In the process of coal mining, coal and gas outburst is one of the most severe disasters, which is accompanied by the outbursts of CO₂, CH₄, N₂, and other gases. Since the intensity of the outburst is affected by the adsorption characteristics of different gases, the study of the adsorption characteristics of multi-gas in the coal body is of great significance for the prevention and control of coal and gas dynamical outbursts in coal mining. In this paper, the self-developed adsorption-instantaneous pressure relief test system for gas-containing coal was used to study the damage characteristics of multi-gas in briquette adsorption-instantaneous pressure relief and to characterize coal adsorption expansion deformation and instantaneous pressure relief deformation quantitatively. The results showed that under the same temperature and pressure conditions, the adsorption expansion deformation capacities of different gases were in the order of CO₂ > CH₄ > N₂. With the increasing pressure of pressure relief, the damage of the coal body tended to be more significant. Although the briquette exhibited isotropic mechanical properties, the process of adsorption expansion deformation was not completely consistent with the isotropy of deformation, in which the axial strain was slightly larger than the radial strain. Moreover, it was found that the adsorption equilibrium time was positively correlated with gas pressure and gas adsorption characteristics.

Hydromechanical coupling in rock masses is an important issue for many rock mechanics and hydrogeology applications. The change of a water-bearing state will induce the fracture of the intact rocks and further accelerate the shear slip instability of the sheared surface. To investigate the weakening effect of water content on the mechanical properties of a rock mass, laboratory direct shear tests combined with three-dimensional analysis of sheared surfaces were carried out on sandstone samples with different water contents. The variogram parameters, sill and range, were applied to quantify the morphology of shear fracture surfaces, to reflect the shear failure process of the intact rock, and to provide a basis for resliding instability of jointed rock. It was determined that the sill represents the height of the fluctuation body in the fracture surface and the range represents the single fluctuation body and may reflect the frequency of fluctuations. The test results revealed that the increase in water content had a clear weakening effect on the shear strength and deformation behavior of rock, especially under saturated conditions. Moreover, the distribution of water in the samples directly affected the crack initiation and propagation and characteristics of the fracture morphology.

CO₂ is a potential fluid for absorbing and accumulating thermal energy; an accurate and fast calculation method for the heat capacity is essential for the study of the flow state near the critical point. However, the calculation of the heat capacity near the critical point by the equations suggested by NIST can easily be divergent, such as for CO₂, nitrogen, methane, etc. Therefore, an explicit fitting equation was studied. The fitting equation, which used density and temperature as variables and contained three constants, was derived from the nature of heat capacity change (molecular kinetic energy and potential energy). Based on the heat capacity data of the NIST WebBook, the heat capacity of CO₂ is taken as the example for the equation deduction and parameter fitting. The three constants were defined in order by Origin fitting software. By this new approach, it is found that the heat capacity at the critical point is below 1% deviant from that of the NIST WebBook. Moreover, the heat capacities that are difficult to be calculated in the NIST WebBook are well calculated. The study shows that the fitting equation is efficient for the prediction of heat capacity of gases near the critical point.