Aug 2026· Engineering Research Express· Vol 8· 0 citations· 38 references
Physics
Abstract
During underground excavation, structural instability and failure of coal-rock masses are major causes of engineering accidents. This study focuses on the coal mass ahead of the excavation face and divides into a multi-layer composite structure to systematically analyze the mechanical response characteristics of the combined coal mass under static and dynamic loading. Drop hammer impact tests were conducted to investigate the crack propagation and failure morphology of the combined coal mass. The results show that, under static loading, single-layer coal mainly exhibited X-shaped shear failure, whereas the combined coal mass showed V-shaped layered spalling failure. Under dynamic loading, compressive failure dominated in the central region, while shear failure mainly occurred at the four corners, and the damage was more pronounced along the minor axis direction. Two crack patterns were observed on the coal surface, simple radial cracks and complex intersecting radial and circumferential cracks. Under the combined effects of rectangular geometry and impact loading, the radial cracks of the specimen show a structural tendency to preferentially propagate along the minor axis direction. Under impact loading, the combined coal mass exhibited an overall spindle-shaped failure morphology in the axial direction. In the damage zone, the superposition of tensile stress and energy accumulation made the coal mass more susceptible to failure, resulting in a greater number of radial and circumferential cracks. These findings provide a scientific theoretical basis for revealing the incubation mechanisms of coal-rock dynamic disasters and optimizing disaster prevention and control measures under mining-induced disturbance conditions.
Overburden rotation and mining disturbance promote deep coal fracture and spalling, potentially inducing dynamic hazards, while the coal–rock thickness ratio largely governs the composite’s dynamic response and failure severity. Based on the geological conditions of a typical deep coal mine, SHPB tests were performed on coal–sandstone composite specimens with four systematically varied coal-to-rock ratios (C:R = 1:0, 2:1, 1:1, and 1:2). High-speed photography and the digital speckle correlation method (DIC) were integrated to capture displacement, strain, energy, and fragmentation fields throughout progressive dynamic compression. Experimental data revealed four findings: (1) Crack development follows a sequential evolution process of initiation, propagation, and failure. Higher impact air pressure accelerates crack development and coalescence, resulting in a higher degree of specimen fragmentation and fewer large blocks. Within the tested range of coal–rock ratios, an increase in the rock proportion accelerates coal fracture, which is attributed to the significantly higher density and hardness of rock compared to coal. (2) Energy evolution consistently follows three stages: absorption, accumulation, and dissipation. Under identical impact pressure, a higher rock ratio elevates equivalent stiffness and wave impedance, leading to monotonic increases in peak stress, peak strain, absorbed energy, and dissipated energy. (3) The fragmentation degree exhibits a pronounced dependence on impact pressure. Specifically, for the pure coal specimen (C:R = 1:0), when the impact pressure increases from 0.3 MPa to 0.7 MPa, the mass percentage of coarse debris (>30 mm) drops from 73.37% to 18.57%, whereas that of fine particles (<4 mm) rises from 15.69% to 35.24%. (4) Under identical impact conditions, a higher rock proportion leads to increasing trends in all measured indicators, including peak stress, strain, and energy accumulation and dissipation, which are consistent with the superior mechanical properties of the rock. Based on these observations, it can be inferred that the wave impedance mismatch and stiffness ratio at the coal–rock interface play a key role in controlling stress wave transmission/reflection and strain incompatibility; however, the individual contribution of each factor warrants further dedicated investigation.
Jiaxin Dang, Jianwei Li, Min Tu et al.· Fractal and Fractional· 0 citations
The load-bearing and damage characteristics of coal seams vary under different geological conditions. To investigate the failure characteristics of coal bodies under hard roof conditions, this study is set against the backdrop of the Zhangji Coal Mine's 11,129 work face. By employing a combination of physical experiments, numerical analysis, theoretical calculations, and field validation, we explore the load-bearing capacity of coal bodies and their damage characteristics. The research findings indicate the following: (1) During the coal seam extraction process, the thick hard sandstone roof has a large span and exhibits minimal deformation, thus providing support for the overlying weak rock strata within a certain range. Following the implementation of pre-splitting blasting, the initial fracture step distance of the roof was reduced to 45 m, while the periodic fracture distance decreased to between 10 and 30 m. (2) The coal rock exhibits energy accumulation and dissipation at the moment of bearing stress or fracture. When the roof initially collapses, the peak stress within the coal body reaches 33.1 MPa, with a stress concentration coefficient of 1.7. The compressive displacement of the coal body within the stress concentration zone ranges from 2.8 to 12.1 cm. Energy accumulates within the coal body, reaching a maximum value of 124 kJ/m
3
, while the energy of the load-bearing layer above the goaf accumulates between 62.3 and 103 kJ/m
3
. (3) Based on the mechanical equations governing the load-bearing state of coal rock, a quantitative analysis was conducted on how four indicators—fracture step distance, distance from the rock layer to the work face, elastic modulus of the rock layer, and thickness of the rock layer—affect the coal body under dynamic and static load conditions, revealing the primary influencing factors. (4) Considering the geological conditions of the 11,129 work face, a pre-splitting blasting depressurization scheme was proposed using a fan-shaped hole grouping arrangement to reduce the fracture step distance of the hard rock layer. Upon the initial fracture of the roof, the support pressure in the lower section of the work face was consistently between 18.8 and 22.7 MPa. When the work face advanced through the pre-splitting blasting area (exceeding 700 m), the pressure in the middle support increased from 14.7 to 18.3 MPa to between 30.0 and 32.3 MPa, with a maximum recorded support pressure of 35.3 MPa. Field data indicate that the pre-splitting blasting scheme for the work face achieved the desired results. The study outcomes provide insight into the overall failure modes of coal rock bodies under the geological conditions of directly overlying hard roofs, thereby offering references for further investigation into the load-bearing characteristics of coal bodies and the calculation of crack propagation.
Jiaxin Dang, Jianwei Li, Min Tu et al.· Geomechanics and Geophysics...· 0 citations
Variations in coal-seam thickness affect the load-bearing structure and electrical response of coal–rock composites, contributing to dynamic disasters in coal-thickness variation zones. To investigate failure mechanisms and resistivity precursors, conductive coal–rock analogue materials with similar mechanical properties were prepared. Composite specimens with rock-to-coal thickness ratios of 1:1, 1:2, and 1:3 were tested under uniaxial compression with synchronous resistivity monitoring, and PFC3D simulations were used to analyze crack evolution and damage accumulation. As the coal proportion increased, peak strength decreased from 18.73 to 15.62 MPa, and failure strain decreased from 2.45 to 2.20%. The total input energy and elastic energy storage capacity also declined, indicating weakened load-bearing and energy storage capacities and earlier damage localization. During loading, resistivity evolves through compaction‑induced reduction, elastic stabilization, pre‑peak rise and failure fluctuation. The failure-stage resistivity increased by 1.27–1.33 times, and the pre-peak resistivity rise preceded the macroscopic stress drop, providing a precursor window for instability identification. PFC3D results reproduced the experimental responses and failure modes, showing that increased coal thickness promoted earlier crack clustering and coalescence, with shear cracks dominating near peak stress. The normalized damage variable based on broken particle bonds corresponded well with resistivity evolution. A resistivity increment index was developed to quantify the transition from stable fluctuation to sustained increase, enabling identification of the precursor stage from stable crack growth to accelerated unstable coalescence. These findings provide a basis for failure-mechanism analysis and resistivity-based warning in coal-thickness variation zones.
Chenglin Tian, Jia-Li Liu, Jian-Lei Liu et al.· Scientific Reports· 0 citations
The coal–roof/floor combination system is a special geological structure consisting of both coal and roof/floor materials, which often leads to the occurrence of impact failure. The instability and failure of the coal seam are not caused by a single disturbance, but often occur under repeated loading and unloading processes under the action of mining stress. Thus, research on the impact failure, especially the energy evaluation of coal–rock combination materials under cyclic loading and unloading, is of great significance for understanding the rock burst mechanisms of deep coal mines. This paper focuses on the combination material formed by coal seam and roof and floor rock. Taking the #9 coal seam and roof and floor sandstone from the Zhangshuanglou Coal Mine as the test subjects, conventional triaxial compression and cyclic loading and unloading tests were conducted on sandstone, coal, and coal–rock combination material, respectively. Based on the strain energy evolution characteristics, the failure behavior of the coal–rock combination materials throughout the entire process of energy accumulation, dissipation, and release during cyclic loading and unloading are discussed. The research finds that the macroscopic failure behavior of the tested coal–rock combination specimens is dominated by the weaker coal component, and there are marked differences between the tested sandstone and coal components in their respective energy storage capacities, release characteristics, and dissipation behavior. On the basis of these measured differences and of CT-confirmed failure localization within the coal layer, it is inferred—as a mechanistic working hypothesis rather than a directly demonstrated result—that the main driving energy for the impact failure of the coal component may originate from the elastic strain energy stored in the roof/floor sandstone components, released preferentially toward the coal through their interfaces. For mining and excavation at high-in-situ-stress mining areas, the essence of the impact failure of surrounding rock is the non-coordination of energy storage and release between the roof and floor rock materials and the coal seam. The key to preventing impact failure is to eliminate the differences in energy storage and release between different rock materials in the coal seam.
P. Yin, Chun Liu, Peng-Xiang Wang et al.· Applied Sciences· 0 citations
The long‑term performance and structural integrity of steam‑turbine discs are strongly influenced by crack‑growth behavior under combined thermal stresses and mechanical loading. In this study, a comprehensive analytical framework based on finite element analysis (FEA), mixed‑mode fracture‑mechanics evaluation (Modes I, II, and III), and fatigue crack‑growth modeling using the Paris law is presented. The results indicate that Mode II plays the dominant role in the stress‑intensity distribution and crack‑growth behavior of the investigated turbine disc, while Modes I and III also contribute and cannot be neglected. Therefore, safety assessment based solely on Mode I analysis may lead to inaccurate evaluations of structural integrity. The calculated effective stress‑intensity factor was compared with the fracture toughness of 12Cr steel, showing that the turbine disc currently operates within a safe margin against instantaneous fracture; however, gradual fatigue crack growth under thermo‑mechanical loading conditions remains possible. The crack‑growth analysis further demonstrates that a significant portion of the fatigue life is spent during the stable slow‑growth phase as the crack propagates from small initial sizes to intermediate lengths. The proposed fracture‑mechanics‑based approach provides a reliable tool for condition monitoring, inspection planning, and remaining‑life assessment of steam‑turbine discs, thereby contributing to improved operational safety and maintenance decision‑making.
Unknown authors· Journal of Modern Mechanical...· 0 citations
The heterogeneous occurrence of coal-seam thickness represents a common geological characteristic in underground mining. Variations in coal thickness can directly alter the instability-failure behavior of coal–rock systems, thereby triggering various dynamic disasters. Therefore, revealing failure and disaster-inducing mechanisms of coal–rock systems dominated by coal-thickness effects is critical for deep mining engineering design as well as dynamic disaster prevention and control. To this end, uniaxial compression tests combined with acoustic emission (AE) monitoring were performed on coal–rock combinations with different coal thicknesses. The evolution laws of characteristic strengths (uniaxial compressive strength, initiation strength, and damage strength) versus coal thickness were systematically analyzed. Using full-process spatial localization of internal damage derived from absolute AE energy, an instability evolution model for coal–rock combinations was established. Furthermore, intrinsic disaster-inducing mechanisms governing coal–rock system instability under coal-thickness regulation were summarized, with corresponding engineering prevention-control suggestions put forward. The results show that: (1) UCS, initiation strength, and damage strength of specimens exhibit a nonlinear negative correlation with coal thickness. Initiation strength and damage strength account for approximately 50% and 75% of UCS, respectively; (2) Increasing coal thickness weakens the confinement effect of upper- and lower-sandstone, which shifts the dominant failure zone gradually from coal–rock interfaces to coal interiors. Meanwhile, internal energy accumulation-release processes of combinations present staged evolution characteristics; (3) Different coal thicknesses produce distinct disaster-evolution paths for coal–rock systems. Larger coal thickness corresponds to higher risks of high-energy dynamic disasters. Accordingly, a differentiated hierarchical prevention strategy of “thin protection, medium pressure relief, and thick control” was proposed. These findings provide a theoretical basis for mine engineering design and dynamic disaster prevention-control under dominant coal-thickness effects.
Baochen Wang, Yanwei Duan, Kai Ren et al.· Processes· 0 citations
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