Micro-deformation and fracture evolution of in-situ coal affected by temperature, confining pressure, and differential stress

Abstract

The actual micro-deformation and fracture-evolution of in-situ coal seam are investigated in this paper through simulation experiment from three aspects: temperature, confining pressure, and differential stress. Firstly, the heatable triaxial-compressor is employed to reconstruct the evolutionary process of the coal seam. Then, the CT slices of the compressed samples in 3D, matching with the optical micrographs, are applied to analyze the coal micro-deformation. The effect of each factor on coal fracture evolution is discussed through CT models from the three-axis direction. Finally, this paper proposes the brittle & ductile deformation law of coal and the evolutionary pattern of tectonically deformed coals in the shallow crust. The main results are presented as follows: (1) The three factors have an individual mechanism on coal micro-deformation. Brittle deformation is independent of temperature and closely related to differential stress. Ductile deformation is divided into low-temperature and high-temperature. (2) Most fractures extend along the orientation similar to differential stress and always develop densely in the stress-concentrated region. These three factors in different stages have various effects on coal fracture evolution. (3) At low temperature, the evolutionary order of tectonically deformed coals is cataclastic-, schistose-, mortar-, granulitic-, scaly-, wrinkle-, and mylonitic coal; Ductile deformed coal evolves from parts of brittle deformed coal. These conclusions are helpful to understand the process of micro-deformation and fracture-evolution of in-situ coal.