To reveal the deterioration mechanism of coal-rock assemblages under chemical corrosion and dynamic loading, chemical corrosion and dynamic impact experiments were conducted. Under different chemical corrosion conditions, the weakening characteristics, observable characteristics, softening characteristics of the dynamic parameters, dynamic failure characteristics, dynamic failure forms and dynamic microscopic characteristics were analyzed. Under each corrosion condition, the dynamic elastic modulus, dynamic deformation modulus and dynamic peak intensity tended to decrease with immersing time. The dynamic elastic modulus, dynamic deformation modulus and dynamic peak intensity exhibited an inverted U-shaped trend. Under dynamic impact, the failure process of acidly corroded samples can be divided into the following stages: the initial stage, elastic energy accumulation stage, local failure of coal and secondary rock crack expansion stage, coal fragment ejection stage, rock spalling stage and complete instability stage. Under dynamic impact, failure modes exist: coal crushing failure, rock fragmenting failure, rock splitting failure and full splitting failure. After impact failure, sample fragments are distributed in powder, granular, cone and block forms. Based on Zhu-Wang-Tang nonlinear viscoelastic properties, a model considering chemical corrosion and impact damage was proposed. The combined effects of chemical and impact-induced damage on the dynamic mechanical properties of coal-rock assemblages were systematically analyzed.

Acquiring pristine deep lunar regolith cores with appropriate drilling tools is crucial for deciphering the lunar geological history. Conventional thick-walled drill bits are inherently limited in obtaining deep lunar regolith samples, whereas thin-walled coring bits offer a promising solution for lunar deep drilling. To support future lunar deep exploration missions, this study systematically investigates the failure mechanisms of lunar regolith induced by thin-walled drilling tools. Firstly, five thin-walled bit configurations were designed and evaluated based on drilling load, coring efficiency, and disturbance minimization, with Bit D demonstrating optimal overall performance. And the interaction mechanisms between differently configured coring bits and large-particle lunar regolith were elucidated. Coring experiments under critical drilling parameters revealed an operational window for the feed-to-rotation ratio (FRR of 2.0-2.5), effectively balancing drilling load and core recovery rate. Furthermore, a novel theoretical framework was developed to characterize dynamic drilling load parameters, supported by experimental validation. Based on these findings, practical strategies are proposed to mitigate drilling-induced disturbances, including parameter optimization and bit structural improvements. This research could provide valuable insights for designing advanced lunar deep drilling tools and developing drilling procedures.

Prolonged cyclic water intrusion has progressively developed joints in the hydro-fluctuation belt, elevating the instability risk of reservoir bank slopes. To investigate its impact on joint shear damage evolution, joint samples were prepared using three representative roughness curves and subjected to direct shear testing following cyclic water intrusion. A shear damage constitutive model considering the coupling effect of cyclic water intrusion and load was developed based on macroscopic phenomenological damage mechanics and micro-statistical theory. Results indicate: (1) All critical shear mechanical parameters (including peak shear strength, shear stiffness, basic friction angle, and joint compressive strength) exhibit progressive deterioration with increasing water intrusion cycles; (2) Model validation through experimental curve comparisons confirms its reliability. The model demonstrates that intensified water intrusion cycles reduce key mechanical indices, inducing a brittle-to-ductile transition in joint surface deformation — a behavior consistent with experimental observations; (3) Damage under cyclic water intrusion and load coupling follows an S-shaped trend, divided into stabilization (water-dominated stage), development (load-dominated stage), and completion stages. The research provides valuable insights for stability studies, such as similar model experiments for reservoir bank slopes and other water-related projects.

Coal pillars are critical supporting structures between underground coal gasification gasifiers. Its bearing capacity and structural stability are severely threatened by high-temperature environments. To elucidate the high-temperature deterioration mechanism of coal pillars at multiple scales, coal strength features as a function of temperature were investigated via uniaxial compression and acoustic emission equipment. The pyrolysis reaction process and microstructure evolution were characterized via X-ray diffractometer (XRD), scanning electron microscope (SEM), thermogravimetric (TG), Fourier transform infrared spectroscopy (FTIR), and computed tomography (CT) tests. Experimental results reveal a critical temperature threshold of 500 °C for severe degradation of the coal bearing capacity. Specifically, both the strength and elastic modulus exhibit accelerated degradation above this temperature, with maximum reductions of 45.53% and 61.34%, respectively. Above 500 °C, coal essentially undergoes a pyrolysis reaction under N₂ and CO₂ atmospheres. High temperatures decrease the quantity of O₂-based functional groups, growing aromaticity and the degree of graphitization. These changes induce dislocation and slip inside the coal crystal nucleus and then lead to deformation of the coal molecular structural units and strain energy generation. This process results in a great increase in porosity. Consequently, the stress deformation of coal increases, transforming the type of failure from brittle to ductile failure. These findings are expected to provide scientific support for UCG rock strata control.

To investigate the instability mechanisms of heterogeneous geological structures in goaf area roofs, three-point bending tests (TPBT) and numerical simulations are performed on composite coal-rock (CCR). Acoustic emission (AE) monitoring is employed to analyze key parameters, establishing a multi-parameter quantitative system for CCR fracture processes. The impact of lithological homogeneity on fracture evolution and energy migration is examined. Results show that CCR exhibits a three-stage mechanical response: weak contact, strong contact, and post-peak stages, each with distinct crack evolution patterns. A positive correlation is found between lithological homogeneity and tensile crack proportion. No significant correlation is observed between AE average frequency (AF) and AE counts across different lithological CCR; however, peak frequency (PF) displays clear lithology-dependent characteristics. The regulatory effect of the rock homogeneity coefficient (φ) on crack derivation mechanisms is quantified, yielding mathematical relationships between fracture strength (f), crack propagation path angle (β), crack fractal dimension (D), and φ. The study highlights how different fracture modes alter energy migration pathways, confirming the coupling effect of grain distribution on mechanical response and crack propagation, and the influence of parameter ϕ on critical energy release zones. These findings offer new insights into CCR failure mechanisms for mining safety.

After the excavation of deep mining tunnels and underground caverns, the stability of surrounding rock controlled by structural planes is prone to structural damage and even engineering disasters due to three-dimensional stress redistribution and multi-directional dynamic construction interference. However, the shear mechanical behavior, fracture evolution mechanism and precursor characteristics of rockmass under true triaxial stress and multi-directional coupling disturbance are not unclear. Therefore, this study carried out true triaxial shear tests on limestone intermittent structural planes under uni-, bi- and tri-directional coupling disturbances to analyze its mechanical behavior, fracture evolution mechanism and precursor characteristics. The results show that as the disturbance direction increase, the shear strength of limestone generally decreases, while the roughness of structural planes and the degree of anisotropy generally exhibit an increasing trend. The proportion of shear cracks on the structural plane increases with the increase of shear stress. The disturbance strain rate before failure shows a U-shaped trend. Near to disturbance failure, there were more high-energy and high-amplitude acoustic emission events near the structural plane, and b-value drops rapidly below 1, while lgN/b ratio increased to above 3. These findings provide experimental recognition and theoretical support for assessing the stability of rockmass under blasting excavation.

Geological sequestration of CO₂ is critical for deep decarbonization, but the geomechanical stability of coal reservoirs remains a major challenge. This study integrates nanoindentation, XRD/SEM-EDS chemo physical characterization and 4D CT visualization to investigate the time-evolving mechanical degradation of bituminous coals with ScCO₂ injection. The main results show that 4 d of ScCO₂ treatment caused 50.47%-80.99% increase in load-displacement deformation and 26.92%-76.17% increase in creep depth at peak load, accompanied by 55.01%-63.38% loss in elastic modulus and 52.83%-74.81% reduction in hardness. The degradation exhibited biphasic kinetics, characterized by rapid surface-driven weakening (0-2 d), followed by stabilized matrix-scale pore homogenization (2-4 d). ScCO₂ preferentially dissolved carbonate minerals (dolomite), driving pore network expansion and interfacial debonding, while silicate minerals resisted dissolution but promoted structural homogenization. These coupled geochemical-mechanical processes reduced the mechanical heterogeneity of the coal and altered its failure modes. The results establish a predictive framework for reservoir stability assessment and provide actionable insights for optimizing CO₂ enhanced coalbed methane recovery.

Coal and gas outbursts constitute a critical hazard in underground mining operations, characterized by rapid transitions from localized instability to catastrophic failure. Understanding the relationship between initial characteristics and final outburst scale remains a fundamental challenge in geomechanics. This study conceptualizes outbursts as deterministic cascade systems through integrated physical simulations combining high-sensitivity infrasound monitoring with energy analysis under controlled gas pressure (0.5-1.0 MPa) and confining stress (5-10 MPa) conditions. Our complementary analytical algorithms—the absolute amplitude integral and predominant period function—revealed characteristic step-wise patterns in outburst development. Quantitative analysis established a robust correlation (R²=0.91) between initial acoustic response and final outburst intensity. Energy analysis demonstrated that gas expansion dominates the outburst process (91.81%-99.09% of total energy), with desorption gas contributing 59.1%-77.7%. Time-frequency analysis showed systematic frequency migration from high (12-15 Hz) to low (4-8 Hz) bands during outburst progression, reflecting hierarchical spatial scale expansion. The concentrated energy release (>20% of total) within initial 0.2 s provides a mechanistic basis for the deterministic nature of outburst evolution. These mechanistic insights establish a quantitative framework for developing physics-based monitoring protocols and risk assessment methodologies applicable to underground coal mining operations.

Salt caverns are widely used for energy storage. During gas storage, the internal gas pressure fluctuates cyclically in response to energy demand, making it essential to assess how these pressure variations affect rock deformation. In this study, experiments were conducted under different cyclic gas pressure conditions to investigate this effect. The findings indicate that (1) the deformation process of salt rock can be segmented into three stages: the deceleration stage, the steady-state stage, and the acceleration stage. (2) When the axial pressure remains constant, both axial and radial deformations exhibit a stepwise increasing trend in response to cyclic gas pressure variations. Similarly, under axial graded loading, the deformations also demonstrate a progressive rise. By analyzing the deformation differences and model coefficient fluctuations within a single gas pressure cycle, it is found that radial deformation is higher sensitive to changes in cyclic gas pressure. (3) The axial deformation shows a stepwise increase, and the radial deformation showed a cyclic change with changing gas pressure. Therefore, the cyclic gas pressure influence factor α, axial loading influence factor β, and state variable σ∗ are introduced to develop a viscoplastic ontological model that accounts for the impacts of cyclic gas pressure, confining pressure and axial stress. Validated by the deformation data, the new model can better fit both the axial deformation and the radial deformation of the three stages and has strong applicability and accuracy by changing only fewer parameters. The state variable rate shows the same stage as the deformation rate and residual strain of salt rock, which can better reflect the internal hardening of salt rock.

In the steel slag-based mine backfill cementitious material systems, the hydration reaction mechanisms and synergistic effects of steel slag (SS), granulated blast furnace slag (GBFS), and desulfurization gypsum (DG) are crucial for performance optimization and regulation. However, existing studies have yet to fully reveal the underlying synergistic mechanisms, which limits the application and promotion of high SS content in mine backfill and low-carbon building materials. This study systematically explores the synergistic effects between various solid wastes and their regulation of the hydration process in the SS-based cementitious system through multi-scale characterization techniques. The results show that GBFS, by releasing active Si⁴⁺ and Al³⁺, triggers a synergistic activation effect with Ca²⁺ provided by SS, promoting the formation of C-S-H gel and ettringite, significantly optimizing the hardened paste microstructure. When the GBFS content reaches 30%, the C-S-H content increases by 40.8%, the pore size distribution improves, the proportion of large pores decreases by 68.7%, and the 90-day compressive strength increases to 5 times that of the baseline group. The sulfate activation effect of DG accelerates the hydration of silicate minerals, but excessive incorporation (>16%) can lead to microcracks caused by the expansion of AFt crystals, resulting in a strength reduction. Under the synergistic effect of 8% DG and 30% GBFS, the hydration reaction is most intense, with the peak heat release rate reaching 0.92 mW/g and the cumulative heat release amount being 240 J/g. By constructing a “SS-GBFS-DG-cement” quaternary synergistic system (mass ratio range: SS:GBFS:cement:DG=(50-62):(20-40):10:(8-12)), the matching of active components in high-content SS systems was optimized, significantly improving microstructural defects and meeting engineering application requirements. This study provides a theoretical basis for the component design and performance regulation of high-content SS-based cementitious materials.