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Due to the typical instability characteristics of the slope, slope coal mining will further aggravate the deformation and instability of the slope. Therefore, we use FLAC3D slope structure model to analyze and predict the deformation, failure and stability of the slope coal under different mining conditions. The result shows that the expansion form and range of the plastic zone of the rock mass inside the slope are different different mining conditions, and the disturbance and damage to the slope flat plate are also different; compared with the downhill stoping, the uphill stoping is worse than the downhill stoping in terms of length and slope stability; the downhill stoping can ensure the stability of the slope to a certain extent; although there is a local slip phenomenon, the overall stability is better, and the instability phenomenon exists in the reverse slope mining slope; the upper coal seam mining slope has local instability, and the overall stability is good. The lower coal seam plastic zone is far away from the slope flat plate, and its stability is better than that of the upper coal seam. It can be concluded that the slope stability is related to the mining depth. The greater the mining depth, the better the slope stability.

In the process of side-wall coal mining, the rock mass of slope undergoes complex mechanical evolution, which involves the change of original rock stress, the extension of deformation failure zone, the stability of slope and so on. Therefore, it is very important to choose proper mining direction and effective control measures for the stability of side slope. In view of the above problems, we propose two schemes to control the stability of side slope, which is backfill pressure foot and partial backfill in reverse slope. The results show that the deformation, failure and stability of side-slope coal are related to the direction of mining, and the strength and depth of rock mass failure area are weaker than that of reverse-slope coal mining, and the overall stability is better, the stability of the mining slope in reverse slope will attenuate, resulting in the shear instability of the flat plate, and the length of the working face is smaller than that of the mining along slope, so the mining along slope is better than that in reverse slope according to the development and stability of the slope deformation and failure area of the two stoping schemes, the backfilling foot and the local backfilling scheme are proposed to control the slope stability, the backfilling foot can change the original structure shape of the slope, so that the movement of the rock mass inside the slope can be alleviated, and the development of the failure area can be controlled, it can effectively support the deformed rock mass inside the slope, restrain the extension of the failure area, slow down the failure caused by the working face, and finally control the stability of the slope.

In order to find out the influence of water immersion and air drying process on the macroscopic characteristics and microstructure changes of coal spontaneous combustion, the low-temperature oxidation characteristics of non-caking raw coal and long-term soaked and air-dried coal were experimentally studied, and the effects of soaking time and particle size on the gas generation and activation energy of coal during the oxidation heating process were analyzed. As an explanation in support of the influence of water immersion on the spontaneous combustion and oxidation characteristics of coal, the variation of relative content of oxygen-containing functional groups and the mechanism of gas generation were analyzed. The results indicated that CO and CO2 are the main components of the gas generated by coal oxidation reaction. Compared with raw coal, the gas production of coal samples after 90 days and 180 days soaking and air-drying is higher in the process of oxidation heating. In the accelerated oxidation stage, the activation energy decreased by 2.72 kJ/mol and 35.74 kJ/mol, respectively, which indicates that the coal sample after long-term soaking has a higher spontaneous combustion tendency than that after short-term soaking. Water plays a promoting role in the formation of oxygen-containing complexes, resulting in the relative content of oxygen-containing functional groups in soaked coal being higher than that of raw coal. Meanwhile, -COOH and C=O are the main sources of CO2 and CO respectively, which could explain the phenomenon of higher concentration of CO2 and CO produced by soaked coal than that by raw coal.

To investigate the combustion characteristics of multiple fire sources in the tunnel caused by 'jumping' discontinuous fire spread, we utilized scaled model experiments, numerical simulation software, and theoretical research. Our study focused on analyzing the influence of different fire source powers on the temperature characteristics of double fire sources in the tunnel. We examined the temperature characteristics, critical wind speed, and change rule under various wind speeds, fire source spacing, and fire source powers. Additionally, we explored the temperature characteristics, critical wind speed, and change rule of different fire source powers under varying wind speed conditions. The mathematical model for roof temperature decay and the temperature decay coefficients of dual source fires were established through the analysis of scale-down model experiments and numerical simulations. In comparison to single-source fires, the temperature variations in the tunnel of dual source fires exhibit a more intricate pattern, with higher average temperature and temperature peak values. These values are influenced by factors such as fire source spacing and power. Numerical simulation software was utilized to investigate the impact of fire source spacing at 10 m, 15 m, and 20 m, as well as the effect of varying fire source power on the temperature distribution within a tunnel under consistent fire source position and growth coefficient. The study revealed that, with consistent double fire source position and ventilation conditions in the tunnel, the upstream fire source exhibited greater power than the downstream fire source, resulting in the lowest average and peak temperatures in the tunnel. This observation could potentially enhance escape and rescue operations within the tunnel. Similarly, the lowest average and peak temperatures in the tunnel were also identified, offering potential benefits for optimizing escape and rescue strategies in tunnel scenarios. [ABSTRACT FROM AUTHOR]

Eighty-eight free-field strong ground motion observation datasets obtained by the National Strong Motion Observation Network System of China for the Jiuzhaigou Ms7.0 earthquake were used to study the characteristics of the strong ground motion and the site response. In this study, we calculated the VS30 of the near field station and compared the observed values of the horizontal peak acceleration and peak velocity with the CB2014 ground motion prediction models developed by Campbell et al. (2014). The results indicate that the observed values of the horizontal peak acceleration and peak velocity of the Jiuzhaigou earthquake are both smaller than the predicted values obtained from the ground motion prediction equations. By regressing the spatial variation curves of the D SR (5–95%) and D SR (5–75%) ground motion durations, and comparing them with Bommer’s (2009) ground motion duration prediction curve, it was found that the duration of the Jiuzhaigou earthquake was greater than that obtained from the global empirical prediction equation. The scope of the source duration corresponding to the D SR (5–75%) duration is 2.76–4.28 s, and the scope of the source duration corresponding to the D SR (5–95%) duration is 8.88–10.36 s, which are close to the peak time and completion time of the seismic moment release during the source rupture process. The linear elastic acceleration response spectra of 11 stations within 100 km of the fault were calculated for comparison with the design spectrum. It was concluded that the range of the predominant period of the response spectrum was 0.05–0.26 s, which is less than the natural vibration period of the local multistory building. However, the response spectrum value recorded by station 51JZZ is greater than the design spectrum of the 8° rare earthquake and the observation values of the nearby strong ground motion stations. Through analysis of the H/V spectrum ratio and the case of station 51JZZ, which is closest to the epicenter, this phenomenon was concluded to be related to the magnification effect of the near-surface soil layer and the nonlinear response of the site under the action of strong earthquakes.

To investigate resistance change in the fire area of a roadway caused by roadway fires, a mathematical calculation model for thermal resistance is developed. Theoretical research is conducted to analyze the factors influencing resistance change through theoretical derivation, revealing that temperature is a key factor contributing to the change in thermal resistance. By leveraging the correlation between changes in CO concentration and temperature on the downwind side of the roadway within the fire zone, researchers developed mathematical models to predict temperature increases at various points downwind of the fire source. These models were then used to determine the mathematical relationship governing the change in thermal resistance. The accuracy of the numerical simulation software was validated using Fluent numerical simulation software and scaled-down model experiments. Full-scale numerical simulation experiments were conducted to investigate the fire characteristics of roadway fires and validate the thermal resistance mathematical model. The results indicate that the thermal resistance in the numerical simulation is 7.55 Pa at 20m from the fire source and 5.54 Pa at the end of the roadway. The decrease in resistance is linear. The minimum error between the thermal resistance calculated by the mathematical model and the gradient of the pressure drop in the numerical simulation is 0.03 Pa, approximately 2.3%. Furthermore, the fitting degree of the pressure drop in each section is as high as 97.7%. The calculation model demonstrates high accuracy and offers a theoretical foundation for investigating fire resistance in tunnel fire. [ABSTRACT FROM AUTHOR]

Photocatalytic reactions during the daytime, alongside aqueous-phase reactions occurring during both daytime and nighttime, are identified as the two primary processes facilitating the conversion of aerosol iron (Fe) from the insoluble state to the soluble state within the atmospheric environment. This study investigated the levels of total Fe (Fe T) and soluble Fe (Fe S) in PM 2.5 samples collected during daytime and nighttime in Qingdao, a coastal city in eastern China, evaluating the distinctive roles of these two pathways in enhancing aerosol Fe solubility (%Fe S , defined as the ratio of Fe S to Fe T). Under clean and humid conditions, characterized by prevailing sea breezes and a relative humidity (RH) typically above 80 %, an average daytime %Fe S of 8.7 % was observed, which systematically exceeded the nighttime %Fe S (6.3 %). Photochemical conversions involving oxalate contributed to the higher %Fe S observed during daytime. Conversely, in scenarios where air masses originated from inland areas and exhibited slightly polluted, daytime %Fe S (3.7 %) was noted to be lower than the nighttime %Fe S (5.8 %). This discrepancy was attributable to the variations in RH, with nighttime RH averaging around 77 %, conducive to the more efficient generation of acidic compounds, thereby accelerating Fe S production compared to the daytime, when RH was only about 62 %. Furthermore, the oxidation rates of sulfur (SOR) displayed a strong correlation with RH, particularly when RH fell below 75 %. A 10 % increase in RH corresponded to a 7.6 % rise in SOR, which served as the primary driver of the higher aerosol acidity and %Fe S at night. These findings highlight the RH-dependent activation of aqueous-phase reactions and the augmentation of daytime photocatalysis in the formation of Fe S in the coastal moist atmosphere. [ABSTRACT FROM AUTHOR]

In order to reduce the disturbance energy loss in the process of inlet diversion and outlet jet flow of parallel fan station, taking the parallel connection of two fans as an example, a high-efficiency and low resistance parallel station structure improvement mode is proposed, and the ventilation efficiency and local resistance coefficient formulas of the fan station are deduced based on the principle of aerodynamics. The similar model and the numerical model based on FLUENT software are established to measure the resistance of the improved structure, and the variation laws of the efficiency of the machine station, the local resistance coefficient and the wind speed of the tunnel section are verified. The results show that the efficiency of the improved structure is about 1% higher than that of the general structure fan station, and the local resistance coefficient is about 12% lower.

To improve the ventilation efficiency of mine engine station, aiming at the minimum local resistance coefficient of engine station, the orthogonal numerical simulation test was carried out by selecting four influencing factors including diffusion angle of engine station, roadway length in air inlet, contraction angle and roadway length in air outlet and setting reasonable levels. The results show that the main and the secondary factors affecting the local resistance coefficient of the machine station are diffusion angle, contraction angle, tunnel length in the inlet and the tunnel length in the outlet. With the change of roadway wind speed, the optimal structural parameters of the station are different. When the roadway wind speed is 1.2 m/s to 1.5 m/s, the optimal combination of the structure is 60° diffusion angle, 30° contraction angle, 9 m of roadway length in the inlet section and 6 m of roadway length in the outlet section. When the wind speed is 1.5 m/s to 2 m/s, the local resistance coefficient of 10 m station is selected as the roadway length in the wind outlet section.

To study the mechanical properties changes and deformation of the underground coal pillar dam body in the mine goaf in the underground working environment, the Lijiatun Coal Mine is taken as the research background, and the laboratory similar simulation and FLAC3D numerical simulation method are adopted. The coal samples from 3-1 coal seam of Lijiatun Coal Mine were processed into standard samples according to ISRM. The samples were subjected to water immersion treatment for a certain period of time, and the mechanical properties analysis experiments were carried out. Subsequently, numerical simulation technology was used to simulate the actual working environment of the coal pillar dam and analyze the mechanical properties and deformation of the coal pillar dam. The study shows that water has a softening effect on coal samples. With the increase of water immersion time, the unidirectional compressive strength and unidirectional tensile strength of coal samples have decreased, but there is no regular decreasing trend; under the combined action of the overburden pressure, the coal pillar immersed surface is prone to horizontal deformation, the deformation gradually increases with time, and the deformation near the bottom plate is the largest, so that the on-site coal pillar is more vulnerable to damage.

The stability of the joint between the groundwater reservoirs in the mined-out area of the mine is one of the key factors for the safety and stability of the entire underground reservoir. To investigate the deformation and failure law of the joint under the working conditions, laboratory simulation and FLAC3D numerical simulation technology were used to analyze and monitor the force and deformation of the joint under the working conditions. The experimental and simulation results show that the inside of the boundary between the dam and the joint is the part with the most severe pore water pressure; the softening effect of water reduces the mechanical properties of the contact surface, and the moisture immersed in the pore crack makes the specimen fuller, which indirectly enhances the ability of the dam to resist external pressure, and enhances the mechanical strength of about 23%; the ultimate instability and failure of the joint is the consequence of the gradual expansion and extension of the internal damage at the junction, so we choose the joint material and pay attention to the connection. Reducing the pore cracks inside the joint is a crucial step to ensure the safety and stability of the dam.

To study the change of stability and safety degree of mine goaf reservoir under vibration environment, taking Lijiahao Coal Mine as the research background, the stability and safety of the main parts of the goaf reservoir are analyzed and studied under the continuous existence of earthquake or other earthquakes by using the method of formula derivation and similar simulation experiment in laboratory. Since the dam body is a key part of supporting the normal operation of goaf reservoir, the dynamic response formula of the dam body under the action of earthquake is analyzed to obtain the dynamic response of the dam body under the condition of earthquake. At the same time, through the research of similar simulation experiments in the laboratory, the variation of the safety degree of the whole goaf after disturbance is obtained under the condition that the vibration in the goaf continues to exist. With the increase of seismic intensity, the overall safety of the reservoir decreases. And under the condition that the source location is known, the closer the source is, the less safe it is.