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.

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.

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.

The surrounding rock of roadways often contains complex joint fractures, holes of different sizes, and other internal structural characteristics, which seriously affect their stability. Indoor physical model tests are one of the main ways to study the stability of engineering rock masses. However, traditional methods struggle to produce physical models with exactly the same structures and properties, and the mechanical properties and internal structures of physical models differ considerably from those of in-situ rock masses, which greatly limits the scientific nature of physical model tests in reflecting the actual engineering roadway. In recent years, the rapid development of 3D printing technology has effectively made up for the shortcomings of traditional methods. At the level of material research and development, sand-powder 3D printing coal-rock-like materials with high similarity to natural coal-rock in mechanical behavior are successfully prepared by systematically regulating printing matrix, particle gradation, binder saturation, and glass fiber content. This progress lays a material foundation for the production of physical models. At the level of mechanism research, based on mechanical tests on anchorage bodies using such coal-rock materials, the anchorage mechanisms of supporting elements such as bolts have been systematically revealed. These tests verify the feasibility of using these materials to simulate the anchorage in natural rock masses and provide a theoretical basis for the design of supporting structure. Finally, at the level of physical model tests, researches have employed the sand-powder 3D printing technology with the layered printing process to construct physical models of anchored roadways under the conditions of both intact surrounding rock and fractured surrounding rock. The influence of cracks on the deformation and failure law of roadway is quantitatively analyzed with the aid of the biaxial loading system and the digital speckle technique (DIC). The failure modes revealed by the tests are highly consistent with the field observation results. Collectively, these studies confirm that the sand-powder 3D printing technology can achieve high-precision reconstruction with respect to material properties, internal structure, and mechanical response, effectively overcoming the shortcomings of traditional model tests and showing good application prospects and scientificity in physical simulation research of rock mass engineering.

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.

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.

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.

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.