To address issues such as insufficient stirring of resin anchoring agent, inadequate filling in reamed areas, eccentricity of cable bolts, and damage to hole walls during cable bolts reaming anchoring in soft rock roadways, a resin anchoring enhancement technology based on the Multi-segment Reaming Anchoring Enhancement (MRAE) component was proposed. Through theoretical analysis, the mechanisms of MRAE, including the "graded crushing-gradient stirring", the synergistic flow control of "ascending guidance-sealing", and the "centralized limiting-radial support" were revealed, and the mechanisms by which MRAE enhances the stirring effect of resin anchoring agent, the strength of the anchor solid, the pull-out resistance, and the centering performance of the cable bolt were also clarified. Besides, numerical simulations were conducted to comparatively analyze the characteristics of the stirring flow field of resin anchoring agent between MRAE and ordinary cable bolts, verifying that MRAE enhances the migration speed and diffusion range of resin. Moreover, laboratory experiments were performed to study the influence of MRAE on the drilling thrust, torque, and pull-out force of cable bolts. The results show that the average peak pull-out force of the enhanced anchoring group (36.5 kN) is 2.5 times that of the ordinary anchoring group (14.9 kN), and the centering degree is significantly improved. Field tests further verify the effectiveness of this technology. In soft rock roadways, both the pull-out force and pre-tightening force of the enhanced anchoring cable bolts meet the design values. The roof separation displacement is reduced by a factor of 1.52 compared with ordinary anchoring. Even under non-reaming conditions, its anchoring force still meets engineering requirements. The research results provide a theoretical basis and technical support for improving the anchoring quality of cable bolts in soft rock roadways.

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.

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.

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.

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.

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.

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.

The particle size distribution of gangue aggregates and the curing age are the key factors affecting the mechanical properties of cemented gangue backfill. To study the mechanical properties and damage evolution characteristics of backfill with different particle size distributions of aggregates at different curing ages, coal gangue was used as the aggregate and fly ash as the auxiliary cementitious material to prepare cemented backfill. The mechanical properties, microstructure and fracture evolution characteristics of backfill with different aggregate particle size distributions were studied. Based on the dissipated energy, a damage constitutive model of the backfill considering the curing age effect was established, further revealing the energy damage evolution process of the backfill. The results show that the compressive strength and elastic modulus of the backfill with different aggregate size distribution increase with the extension of curing age. The elastic modulus and peak stress of the backfill with a particle size distribution of 0-5 mm are the highest, the backfill with a particle size distribution of 0-10 mm is the second, and the backfill with a particle size distribution of 5-10 mm is the smallest. Under uniaxial compression, the backfill with the particle size distribution of 0-5 mm maintained good integrity, and the extension of curing age could restrain the expansion and penetration of failure cracks, and improve the integrity of the sample. The microstructure density of the backfill with the aggregate size distribution of 0-5 mm is the best, and the extension of curing age reduces the size and range of the void structure inside the backfill, and improves the microstructure density. The total energy, elastic strain energy and dissipative energy of the backfill with different aggregate particle size distribution increased quadratic function with the increase of curing age, and the change of aggregate particle size distribution and curing age had no effect on the energy accumulation and dissipation process in the backfill. The established damage constitutive model considering the effect of curing age can accurately reflect the stress distribution under load of the backfill, and the damage evolution of backfill can be divided into four stages: initial damage stage, damage stable stage, damage accelerated growth stage and damage failure stage.

In cold-region rock engineering, ice-filled fractures significantly weaken the mechanical properties of rock masses, which severely impacts the safety and stability of projects. To investigate the mechanical behavior and failure mechanisms of ice-filled fractured rock masses, uniaxial compression tests, acoustic emission monitoring, and discrete element numerical simulations were conducted in this study. On this basis, the mechanical properties and failure mechanisms of ice-filled fractured sandstone were systematically examined, with a focus on how fracture thickness (5–30 mm) and dip angle (0°–90°) influenced rock mass strength, elastic modulus, energy evolution, and crack propagation. The results show that compressive strength, elastic modulus, and pre- and post-peak energy all decrease non-linearly with the increase in fracture thickness, among which the elastic modulus drops by 20%–34%. The fracture dip angle was found to dominate the classification of failure modes. Vertical fractures (90°) exhibit the highest strength (23.56 MPa) due to efficient stress transfer, while low-angle fractures (15°–30°) experience a 30%–45% reduction in strength due to interface shear effects. Three failure modes were identified: ice layer crushing (α≤15°), interface slip (15°–75°), and rock main fracture (α≥75°). A micro-parameter system for the ice-rock composite medium was developed based on the PFC discrete element model, achieving over 90% agreement between simulation results and experimental data. By considering the coupling effects of fracture thickness and dip angle, the D-P strength criterion was modified, and the theoretical values deviate from experimental data by less than ±5% These findings provide theoretical support for the stability evaluation and disaster prevention in cold-region rock engineering and lay the groundwork for studying ice-rock interaction mechanisms in complex freeze-thaw environments.