Abstract:

To deeply understand the true triaxial mechanical characteristics of coal-rock combinations under mining disturbance, the octahedral shear stress theory was adopted to systematically study the true triaxial mechanical characteristics and energy evolution mechanism of coal-rock combinations affected by the interface inclination angle during mining disturbance. Finally, based on Drucker-Prager criterion, a true triaxial damage constitutive model for coal-rock combinations considering the influence of the interface inclination angle was established. The results show that during the excavation disturbance stage, the axial strain of the coal-rock combination increases linearly with time. The energy is mainly converted into elastic energy, and the dissipative energy gradually increases as the strain increases. When the interface inclination angle exceeds 60°, the shear stress increases significantly, and the node of shear stress increase is postponed to the end of the excavation stage. During the mining stage, the energy of the specimen is mainly used for deformation and failure. When the interface inclination angle is less than 60°, the specimen undergoes two deformations before the shear stress reaches the strength limit. At the end of the mining disturbance, there are two sudden increase nodes in strain, and then the shear stress drops sharply, with the proportion of dissipative energy approaching 1. When the interface inclination angle is greater than 60°, the peak value of axial strain decreases, the sudden increase node of strain is postponed and is synchronized with the sudden drop node of shear stress, and the deformation and failure of the combination mainly depend on the rock mass part. After model verification, the goodness of fit is higher than 90%.

Key words: true triaxial, coal-rock combination specimen, mining disturbance, mechanical characteristic, constitutive model