Hydraulic measures are extensively employed in coal mining to enhance the permeability of coal seams and facilitate gas extraction, a practice of paramount importance in the prevention and control of gas disasters. However, external water intrusion will alter the desorption and migration laws of gas in coal. The extant research has not yet clarified the optimal water injection parameters of coal samples with different particle sizes, nor has it quantitatively characterized the inhibitory effect of water on gas desorption. Additionally, the conventional experimental apparatus employed in this study utilizes multi-directional water-bearing coal samples that are filled with gas, which is not consistent with the actual process of water injection in gas-bearing coal seams. The uneven distribution of water in the coal sample has a significant impact on the repeatability and reliability of the experiment. Consequently, this paper independently designs a set of gas-containing coal water injection-desorption experimental systems. This study aims to optimize the water injection parameters of coal samples of varying size, to analyze the gas desorption law under the action of water, to provide an experimental basis for water injection and outburst prevention, and to construct a practical teaching platform for mine safety engineering courses.

In this study, an experimental apparatus was developed, comprising a vacuum degassing system, a gas-water injection system, a stirring and isothermal adsorption equilibrium system, and a gas desorption test system, which was self-built. The apparatus is capable of simulating the on-site water injection process and the uniform wetting of coal samples. Four distinct particle sizes (0.1–0.2 mm, 0.2–0.6 mm, 0.6–1 mm, 1–3 mm) were obtained by crushing and screening coal samples from the Qinshui Basin, and subsequent industrial analysis was conducted. The single-factor variable method is employed to investigate the impact of water injection flow rate, stirring speed, stirring time, and gas adsorption equilibrium pressure on the wetting uniformity of coal samples. The standard deviation of the water content at six measuring points in the coal sample tank is employed to assess the wetting uniformity. In accordance with the optimal water injection parameters, six levels of water content (1%, 2%, 4%, 6%, 8%, and 10%) were utilized in conjunction with the adsorption equilibrium pressure of 1 MPa to execute gas desorption experiments. The variation characteristics of the gas desorption amount of coal samples with varying particle sizes over time were obtained.

The experimental findings demonstrate that the wetting uniformity of coal samples is influenced by the water injection flow rate, stirring speed, and stirring time. The optimal parameters for different particle sizes exhibit slight variations. The equilibrium pressure of gas adsorption exerts a negligible influence on the wetting uniformity. The wetting uniformity of the 1–3 mm coal sample is optimal when the water injection flow rate is set at 1.0 mL/min, the stirring speed is maintained at 20 rpm, and the stirring time is extended to 90 min. The optimal water injection flow rate of 0.6–1 mm, 0.2–0.6 mm, and 0.1–0.2 mm coal samples is 1.2 mL/min, and the optimal stirring speed is 20 rpm. The optimal mixing time for coal samples with a diameter of 0.6-1 mm and 0.2–0.6 mm is 90 min, while for coal samples with a diameter of 0.1–0.2 mm, the optimal mixing time is 120 min. The presence of water has a substantial inhibitory effect on gas desorption. As the water content increases from 1% to 10%, the total gas desorption amount gradually decreases within 120 min. The initial decrease is substantial, while the subsequent period tends to be more gradual. A comparison of the water content at 1% with the cumulative gas desorption amount indicates a decrease of 12.00%, 28.29%, 44.07%, 57.83%, and 63.12%, respectively, when the water content was 2%, 4%, 6%, 8%, and 10%. The experimental findings demonstrate that the inhibitory effect increases in proportion to the increase in water content; however, this increase exhibits a gradual decline.

The research demonstrates the efficacy of the self-developed experimental system in simulating the field water injection process, achieving uniform wetting of coal samples, and enhancing the repeatability and reliability of experimental results. The optimal water injection parameters of coal samples with different particle sizes obtained in this paper can provide a precise parameter basis for on-site water injection outburst prevention projects. Water injection effectively suppresses the rapid desorption of gas in high gas or outburst coal seams, mitigating the risk of coal and gas outbursts. This assertion is substantiated by both theoretical and experimental evidence, providing a robust foundation for gas disaster control measures. Moreover, this paper presents an experimental apparatus for the instruction of mining safety engineering, thereby enabling students to engage in the entirety of the experiment. This approach facilitates an in-depth comprehension of the coal-water-gas interaction mechanism, cultivates proficiency in engineering-oriented experimental methodologies, resolves the discrepancy between theoretical and practical learning in conventional teaching methods, and enhances students’ engineering practice abilities and innovative thinking.

To reflect a more similar original stress environment and to make the research on the influence of gas on the mechanical properties of coal bodies in the coal mining process more convincing, a triaxial stress loading experiment on gas-containing coal is introduced. On the one hand, the experimental teaching scheme for studying the strength and deformation characteristics of coal based on the triaxial stress loading experiment can be concretized. On the other hand, it can be helpful for students to understand the mechanical characteristics and adsorption deformation characteristics of gas-containing coal, which lays a foundation for subsequent in-depth research.

In this study, with the help of a coupling instrument to measure the adsorption, mechanics, and seepage characteristics of coal, the actual stress environment of coal is simulated by adjusting the loading module and the triaxial stress loading experiment on coal under different confining stress and gas pressure conditions is carried out. Among them, the magnitude of the axial stress and confining stress applied to the coal body can be achieved accurately by adjusting the hydraulic pump, and the required gas pressure can be achieved by adjusting the valve of the gas cylinder. First, the coal samples are sealed in the equipment, and the confining stress and gas pressure are adjusted to the target values. Second, the axial stress is continuously loaded until the coal body is damaged. Finally, according to the automatically recorded full stress–strain curves of coal samples, the specific values of peak stress, axial strain, radial strain, and volumetric strain of coal under different initial conditions can be obtained. Then, the maximum and minimum principal stress values under different stress conditions are plotted in a Cartesian coordinate system and fitted using the Mohr–Coulomb formula, and the cohesive force and internal friction angle of coal samples can be calculated. In addition, the weakening law of the free gas and adsorbed gas on the strength of the coal body can be obtained.

Notably, the free and adsorbed gases have a certain degree of weakening on the strength of the coal body, and the effect of free gas is more obvious. In addition, the change of the confining stress can also affect the weakening ability of gas. When the confining stress increases, the weakening rate of the coal strength by gas slightly decreases. Furthermore, with the help of a theoretical calculation method and a laboratory test method, the adsorption volumetric strain of the coal body is obtained. The result of the theoretical calculation method is smaller than that of the laboratory test method because the calculated bulk strain value arising from the effective stress is slightly lower than the actual value.

The application of the triaxial stress loading experiment on gas-containing coal enriches the research process of coal body mechanical properties. In addition, by introducing the coupled adsorption–mechanics–seepage characterization system into the experimental teaching in the mine safety engineering course, a platform combining practice and theory has been set up, which not only facilitates the investigation of the mechanical properties and adsorption deformation of gas-containing coal but also provides an interactive platform for students to cultivate their innovative thinking.