Search Results (1,065)

Brittle geomaterials such as coal and rock are prone to unstable failure under high stress and dynamic disturbances, where rapid release of stored elastic strain energy can trigger dynamic disasters. Polyurea, a high-strength and high-ductility elastomer, can form a continuous flexible coating on the surface of coal/rock to regulate their deformation–fracture behavior. Here, uniaxial compression tests were performed on coal specimens coated with polyurea layers of different thicknesses (0–1.25 mm). Acoustic emission (AE) and digital image correlation (DIC) were jointly employed to characterize macroscopic deformation, microcrack evolution, fracture-mode transition, and energy partitioning. The results show that polyurea provides passive lateral confinement that suppresses lateral expansion and shifts macroscopic failure from brittle splitting to progressive ductile damage. AE-based AF–RA analysis indicates that thicker coatings increase the normal stress and shear resistance along potential fracture planes, promoting a microfracture transition from shear-dominated to tension-dominated cracking. Energy analysis demonstrates that the coating enhances pre-peak energy dissipation via coordinated deformation with the coal, while thicker coatings (≥1.00 mm) exhibit pronounced post-peak elastic tensile deformation to absorb and buffer fracture-released energy, impeding the instantaneous energy release typical of bare coal. Moreover, the elastic energy index shows that polyurea markedly reduces impact tendency, with an appropriate thickness stabilizing specimens from strong to weak/non-impact propensity. These findings clarify the coupled confinement–fracture–energy regulation mechanisms of polyurea coatings and provide quantitative guidance for coating-thickness design to mitigate dynamic failure hazards in brittle materials. Full article

The Huainan Mining Area features extensively developed, fragmented-soft and low-permeability coal seams, characterized by low porosity and permeability, complex geological structures, and significant difficulty in coalbed methane (CBM) drainage. Horizontal wells with staged fracturing in the coal seam roof have become a key method for regional gas control. To further enhance the volume fracturing stimulation effect and single-well gas production, this study targets the horizontal well group in the roof of the No. 8 coal seam in the Huainan Mining Area as the research object. A saturated volume fracturing technology for horizontal wells in the coal seam roof, centered on the concept of a high pump rate (18–20 m³/min) and a high proppant volume (>250 m³/stage), is proposed. This study investigates the fracture propagation mechanisms and fracturing parameter optimization of this technology, and conducts engineering application to verify its stimulation effect. Increasing the fracturing pump rate improves the proppant-carrying capacity of the fracturing fluid, successfully enabling high-rate and high-volume proppant placement. Optimization of the perforation parameters—12 holes per m per cluster and a cluster spacing of 15–25 m—utilizes high perforation friction and moderate stress interference to promote balanced initiation and propagation of multiple fractures within a stage. The optimized ‘saturated’ injection mode, with a single-stage fluid volume exceeding 2400 m³, a single-stage proppant volume exceeding 250 m³, and a maximum sand ratio exceeding 20%, combined with a multi-size proppant mixture, enables full propping of both main and branch fractures. Microseismic monitoring shows that the hydraulic fracture extension length increased by approximately 50% compared to conventional wells, significantly enlarging the stimulated reservoir volume (SRV). Saturated fracturing achieved stable gas production of 2000 to 3000 m³/d, with average production ramp-up rates of 21.47–26.40 m³/d (five times higher than the 5.34 m³/d of the conventional well), and the stable plateau period was notably extended from 36 days to over 150 days. The saturated volume fracturing technology proposed in this study provides an important reference for efficient CBM extraction and surface gas control in mining areas with similar geological conditions. Full article

This study investigates the fracture development and caving mechanisms in longwall coal mining using powered roof supports (PRSs), simulated with the Finite–Discrete Element Method (FDEM) in Geomechanica’s Irazu platform. It is presented as an application study demonstrating the ability of this established FDEM platform to simulate fracture evolution and caving in a longwall environment, rather than as the development of a new model, criterion, or algorithm. A numerical model of a longwall face, including canopy, shield, and base components, was constructed in SolidWorks and imported for simulation. Fractured and intact coal zones were defined, and boundary conditions were applied to represent the mining advance sequence. Stress redistribution, fracture initiation, and subsequent caving behind supports were analyzed both with Irazu’s native tools and through advanced visualization in ParaView. Results revealed that fracture initiation occurs at the roof–canopy interface, propagating towards the gob and floor, eventually forming an elliptical caving pattern. Stress analysis highlighted critical loading at both canopy–roof and base–floor contacts, consistent with patterns reported in field and theoretical studies. Energy maps reveal elastic energy buildup prior to first break and its stepwise release during fracture propagation and caving. This application demonstrates the potential of FDEM to capture both the mechanical response of supports and the evolution of coal fractures, offering valuable insights for optimizing support design and ensuring roadway stability. These findings contribute to improved prediction and management of strata behavior in underground coal mining, bridging numerical modeling with practical engineering applications. Full article

Freeze–thaw cycles cause mechanical deterioration and instability of slope rock masses in open-pit coal mines located in the cold regions of Northwest China. In this study, the research object is fine-grained sandstone from the Yan’an Formation in the Tarangole mining area of the Ordos Basin. Here, indoor freeze–thaw cycling, uniaxial compression, and triaxial compression tests were conducted to systematically analyze the deformation behavior, strength evolution, and failure modes of the sandstone under varying numbers of freeze–thaw cycles, freezing temperatures, and confining pressures, thereby revealing its freeze–thaw damage mechanism. The results show that the number of freeze–thaw cycles is the dominant factor affecting the elastic modulus. Freezing temperatures (especially between −5 °C and −15 °C) and the number of freeze–thaw cycles (particularly the first 10 cycles) significantly reduce peak strength. In addition, confining pressure can significantly enhance the resistance to deformation (under 15 freeze–thaw cycles, the elastic modulus increases by 181.8% as confining pressure rises from 0 to 2 MPa). Within the low confining pressure range (0–1.5 MPa), peak strain decreases monotonically with increasing confining pressure and is independent of the number of freeze–thaw cycles. Finally, the increase in the number of freeze–thaw cycles and the decrease in temperature jointly promote crack development, and the failure mode shifts from pure shear to a shear-tension composite mode. The underlying cause lies in the evolution of interparticle cementation within the soil skeleton and in the associated pore–crack structure. In addition, based on fracture damage mechanics and the modified Weibull distribution, a damage evolution equation and a constitutive model for sandstone considering freeze–thaw cycles and temperature effects were established and validated. Therefore, the research findings can provide a theoretical basis for slope support, freeze–thaw disaster prevention and mitigation, and stability assessment in the Tarangole mining area and other cold regions. Full article

Fractured coal in the residual-strength stage is a primary medium for gas migration and drainage in deep mining areas. To investigate the hydro–mechanical seepage response of post-peak fractured coal under constant-pressure-difference conditions, triaxial CO₂ seepage tests were conducted on coal specimens collected from the Xinyuan Coal Mine. A Weibull-based damage constitutive model was established to characterize the confining-pressure-induced hysteresis in the damage-evolution path. The flow-rate evolution and Reynolds number analysis indicated that gas flow remained within the linear Darcy regime. A controlled-variable analysis was used to examine the competing effects governing permeability evolution. Mechanical compaction induced an exponential decrease in permeability, whereas the decrease in permeability with increasing pore pressure was interpreted, within the proposed model framework, as the combined effect of possible adsorption-induced matrix swelling and weakened gas slippage. To address the limitations of conventional constant-slip-factor models, a pressure-dependent slip modulation coefficient was introduced into a composite permeability equation incorporating effective stress, adsorption-related deformation, and dynamic gas slippage. Global nonlinear fitting yielded R² = 0.97 and an RMSE of 0.1909, with the residuals generally distributed around zero, supporting the fitting reliability of the model within the investigated stress–pressure range. Response-surface analysis identified mechanical compaction as the dominant controlling mechanism, while adsorption-related deformation and gas slippage acted as secondary correction mechanisms. The proposed framework provides a quantitative basis for distinguishing the mechanical and fluid-related effects governing permeability evolution in post-peak fractured coal. Full article

Geological disasters are frequently triggered in steep mountainous mining areas due to the coupling effects of underground excavation and slope stability, yet the applicability of traditional rock movement theories in such terrains remains unclear. This study investigates an extremely steep coal mine in southwestern China, integrating engineering geological surveys, unmanned aerial vehicle (UAV) measurements, InSAR monitoring, and rock movement theoretical calculations to analyze the impact of mining on mountain deformation and slope stability. The results show that the study area exhibits steep slopes (55–85°) and gently inclined, reverse-layered rock masses controlled by structural fracture zones, creating a geological environment prone to mining-induced landslides. The 1151 working face lies at a depth of 286–470 m, with a protective coal pillar of approximately 160 m left between the excavation and the cliff zone. InSAR monitoring indicates cumulative LOS deformation rates of −0.98 to 0.55 cm/a, with subsidence concentrated above the working face, while existing landslides in the cliff zone show no significant deformation. Comparison between theoretical calculations and InSAR inversion reveals that InSAR boundary angles (downslope 61–68°, upslope 67–73°) exceed theoretical predictions (downslope 48–52°, upslope 55°), indicating that complex topography and rock mass structure constrain mining-induced deformation propagation. The findings demonstrate that appropriately designed protective coal pillars and avoidance of unstable slopes can effectively mitigate the impact of mining-induced disturbances on existing hazards. This study provides valuable reference for landslide risk assessment and disaster prevention in extremely steep mining regions. Full article

The Ordos Basin contains abundant deep coalbed methane (CBM) resources, whose efficient development largely depends on the effective implementation of large-scale volumetric fracturing technologies. To comprehensively evaluate the fracability of deep coal reservoirs in this basin, this study focuses on the No. 8 coal seam of the Benxi Formation. Based on rock mechanical experiments and well-logging data, multivariate linear regression models were established to predict Young’s modulus (E) and Poisson’s ratio (μ). The Huang model was applied to determine the three principal in situ stresses of the coal seam. Furthermore, a comprehensive fracability evaluation model was constructed by integrating three key indicators, namely brittleness index (BI), horizontal stress difference (Δσ_h), and tensile strength (S_t). The entropy evaluation method was used to determine the weights of these indicators, and the fracability index (F) of deep coal reservoirs was calculated. The results show that the weights of the factors controlling fracability decrease in the following order: tensile strength (0.434), brittleness index (0.332), and horizontal stress difference (0.234). The No. 8 coal seam in the northern and southern parts of the basin, including the Daning–Jixian, Shenfu, Jiaxian, northern Yulin, and southern Yanchuan areas, exhibits relatively favorable fracability, whereas northern Liulin and southern Yulin show comparatively poor fracability. In addition, the fracability index shows a clear positive correlation with the peak gas production of vertical CBM wells. Based on this relationship, the deep coal reservoirs were classified into three categories: Class I reservoirs (F > 0.55), characterized by high fracability and high production potential; Class II reservoirs (0.50 ≤ F ≤ 0.55), characterized by moderate fracability and moderate production potential; and Class III reservoirs (F < 0.50), characterized by low fracability and low production potential. These findings provide a scientific basis for identifying fracturing sweet spots and for the classification evaluation of deep CBM resources in the Ordos Basin. Full article

Coal surface morphology plays a pivotal role in advanced coal processing operations, encompassing comminution, beneficiation, flotation kinetics, and intelligent process optimization. However, conventional characterization approaches are inherently labor-intensive and susceptible to inter-operator subjectivity, hindering their integration into autonomous industrial monitoring systems. To surmount these challenges, this study proposes an explainable morphology-aware coal surface characterization framework that synergizes unsupervised pseudo-label generation, targeted data augmentation, and explainable artificial intelligence. Initially, a high-dimensional feature set comprising grayscale intensity statistics, entropy, edge density, and Gray-Level Co-occurrence Matrix descriptors was extracted from 454 coal surface images. Subsequently, Principal Component Analysis and K-means clustering were implemented to identify intrinsic morphology-driven structural patterns, generating robust pseudo-labels without manual annotation. These pseudo-classes were utilized to train and benchmark multiple transfer learning architectures, including EfficientNetB0, VGG16, and MobileNetV3. Experimental results demonstrated that MobileNetV3 achieved superior classification efficacy under a strict leakage-safe evaluation configuration, exceeding 90% across key performance metrics while offering significantly lower computational complexity—ideal for edge-computing deployment. Furthermore, Grad-CAM-based interpretability analysis validated that the models focused on physically significant morphological features, such as fracture boundaries and heterogeneous texture transitions. These findings indicate that the proposed framework provides a robust, computationally efficient, and interpretable decision-support tool for smart beneficiation and intelligent industrial coal processing environments. Full article

Tight gas is a critical unconventional energy resource, yet the geological characteristics and accumulation processes of tight gas in China’s Songliao Basin remain poorly documented. This study aims to investigate the tight gas system in the Songliao Basin as a representative continental basin, with key objectives including evaluating source rock and reservoir properties via mineralogical and geochemical analyses, characterizing lithologies and pore types, determining the gas charging mechanism in tight media, and identifying the main controlling factors for accumulation. Geochemical results indicate that the Shahezi Formation contains medium to good mudstones and excellent coals. Reservoirs consist of tight sandstones and conglomerates deposited in fan delta and braided river delta systems, with pore spaces dominated by dissolution pores and microfractures, resulting in ultra-low porosity and permeability. Conventional buoyancy-driven migration is ineffective; instead, gas charging is driven by hydrocarbon generation expansion force, creating overpressure that expels pore water and forces gas into reservoirs through fault-sand conduits. Accumulation is controlled by continuous gas supply from thick, highly mature source rocks, dissolution-enhanced and fracture-dominated reservoir space, and sufficient source–reservoir pressure difference. This study elucidates tight gas characteristics and accumulation mechanisms in continental basins, providing data applicable to both continental and marine settings. Full article

Shallow-buried coal seams in western China are commonly overlain by deeply incised gully terrain, where mining is often accompanied by coal-wall spalling and abnormal increases in support resistance, which affect safe and efficient production. To investigate overburden failure during shallow-buried coal seam mining under gully terrain and to clarify the support–resistance mechanism, a typical working face was selected as the engineering background. Physical similarity simulation, 3DEC numerical simulation, and theoretical analysis were used to analyze overburden failure characteristics and the coupled evolution of the stress, displacement, and fracture fields. Mechanical models of key-stratum fracture and a support–resistance estimation model were established to reveal the influence of overburden-thickness variation on key-stratum fracture and support resistance. The results show that overburden failure in gully areas exhibits pronounced stage-dependent and asymmetric characteristics. In the similarity simulation, the initial fracture intervals of the key stratum in the downhill section were 32 m and 36 m, indicating an asymmetric fracture pattern with a shorter span on the left side and a longer span on the right side. In the uphill section, the periodic fracture interval of the key stratum decreased from 30 m to 24 m as the overburden thickness increased. During overburden failure in gully areas, the three fields exhibited a coupled relationship: stress concentration at the working face caused overburden failure and subsidence, which promoted fracture propagation, whereas stress redistribution in the goaf compacted the fractured overburden and promoted fracture closure. The overburden failure characteristics differed significantly between mining stages. During downhill mining, the key stratum behaved as a fixed-ended beam with a relatively large fracture interval, whereas during uphill mining, it formed a cantilever beam, and its fracture interval decreased with increasing overburden thickness. The loading mechanism of support resistance was shown to be jointly controlled by variations in gully overburden thickness and key-stratum fracture. During downhill mining, support loading increased gradually under the support of the fixed-ended beam key stratum. During uphill mining, support loading exhibited periodic abrupt increases under the combined effects of increasing overburden thickness and periodic fracture of the cantilever-beam key stratum. These findings provide a theoretical basis for strata pressure control at working faces in gully areas. Full article

The permeability of coal seams plays a critical role in the efficiency of coalbed methane extraction and gas disaster prevention. Traditional permeability models often overlook the anisotropic and dynamic evolution characteristics of coal under varying stress and gas adsorption conditions. This paper proposes a novel permeability evolution model that integrates the effects of effective stress variation and gas sorption-induced deformation on coal permeability. Starting from the concept of face porosity and utilizing a representative voxel approach, the model incorporates the anisotropy of mechanical parameters and adsorption expansion strain to derive the evolution of permeability in three dimensions. The model is validated against experimental permeability data from two distinct coal samples (Sulcis and Sydney), demonstrating its ability to accurately capture permeability changes under different boundary conditions. Furthermore, the concept of “internal expansion strain coefficient” is introduced to quantify the impact of adsorption-induced matrix deformation on permeability. The model provides a theoretical foundation for predicting gas flow behavior in coal seams under complex in-situ conditions and offers significant insights into the optimization of gas extraction strategies. Full article

Grouting and sealing in gas drainage boreholes are two of the critical measures to ensure efficient coal seam gas extraction. However, traditional cement grouting often leads to debonding and cracking of the slurry–coal cemented body under external load, resulting in poor sealing performance. To suppress crack propagation and achieve borehole reinforcement and efficient sealing, this study compares the mechanical properties and crack evolution characteristics of slurry–coal cemented samples grouted with different modified materials. Five types of cement-based sealing materials, including ordinary Portland cement, were used for grouting coal rock in boreholes. By employing an acoustic emission signal acquisition system and a non-contact full-field strain measurement system, the tensile mechanical properties of coal before and after grouting were compared. The influence of material properties on the reinforcement capacity of borehole coal was analyzed, along with the failure process characteristics and final failure morphology of the slurry–coal cemented body under Brazilian splitting load. Finally, the effects of material toughness and bond strength on the brittleness index and failure mode of the slurry–coal cemented samples under Brazilian splitting conditions were discussed. The results show that the tensile strength improvement rates of the samples were 26.9%, 55.3%, 48.4%, 8.6%, and 45.6%, respectively. Distinct from previous studies focusing on fractured grouting or intact coal rock, this work for the first time systematically reveals the non-monotonic influence of the combination of material toughness and bond strength on the reinforcement effect of borehole coal samples and proposes an evaluation framework based on quantitative acoustic emission crack type analysis and the concept of effectiveness threshold. The varying degrees of tensile strength enhancement indicate differences in the reinforcement capabilities of grouting materials with different properties. The acoustic emission signals during the failure process of the slurry–coal cemented body exhibited typical stage-specific characteristics, though material properties altered the failure modes. By quantifying the intrinsic properties and crack characteristics of the slurry–coal cemented body using the brittleness index and grayscale histograms, this study provides a theoretical basis for guiding efficient sealing of gas drainage boreholes through an in-depth understanding of the mechanical behavior and crack evolution of borehole coal samples before and after grouting under Brazilian splitting conditions. Full article

The desert bottomland of Northern Shaanxi, China, features an ecologically fragile environment with a pronounced mismatch between abundant coal resources and scarce water resources. Large-scale coal mining often impairs the water-resisting capacity of overlying strata, leading to shallow groundwater depletion, surface drought, and vegetation degradation. This study focuses on determining the height of the water-conducting fractured zone (WCFZ) and assessing shallow groundwater loss in such ecologically sensitive mining areas. Through analysis of measured WCFZ heights, the empirical formulas currently specified in national codes are found to be inapplicable to the study area. A multi-factor nonlinear prediction model, better suited to local conditions, is therefore established using multiple nonlinear regressions. Taking the Jinjitan Coal Mine as a case study, a 3D hydrogeological conceptual model is developed using FEFLOW to simulate phreatic water responses to mining activities. The results indicate a maximum phreatic water drawdown of 3–4 m, with post-mining burial depths predominantly ranging from 5 to 8 m, reaching a warning level that requires attention and mitigation. This study provides a valuable reference for water hazard prevention and ecological protection in desert bottomland regions. Full article

With deep coal mining in China, high in situ stress frequently causes severe floor deformation, bolt-cable support failure, and excessive floor heave, which critically threaten mine safety. In this study, we use physical experiments, numerical simulation, and theoretical analysis to explore how hydraulic fractures with different azimuth angles affect stress transfer in roadways under floor dynamic pressure. Prefabricated fractures simulate weak planes induced by hydraulic fracturing. Uniaxial compression tests and PFC2D fluid–solid coupling simulations analyze mechanical properties, failure modes, acoustic emission behavior, and stress distribution. Results show that fracture azimuth significantly controls rock damage and failure modes. As the angle increases from 0° to 90°, failure changes from gradual degradation to sudden instability. Peak strength first decreases then increases, reaching the minimum at 22.5°, while roadway damage is minimal at 45°. Small-angle fractures lead to shear failure with clear precursors, and large-angle fractures cause sudden tensile failure. Hydraulic fractures form directional stress-relief zones and enable effective stress transfer and pressure relief. The results support parameter optimization of hydraulic fracturing and stability control for deep roadways under floor dynamic pressure. Full article

Using solid wastes to fabricate sustainable backfill materials for mining engineering is crucial for environmental sustainability worldwide. In this study, the use of coal gangue aggregates as a sustainable alternative to natural aggregates in geopolymer gel backfill materials was explored, which contributes to green mining development. Through uniaxial compression tests, the effects of fine gangue content, mass concentration, and the binder content of geopolymer backfill materials on the compressive behavior of coal gangue geopolymer gel backfill–rock combinations (CGBRC) were systematically evaluated. Digital Image Correlation (DIC) and acoustic emission (AE) techniques were employed to reveal the strain field evolution and damage progression of CGBRC. Results show that as the content of fine coal gangue increases, the compressive strength first increases and then decreases. Compared with the compressive strength at a 20% content, the compressive strength at a 40% content increased by 33.2%, while the elastic modulus increased by 11.2%. Meanwhile, with the increase in mass concentration and binder content, the compressive strength and elastic modulus of coal gangue geopolymer filling materials show an increasing trend, reaching peak values at 86% mass concentration and 32% binder content, respectively. The strain concentration zones mainly form near the backfill interface, with propagation paths governed by backfill strength. Damage evolution undergoes three stages including rapid accumulation during compaction, gradual development in the elastic-plastic stage, and abrupt acceleration at failure. The interfacial debonding behavior is primarily influenced by the strength difference between the backfill and surrounding rock. Specimen failure is dominated by brittle shear fracture, categorized into three modes based on crack paths relative to the backfill, which include penetrating backfill failure, axisymmetric interface failure, and centrally symmetric interface failure. These findings offer theoretical and technical support for coal gangue resource utilization and green mining practices, advancing sustainable solid waste management. Full article