Permeability is one of the most important parameters for characterizing fluid flow and production from reservoirs. In this paper, experimental studies on the percolation, permeability, and adsorption of supercritical CO2 in coal seams were carried out, taking into account the effects of injection pressure and temperature, comparing the changes in longitudinal wave velocity of specimens before and after the tests, and analyzing the permeability effect of supercritical CO2 on raw coal specimens. The test results showed that when the volume stress was 36 MPa, the permeability of supercritical CO2 in coal increased by 93%, on average, compared with that of CO2. The modified D-R model was used to fit the adsorption data, and it was found that the excess adsorption capacity of supercritical CO2 by coal decreased with increased pressure, with a maximum value of approximately 8 MPa. When the temperature increased by 10°C, the adsorption capacity decreased by 8.3%, on average. In the subcritical CO2 state, the trend of excess CO2 adsorption in coal was consistent with that of absolute adsorption, which was 16% higher than that of excess adsorption, on average. After the action of supercritical CO2, the propagation velocity of the longitudinal wave in the sample decreased significantly, indicating that supercritical CO2 can effectively promote the development of pores and fractures in the coal sample, with an obvious anti-reflection effect on the coal seam and the best permeability enhancement effect at 35°C.

An accurate description of the mechanical properties and deformation characteristics of a structural plane of a rock mass with a large chamber or slope under the ultimate stress with periodic stress disturbances is of great significance to ensure the stability and safety of underground rock engineering. By theoretically analysing the strength effect of a structural plane of a rock mass under dynamic disturbance, a criterion for the occurrence of shear damage on a structural plane of a compressed rock mass under dynamic disturbance is proposed. The results of the cyclic disturbance kinetic test show that there is a disturbance threshold for the shear failure of the structural plane under different disturbance stresses. When the disturbance stress is lower than the disturbance threshold, the cumulative plastic strain stabilizes with an increasing number of cycles; when the disturbance stress is higher than the disturbance threshold, an S-shaped curve of cumulative plastic strain versus the number of cycles is observed, revealing the progressive damage process and mechanism of such a rock structure plane under periodic dynamic disturbance. Based on perturbation concept theory, the relationship between the accumulated plastic strain and the number of cyclic loadings is similar to the relationship between strain and time, the creep curve. A new nonlinear viscous element is proposed, and the nonlinear element and the deformation element considering structural plane closure and sliding are combined with the Burgers model to form an 8-element nonlinear viscoelastic‒plastic creep constitutive model. Using the global optimization algorithm of 1stOpt, model validation and parameter identification are performed on the experimental data, and the results show that the model curve has a very good agreement with the experimental data. The model can accurately reflect the deformation characteristics of a structural plane of a rock mass under periodic dynamic disturbance. These research results provide a new idea for analysing disturbance-induced geohazards.

To analyze the safety of geological engineering, experimental research on the mechanical properties of the rock joint plane is critical. In this paper, triaxial compression tests are carried out on rock specimens with the different prefabricated joint planes, including different dip angles, roughness, confining pressure and surrounding rock strength, and the strength characteristics, failure modes, stress evolution laws, and crack propagation laws are revealed. The test results show that when the specimen is damaged, the strain, peak stress, and residual strength all increase with the increase of roughness, confining pressure, and strength of surrounding rock but decrease significantly with the increase of joint plane angle. With the increase of stress, the stress-strain curve shows multiple fluctuations, indicating that the specimen occurs multiple slip-stable phenomena during the loading process. With the increase of the angle, the multiple cracks of the specimen gradually merge, and the cracks are always vertical to the joint plane, showing splitting failure. As the roughness of the joint plane increases, the possibility of the joint plane sliding becomes smaller, and the splitting mode of the specimen develops from multiple fractures to a single fracture. As the strength of the surrounding rock increases, the slope of the stress-strain curve gradually increases, and the splitting mode develops from a small number of single splits to multiple splitting penetration failures. The increase of the confining pressure significantly improves the failure strength of the specimen, and the crack number of the damaged specimen also increases significantly. The research results provide theoretical support for scientific analysis of the stability of underground engineering under the disturbance of fissures or faults.

Accurate description of the mechanical properties and deformation characteristics of the structural plane of a large chamber or slope rock mass under the ultimate stress with periodic stress disturbances is of great significance to ensure the stability and safety of underground rock engineering. By theoretically analyzing the strength effect of the structural face of a rock mass under dynamic disturbance, a criterion for the occurrence of shear damage on the structural face of a compressed rock mass under dynamic disturbance is proposed. The results of the cyclic disturbance kinetic test show that there is a disturbance threshold for the shear failure of the structural plane under different disturbance stresses. When the disturbance stress is lower than the disturbance threshold, Cumulative plastic strain stabilizes with increasing number of cycles; when the disturbance stress is higher than the disturbance threshold, S-shaped curve of cumulative plastic strain versus number of cycles. Revealing the progressive damage process and mechanism of rock structure surface under periodic dynamic disturbance. Based on the perturbation concept theory, the relationship between the accumulated plastic strain and the number of cyclic loading is similar to the relationship between strain and time in the creep curve of rocks, a new nonlinear viscous element is proposed, and the nonlinear element and the deformation element considering structural surface closure and sliding are combined with the Burgers model to form an 8-element nonlinear viscoelastic-plastic creep constitutive model. Using the global optimization algorithm of 1stOpt, the model validation and parameter identification are performed on the experimental data, and the results show that the model curve has a very good agreement with the experimental data. The model can accurately reflect the deformation characteristics of the structural plane of a rock mass under periodic dynamic disturbance. The research results give a new idea to analyze power disturbance-induced geohazards.

In order to study the energy evolution characteristics and damage mechanism of coal-rock assemblages with different inclination angles in the process of deformation and damage under different circumferential pressures. The test results show that: the damage of the specimens is mainly caused by bevel shear damage and tensile damage; the deformation and damage of the coal rock assemblage are distributed as a negative exponential function of the inclination angle, and the change of the surrounding pressure has a significant effect on the energy; based on the brittleness index value of the coal rock assemblage, the evolution of the brittleness index and Based on the brittleness index values, the evolution law between the brittleness index and the inclination angle and the surrounding pressure of coal rock assemblage is explored, and the mechanism of the change of inclination angle in the deformation and damage of coal rock assemblage with different inclination angles on the plastic yielding degree, energy dissipation level, crack extension and fracture speed in the pre-peak stage is revealed.