Extracting aluminum from FA is an effective way to improve its utilization rate. Since aluminum oxide is found in high polymerization degree, inert substances such as mullite and sodium aluminosilicate make the reaction process difficult because of their stable chemical properties; within these highly polymerized matrices, the chemical stability of alumina typically persists across a broad temperature range from 1000 °C to over 1600 °C. To address the issue of stable mullite structure that hinders aluminum extraction, a combined acid-base method using sodium carbonate as an activating agent and hydrochloric acid at a temperature of 100 °C as a leaching agent is employed. XRD and SEM were used to analyze the phase characterization and microstructure of fly ash before and after activation and acid leaching, examining the effects of activation parameters and acid leaching parameters on the activation of FA and the aluminum extraction rate. The research results indicate that after calcination activation, mullite is transformed into zeolite, which is easily soluble in acid, and the aluminum within the activated molten material is transferred to the filtrate through acid leaching, achieving the goal of extracting aluminum. Under the activating conditions with sodium carbonate flux, the Al-O bonds in mullite are broken, the crystal structure is transformed, and the aluminum compounds obtained from hydrochloric acid leaching have a stable form of existence, which has a low impact on the error of the experimental results. When the material ratio of fly ash to sodium carbonate is 1:0.7, after reacting at a calcination temperature of 880 °C for 1.5 h, and leaching in 6 mol/L hydrochloric acid at 100 °C with a solid-liquid ratio of 1:6 for 2 h, the extraction rate of aluminum in fly ash is the highest, reaching 97%.

The mining area along the border of Inner Mongolia and Shaanxi generally contains two thick layers of confined aquifer sandstone, which form a composite hard roof. This constitutes the main hidden risk affecting the safe production of coal seams in this region.The composite hard roof is formed by two layers of thick confined water‐bearing sandstone in the border mining area of Inner Mongolia and Shaanxi and is the main hidden danger affecting the safe production of coal seams. To clarify the evolution law of mining‐induced water‐conducting fractures under such occurrence conditions and prevent roof water damage, this paper comprehensively uses laboratory tests, theoretical analysis and UDEC numerical simulation methods to study the fracture characteristics and migration laws of high and low thick sandstones. The instability conditions of confined water‐bearing sandstones in different layers are analyzed, the distribution law of water‐conducting fractures is expounded, and the evolution characteristics of fractures are further quantitatively described by fractal theory. The results show that the overburden rock transport in the quarry is controlled by the composite rock beams, and the high rock beams will form a “masonry beam” structure, while the low rock beams will form a “step” structure under the influence of secondary displacement and rotation; the superposition of the initial breakage of the composite rock beam and the cycle breakage forms the “pulse” water influx characteristic and the “slow increase—sudden increase—stable” fissure development law; the change of the number of fractures is closely related to the transportation of the composite rock beams, which is divided into three stages of “slow growth‐accelerated growth‐periodic increase.” The fractal dimension quantitative cloud diagram further characterizes that the overall development pattern of water‐conducting fissures remains unchanged under the influence of mining, and the main water‐conducting channels are the fall zone and the vertical breakage fissure zones on both sides. The research results of this paper will provide a scientific basis for water control work in the working face under similar stratigraphic conditions.

This study investigates the influence of oil well anchoring on overburden stability in coal, oil, and gas co-mining areas, combining mechanical theory and numerical simulations to systematically analyze the mechanical characteristics. First, a mechanical model of oil well anchoring was developed by considering the coupled interaction between the wellbore cement sheath and the surrounding rock, and the relationship between oil well anchoring and changes in the friction angle, cohesion, compressive strength, and Young’s modulus of the surrounding rock. Subsequently, a three-dimensional numerical simulation using FLAC3D 7.0 was conducted to analyze stress redistribution, displacement field evolution, and plastic zone distribution around the oil wells under different burial depths. The results indicate that as the burial depth increases, the peak stress around the oil wells rises from 0.37 MPa to 2.24 MPa, the displacement influence range expands from 18 m to 43 m, and the plastic zone remains confined between 0.9 m and 1.6 m. No significant stress coupling effects are observed between the well groups. These findings demonstrate that the anchoring effect of oil wells effectively regulates the stratigraphic stress field, mitigates overburden deformation, and enhances wellbore stability in coal, oil, and gas co-mining areas, providing a crucial theoretical basis and engineering reference for enhancing overburden stability in coal–oil co-mining areas.

In geotechnical engineering, traditional anchor bolts often have problems such as an insufficient bearing capacity, their ease of loosening, and an unsatisfactory support effect under complex geological conditions (such as soft soil or broken surrounding rock), resulting in it being difficult to guarantee engineering stability. In order to solve these problems, this paper studies the supporting performance of a hollow grouting anchor with an umbrella-shaped expansion head with an expansion pipe. Through theoretical analysis, mechanical performance analysis, and experimental analysis, the supporting mechanisms and mechanical characteristics of a hollow grouting anchor with an umbrella-shaped expansion head are systematically discussed. The calculation formula for the maximum pull-out force of the umbrella-shaped expansion head is clarified, and the fixed range of the expansion body section in relation to the loose ring is quantified. Based on the analysis results, the structural parameters and material properties of the bolt were optimized, and the optimization effect was verified by numerical simulation. The results show that the optimized bolt has significantly improved the pull-out bearing capacity, shear resistance, and reinforcement effect on the soil. The maximum pull-out force of the umbrella-shaped expansion head can be increased by up to 35%, and the fixed range of the expansion body section can be expanded by 45%. The research provides an efficient and reliable support solution for geotechnical engineering fields, such as roadway engineering and tunnel engineering, which significantly improves the stability and safety of engineering under complex geological conditions. At the same time, it provides an important theoretical basis and practical reference for the design and construction of similar projects.

To address the limitations of traditional hardened concrete road surfaces in coal mine tunnels, which are prone to damage and entail high maintenance costs, this study proposes using modular concrete blocks composed of fly ash and coal gangue as an alternative to conventional materials. These blocks offer advantages including ease of construction and rapid, straightforward maintenance, while also facilitating the reuse of substantial quantities of solid waste, thereby mitigating resource wastage and environmental pollution. Initially, the mineral composition of the raw materials was analyzed, confirming that although the physical and chemical properties of Liangshui Well coal gangue are slightly inferior to those of natural crushed stone, they still meet the criteria for use as concrete aggregate. For concrete blocks incorporating 20% fly ash, the steam curing process was optimized with a recommended static curing period of 16–24 h, a temperature ramp-up rate of 20 °C/h, and a constant temperature of 50 °C maintained for 24 h to ensure optimal performance. Orthogonal experimental analysis revealed that fly ash content exerted the greatest influence on the compressive strength of concrete, followed by the additional water content, whereas the aggregate particle size had a comparatively minor effect. The optimal mix proportion was identified as 20% fly ash content, a maximum aggregate size of 20 mm, and an additional water content of 70%. Performance testing indicated that the fabricated blocks exhibited a compressive strength of 32.1 MPa and a tensile strength of 2.93 MPa, with strong resistance to hydrolysis and sulfate attack, rendering them suitable for deployment in weakly alkaline underground environments. Considering the site-specific conditions of the Liangshuijing coal mine, ANSYS 2020 was employed to simulate and analyze the mechanical behavior of the blocks under varying loads, thicknesses, and dynamic conditions. The findings suggest that hexagonal coal gangue blocks with a side length of 20 cm and a thickness of 16 cm meet the structural requirements of most underground mine tunnels, offering a reference model for cost-effective paving and efficient roadway maintenance in coal mines.

Aiming at the problems of the complex in situ stress measurement process, difficult measurement and long-term monitoring, it is particularly important to design a three-dimensional borehole full stress monitoring method based on the principle of rock mass rheological stress recovery, which lays a foundation for underground construction, such as roadway engineering and tunnel engineering. Through theoretical calculation and mechanical analysis, the magnitude, direction and inclination of the stress at any point in the borehole of the geological body are analyzed. Based on this, a three-dimensional borehole full stress monitor is constructed. At the same time, the rheological stress change process of rock mass around the borehole is analyzed by numerical simulation, the rationality of the three-dimensional borehole full stress monitor is determined, and a new method of borehole surrounding rock stress monitoring is proposed. The results show that: (1) the stress monitoring of the surrounding rock can be realized by the stress recovery principle of a rock mass rheological borehole, and it can be monitored for a long time; (2) the three-dimensional borehole total stress monitor can reflect the size and direction of the six principal stresses of the surrounding rock stress through eight measuring points; (3) the design structure and mechanical properties of the three-dimensional borehole full stress monitor are reasonable, and the linearity and sensitivity of the hydraulic membrane material are reasonable, which can meet the standards of long-term monitoring.