressure. (3) It is determined that the degree of damage and fracture caused by the outburst elastic strain energy to the coal sample is at the end of the stable crack propagation stage.