In this paper, to reflect a real fire combustion situation of stilted buildings with a typical wooden structure, we used FDS numerical simulation software to study the suppression effect of a fine-water-mist fire-extinguishing system under different working conditions. The influences of different mist droplet diameters, spray flows, and nozzle densities on the temperature change in the combustion area were analyzed and compared. The particle sizes of fog droplets exhibited a significant impact, indicating that the smaller the particle size, the faster the vaporization rate and the better the cooling effect. The cooling effect was better when the particle size was 150 μm or less when compared to the particle sizes of 200 and 300 μm. As the spray flow rate and nozzle density were increased, the fire field temperature decreased, and the cooling effect was enhanced, optimal at a water-mist flow rate of 8 L/min. Therefore, given the possible working conditions, the spray flow rate and the nozzle density should be high, while a suitable droplet size should be selected to achieve the best fire-extinguishing effect.

This study presents the fire performance of typical components of wood structure buildings. The wooden beams and floor slabs, quite common in wood structure buildings, were burned with different fire exposure times by a pool fire source. Then, the surface temperature evolution and the charring rate were recorded and analyzed. The results show that the flashover and re-ignition phenomenon occurred in all wood materials under the burning pool fires. The glulam beam cross-section was U-shaped, and the maximum charring rates of glulam beam, cross-laminated timber floor, and cross-laminated timber partition board were 0.833 mm/min, 1.538 mm/min, and 0.435 mm/min, respectively. It can be seen that the combustion behavior time of specimens with different cross-section thicknesses is different. If the thickness of the specimens is appropriately increased, their combustion behavior time can be significantly improved.

To address the difficult problem of coal seam gas control that has arisen as a result of the recent development of deep coal mining, hydraulic fracturing technology is applied to the coal seam, the dual porous medium theory is used, and a multi-scale flow model of coal gas is constructed under certain assumptions. The dynamic evolution law of coal porosity and permeability is studied according to the gas multi-scale diffusion equation, gas-bearing coal seepage equation, and other theories. To study the variation law of important parameters such as coal seam pressure and drainage influence range in the process of coal and gas drainage, numerical simulation software is used, and industrial tests are supplemented to verify energy efficiency. The study found that using hydraulic fracturing technology to enhance the permeability of coal seams can significantly improve the average gas extraction concentration, and the maximum increase in the extraction net flow after fracturing is about 60% compared with that no fracturing, and can effectively suppress the attenuation of the extraction flow due to the extension of the extraction time, effectively improving the gas extraction effect of the test borehole. Simultaneously, if other auxiliary measures are implemented, the permeability enhancement effect may be more stable.

It is very important to study the influence of water content on the mechanical properties of coal rock to prevent rock burst and roadway instability under dynamic disturbance. In this study, the split Hopkinson pressure bar (SHPB) test system was applied to conduct three-dimensional dynamic and static impact tests on natural and water-saturated coal samples at different strain rates to determine the dynamic mechanical properties of a series of water-bearing coal samples. Based on the new data, we discuss the strength, deformation, crushing energy dissipation, and fractal characteristics of natural and saturated coal rocks. We specifically focus on the different effects of hydraulic pressure on crack propagation under static and dynamic loads. Our results document a well-defined linear relationship between the peak stress and the strain rate of coal in the natural state and the water-saturated state. Once the impact rate reaches a certain value, a double peak phenomenon is observed, and the curve shows a certain leap. The critical impact velocity of the curve leap is ca. 9.485~10.025 m/s. At the same strain rate, the average peak stress in the water-saturated state is ca. 2.684% higher than that in the natural state. The secant modulus of the two states generally increases with the rise in strain rate, but the scatter of the results is large. The average secant modulus of the water-saturated coal sample increases by 2.309% compared with the natural state. The energy consumption density and absorbed energy of saturated and natural coal samples rise with the increase in strain rate, and both show a well-defined power–function relationship. However, under the same condition, the absorbed energy and absorbed energy density of water-saturated coal samples are higher than that of natural coal samples. The fractal dimension of water-saturated coal rises with the increase in strain rate and energy consumption density, showing a strong linear and quadratic relationship, respectively. Under dynamic loading, the cohesive force, jointly generated by free water and the Stefan effect, hinder the expansion of coal and rock fractures, thus improving the compressive strength of coal and rock. The study provides a reliable theoretical basis for preventing rock burst and providing roadway support.

Sealing materials play an important role in the safety of coal mine production. To improve the efficiency of coal mine gas mining, it is necessary to optimize the performance of the sealing materials. In order to develop new sealing materials with better performance, it is necessary to improve the formula of the cement materials. In this study, poly­(vinyl alcohol) fiber (PVAF), polypropylene fiber (PPF), nanosilica (NS), and their composite materials were added to the composite cement-based materials of Portland cement and sulphoaluminate cement, respectively, and a new cement-based hole sealing material was prepared. The effects of these additives on fluidity, setting time, and compressive strength of cement-based sealing materials were studied through experiments. X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and pore size analysis were used to study the influence of composite fiber and nanosilica on the properties of the cement system. The results show that PVAF, PPF, and NS all effectively improve the mechanical properties and stability of the cement system, in which PPF: PVAF = 3:1 and the content of nanosilica ranges from 0% to 3%, and the performance of the cement system can be improved. When the content of NS is 3%, PPF is 0.05%, and PVAF is 0.15%, the compressive strength at 28 days reaches 30.5 MPa. The addition of NS can make the hydration degree of cement materials higher, and PVAF and PPF can improve the distribution of hydration products, reduce the generation of harmful pores with pore size greater than 10 nm in the cement pore system, and significantly improve the properties of materials. This effectively maintains the stability of the borehole in the process of gas drainage, improves the gas drainage concentration of the borehole, and enhances the gas drainage effect.