Abstract:
The coal rock contains a variety of bedding structures, and typically shows transversely isotropic characteristics at the macroscopic level, which has a significant influence on the damage and energy evolution of the coal rock. Based on the energy dissipation theory, the elastic-plastic strains, damage variables and energy expressions for the deformation and damage process of coal rocks with different bedding dip angles were deduced, and the energy dissipation-damage constitutive model was established considering different bedding dip angles, which quantitatively characterizes the correspondence between bedding dip angles, damage variables and peak energies, and the effects of bedding dip angle on the mechanical and energetic response characteristics of coal rocks under loading were investigated. The results showed that the energy conversion of coal rock with different bedding dip angles showed a stage-by-stage evolution, corresponding to different damage stages; under the conditions of constant axial pressure unloading confining pressure and conventional triaxial loading with different confining pressures, the peak elastic energy and dissipation energy showed a U-shaped trend of decreasing and then increasing with the increase of bedding dip angle, which basically corresponds to the change of the peak strength of coal rock with the change of bedding dip angle. The changes of the peak strength of coal rock with the bedding dip angle basically corresponded to the changes of the bedding dip angle, and the changes were most sensitive when the bedding dip angle is 60°−90° and 45°−90° under the two conditions respectively, which is manifested in the anisotropy of the energy angle. According to the energy dissipation process of coal rocks with different bedding dip angles, the energy dissipation-damage constitutive model considering bedding dip angle was further constructed, and the published test data were quoted for verification and analysis. The results showed that the model can better describe the deformation and damage characteristics of coal rocks with different bedding dip angles under the loading conditions of conventional triaxial compression and constant axial pressure unloading confining pressure, which indicates that the constructed model has better applicability. The evolution of dissipation energy
Ud and damage variable
D of coal rocks with different bedding dip angles showed good consistency. With the increase of axial strain, both of them went through the process from slow to sharp and then tend to be gentle, showing a general “S” shaped change trend. With the increase of bedding dip angle, the damage variable
D and dissipated energy
Ud both showed a "U" trend of a first decrease and then increase, and when the bedding dip angle is 90°, coal rocks with different bedding dip angles have a "U" trend of decreasing and then increasing. When the dip angle of the bedding is 90°, the peak dissipation
Ud and the damage variable
D reached the maximum value, and the coal rock was extremely vulnerable to damage. The results of the study can be used as a reference for exploring the law of mine pressure behavior, the induced mechanism of coal roadway gang instability and the prevention of mine disasters such as pressure bump.