Understanding the mechanical behavior of diagenetic mineral granules and interfaces in granite provides essential experimental references for constructing micromechanical models of granite. The micromechanical behavior of Yanshanian granite is investigated using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and nanoindentation tests. The results demonstrate transitional mechanical properties at mineral interfaces. The elastic modulus and hardness exhibit intermediate values between adjacent mineral phases. The higher plasticity indices at the interfaces suggest higher plastic deformation capacity of hard-phase minerals in these regions. Additionally, fracture toughness measurements of minerals and interfaces were obtained, with interfacial values ranging from 0.90 to 1.63 MPa·m^0.5. The analysis of mechanical property relationships shows a significant positive linear correlation between rock-scale elastic modulus and fracture toughness. However, this correlation is substantially lower at the mineral scale, demonstrating a scale effect in the relationship of different mechanical properties.

To elucidate the fracturing mechanism of deep hard rock under complex disturbance environments, this study investigates the dynamic failure behavior of pre-damaged granite subjected to multi-source dynamic disturbances. Blasting vibration monitoring was conducted in a deep-buried drill-and-blast tunnel to characterize in-situ dynamic loading conditions. Subsequently, true triaxial compression tests incorporating multi-source disturbances were performed using a self-developed wide-low-frequency true triaxial system to simulate disturbance accumulation and damage evolution in granite. The results demonstrate that combined dynamic disturbances and unloading damage significantly accelerate strength degradation and trigger shear-slip failure along preferentially oriented blast-induced fractures, with strength reductions up to 16.7%. Layered failure was observed on the free surface of pre-damaged granite under biaxial loading, indicating a disturbance-induced fracture localization mechanism. Time-stress-fracture-energy coupling fields were constructed to reveal the spatiotemporal characteristics of fracture evolution. Critical precursor frequency bands (105-150, 185-225, and 300-325 kHz) were identified, which serve as diagnostic signatures of impending failure. A dynamic instability mechanism driven by multi-source disturbance superposition and pre-damage evolution was established. Furthermore, a grouting-based wave-absorption control strategy was proposed to mitigate deep dynamic disasters by attenuating disturbance amplitude and reducing excitation frequency.

This study mainly investigates the influence of pore water characteristics on the adsorption properties of coalbed methane through integrated low field nuclear magnetic resonance (LF-NMR), adsorption experiments, and molecular dynamics (MD) simulations. Pore water states in three coal ranks were characterized during progressive hydration. Multi-scale analysis revealed how pore water evolution regulates methane adsorption processes. During the diffusion-dominated stage (M2-M3), adsorbed water penetrates into the micropores. In the highly wettable brown coal (L1), the adsorbed water content reaches 2.12 g while in the anthracite (A1), it is only 0.29 g. During the active water injection stage (M4-M6), non-adsorbed water dominates in anthracite (over 85% of the total water content of 4.01 g), while adsorbed water remains dominant in lignite (over 60% of the total water content of 3.52 g). Water content plays a key role in methane adsorption in coal. During the water addition phase, the influence of methane adsorption on medium-to-low-rank coal is relatively weak, while the methane adsorption capacity of high-rank coal A1 shows a significant decrease during both the water diffusion and water addition phases, corresponding to a reduction in Langmuir volume of 21.22 cm³/g. Molecular dynamics (MD) results further show that the free energy between molecules on the surface of hydroxyl-modified coal increases, with hydroxyl groups driving electrostatic interactions between coal and water molecules. Increased steric hindrance inhibits hydrogen bond formation and reduces the rate of hydrogen bond growth. There is a significant correlation between pore water content and coal-water molecular interaction energy, which cross-scale validates the results of LF-NMR testing and MD simulations.

Fracability evaluation is critical for efficiently extracting deep shale gas using hydraulic fracturing to avoid blind drilling and fracking. However, existing fracability indices often fail to systematically consider the mechanical behavior of rocks at high temperatures and high pressures (HTHP), coupled with geostress distributions and heterogeneous reservoir characteristics. This critical omission limits their effectiveness in accurately identifying the optimal fracability sweet spots within deep reservoirs. In this work, a fracability evaluation model was proposed based on the combined weighting method, integrating the improved brittleness index, rock strength, geostresses and natural weakness characteristics. A fracability grading evaluation was carried out to determine the potential fracture characteristics corresponding to shales with different fracability levels. Additionally, the fracability index was used for field validation and applications. Results show that rock brittleness and fracability are not equivalent for deep reservoirs. The fracability index is closely related to the pay zones and actual gas production, with a correlation as high as 84%, implying that the proposed method has practical significance in both experimental and field applications. The above findings can provide theoretical guidance for the selection of fracturing candidates and the optimal design of fracturing in deep resource development.

The geological tectonic zone is closely related to outburst. Taking the outburst coal bodies in tectonic zones as the research object, combined with DIC and AE monitoring technologies and discrete element simulation, the mechanical response, crack evolution and energy characteristics of coal bodies under different loading rates (impact disturbances) were studied. The results show that both the uniaxial compressive strength and elastic modulus are positively correlated with the loading rate, with a maximum increase in compressive strength of 25.15%. The uniaxial compressive strength is more sensitive to impact disturbances. The failure modes of coal bodies can be divided into the "slip-crack synchronization (S & C) type" and the “crack-first-then-slip (C & S) type”. The slip in tectonic zones is more severe at high loading rates. At low loading rates, shear cracks dominate (60.01%), while the proportion of tensile cracks increases significantly (70.52%) at high loading rates. Additionally, the rate of axial crack growth decreases as the loading rate increases. The peak values of total energy and dissipated energy increase significantly with the loading rate, and the peak energy of the C & S type is greater than that of the S & C type. Energy is preferentially released through the slip of tectonic zones and the propagation of radial cracks.

China’s deep coalbed methane (CBM) resources demonstrate immense potential with extensive developmental prospects. However, the coupling relationship between the negative adsorption effect and the positive desorption-promotion effect under high-temperature conditions remains unclear. In this study, a self-built high-temperature adsorption-desorption system was used to investigate the coupled effects of temperature and coal rank on methane adsorption-desorption behavior in deep CBM. The results show that elevated temperatures significantly reduce methane adsorption capacity, with high-rank coals exhibiting greater sensitivity. Conversely, high-temperature conditions significantly enhance methane desorption and diffusion behavior, accelerating initial desorption rates, enabling rapid gas release in a short period, and thus improving desorption efficiency. The desorption volume and desorption-diffusion rate exhibited an asymmetric U-shaped variation with coal rank. By coupling the positive and negative effects of temperature and defining the desorption ratio, it was found that a 10 K increase in temperature raised the desorption ratio by 3.78%-8.05%. Finally, an effective gas content prediction model is proposed, and the key regulatory role of temperature in the resource potential and gas production characteristics of deep CBM is clarified. These findings can provide theoretical guidance for the subsequent optimization of deep CBM exploration and development strategies.

To study the relationships between rock mass crack propagation and damage and confining pressure under blast impact loading during straight-hole cut blasting, tests were performed under different confining pressures. Then, the characteristics of rock mass crack development were analyzed, and the pressure resistance values of core samples before and after blasting were compared to study the trends of rock mass damage. Moreover, a three-dimensional numerical simulation model was established by LS-DYNA to analyze the stress wave propagation, cavity shape and crack propagation characteristics under different confining pressures. The propagation of rock blasting cracks is negatively correlated with the confining pressure. The greater the confining pressure, the shorter the crack development time. Additionally, the crack width is reduced from 0.4-1.7 to 0.04-1.4 mm, and the length is shortened from 280 to 120 mm. A comparison of the compressive strength revealed that blasting reduces the compressive strength of the rock mass. The greater the distance from the explosion source, the lower the degree of strength attenuation. An increase in the confining pressure can inhibit strength attenuation. Numerical simulations revealed that under the same confining pressure, the stress first peaks at the bottom of the blast hole. The greater the confining pressure, the longer the stress peak duration, the smaller the cavity volume, and the shorter the crack propagation length and depth. Under a confining pressure of 4 MPa, the longest crack was only 154.5 mm in length and 102 mm in depth. The research results provide a scientific basis for controlling rock damage and optimizing design in the excavation of deep rock roadways by blasting.

Hydraulic fracture growth is significantly influenced by the minimum horizontal principal stress gradient and the fracturing fluid pressure gradient. However, these gradients are often neglected in scaled physical modeling experiments due to difficulties in reproducing them. This study uses centrifugal hypergravity to simulate both gradients and investigate their effects on fracture propagation. Artificial mortar specimens (ø200 mm×400 mm) are fractured under 1g (normal gravity), 50g, and 100g. Results show that compared to 1g, fractures under 50g and 100g exhibit increasingly uneven propagation, with higher g-values leading to greater asymmetry. To interpret this, a theoretical analysis based on fracture mechanics is conducted. When the fluid pressure gradient exceeds the stress gradient, a positive net gradient is generated, increasing net pressure at the lower fracture tip. This raises the stress intensity factor at the lower tip, promoting downward growth. As g increases, the disparity becomes more significant, resulting in greater fracture deviation. In conclusion, this study, for the first time, has verified and explained that the net gradient can change the propagation of hydraulic fractures, providing important guidance for wellbore placement under stress gradients.

Underground engineering in extreme environments necessitates understanding rock mechanical behavior under coupled high-temperature and dynamic loading conditions. This study presents an innovative multi-scale cross-platform PFC-FDEM coupling methodology that bridges microscopic thermal damage mechanisms with macroscopic dynamic fracture responses. The breakthrough coupling framework introduces: (1) bidirectional information transfer protocols enabling seamless integration between PFC’s particle-scale thermal damage characterization and FDEM’s continuum-scale fracture propagation, (2) multi-physics mapping algorithms that preserve crack network geometric invariants during scale transitions, and (3) cross-platform cohesive zone implementations for accurate SHTB dynamic loading simulation. The coupled approach reveals distinct three-stage crack evolution characteristics with temperature-dependent density following an exponential model. High-temperature exposure significantly reduces dynamic strength ratio (60% at 800 °C) and diminishes strain-rate sensitivity, with dynamic increase factor decreasing from 1.0 to 2.2 (25 °C) to 1.0-1.3 (800 °C). Critically, the coupling methodology captures fundamental energy redistribution mechanisms: thermal crack networks alter elastic energy proportion from 75% to 35% while increasing fracture energy from 5% to 30%. Numerical predictions demonstrate excellent experimental agreement (±8% peak stress-strain errors), validating the PFC-FDEM coupling accuracy. This integrated framework provides essential computational tools for predicting complex thermal-mechanical rock behavior in underground engineering applications.

Web pillars enduring complex coupled loads are critical for stability in high-wall mining. This study develops a dynamic failure criterion for web pillars under non-uniform loading using catastrophe theory. Through the analysis of the web pillar-overburden system’s dynamic stress and deformation, a total potential energy function and dynamic failure criterion were established for web pillars. An optimizing method for web pillar parameters was developed in highwall mining. The dynamic criterion established was used to evaluate the dynamic failure and stability of web pillars under static and dynamic loading. Key findings reveal that vertical displacements exhibit exponential-trigonometric variation under static loads and multi-variable power-law behavior under dynamic blasting. Instability risks arise when the roof’s tensile strength-to-stress ratio drops below 1. Using catastrophe theory, the bifurcation set Δ<0 signals sudden instability. The criterion defines failure as when the unstable web pillar section length l₁ exceeds the roof’s critical collapse distance l₂. Case studies and simulations determine an optimal web pillar width of 4.6 m. This research enhances safety and resource recovery, providing a theoretical framework for advancing highwall mining technology.

Under external disturbances, the shear mechanical responses and debonding failure mechanisms at anisotropic interfaces of anchoring system composed of multiphase media are inherently difficult to characterize due to the concealment nature of interfacial interactions. This study establishes an equivalent shear model for a bolt-resin-rock anchoring system and conducts direct shear tests under dynamic normal load (DNL) boundary from both laboratory experiments and discrete element method (DEM) simulations. The research investigates the influence of normal dynamic load amplitude (A_n) and rock type on shear strength parameters, elucidating the evolutionary characteristics and underlying mechanisms of shear load and normal displacement fluctuations induced by cyclic normal loading, with maximum shear load decreasing by 36.81% to 46.94% as A_n increases from 10% to 70% when rock type varies from coal to limestone. Through analysis of strain field evolution, the critical impact of rock type on localization of shear failure surface is revealed, with systematic summarization of differentiated wear characteristics, failure modes, and key controlling factors associated with shear failure surface. Mesoscopic investigations enabled by DEM simulations uncover the nonuniform distribution of contact force chains within the material matrix and across the anisotropic interfaces under various DNL boundaries, clarify rock type dependent crack propagation pathways, and quantitatively assess the damage extent of shear failure surface, with the anisotropic interface damage factor increasing from 34.9% to 56.6% as A_n rises from 10% to 70%, and decreasing from 49.6% to 23.4% as rock type varies from coal to limestone.

The superconducting high gradient magnetic separation (S-HGMS) technology can be used to effectively extract silica from iron ore tailings (IOTs). However, particle agglomeration in strong magnetic fields poses a challenge in achieving optimal performance. In this study, we investigated the agglomeration of IOT particles and the mechanisms for its inhibition through surface analysis, density functional theory (DFT), and extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory. Hematite was found to exhibit the highest magnetic moment among the minerals present in IOTs, making it particularly prone to magnetic agglomeration. The addition of the dispersant SDSH into the slurry was essential in promoting the dispersion of IOT particles during the S-HGMS process. This dispersant hydrolyzed to form HPO₄^2- and RSO₃^- groups in the solution, which then chemically adsorbed onto the metal ions exposed on the surfaces of non-quartz particles, increasing interparticle electrostatic repulsion. Furthermore, the RSO₃^- groups physically adsorbed onto the surface of quartz particles, resulting in strong steric repulsion and enhancing the hydrophilicity of the particle surfaces, thereby inhibiting magnetic agglomeration between the particles. Under optimal conditions, the SiO₂ grade of the obtained high-grade silica powder increased from an initial value of 76.32% in IOTs to 97.42%, achieving a SiO₂ recovery rate of 54.81%, which meets the requirements for quartz sand used in glass preparation. This study provides valuable insights into the magnetic agglomeration of IOT particles and its inhibition while providing a foundation for regulating S-HGMS processes.