Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces, where irregular coal wall surfaces significantly affect the contact and support effectiveness of the support plate, thereby impacting stability. Through a combination of theoretical analysis, mechanical testing, and numerical simulations, this study establishes a mechanical model of irregular coal wall surfaces to investigate the effects of the undulation period and undulation height on coal wall failure characteristics. This research reveals the mechanical response mechanisms of irregular coal wall surfaces and proposes an innovative method to enhance coal wall stability by improving the supporting cushion material of the support plate, which was validated through numerical simulations. The results show that the undulation height and undulation period significantly influence the macroscopic mechanical parameters of the samples, with the undulation height exerting a more pronounced effect. The strength of the samples with undulating surfaces is approximately 50%-60% that of the samples with flat surfaces. The failure mode under uniaxial compression is predominantly tensile, resulting in long and slender block fragments with a characteristic “III”-shaped tensile fracture pattern. During the loading process, samples with undulating surfaces dissipate energy at all stages, with a greater proportion of energy dissipation occurring during the early loading stage because of structural damage and the formation of internal cracks. The surface compressive and tensile stresses are correlated with the curvature radius of the convex surface and the elastic modulus of the supporting plate. Reducing the elastic modulus of the supporting plate material can effectively alleviate the stress concentration at convex locations and increase the peak strength. This study provides theoretical foundations and technical references for the prevention and control of coal wall spalling in deep thick coal seam mining.

In recent years, the study of chalcopyrite and pyrite flotation surfaces using computational chemistry methods has made significant progress. However, current computational methods are limited by the small size of their systems and insufficient consideration of hydration and temperature effects, making it difficult to fully replicate the real flotation environment of chalcopyrite and pyrite. In this study, we employed the self-consistent charge density functional tight-binding (SCC-DFTB) parameterization method to develop a parameter set, CuFeOrg, which includes the interactions between Cu-Fe-C-H-O-N-S-P-Zn elements, to investigate the surface interactions in large-scale flotation systems of chalcopyrite and pyrite. The results of bulk modulus, atomic displacement, band structure, surface relaxation, surface Mulliken charge distribution, and adsorption tests of typical flotation reagents on mineral surfaces demonstrate that CuFeOrg achieves DFT-level accuracy while significantly outperforming DFT in computational efficiency. By constructing large-scale hydration systems of mineral surfaces, as well as large-scale systems incorporating the combined interactions of mineral surfaces, flotation reagents, and hydration, we more realistically reproduce the actual flotation environment. Furthermore, the dynamic analysis results are consistent with mineral surface contact angle experiments. Additionally, CuFeOrg lays the foundation for future studies of more complex and diverse chalcopyrite and pyrite flotation surface systems.

Rapid and accurate recognition of coal and rock is an important prerequisite for safe and efficient coal mining. In this paper, a novel coal-rock recognition method is proposed based on fusing laser point cloud and images, named Multi-Modal Frustum PointNet (MMFP). Firstly, MobileNetV3 is used as the backbone network of Mask R-CNN to reduce the network parameters and compress the model volume. The dilated convolutional block attention mechanism (Dilated CBAM) and inception structure are combined with MobileNetV3 to further enhance the detection accuracy. Subsequently, the 2D target candidate box is calculated through the improved Mask R-CNN, and the frustum point cloud in the 2D target candidate box is extracted to reduce the calculation scale and spatial search range. Then, the self-attention PointNet is constructed to segment the fused point cloud within the frustum range, and the bounding box regression network is used to predict the bounding box parameters. Finally, an experimental platform of shearer coal wall cutting is established, and multiple comparative experiments are conducted. Experimental results indicate that the proposed coal-rock recognition method is superior to other advanced models.

Borehole pressure relief helps prevent rock bursts. However, this may change the physical and mechanical properties of the surrounding rock, affect the variation of the plastic zone of the roadway, and lead to the failure of roadway support, thus threatening the safety of the roadway. In this paper, the variable angle shear test of drilled specimens under the action of static and dynamic loads is used to study the evolution of mechanical parameters of the specimens and their influence on the plastic zone of the surrounding rock. The shear strength decreases linearly with the increase of drilling diameter. With the increase of pre-static load level and dynamic load amplitude, the cohesion first increases and then decreases, and the internal friction angle decreases. Moreover, the shear failure surface changes from rough to smooth. The reasons include that the static load enhances the tooth cutting effect and the repeated friction of cracks caused by the dynamic load. Borehole pressure relief leads to an increase in the radius of the plastic zone of the surrounding rock following a quadratic function. The research results of this paper provide a theoretical basis for designing drilling unloading parameters and supporting parameters for rock burst roadways.

To ensure the safe implementation of underground reservoirs in abandoned coal mines, this study explores the mechanical behavior and failure mechanisms of coal-concrete composite structures under staged cyclic loading. Specimens with coal-to-concrete height ratios ranging from 0.5:1 to 3:1 were tested, with damage evolution continuously monitored using acoustic emission techniques. Results indicate that while the peak strength of pure materials decreases by approximately 1 MPa under cyclic stress compared to uniaxial compression, composite specimens exhibit strength enhancements exceeding 5 MPa. However, the peak strength of composite specimens decreases with increasing coal height, from 30 MPa at CR0.5 to 20 MPa at CR3.0. The damage state was assessed using the dynamic elastic strain energy index and Felicity ratio, which revealed that composite specimens are more prone to early damage accumulation. Spatial acoustic emission localization further reveals distinct failure modes across specimens with varying height ratios. To elucidate these differences, interfacial effects were incorporated into a modified twin-shear unified strength theory. The refined model accurately predicts the internal strength distribution and failure characteristics of the composite structures. These findings provide a theoretical basis for the structural design and safe operation of underground reservoir dams.

The stability of underground tunnel roofs is strongly influenced by wedge blocks formed by complex joint networks. The mechanical behavior and failure mechanisms of different roof wedge blocks in arched holes were investigated under biaxial stress conditions. The crack evolution and failure modes of the specimens were analyzed through acoustic emission (AE), digital image correlation (DIC), and discrete element method (DEM). Results show significant variations in mechanical properties: specimens T1 (extremely unstable triangular) and T2 (extremely unstable quadrilateral) exhibited higher strength than T3 (extremely stable triangular) and T4 (extremely stable quadrilateral), while support more effectively enhanced the strength of T3 and T4. Failure modes were classified as rock-dominated, wedge-dominated, or co-dominated. Cracks typically initiated near the wedge and propagated outward. Unsupported specimens developed tensile cracks at the hole bottom, shear cracks at the sides, and mixed cracks along wedge boundaries, whereas supported specimens mainly exhibited cracks at the roof and sides. Stress analysis indicated that unsupported conditions induced high stress differences, promoting localized shear failure. Wedge geometry significantly affected shear stress redistribution at the roof. These findings highlight the critical role of support and wedge block geometry in controlling stress distribution and failure mechanisms in arched tunnels.

Coal and rock dynamic disasters are always major hidden dangers threatening mine safety production. Many researchers use cement concrete material as filling and energy-absorption materials. However, the current material toughness is not sufficient to meet the requirements of mine disaster prevention. Based on this, in order to find the optimal-ratio material that combines strength and toughness, the synergistic mechanism of lithium slag (LS), ethylene-vinyl acetate (EVA) copolymer, and polyvinyl alcohol (PVA) fiber mixtures in improving the mechanical properties of cement concrete, as well as the mechanism of microscopic phase evolution, was analyzed through macroscopic experiments, mesoscopic characterization, microscopic analysis, theoretical calculations, and comprehensive evaluation. The stress-strain curves obtained from the uniaxial compressive strength tests of specimens with different admixtures and fibers were investigated, and the characteristics of different stages were analyzed. The mechanical properties of different admixtures and fiber-reinforced materials, including their advantages and disadvantages, were compared through weighted comprehensive evaluation. The entire process of material failure, ranging from pore compaction, crack initiation, crack propagation, specimen instability to crack penetration, was explained via macroscopic fracture morphology, and the mechanical mechanism of how different admixtures affect the mechanical properties of concrete materials was revealed. The microscopic mechanism and the phase-evolution process of how the admixture affects concrete properties were elucidated using X-ray diffraction (XRD), hydration reaction theory, and Fourier transform infrared spectroscopy (FTIR). Furthermore, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was used to reveal the interfacial pore state and element distribution of the internal microstructure of concrete. The results show that PVA fiber bars can play the role of a “skeleton bridge” to improve the toughness of materials. LS can effectively promote the hydration process and cooperate with PVA fiber bars to enhance the mechanical properties of the material. EVA will inhibit the hydration reaction and degrade the material’s mechanical properties through the “organic isolation” effect. In addition, the on-site application has proven that the R3-group materials in this study can effectively inhibit the deformation of the roadway and possess strong reliability. Finally, the advantages and feasibility of LS-and-fiber-reinforced concrete were discussed from four perspectives: environmental protection, economy, disaster prevention, and development. This paper is expected to provide technical reference for the large-scale disposal of solid waste LS, the performance-optimization direction of concrete materials, and the prevention and control of coal and rock dynamic disasters.

Developing hydrothermal resources in highly conductive karst aquifers at deep mine floors is regarded as a potential approach to achieving the co-development of coal and geothermal resources. However, the heat transfer potential of the fracture system in the target reservoir under mining activities remains in suspense. Hence, a coupled thermal-hydraulic-mechanical model was developed for the karst reservoir of Anju coal mine in China, considering non-isothermal convective heat transfer in fractures. This model examined the influence of stress redistribution due to different mining distances (MD) on the effective flow channel length/density and the high/low-aperture fracture distribution. The dynamic heat generation characteristics of the geothermal reservoir were evaluated. Key findings include: Mining-induced stress creates interlaced high-aperture and low-aperture fracture zones below the goaf. Within these interlaced zones, the combined effect of high- and low-aperture fractures restricts the effective flow channel length/density of the fracture network. This contraction of the flow field leads to a significant decline in production flow rate, which consequently reduces both the production flow rate and power as MD increases. This work represents the study of mining disturbances on geothermal production, providing a theoretical foundation for the co-development of coal and geothermal resources.

In cold-region environments, where complex stresses and mining disturbances occur, rock masses are frequently segmented into discontinuous bodies by fractured structural planes, leading to anisotropic physical and mechanical properties. To explore the evolution of microcracks, degradation characteristics, and failure modes of fractured rocks in cold regions under the influence of freeze-thaw cycles, integrating laboratory experiments with the damage mechanics of freeze-thaw cycles. A numerical model for freeze-thaw cycle damage in rocks with various fracture dip angles was developed. The study revealed that the freeze-thaw expansion force generated during the pore water-ice phase transition is the primary driving factor behind freeze-thaw cycle damage. The initiation and propagation of microcracks and micropores, the detachment of matrix particles, and the loosening of clay mineral structures result in the transformation of the rock from a dense to a porous state, causing significant degradation in macroscopic mechanical properties. As freeze-thaw cycles increase, both the uniaxial compressive strength and the deformation modulus of the rock decrease significantly, with the failure mode gradually shifting from brittle instability to brittle-plastic or plastic failure. The findings of this study offer a practical approach to uncovering the mechanical response mechanisms between freeze-thaw damage in fractured rocks and structural planes.

Phenolic foam (PF) has attracted growing attention in plugging areas due to its lightweight, flame retardancy and high fillability, yet its friable character and high reaction temperature severely weaken its potentials toward practical coal mining applications. Herein, a novel phenolic composite material filled with modified fly ash (MFA) geopolymer has been proposed to address the above issues. By modifying fly ash (FA) particles with siloxanes, robust interfacial bonding between the organic PF polymer and inorganic geopolymer network has been established, which enables modulation of their micro-morphologies to optimize their macro performances. The foam structure of PF evolves from an open-cell to a closed-cell morphology with the incorporation of MFA, leading to a decreased pulverization ratio (41%) while enhanced mechanical properties (15%). Compared with neat PF, the composite exhibits faster gelation dynamics during curing, with a maximum reaction temperature as low as only 40 °C. PF/MFA composite show high reliability against gas leakage during a laboratory designed coal mine plugging test. Furthermore, the formation of a silica hybrid char layer with higher graphitization degree and a multiple continuous closed-cell structure following the combustion of PF/MFA effectively inhibits the release of combustible volatiles and toxic gases. It is provided that this strategy of geopolymer filled polymer cross-linking networks with tunable morphology opens up an avenue for advanced mining phenolic filling materials.