To address the lack of a unified energy mapping framework for energy release and damage evolution in rocks, uniaxial compression tests were conducted on sandstone with typical pore configurations. Using acoustic emission (AE) and digital image correlation (DIC) techniques to characterize the energy release characteristics and strain evolution laws during rock fracture process. Based on the principle of energy conservation, the energy conversion efficiency α is defined to correlate AE energy with stored strain energy, and an energy type damage factor D is introduced to quantify the damage accumulation process. The results indicate that when D < 0.4, the damage evolution is relatively stable; When D ≥ 0.4, the damage rapidly intensifies, indicating the failure of the specimen. The study also found a significant time lag between AE energy release and macroscopic deformation, which is consistent with the law in engineering practice that microseismic activity precedes monitoring displacement response. Furthermore, a Lemaitre damage model incorporating α was established, which can effectively characterize the nonlinear evolution process of sandstone from elastic deformation to complete failure. Finally, an energy based rockburst warning index based on α and D was discussed, providing technical path for identifying high-risk areas and preventing rockburst disasters in mining engineering.
The dynamic evolution of in-situ stress during coalbed methane drainage governs coal seam stability, and instability-induced damage critically impacts well productivity. Triaxial deformation and methane adsorption-induced expansion experiments were conducted to investigate the stability evolution mechanisms and controlling factors in mid-deep intact and fractured seams. Results show that permeability surges at the peak stress, then declines sharply and eventually stabilizes. Adsorption pressure correlates positively with adsorption-induced strain, with the maximum volumetric strain of 1.756%. Fractured zones are more prone to instability failure than intact coal seams. Instability failure occurs under normal faulting stress regimes with moderate-to-strong desorption capacity and strike-slip stress regimes with strong desorption capacity. Seams under reverse faulting regimes remain stable. Stress difference, critical desorption pressure, elastic modulus, internal friction angle, cohesion, and fault friction coefficient are inversely related to coal seam stability. In late-stage production, failure of faulted zones in the #2 and #4 coal seams occurred at pore pressures of 1.17 and 1.70 MPa, respectively. These failures induced five abrupt bottom-hole pressure drops, each lasting 26–54 min, severely compromising well productivity. Pore pressure inversion yields fracture-wellbore distances of 15–111 m.
Accurately determining the effective fracture toughness (Keff) of rock-concrete (R-C) bi-materials, governed by interface inclination and ambient temperature, is a prerequisite for assessing their structural stability. This study developed a hybrid NRBO-XGBoost prediction model using the Newton-Raphson-Based Optimizer (NRBO) to tune the hyperparameters of Extreme Gradient Boosting (XGBoost) model. The established model was developed based on 154 datasets obtained from laboratory tests and numerical simulations with the cracked straight-through Brazilian disc (CSTBD) specimens, including twelve input parameters. The NRBO-XGBoost model for Keff prediction was investigated and compared with seven more models. Furthermore, the Shapley Additive exPlanations (SHAP) method was employed to quantify the contributions of inputs to Keff to improve the interpretability of the developed model. Finally, new data were used to validate the model. Evaluation results demonstrate that metaheuristic optimization algorithms significantly enhance the performance of XGBoost, with NRBO-XGBoost performing the best. The models rank from highest to lowest prediction performance as follows: NRBO-XGBoost, WOA-XGBoost, PSO-XGBoost, XGBoost, RF, CatBoost, LightGBM, and AdaBoost. The interpretable analysis shows that the interface inclination angle exerts the dominant influence. The validation results demonstrate that NRBO-XGBoost achieves high predictive accuracy on a new dataset, showing promising implications for practical applications.
Understanding aggregate effects within fault fracture zones is crucial for assessing fault reactivation risks in grouted deep coal mines. This study investigates the compressive-shear damage mechanisms of grouted concrete specimens with varying aggregate contents (20%, 40%, 60%) and particle sizes (1–5 mm, 6–10 mm). Uniaxial compressive-shear tests were monitored synchronously using digital image correlation (DIC) and acoustic emission (AE). Additionally, a calibrated PFC2D discrete element model, incorporating matrix, aggregate, and interfacial transition zones, elucidated the mesoscale mechanisms. Results indicate: (1) peak shear load decreases linearly (R2>0.86) with increasing aggregate content, dropping 64.3% from 20% to 60%, driving a transition from brittle to plastic failure; (2) AE b-value evolution tracks progressive damage, while damage rate k exhibits contrasting size-dependent trends; (3) macroscopic failure modes are synergistically controlled by aggregate size and content; and (4) numerical simulations validate the mesoscale mechanical origins of this brittle-to-plastic transition. These findings reveal the micro-mechanical mechanisms of anisotropic failure and re-strengthening in grouted fault materials, offering vital geological insights into stress evolution and instability precursors during fault reactivation.
Achieving carbon neutrality and large-scale industrial waste utilization requires low-carbon mine backfill materials. This study investigates a strategy to enhance cement-fly ash based composites using CO2 nanobubble water. Normal cement-fly ash based backfill and CO2 nanobubble-modified cement-fly ash based backfill were compared through mechanical and microstructural analyses, including uniaxial compression, mercury intrusion porosimetry, scanning electron microscopy and thermogravimetric analysis. The results demonstrate that CO2 nanobubbles effectively mitigate the strength degradation induced by high fly ash replacement. Compared with normal backfill, the uniaxial compressive strength and elastic modulus of modified samples increased by 6.5–13.4% and 14.8–59.1%, respectively, enabling high-volume fly ash utilization without compromising mechanical integrity. Microstructural analyses reveal that CO2 nanobubble water promotes hydration and in-situ carbonation reactions, leading to the formation of uniformly distributed C-S-H gels and calcium carbonate crystals that refine the pore structure and reduce total porosity by approximately 20%. Thermogravimetric results further confirm that CO2 nanobubble significantly enhance carbonation efficiency, with the maximum carbonation degree reaching 13.07% at a fly ash content of 60%. Balancing performance and cost, the optimal fly ash content is identified within 20–60%, providing a green pathway for mining waste valorization.
Understanding the creep deformation behavior and the evolution of pore-fracture structures (FPSs) in coal under cyclic loading–unloading is crucial for safe extraction and efficient methane utilization. Coal samples were subjected to cyclic loading–unloading creep experiments using online Nuclear Magnetic Resonance (NMR) and Nuclear Magnetic Resonance Imaging (NMRI) techniques. The results revealed the significance of instantaneous plastic and viscoplastic strains during creep, with creep failure modes analyzed using NMRI data and macroscopic fracture distribution. Viscoplastic strain was identified as a key indicator of accelerated failure, and NMRI revealed a transition from splitting–shear to V-shaped shear failure under increasing confining pressure. From a microscopic perspective, real-time T2 spectra monitoring tracked the evolution of FPS at different loading levels, and the geometric mean of the pore structure (T2g) quantitatively described the co-evolution of various pore types. A generalized model was developed to describe coal creep under cyclic loading–unloading, integrating microscopic and macroscopic deformation features and refined using fractal theory. These findings provide theoretical insights and practical guidance for coal extraction and methane management under cyclic loading–unloading creep.
It is challenging to remove feldspar from spodumene at low temperature due to the poor collecting ability and selectivity of conventional collector. In this work, Glycolic acid ethoxylate oleyl ether (GAEOE) was evaluated as a low-temperature resistant collector in the flotation separation of spodumene and feldspar. The flotation performances and the interfacial interaction mechanisms were comprehensively investigated. Micro-flotation experiments showed that GAEOE could realize the efficient separation between spodumene and feldspar at low temperature, producing high-quality concentrate with Li2O grade and recovery reached 6.02% and 81.22%, respectively. Contact angle, induction time and bubble-mineral interaction force measurements proved that GAEOE significantly increased the adhesion force and attachment probability between air bubbles and spodumene, while it exerted negligible influence on feldspar. Zeta potentials and in situ microcalorimetry tests confirmed the stronger affinity of GAEOE toward Ca-activated spodumene than feldspar. Adsorption capacity and turbidity measurements revealed that GAEOE exhibited more stable adsorption with low sensitivity to temperature changes than sodium oleate (NaOL), due to the better solubility and superior dispersion stability at low temperature. XPS and DFT analysis revealed a stable bidentate configuration involving synergistic interactions between the O atoms of C–O and CO groups within GAEOE and Al as well as Ca sites on Ca-activated spodumene surface. These results suggested GAEOE was a promising alternative for conventional fatty acid collectors for spodumene flotation in temperature-sensitive environment.
Brittleness Index (BI), while not universally standardized, is one of the most critical parameters in the assessment of rock failure behavior, drillability, and excavation efficiency in mining; however, its applicability to extraterrestrial environments remains poorly constrained for the In-Situ Resource Utilization (ISRU) mission on Mars. This study qualitatively and quantitatively investigated the mechanistic attributes (compressive strength, σc; tensile strength, σt) and BI of simulated Martian rocks under distinct conditions. Martian analog rock specimens, developed using Mars Global Simulant, were subjected to controlled bulk–scale mechanical tests (uniaxial compression and Brazilian disc tests) to determine σc and σt, supported by SEM–EDS analyses, to validate mineralogical similarity with Martian samples. Results revealed that the simulated Martian rocks are representative of Jezero crater lithologies and exhibit behavior characterized by linear elastic deformation followed by abrupt failure under stress. A gravity-modified brittleness index (BIM1, BIM2, BIM3, and BIM4) was proposed, which yielded lower brittleness thresholds consistent with a mechanically weaker Martian lithosphere. Further, the Martian-specific brittleness classification indicated that the analog Martian rocks fall predominantly within low-to-moderately brittle categories (0.1<BIM4<9.3) under Martian conditions, suggesting favorable drillability and relatively low energy requirements for excavation. These findings offer novel insights into the feasibility of predicting Martian excavation performance for ISRU.
Static cracking demolition agent (SCDA) is an environmentally friendly and cost-effective material with broad potential for building demolition and rock fracturing engineering. Under expansive loading induced by SCDA, the directional fracture mechanisms of symmetrically slotted boreholes remain inadequately understood. Acoustic emission (AE) monitoring, digital image correlation (DIC), and numerical simulations were combined to systematically investigate the regulating mechanism of slot length on fracture behavior. The results indicate that as the slot length increases, the fracture modes transition from competitive propagation of multiple cracks to rapid through-going propagation of the main cracks along the slot direction. The competitive propagation of multiple cracks disperses the expansive energy among the propagating cracks, whereas rapid through-going propagation along the slot concentrates energy release in the slot direction. A critical slot length is identified at which energy release is most intense, causing the cumulative AE energy to first increase and then decrease with increasing slot length. The expansive pressure required for through-going of the main crack decreases progressively as the slot length increases. Once the main crack causes pressure release, the propagation of secondary cracks is suppressed due to insufficient driving force. These findings provide a theoretical basis for achieving controllable SCDA-induced directional fracturing.
In composite coal seams, the gas transfer relationship of structural coal has a significant impact on gas extraction. Regarding the influence mechanism of multi-scale mass transfer (MSMT) of tectonic coal in composite coal seams on gas extraction, the paper has constructed a corresponding multi-physics field coupling model, which systematically investigates gas migration patterns in composite coal seams and the dominant control mechanisms during coal mining. Results indicate that gas extraction efficiency in tectonic coal exhibits significant sensitivity to key parameters, including Poisson’s ratio, matrix elastic modulus, and extraction negative pressure. This reveals the synergistic extraction mechanism in composite coalbeds: highly permeable primary coal dominates pressure gradient formation during initial extraction, effectively driving gas desorption and cross-scale migration in adjacent tectonic coal. However, the low permeability of tectonic coal causes slow pressure decay, becoming a critical bottleneck constraining overall extraction efficiency. Based on this mechanism, a phased differentiated technical approach was proposed that involves hydraulic fracturing to enhance permeability in primary coal combined with CO2 displacement and stepwise negative pressure extraction for tectonic coal. These findings provide crucial guidance for optimizing extraction design and achieving efficient, safe mining in composite coal seams.
To effectively control the large deformation of the surrounding rock under complex conditions, it is often necessary to apply prestress to anchor cables. However, due to the influence of surrounding rock deformation, mining disturbance, and strong impact, anchor cables are often in a dynamic and static coupling stress state. Therefore, it is crucial to study the dynamic and static coupling mechanical characteristics of anchor cables. Based on this, the self-developed dynamic and static coupling test equipment is developed. The dynamic and static coupling mechanical test of anchor cables is conducted. Test results indicate that the energy absorption for anchor cables under the initial load of 350 kN decreased by 69.8% compared to the condition without initial load, and the energy absorption efficiency increased by 6.6 times. The increase of initial load can improve its energy absorption efficiency, but it can also lead to a decrease in its energy absorption. The energy absorption and energy absorption efficiency shows a bilinear variation law with the increase of initial load. On this basis, the energy absorption calculation formula and the support design model of the anchor cable are established. It provides new ideas for the safety control of dynamic disasters in deep engineering.
Under close-distance coal seam (CDCS) mining conditions, surrounding rock failure in gradient offset roadways exhibits pronounced zonal heterogeneity and complex evolutionary behavior. However, existing studies lack a systematic understanding of zonal failure mechanisms and effective full-length, quantitative identification methods, which limits the precise matching between support strategies and surrounding rock failure characteristics. To address this issue, a mechanical model for principal stress distribution in the goaf floor is established, clarifying the spatial variation of principal stresses under different offset distances and providing explicit boundary conditions for plastic zone analysis. Considering the implicit nature of the plastic zone boundary equation and the difficulty of analytical integration, a quantitative calculation framework combining polar coordinate discretization and numerical integration is proposed to determine the plastic zone area and maximum failure depth. Based on this framework, the coupled control mechanism of the principal stress ratio (η) and the orientation of the maximum principal stress (α) on zonal failure evolution is quantitatively revealed. The results indicate that continuous variations in offset distance induce the coupled evolution of η and α, which govern the expansion scale, failure depth, and deflection characteristics of the plastic zone. Furthermore, a geophysical-borehole joint inversion method (GBJIM) is proposed for refined identification of surrounding rock failure zones. The method achieves relative inversion errors of 0.59%–3.37%, satisfying engineering accuracy requirements, and enables continuous, full-length characterization of roadway surrounding rock failure. The inversion results reveal significant spatial variability in failure depth, which undergoes a rapid decrease, followed by an increase, a gradual reduction, and eventual stabilization with varying offset distance, and show good agreement with numerical simulation results. Based on the obtained precise zoning results, a zonal support optimization strategy for the full-length roadway is developed and validated through field application.
The prospective mining of deep-sea polymetallic nodules, a source of strategic critical metals, could cause irreversible damage to fragile deep-sea ecosystems, sparking global scientific, political, and ethical controversies. Consequently, establishing a scientific, credible, and efficient in-situ environmental monitoring system is a core prerequisite for achieving sustainable resource development and effective environmental regulation. This paper reviews the latest progress in in-situ environmental monitoring for polymetallic nodule mining (PNM). First, integrating future commercial mining workflows with current pilot-scale engineering practices, this paper outlines the multi-source environmental disturbances of PNM. The review then analyses impact mechanisms and monitoring strategies for five key areas: physical oceanography, marine chemistry, geology, marine biology, and sediment plumes. Finally, by assessing typical international monitoring campaigns, the paper distils key scientific findings and identifies core challenges. In-situ monitoring indicates that under the specific environmental conditions of PNM areas, mining plumes primarily propagate as near-bottom gravity currents, and that damage to benthic habitats can persist for decades. However, significant technical bottlenecks and scientific uncertainties remain in quantifying micro-scale processes, conducting continuous long-term observation of ecological recovery, and enabling real-time fusion of multi-platform data.
Understanding the dynamic behavior of rocks under confining conditions is essential for elucidating the failure mechanisms of deep rock masses. In this study, triaxial compression tests on granite were conducted at intermediate strain rates to systematically investigate the effects of confining pressure and strain rate on rock strength and deformation behavior. The roles of these factors in energy dissipation and damage evolution were clarified, and a stage-dependent damage constitutive model based on dissipated energy was established. The results show that both confining pressure and strain rate significantly enhance rock strength and deformation resistance, with confining pressure playing a more dominant role. The proportion of dissipated energy exhibits an overall trend of initial decrease followed by subsequent increase, corresponding to the transition from crack compaction and closure to crack development and propagation. A two-stage damage model incorporating initial damage recovery is proposed and demonstrates improved predictive capability compared with conventional models. Confining pressure suppresses damage development, whereas strain rate promotes it. In addition, higher confining pressure and strain rate increase the occurrence of transgranular cracking, revealing the mechanisms underlying enhanced energy dissipation and smoother fracture surfaces.
This study investigates the influence of porosity on the Mode I fracture behavior of granite and the predictability of catastrophic failure. Pores are defined in a broad sense to include intrinsic pores and microcrack-type defect structures that collectively contribute to rock heterogeneity. Granite specimens were heat-treated at ambient temperature, 450 degrees C, and 900 degrees C to induce porosity variations, which were quantified using Nuclear Magnetic Resonance (NMR). Three-point bending (TPB) tests were conducted with real-time monitoring using Digital Image Correlation (DIC) and Acoustic Emission (AE). The results show that increasing porosity significantly reduces rock strength, fracture toughness, and fracture energy. As porosity increases from 0.68% to 1.33%, the crack initiation and unstable fracture toughness decrease by 94.6% and 87.0%, while crack mouth opening displacement (CMOD), fracture process zone (FPZ) size, and fracture surface roughness increase. AE results indicate that low-porosity specimens exhibit few high-energy events typical of abrupt brittle fracture, whereas high-porosity specimens generate numerous low-energy events associated with distributed microcrack coalescence. Time-Reversed Omori Law (TROL) analysis shows that higher porosity leads to predicted failure times closer to actual collapse, indicating improved predictability. These results demonstrate that pore-related heterogeneity plays a key role in regulating fracture behavior and catastrophic failure predictability. (c) 2026 China University of Mining & Technology. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Drilling and blasting in foliated rock masses widely occur in tunnel engineering and mining operations. However, the effects of schistosity on rock fragmentation and energy dissipation behavior remain insufficiently understood. This study first conducts schist blast testing to investigate the influences of schistosity characteristics on rock fragmentation pattern and fragment size distribution, utilizing image processing to analyze the variations in fragment shape and fracture energy dissipation. Finite element models of schist blasting are then developed to simulate the successive process of detonation-induced stress propagation, crack network evolution and rock fragmentation. Blast testing and following image analysis reveal that schist fragments exhibit pronounced foliated features, with many fragments displaying platy shapes, and the average aspect ratio of rock fragments is primarily concentrated in the range of 0.5–0.7. When the schistosity is perpendicular to borehole and the proportion of harder rock matrix increases, the mean fragment size increases, the uniformity of fragment size distribution reduces, and thus the rock fragmentation performs worse. The mean aspect ratio of fragments increases with rounder rock fragments. Compared to blasting with schistosity perpendicular to borehole, blasting with schistosity parallel to borehole consumes more explosive energy, with an average increase of 27.28% in blast testing. Numerical simulations demonstrate that during the propagation of stress waves in schist, cyclic reflections occur at schistosity planes, mainly resulting in fracture and breakage in the weaker rock matrix. This leads to blast-induced cracks growing parallel to schistosity planes at intervals, forming flattened rock fragments with relatively small aspect ratios. The current findings suggest that schistosity perpendicular and parallel to borehole is unfavorable and favorable for rock fragmentation, respectively. Thus, in blasting engineering practice with simple layered structures, aligning the borehole with the dominant schistosity direction is an effective strategy for optimizing rock fragmentation performance, particularly when the harder rock matrix constitutes a large proportion.
Accurate mechanical parameters are crucial for deep rock engineering. Traditional two-dimensional strength models often fail to reflect the complex three-dimensional mechanical properties of deep rock mass. This study proposes an elastoplastic constitutive model based on the smooth GZZ strength criterion, incorporating a non-associated flow rule to account for rock dilatancy. The model was numerically implemented and validated against theoretical and experimental results. Applied to a deep-buried tunnel, it determined the scale-dependent uniaxial compressive strength (UCS) and Geological Strength Index (GSI) of the rock mass. Numerical experiments revealed a transition from brittle to ductile failure with increasing confining pressure. Both the strength and GSI increase nonlinearly with confining pressure. The impacts of the plastic flow rule and rock matrix strength criterion on these parameters were quantitatively analyzed. At high confining pressures, neglecting dilatancy leads to their overestimation. Compared to the proposed model, using the Hoek-Brown criterion for the rock matrix fails to capture continuous hardening and yields conservative strength predictions under high confinement. Overall, the proposed model offers an improved tool for predicting rock mass strength and GSI under high confinement, with direct implications for the design and stability assessment of deep underground excavations.
Pyrrhotite, a gangue mineral involved in the separation of polymetallic sulfide ore, is prone to oxidation, which deteriorates the pulp environment and reduces flotation efficiency. In this study, the oxidation-corrosion characteristics of pyrrhotite were systematically investigated, revealing the influence of pulp oxygenation and pH on surface oxidation-corrosion, as well as the mechanism. Dissolved oxygen measurements and inductively coupled plasma emission spectroscopy demonstrated that elevated pulp pH enhances the oxidation kinetics and extent. Under acidic conditions, pulp aeration intensifies Fe-dominated asymmetric corrosion, generating Fe-deficient/S-abundant surfaces. Conversely, pulp aeration is conducive to the selective corrosion of S under alkaline conditions, yielding Fe-abundant/S-deficient surfaces. X-ray photoelectron spectroscopy revealed that enhancing the aeration intensity or raising the pH promotes the oxidation of Fe and S sites and accelerates the hydroxylation of Fe site. Supported by the surface etching analysis, the hierarchical oxidation pathways were clarified: Fe(II)-S-Fe(III)-S-Fe(III)-O, S2 S22 S2n SO2 4 , and Me-O-Me-OH-H2O. Scanning electron microscopy combined with energy dispersive spectroscopy further confirmed the hierarchical oxidation and asymmetric corrosion characteristics, with corrosion becoming more pronounced as oxidation progresses. These findings elucidate the transformation of surface states and provide a theoretical foundation for understanding the reactivity of pyrrhotite during pretreatment and flotation. (c) 2026 China University of Mining & Technology. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Understanding the mechanisms and mitigation strategies for disturbance-induced rockbursts is essential for ensuring safety in deep rock engineering. To evaluate the effectiveness of drilling pressure relief, uniaxial compression tests were conducted on high-stress, cavity-containing sandstone under low-frequency disturbance loading at various amplitudes. Progressive damage was monitored using acoustic emission and digital image correlation. The threshold disturbance amplitude required to trigger dynamic failure was 25% of uniaxial compressive strength, which was significantly higher than that of intact sandstone. During the stable-damage stage, damage accumulated primarily through small-scale tensile fracturing, whereas large-scale shear fractures developed at later stages, initiating and propagating macrocracks that signalled impending structural instability. The energy-storage limit of cavity-containing sandstone was found to be independent of the loading path. The input energy during disturbance was stored as elastic strain energy and rapidly exceeded its storage limit, thereby driving crack propagation and rockburst failure. An energy pre-release ratio (EPR) was introduced to quantify the premature release of elastic strain energy induced by cavity instability. For all disturbance amplitudes, the EPR exceeded 45%, demonstrating that the cavity effectively mitigates disturbance-induced rockbursts. The results of this study provide a theoretical basis for evaluating the effectiveness of drilling pressure relief in mitigating disturbance-induced rockbursts.
Understanding the microscopic reaction mechanisms of high-temperature smoldering combustion (SC) is essential for efficient fire management. This study adopted high-temperature in-situ FTIR and DSC techniques to investigate the real-time evolution laws of 11 typical functional groups and their correlation with heat release during SC of long-flame coal. The reaction kinetics mechanism of typical functional groups under time-scale effects (TSE) was revealed. The results demonstrated that reduced oxygen level (100%-21%, 16%-1%) mainly affects coal combustion performance by restricting or delaying the rapid consumption of typical functional groups. Heat release restriction follows a two-stage linear model, with sensitivity to this limitation being about 21 times higher from 21%-3% to 3%-1% oxygen level. Aliphatic hydrocarbons at low temperatures and carboxyl/carbonyl groups at high temperatures exhibit the highest correlation degree with heat release. Aliphatic hydrocarbons determine the early-stage ignition capability of coal, while aromatic hydrocarbons (benzene rings) govern the burnout capability, and oxygen-containing functional groups dictate the burnout characteristics and maximum heat release intensity. The sensitivity to TSE follows the sequence: benzene rings approximate to oxygen-containing functional groups > aliphatic hydrocarbons > hydroxyl groups, and oxygen-limited conditions > normal oxygen conditions. Kinetic studies confirm that the activation energies under oxygen-limited conditions (3%, 50-100 kJ/mol) are lower than those under normal-oxygen conditions (140-200 kJ/mol). An oxygen level of 3% can be adopted as a critical safety threshold for the on-site sealing management of fire zones. (c) 2026 China University of Mining & Technology. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
