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.

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 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.

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.

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.

Deep mining of coal resources is commonly accompanied by high in-situ stress and progressive energy accumulation, which can readily trigger dynamic disasters such as rock bursts. From the perspective of material toughening, elucidating the impact-mitigation mechanisms of coal-based cemented fill materials and establishing an quantitative characterization and evaluation index system for toughening based on the energy dissipation theory are emerging as promising approaches for achieving impact-mitigation control and optimizing material-oriented design. To clarify the impact-mitigation mechanisms, this study employed coal-based solid wastes as the primary constituents and systematically investigated the coupled effects of aggregate gradation, binder-to-aggregate ratio, curing age, and fiber toughening through uniaxial compression tests, energy evolution analysis, rock burst propensity assessment, and scanning electron microscopy (SEM). The results indicate that aggregate gradation, binder-to-aggregate ratio, and curing age exert significant influences on the mechanical performance of the cemented fill. The uniaxial compressive strength grows with the increase in curing age, and rises first and falls subsequently with the increases in Talbot index n and binder-to-aggregate ratio, reaching an optimum at a curing age of 28 d with n=0.6 and a binder-to-aggregate ratio of 2.5∶1. The incorporation of polypropylene fibers markedly enhances the compressive strength and improves post-peak ductility, broadens the energy-dissipation pathways, and enables sustained absorption and dissipation of externally imposed impact energy during the post-peak failure stage. Based on the energy dissipation theory, a FIMI-Lite impact-mitigation evaluation framework comprising five indices (energy dissipation ratio, dynamic toughness index, residual load-bearing ratio, brittleness index, and equivalent vibration isolation coefficient) was proposed to quantitatively characterize the impact-mitigation performance of cemented fill materials. Comparative analyses show that fiber-toughened fills outperform the conventional counterparts across all indices, with the fiber-toughened fill at n=0.4 achieving the highest comprehensive FIMI-Lite score. SEM observations reveal that an appropriate gradation promotes the formation of a dense load-bearing skeleton, whereas the incorporation of fibers conduces to constructing a three-dimensional "particle-cementitious matrix-fiber" network. The synergy of these two factors refines the pore structure, retards crack propagation, and enables stepwise energy absorption and progressive release. The above microstructural findings establish a mechanistic linkage to the macroscopic impact-mitigation performance. The proposed approach provides a scientific basis for optimizing the design of coal-based cemented fill materials and for preventing and controlling coal burst hazards in deep coal mining.

Aiming at the problem of coal pillar instability in the fully mechanized mining face section of hard roof and floor, taking the section coal pillar of the track haulage roadway in the 1016 working face of a certain mine in Xinjiang as the engineering background, through theoretical analysis, numerical simulation and field test research methods. The movement law of overlying strata in the working face was analyzed. The causes of energy accumulation in the coal pillar under the condition of hard roof and floor were proposed. The function relationship between the elastic strain energy density in the coal pillar and the first and third principal stresses was studied. According to the theory of elasticity, the stress and energy distribution laws in the coal pillar under different stress concentration coefficients were obtained. The research shows that after the upper working face is mined, the thick and hard basic roof will form a "long cantilever beam" structure, causing the load in the coal pillar to increase. Due to the significant difference in strength between the coal mass and the roof and floor, the energy input from the outside into the "roof-coal pillar-floor" system mainly accumulates in the coal pillar in the form of elastic strain energy. The elastic strain energy at any position in the section coal pillar can be roughly regarded as a positive correlation with the first and third principal stresses. The junction of the elastic and plastic zones in the coal pillar and the surrounding area are the main parts where the elastic strain energy is accumulated, while the accumulation degree of elastic strain energy in the broken zone of the coal body is relatively small. The deterioration of the stress environment of the coal pillar after the roadway is excavated, the release of the accumulated energy in the coal pillar is the main reasons for the deformation and failure of the coal pillar. The prevention and control technology of "intensive drilling in the roof + coal pillar drilling pressure relief + strengthening support" was proposed, and the field application effect was obvious.

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.

To investigate the instability and deformation characteristics of thick hard roofs overlying open roadways in deep mines, this study employs the sixth mining area of Dongtan Coal Mine(Yanzhou mining district)as an engineering case. A Timoshenko beam model on an elastic foundation was established to characterize roof deflection, incorporating structural and mechanical properties of thick hard strata. Analytical solutions for bending moment, shear force, and deflection were derived, revealing significant influences of roof layer position, thickness, and strength on roadway deformation-validated through numerical simulations. Key findings include: ① Roof flexural fracturing is critically controlled by thick hard roof properties. Maximum subsidence and fracture dimensions exhibit negative correlations with roof layer elevation: each 5 m elevation increase reduces subsidence by 16%-37%. Lower-layer roofs develop fractures deeper within coal walls, generating larger fractured blocks. The influence of roof thickness and strength evolves through two stages: During initial roadway development, thick hard roofs form stable, high-capacity cantilever structures where subsidence negatively correlates with thickness/strength. Subsequent intense mining triggers cantilever fracture, releasing dynamic loads that dominate roadway deformation. At this stage, thickness and strength positively influence fracture dimensions and energy release, intensifying roadway destabilization. ② Roadway deformation progresses through static load-dominated and dynamic load-expansion stages. Initially, the cantilever transfers static loads to deeper coal, expanding plastic zones. Post-fracture, the absence of immediate roof buffering allows dynamic stress waves to directly intensify surrounding rock damage. ③ Field tests demonstrate that hydraulic fracturing combined with deep-hole blasting reduces dynamic impact energy by 60%. Integrated with high-preload anchor cables and grouting, this limits roof subsidence to <300 mm. Optimizing advance rates to 3 m/day reduces high-energy seismic events by 65%. This research elucidates the mechanical mechanisms of impact-induced failure beneath thick hard roofs and proposes a targeted control strategy integrating directional roof cutting, multi-level support, and advance rate optimization. The outcomes provide theoretical and technical foundations for roadway stability control in deep mining environments under thick, hard, directly overlying strata.

This study, through laboratory experiments, investigates the effects of freeze-thaw (F-T) cycles on the fracture characteristics of sandstone under seasonal freezing conditions on the Qinghai-Tibet Plateau. Sandstone samples were first pretreated with F-T cycles in a temperature range of 20 ℃ to −20 ℃ and then subjected to impact three-point bending tests with the aid of a SHPB system. In the meantime, the evolution of the fracture process zone (FPZ) was analyzed via high-speed camera recordings and Ncorr digital image correlation software. The results demonstrate that F-T cycles induce mechanical property degradation in sandstone, which in turn affects its dynamic fracture behavior. As F-T cycles increase, the time required for pre-existing crack penetration extends, the crack opening width within the same time interval increases, and the time needed to achieve an equivalent opening width decreases. Crack opening velocity is significantly suppressed by F-T cycles before 111 ms, while this influence dininishes afterward, indicating that F-T effects predominantly govern the initial crack tip propagation stage. The evolution of the FPZ can be divided into two stages: expansion and contraction. To be specific, in the initial stage, microcracks cluster near the crack tip, and the FPZ expands with the increase in load. After main crack penetrates, the FPZ contracts and eventually dissipates due to energy release. F-T cycles promote the formation of a substantial number of pores within the sandstone, enhancing its energy absorption capacity. As a result, FPZ peak values are reduced and peak stresses occur earlier, accompanied by a transition in failure mode from brittle to ductile, characterized by prolonged crack propagation time and reduced initial opening velocity. The research results can provide basic experimental data reference for the dynamic disaster relief of engineering rock masses in cold regions.