As a solid waste produced by coal combustion, fly ash will cause serious environmental pollution. However, it can be considered as a sustainable and renewable resource to replace partial cement in grouting materials. Fly ash grouting materials re-cement the broken rock mass and improve the mechanical properties of the original structure. It can reinforce the broken surrounding rock of mine roadway. The utilization of fly ash also reduces environmental pollution. Therefore, this paper establishes a new material mixture ratio optimization model to meet the requirement of material property through combining the methods of experimental design and numerical analysis. Based on the Box–Behnken design with 3 factors and 3 levels, a mathematical model is constructed to fit the nonlinear multiple regression functions between material properties and raw materials ratios. The influence of raw materials is analyzed on material properties (the material’s 7-day uniaxial compressive strength, initial setting time, and slurry viscosity). Then, 80 Pareto solutions are obtained through NASG-II algorithm which takes the regression functions as the objective functions for multi-objective optimization of the grouting material ratio. Finally, the best ratio solution of water-cement ratio—0.71, silica fume content—1.73%, and sodium silicate content—2.61% is obtained through the NNRP-TOPSIS method.

This paper takes the bottom pumping roadway of 33190 machine roadway in the No.10 mine of China PingMeiShenMa Group as the engineering background. This mine is a hydrothermal mine, with strong heat conduction and thermal convection activities between the surrounding rock and geothermal water. This forms a geothermal anomaly area, making the overall temperature of the surrounding rock temperature field increase and affecting the mine thermal environment. According to the measured field data and the engineering geological conditions of the roadway, a roadway seepage-heat transfer model is constructed using the comsol numerical simulation software, emulating the effect of geothermal water upwelling to the roadway through random cracks in the surrounding rock at different temperatures and pressures, which has an impact on the airflow temperature field of the roadway. The study shows that the evolution law of the airflow temperature field in the roadway under different water upwelling temperatures and pressures is roughly the same, and the temperature at the entrance of the roadway is almost unchanged: the heating rate is 0, and then increases linearly. The variation in the airflow outlet temperature is analyzed, both under the conditions of same temperature but different pressure, and under the same pressure but different temperature. The water upwelling temperature and the cooling efficiency are positively correlated, and the overall growth rate of the airflow temperature is positively correlated with the water upwelling temperature and pressure; however, the effect of temperature is far greater than that of pressure. The upwelling temperature of geothermal water is the main influencing factor on the temperature field of the airflow in the roadway. Therefore, it is possible to reduce the temperature of upwelling water by laying heat insulation materials on the bottom plate, evacuating geothermal water and circulating cold-water by injection, so as to improve the thermal environment of water-heated mines and increase their production efficiency.

The gradual shortage of fly ash caused by the closure of coal‐fired power plants in some areas has stimulated increased research into novel pozzolanic supplementary cementitious materials (SCMs), with a particular focus on landfilled coal ash (LA). A novel hybrid alkaline cement (HAC) was developed using 70% LA and 30% ordinary Portland cement (OPC), together with small amounts of sodium sulfate and sodium citrate as sustainable hydration activators. The reaction kinetics, mineralogical composition, and microstructure of HACs were thoroughly investigated using conduction calorimetry analysis, strength testing, X‐ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT‐IR), scanning electron microscopy–energy‐dispersive spectroscopy (SEM‐EDS), and magic angle spinning–nuclear magnetic resonance (MAS–NMR). The effects of sodium citrate and sodium sulfate on the reaction process and product formation in the OPC–LA system were clearly identified. The retarding effect of citrate‐Ca and accelerating effect of sulfate‐Ca led to a modification of wavenumbers in the C–(A)–S–H gel IR bands, and consequently respectively played different roles on activating the LA. Results show that the strength performance of HACs (CA37SuCi group) even without ratio optimization achieve the level of P.O. 32.5. The cost and CO ₂ emission during laboratory level production of CA37SuCi group are 56.2% and 57.38% less than those of P.O. 42.5, respectively. An evaluation of technical, economic, and environmental aspects suggests that LA‐based HACs can contribute significantly to energy conservation and emission reduction in the cement industry, while also offering potential solutions to the regional shortage of fly coal ash.

The symmetrical fissures located within the surrounding rock of the roadway (borehole) in tunnel engineering activities can easily induce damage and instability of the surrounding rock. Therefore, studying the impact of perforated symmetrical fissures on the mechanical properties of rock with a hole has significant practical significance. Based on indoor experimental results, conventional triaxial compression simulations were performed on symmetrical fissure-hole sandstone using PFC2D. The impact of the dip angle and length of symmetric fissures on the mechanical properties of the hole-containing sandstone was analyzed. Furthermore, the relationship between crack propagation and the macroscopic mechanical properties of the specimen was discussed. The results show that: (1) The deterioration effect of symmetric fissures on hole-containing sandstone can be controlled by increasing the fissure dip angle, suppressing the stress drop phenomenon. However, increasing the fissure length exacerbates the deterioration effect. (2) The effect of symmetrical fissure dip angle on the displacement field near the hole decreases with increasing dip angle while increasing fissure length exacerbates the effect of fissures on the displacement field. (3) As the angle between the fissure and the vertical principal stress increases, the degree of tensile failure weakens while the degree of shear failure increases. (4) During the crack development phase, the extension of the stress concentration zone drives rapid crack growth. It exhibits a stress drop in the macroscopic mechanical properties, followed by the evolution of the stress field with loading, allowing rapid expansion of the microcracks and eventually leading to rock destabilization damage.

In deep coal mines characterized by high temperature, high humidity, high-salinity water, and elevated ground stress, stress corrosion cracking (SCC) of bolts is widespread, causing frequent instability of roadway surrounding rock and hindering long-term stability. This study systematically examines the failure characteristics of anchorage materials in highly corrosive roadways and clarifies the effects of deep-mine temperature and humidity on material corrosion. Long-term corrosion tests on bolts reveal changes in mechanical properties and macroscopic morphology and elucidate the intrinsic mechanisms of SCC. The results show that with the increase in corrosion time, the yield strength, ultimate load and elongation of the anchor rod decrease by up to 11.8%, 13.6%, and 7.08%, respectively. Under high stress, localized corrosion pits form on bolt surfaces, rupturing the oxide film and initiating rapid anodic dissolution and cathodic hydrogen evolution. Interaction between corroded surfaces and microcracks produced by internal impurities leads to progressive damage accumulation and ultimate fracture of the bolts. These findings provide guidance for corrosion protection of coal mine roadway support materials and for improving the long-term performance of roadway supports.

Achieving the sustainable development and utilization of mining energy resources necessitates the promotion of coordinated extraction of coal and geothermal resources. However, the direct discharge of untreated mine water not only leads to the dual wastage of water and geothermal resources but also poses environmental risks such as heavy metal contamination. Consequently, establishing an integrated green mining model that combines the recovery of coal, water, and geothermal energy has become an imperative for the sustainable development of the industry. Within this context, ensuring the stability of the floor strata during simultaneous coal mining and geothermal extraction represents a critical scientific challenge determining the safe and efficient implementation of this integrated technology. This study first presents the overall framework of a Simultaneous Extraction of Coal and Geothermal Resources (SECGR) technical system. Subsequently, through theoretical modeling and numerical simulation, we systematically studied the dynamic stress redistribution patterns and failure mechanisms within the bottom strata during the mining disturbance and extraction unloading process (MD-EU). The findings reveal that the vertical stress field exhibits an asymmetric distribution under the combined mining operations, while the shear stress field forms a distinctive saddle-shaped arch structure. The failure process of the floor strata undergoes four typical stages: the pristine state, crack initiation, crack propagation, and crack coalescence. Based on this, three characteristic zones are identified: the mining-induced failure zone, the water-resistant zone, and the unloading-activated zone. Finally, the Burgers viscoelastic model is employed to successfully quantify the time-dependent evolution of rock mass damage following mining-induced stress release. The research outcomes provide crucial theoretical support and technical guidance for safely advancing multi-energy coordinated extraction and enhancing the comprehensive resource utilization efficiency of mining systems.