As the mining of mineral resources extends to depths, the importance of cemented backfill in maintaining stope stability and achieving green mining has become increasingly prominent. The cemented backfill is a multi-phase heterogeneous material. After the filling slurry is filled into the stope, the mechanical properties of the cemented backfill are affected by the coupling of multiple factors such as material composition, maintenance conditions, external loads, and seepage fields. It shows significant spatiotemporal evolution and nonlinear characteristics. Solving the quality problems of the cemented backfill induced by seepage has far-reaching theoretical value and engineering practical significance for ensuring safe, efficient, and green mining of mines. In recent years, fruitful results have been achieved in the mechanical evolution characteristics, failure characteristics and fluid-solid coupling response of cemented backfill at macro-fine-micro scales. First, the influencing factors and evolution rules of the strength of the cemented backfill are summarized from the aspects of cementitious material type, proportioning parameters, maintenance conditions, etc., and the spatiotemporal evolution characteristics of the cemented backfill are clarified. Second, the failure mode and crack propagation behavior of the cemented backfill under static and dynamic loads are summarized, and a comparative analysis is conducted with the failure theory of rock-like materials. Furthermore, the application results of multi-scale observation methods based on SEM, XRD, CT scanning, acoustic emission and other methods in revealing the intrinsic relationship between the microstructure evolution and macroscopic mechanical behavior of the cemented backfill are summarized; the mechanical response and damage evolution mechanism of the cemented backfill under the action of seepage-stress coupling are focused on, and the characteristics, limitations of indoor tests and numerical simulation methods are reviewed. Finally, in view of the problems in current research such as insufficient universality of constitutive models, unclear multi-scale mechanisms, and disconnected field applications, future development directions such as constructing a time-varying damage-seepage coupling model, developing a multi-scale collaborative observation and simulation platform, and promoting a closed-loop research system of "indoor experiments-numerical simulation-field monitoring" are proposed, in order to provide theoretical support and technical reference for performance improvement, stability evaluation, and engineering applications of the cemented backfill in deep complex environments.

Deep coal mining is confronted with complex geological conditions and strong engineering disturbances. The environment characterized by high geostress, high gas pressure, high geothermal temperature, and intense mining disturbance frequently induces nonlinear large deformation and catastrophic instability of surrounding rock, which seriously restricts the safe and efficient exploitation of deep geological resources. To investigate the mechanical response and energy evolution characteristics of coal and rock under deep true triaxial stress conditions, true triaxial tests were conducted on raw coal, sandstone, and composite coal-rock specimens under different intermediate principal stresses with the aid of a multifunctional true triaxial fluid-solid coupling testing system. The results show that composite coal-rock exhibits stronger plastic deformation capacity and a smaller post-peak stress drop. The dissipated energy of coal increases significantly after the peak, whereas that of sandstone accelerates during the plastic stage. The energy evolution of composite coal-rock approaches sandstone at low stress and resembles coal at high stress. For coal, the fluctuation peaks of the energy release rate (\begin{document}$ {G}_{{\mathrm{e}}} $\end{document}) and energy dissipation rate (\begin{document}$ {G}_{{\mathrm{d}}} $\end{document}) occur near the strength peak, and an increase in \begin{document}$ {\sigma }_{2} $\end{document} reduces their amplitudes. For sandstone, the fluctuation peaks appear in the yield stage, but the influence of \begin{document}$ {\sigma }_{2} $\end{document} is relatively weak. Composite coal-rock exhibits gentle but high-amplitude post-peak fluctuations, which are markedly suppressed by the increase in \begin{document}$ {\sigma }_{2} $\end{document}. Post-peak elastic energy release has a greater effect on the brittleness index than pre-peak elastic energy storage. Coal failure is mainly controlled by a single dominant crack and is weakly affected by \begin{document}$ {\sigma }_{2} $\end{document}, whereas sandstone exhibits a more complex fracture network at low \begin{document}$ {\sigma }_{2} $\end{document} and a simpler pattern at medium and high stress levels. In composite coal-rock, secondary cracks in the sandstone layer propagate along the \begin{document}$ {\sigma }_{1} $\end{document} direction, while those in the coal seam propagate along the \begin{document}$ {\sigma }_{3} $\end{document} direction. These results provide theoretical support for surrounding rock control and dynamic disaster prevention in deep resource extraction.

In deep coal mines, the prominent conflict between the high in-situ stress and the low strength of soft surrounding rock frequently induces large-scale deformation disasters that pose a severe threat to safe production. Borehole pressure relief technology, which improves the strength-to-stress ratio of surrounding rock through stress release and space compensation mechanisms, has achieved remarkable advancements in both theoretical development and engineering practice in recent years. This paper systematically reviewed the research dynamics of borehole pressure relief technology both domestically and internationally, focusing on four aspects, i.e., operational mechanisms, parameter design, model testing, and effect evaluation. The following key conclusions were drawn: ① Pressure relief boreholes facilitate the coordinated regulation of triaxial stresses and compensate for shear dilation by inducing fracture propagation, resulting in a stress distribution pattern characterized by “shallow-pressure relief and deep-bearing capacity” and forming a “pressure relief-support” synergic system when combined with high-strength support. ② Key parameters such as borehole diameter, spacing, and depth significantly influence the pressure relief effectiveness. Although multi-factor coupled design criteria have been preliminarily established, their applicability under complex geological conditions requires further validation. ③ Current technical bottlenecks include an incomplete quantitative evaluation framework for pressure relief effectiveness, unclear energy evolution mechanisms, and underdeveloped theories for dynamic pressure relief-support coupling. Looking forward, research should focus on constructing a “multi-field coupling and static/dynamic synergy” analytical framework and developing dynamic constitutive theories integrating thermal-hydraulic-mechanical-damage (THMD) effects. Innovations in precise pressure relief equipment enabled by while-drilling sensing and intelligent decision-making are also needed. Furthermore, optimizing differentiated support and grouting reinforcement and building an integrated “pressure relief-support-reinforcement” control system will drive borehole pressure relief technology toward intelligent, precise, and large-scale applications.

To address the inadequate understanding of the fracturing behavior of thick-hard strata and the collapse-movement mechanism of overlying strata in 10 m ultra-large mining height faces of extra-thick coal seams, this study took the 122104 working face of Caojiatan Coal Mine as the engineering background. A combined approach involving physical similarity simulation, image processing with statistical analysis, and field monitoring was adopted to investigate the dominant role of thick-hard strata breakage in the overburden collapse and movement process. The engineering applicability and consistency of the model results were verified with field measurements. (1) An automatic fracture extraction and multi-index quantification method based on multi-temporal overburden images was proposed, enabling efficient quantification of parameters such as fracture development height, coverage area, and total length. The results show that the fracture parameters exhibit a pronounced "step-like" jump evolution with face advance, where each abrupt change strictly corresponds to the breakage sequence of specific thick-hard strata (I, II, and III). This quantitatively reveals, from the perspective of fracture evolution, the controlling effect of thick-hard strata breakage on overburden movement. (2) The breakage mechanism of thick-hard strata is characterized as a "cantilever beam-coordinated collapse" process. Before breakage, thick-hard strata form a large-span cantilever beam structure that constrains overburden collapse; when the cantilever reaches its limit, sudden breakage occurs, triggering large-scale coordinated collapse of the overburden, demonstrating typical structural failure characteristics. (3) Field monitoring data, including layered subsidence, mine pressure, and microseismicity, provide effective mutual validation with the model experiments. The coordinated movement mode of strata revealed by the layered subsidence curves aligns well with the "step-like" propagation pattern of fractures observed in the model; mine pressure monitoring indicates that the breakage of thick-hard strata II and III directly induces intense periodic weighting; microseismic monitoring further confirms that the periodic breakage of thick-hard strata constitutes the main source of concentrated energy release in the overburden. These results jointly verify, in terms of spatial evolution and energy release, the field applicability of the mechanism by which thick-hard strata breakage dominates overburden movement. From the perspective of fracture evolution, this study systematically elucidates the mechanism of thick-hard strata breakage-dominated overburden collapse and movement under ultra-large mining height conditions, providing a quantitative theoretical basis for improving overburden movement theory and preventing roof disasters in 10 m ultra-large mining height faces.

The complex environment of mining working faces—including dust, high humidity, and smoke—causes severe feature degradation in monitoring images under varying fog concentrations. Moreover, existing dehazing models trained mainly on synthetic data exhibit domain gaps with real mining fog, limiting intelligent monitoring effectiveness and posing safety risks. This study proposes a dehazing method for working face images based on fog grading and domain differences. First, fog evaluation metrics guide image grading, enabling adaptive network selection for light and dense fog scenarios. Second, a contrastive learning strategy refines negative samples based on fog concentration, improving feature discrimination and cross-domain generalization. Finally, an unsupervised fine-tuning strategy with cyclic consistency mitigates domain bias between synthetic and real fog images without requiring annotations. Experiments show that the proposed method outperforms existing approaches on both synthetic and real datasets, supporting safe and intelligent monitoring in coal mines.

As the mining depth of steeply inclined and extremely thick coal seams continuously increases, the rock burst disasters associated with them are becoming increasingly severe. The rock burst-inducing factors exhibit diversity and keep evolving, which poses difficulties to precise prevention of rock bursts. To address these issues, this paper explored the evolutionary patterns of inducing factors in a typical steeply inclined and extremely thick coal seams mine in Xinjiang by means of case analysis, field monitoring, and theoretical analysis. By analyzing five typical rock burst events in the mine, the main inducing factors were found to be steeply inclined roofs, intermediate rock pillars, remaining coal pillars, mining depth, mining intensity, and horizontal tectonic stress. Moreover, an improved analytic hierarchy process incorporating triangular fuzzy numbers was proposed to quantitatively evaluate the weights of these inducing factors and characterize their evolutionary patterns. The results disclose that steeply inclined roofs and intermediate rock pillars possess the highest weights and constitute the most significant inducing factors, and their weights keep growing with the continuous mining of coal seams. The weights of mining depth and horizontal tectonic stress generally rise with the continuous mining of coal seams, which reflects their enhanced inducing effects. In contrast, the weight of remaining coal pillars generally shows a decreasing trend, suggesting their gradually diminishing influence within the gob on rock bursts. The weight of mining intensity also decreases overall. Fianlly, the evolutionary patterns of inducing factors in steeply inclined and extremely thick coal seams were well verified through mining data analysis, microseismic monitoring, ground stress testing, numerical simulation, and theoretical research. The research results can provide support for precise control of rock bursts in steeply inclined and extremely thick coal seams.

Large-scale development of surface fractures exacerbates ecosystem degradation, damages engineering infrastructure, and poses constraints on regional ecological security and socio-economic development. To characterize the scale characteristics of fractures under high-intensity mining and establish an effective prevention and control system, this study took the 615 working face of Guanbanwusu Coal Mine as the research background. The overlying strata structure was divided under the guidance of the combined rock strata theory, and a fracture-rate-based quantitative characterization method was proposed for the fracture development process. Furthermore, quantitative relationships between the depth-thickness ratio and surface fracture scale parameters (maximum width, average penetration, and average advance distance) were revealed, and the corresponding collaborative control technology was proposed. The following beneficial findings were yielded. The overlying strata damage is divided vertically into four zones (according to the distribution of thick-hard strata and collapsed blocks) and horizontally into five zones (according to the extent of mining influence). Four combined rock strata structures of the overlying strata are determined, and stepwise breakage in overlying strata ultimately drives fractures to the surface. The intensified dilatancy of rock blocks near the goaf enhances the skewness and irregularity of the subsidence curve. The depth-thickness ratio shows a negative linear correlation with the maximum fracture width, and a negative exponential correlation with both the average penetration and advance distance. A decreasing depth-thickness ratio induces a transition in fracture type, from tensile and step-type dominance to collapse and step-type dominance. Based on these findings, the collaborative control technology of surface fractures was proposed. Key measures include optimization of mining sequences to mitigate surface subsidence, geophysical positioning combined with targeted remediation to enhance the stability of the overlying strata structural arch, and zone-specific treatment based on fracture classification and zoning. These measures conduce to facilitating the restoration of the regional ecological environment. This research provides significant insights for safeguarding regional ecological security and human settlements.

The Yushenfu mining area is characterized by shallow coal seams, thin overlying bedrock, and thick loose layers, and most mines in this mining area involve repeated mining of multiple coal seams. Affected by multiple factors such as coal seam mining height and spacing, the spatial interaction of surrounding rock in the upper and lower stopes makes it challenging to accurately predict fracture zone height. In this paper, the fracture zone height under multi-coal seam repeated mining in typical coal mines in the Yushenfu mining area was taken as the research object, and the research methods of physical similarity simulation, theoretical analysis, and deep learning were used. First, the fracture development law under multi-coal seam repeated mining was analyzed. Subsequently, a multi-factor coupling nonlinear regression model was established to describe the relationship between the fracture zone height and key parameters, including coal seam mining height, spacing, burial depth, dip angle, working face length, and interval rock strength. On this basis, the prediction method of fracture zone height under multi-coal seam repeated mining based on the SSA-BP neural network was established, and its accuracy was verified. The results indicate that the fracture development under repeated mining in Ciyaota Coal Mine exhibits a three-stage characteristic, i.e., localized slow growth, nonlinear rapid increase through interconnection, and dynamic stabilization. The ultimate height of the fracture zone reaches 139.0 m. The nonlinear regression model incorporating the coupled effects of coal seam mining height, interlayer spacing, strength of intervening rock strata, and working face length achieves an R² value of 0.880, confirming these parameters as key influencing factors for the fracture zone height. Compared to predictions from traditional empirical formulas and the BP model, the SSA-BP model demonstrates reductions in MAPE values by 22.96% and 6.70%, respectively, and attains a low RMSE of 1.79, indicating superior stability. Validation at the 14205 working face of Zhonghui Funeng Coal Mine in the Yushenfu mining area shows a relative error of 1.3% between the predicted and measured heights, well below 5%. The study demonstrates strong generalizability for predicting the height of water-conducting fracture zones under multi-coal seam repeated mining in the Yushenfu mining area and provides valuable insights for water hazard prevention and control under such mining conditions.

Addressing the technical challenges of severe deformation and maintenance difficulties in gob-side roadways with retained pillars under hard roof and thin coal seam conditions during mining-excavation interaction at Binhu Coal Mine, this study employs integrated theoretical analysis, numerical simulation, and field experiments to investigate the movement characteristics of the adjacent goaf-side overlying strata, the morphology of the caving structure, and the induced roadway instability mechanism. Key parameters for roof-cutting pressure relief and roadway protection were optimized and applied in engineering practice. The research indicates that two dominant key strata exist within the overburden of the No. 16 coal seam. Their structural characteristics and mechanical behavior govern the movement patterns and caving structure morphology of the adjacent strata. The dynamic evolution (formation, movement, and caving) of the lateral suspended roof in this zone subjects the roadway surrounding rock to significant multiple dynamic load impacts and high static stress, substantially increasing the risk of roadway instability and failure. Using the maximum principal stress deviatoric as the evaluation indicator, the optimal roof-cutting height and angle were theoretically determined as 16 m and 10°, respectively. Field tests further optimized the blasting parameters, establishing a spacing of 2 m for deep boreholes and 1 m for shallow boreholes. Additionally, a comprehensive support system comprising a primary "bolt-mesh-cable-belt" support combined with temporary reinforcement using "unit hydraulic props" was proposed to enhance the load-bearing capacity of the surrounding rock. Ground pressure monitoring confirmed that roadway deformation was effectively controlled, achieving a self-stabilized state approximately 140 m behind the working face. This validates the effectiveness of the roof-cutting pressure relief technology in resolving the maintenance challenges of gob-side roadways under thin coal seam and hard roof conditions.

The 3-1 coal seam in Menkeqing Coal Mine has strong propensity for rock burst. Given the large coal seam burial depth, high mining intensity, and the presence of a thick composite sandstone roof overlying the coal seam, rock burst disasters are likely to be induced during mining of the working face. Conventional pressure relief measures targeting medium- to high-position thick and hard roofs are limited in both treatment height and range, often failing to achieve the desired pressure relief effect. In response to this problem, dominant disaster-inducing factors for rock burst were analyzed first. On this basis, roof lithology analysis, key strata theory calculation, microseismic monitoring, and strata fracture energy transfer calculation were performed to identify the dominant strata responsible for rock burst and reveal the mechanism of regional fracturing with long boreholes for pressure relief and rock burst prevention. Furthermore, the engineering practice of regional fracturing with long boreholes was conducted, and the corresponding effect analysis was carried out. The results show that the large burial depth of the working face provides sufficient foundation static load. The 3-1 coal seam and its roof and floor have the potential to generate rock burst, and the dynamic load arising from the breakage of the highly integral and continuous composite sandstone roof is the main source triggering rock burst. Regional fracturing with long boreholes was used for advanced prefracturing of the thick and hard composite sandstone roof. After the construction was completed, cracks propagated notably in fractured strata, and a remarkable prefracturing effect was achieved. During mining of the working face, the frequency, energy, and concentration of high-energy microseismic events in the fracturing area were significantly reduced, the intensity and distance of periodic weighting of the working face decreased. The engineering practice demonstrates the effectiveness of regional fracturing with long boreholes in significantly reducing the risk of rock burst disasters and ensuring safe mining of the working face. The research results can provide reference for the prevention and control of rock burst in coal mines with similar conditions.