Airtight walls are vital to prevent spontaneous combustion of residual coal as caused by air leakage. A new type of foamed concrete (FC) was developed to control air leakage. FC specimens of four densities (250, 450, 650, and 850 kg/m³) were prepared for use in a series of physical and mechanical tests. A thickener was used to control the FC shrinkage and collapse. The permeability of the FC decreased approximately exponentially with an increasing density. On the contrary, the compressive strength (σ) and elastic modulus (E) increased in exponential and linear relationship separately with the increase in density, under uniaxial compression conditions. Under triaxial compression, the compressive strength of the FC increased with an increase in confining pressure and appeared slight plastic. The impact experiment showed that the dynamic compressive strength of the FC appeared to be strain‐rate dependent, and it increased with an increase in the strain rate and pressure under a confining pressure. Without a confining pressure, the variation in compressive strength exhibited a slow decrease. Applied FC resulted in a 5 MPa 28‐day compressive strength of the airtight wall with no remaining fissures and with air leakage suppression to the gob.

Mining high-gas coal seams in China has the characteristics mining of deep, high storage and low permeability, and low drainage efficiency, which seriously restrict the efficient prevention and control of mine gas disasters. Based on the characteristics of low viscosity and permeability, phase change pressurization, and strong adsorption potential energy of liquid CO₂, the technology system of liquid CO₂ displacement for high-gas and low-permeability coal seam was developed, and field industrial of low-pressure (0.52.5MPa) and medium-pressure (2.515.0MPa) combined injection test was carried out. In this test, the mode of injection followed by drainage was adopted, and the gas drainage effect was investigated for 30 days. The test results show that the effective influence radius of CO₂ in this test is 20m, and the liquid seepage radius is 5 to 7m. After the injection of liquid CO₂ into coal seam, the average gas drainage concentration and drainage purity of all drainage holes were increased by 3.2 and 3.4 times, respectively, and the gas promotion effect was significant. Taking the liquid CO₂ low-medium-pressure displacement gas test area as the calculation unit, from the comprehensive benefit analysis, compared with the original drainage mode, the liquid CO₂-combined pressure injection process can save 34.7 of the engineering cost and shorten the gas drainage standard time by 45.9. Therefore, the application of this technology has important technical support and reference significance for the efficient management of gas in the same type of mine.