Coal burst is a sudden dynamic disaster that occurs under the superposition of dynamic and static loads, characterized by a violent failure process, concentrated energy release, and complex occurrence mechanism, posing a serious threat to mine safety. To reproduce the failure process of coal burst and reveal its dynamic essence in laboratory conditions, conventional physical simulation methods based on static similarity principles are inadequate to fully capture its dynamic characteristics. Therefore, with the dynamic disaster mechanism of coal burst as the research focus, a coal-rock dynamic similarity criterion system centered on the acceleration similarity ratio is proposed, aiming to establish a theoretical framework for physical simulation that can realistically reflect the dynamic response characteristics of coal burst. Through dimensional analysis, the key parameters involved in the coal burst process were systematically analyzed. Using the acceleration similarity ratio as the primary control parameter, a theoretical equation set of dynamic similarity criteria for coal burst was derived, and a system of dynamic similarity coefficients was constructed, including the stress similarity ratio, elastic modulus similarity ratio, time similarity ratio, and strain rate similarity ratio. By introducing the dynamic similarity coefficient, the coupling relationships and constraint conditions among various similarity ratios were analyzed, and a similarity criterion system describing the impact tendency of physical models was established. Furthermore, based on the derived theoretical relationships, the evolution laws of model strength curves under different geometric similarity ratios were summarized, and the applicable range and parameter intervals of the dynamic similarity criteria were clarified. The results show that the dynamic similarity coefficient is the key parameter governing dynamic similarity relationships, and its value directly determines the similarity of inertia response and energy transfer between the model and the prototype. The optimal geometric similarity ratio and wave velocity similarity ratio for the dynamic similarity criteria were determined. The proposed coal-rock dynamic similarity principle for coal burst breaks through the limitations of traditional static similarity theory, achieves quantitative characterization of inertia effects and energy release behavior, and provides an operable theoretical basis for dynamic physical simulation experiments of coal burst.

The dynamic tensile mechanical properties and damage evolution fracture mechanisms of roof rock media in goaf areas under high-temperature conditions are key to ensuring the safe and green extraction of coal resources above the goaf, especially in cases of coal spontaneous combustion or underground coal gasification. Based on the conclusions from dynamic direct tensile tests of coal–rock media under high-temperature environments, this study employs coupled continuum–discrete numerical methods to establish a separable Hopkinson tension bar system (SHTB) numerical model, a three-dimensional equivalent particle model (GBM) of the roof rock media specimens, and a thermal pipe model representing the thermal damage effects on the roof rock media. Research confirms that the simulation results accurately capture the dynamic direct tensile mechanical behavior of sandstone subjected to high-temperature damage. Under elevated temperatures, the response of coal-bearing sandstone exhibits distinct stage characteristics, as evidenced by the non-monotonic trend in which the slope of the linear relationship between strength and strain rate first increases and then decreases, along with a four-stage evolution pattern of impact tensile damage fracture. Throughout this process, the evolution of mesoscopic force chains serves as the underlying mechanism driving the changes in macroscopic mechanical behavior. In addition, impact velocity is identified as a key parameter influencing the energy dissipation characteristics of the material.

Using coal fly ash (FA) in aeolian sand cemented backfill diverts industrial waste and reduces Portland cement demand, but high contents may impair fresh-state behavior and early-age structural integrity. This study investigated aeolian sand cemented backfill containing 50–80% fly ash by total binder mass using rheological testing, uniaxial compression, acoustic emission (AE) monitoring, and scanning electron microscopy (SEM). Yield stress first increased and then decreased with fly ash content, whereas plastic viscosity showed the opposite trend. At 60% fly ash, yield stress peaked at 31.115 Pa and plastic viscosity reached a minimum of 0.299 Pa·s. At 7 d, increasing fly ash from 50% to 80% reduced uniaxial compressive strength from 2.70 to 1.24 MPa and elastic modulus from 0.287 to 0.141 GPa. The stress–strain response shifted from Type IV to Type VI, accompanied by a tensile-to-shear failure transition. The maximum AE ringing count decreased by 55.0%, while crack-initiation and damage stresses decayed exponentially. SEM revealed less abundant calcium silicate hydrate gel and a progressively looser and more porous matrix at higher fly ash contents, consistent with weakened cementation and cracking resistance. These findings quantify trade-offs among solid-waste utilization, slurry rheology, and early-age structural performance, supporting resource-efficient mixture design.

This study investigates the influence of curing temperature on the creep properties of alkaliactivated slag-loess-based cemented backfill (SLCB) and establishes a constitutive model to accurately describe its full-stage creep behavior, thereby providing a theoretical basis for evaluating the long-term stability of mine backfill structures. Through an integrated approach of laboratory experimentation and theoretical modeling, triaxial step-loading creep tests were performed on SLCB specimens subjected to curing temperatures of 5, 20, 35, and 50 degrees C. The characteristics of creep deformation, deformation rate, long-term strength, and failure stress were systematically analyzed. Based on fractional-order calculus theory, a nonlinear viscoelasticplastic creep model that incorporates temperature effects was developed, and its parameters were identified and validated. The results indicate that the creep behavior of SLCB exhibits typical three-stage characteristics-deceleration, steady-state, and acceleration-with curing temperature exerting a significant influence. As the temperature increased from 5 degrees C to 50 degrees C, the total creep duration extended by a factor of 2.58, the critical stress threshold was elevated, and creep resistance was enhanced. Both instantaneous strain and extreme creep strain decreased linearly with increasing temperature, exhibiting maximum reductions of 45.86 % and 32.93 %, respectively. The long-term strength, determined jointly from isochronous stress-strain curves and the steady-state creep rate method, maintained a stable ratio of approximately 75 % relative to the peak strength, a ratio which was minimally influenced by temperature. The developed fractional-order creep model demonstrates high-precision fitting of the full-stage creep curves across different temperatures and effectively characterizes the coupling effects of temperature, stress, and time. The findings provide critical guidance for the design and assessment of backfill structures subjected to high-temperature environments.

Slurry-infiltrated granular composites offer a sustainable strategy for underground backfilling, in which a pre-formed aggregate skeleton is bonded by an infiltrating slurry to reduce binder use. Their mechanical integrity is governed by slurry retention within intergranular voids rather than uniform mixing. However, a quantitative link between fresh-state rheology and both the resulting bonded configuration and hardened mechanical performance remains insufficiently established. This study develops an experimental–theoretical framework linking slurry rheology, retention behavior, and uniaxial compressive response. Slurries with varying rheology were prepared by adjusting polycarboxylate ether dosage, and infiltration tests were performed using coarse gangue aggregates of different sizes. The retained slurry mass () was measured and used to define a structural state descriptor, the initial bonded volume fraction (), to characterize the initial bonded configuration. A constitutive model is formulated by decomposing total strain into elastic and compaction components, while progressive degradation of bonded regions is described using a statistical damage approach. Model parameters are identified independently from distinct segments of the stress–strain curves to ensure identifiability. Validation using independent mixtures demonstrates that the proposed model captures early-stage compaction, elastic stiffness, peak strength, and post-peak softening, with relative errors generally within 15%. Within the present uniaxial material-point scope, slurry retention provides a measurable link between fresh-state rheology and hardened mechanical performance, supporting rapid comparison and preliminary assessment of load-bearing behavior in slurry-infiltrated granular systems.

To address the high carbon footprint of traditional backfills and the lack of long-term stability data for highwall backfill mining, a low-carbon loess-slag-based cemented backfill (LSCB) was developed. This study investigates the time-dependent mechanical behavior of LSCB through triaxial creep tests under varying curing times (t c ) and confining pressures (6 3 ), supplemented by microstructural characterization. Results indicate that instantaneous strain increases linearly with stress, with the slope decreasing as t c extends but remaining insensitive to 6 3 . Creep strain exhibits nonlinear growth above a critical stress threshold that rises with both t c and 6 3 . Both long-term and creep failure strengths increase nonlinearly with t c and 6 3 , while their ratios to peak strength remain stable. Extending t c promotes geopolymer gel formation to densify the internal structure, and increasing 6 3 constrains crack initiation and propagation. To predict the creep behavior of LSCB, a nonlinear visco-elasto-plastic creep model was established and extended to three dimensions using tensor decomposition and the DruckerPrager criterion. The proposed model outperforms classical models in capturing all creep stages, particularly the accelerated failure phase. This work establishes a theoretical basis for the stability design of green backfill, advancing solid waste utilization in sustainable mining.

The long-term durability of porous soft rocks in cold-region mines is severely threatened by the synergistic degradation of freeze-thaw (F-T) weathering and creep loading. To investigate the influence of freeze-thaw cycle (FTC) frequency and freezing temperature on the creep behavior and damage evolution of weak-layer materials, this study performed F-T cycling, scanning electron microscopy, and uniaxial creep tests on sandy mudstone. The results reveal a distinct damage-creep coupling mechanism governed by progressive microstructural degradation. Under equivalent stress levels, increasing F-T frequency and decreasing temperatures monotonically amplify the instantaneous strain, total creep strain, and steady-state creep rates. A key finding is that the ratio of long-term strength to uniaxial compressive strength remains stable at approximately 70%, aligning closely with the crack-initiation stress regardless of F-T history. As damage accumulates, the failure mode transitions from brittle shear to complex tensile-shear composite fracture, characterized by increased primary crack density and a significant reduction in structural integrity. By defining an environmental damage variable based on elastic modulus degradation, an improved creep constitutive model was established. The model exhibits high fidelity in characterizing F-T induced weakening, providing a physics-based framework for assessing the stability of soft rock structures in high-altitude cold regions.

The roughness of rock fractures has complex features that affect how fluids move through them. This research looks at how gas and water flows change in rough fractures when they are moved using a model based on fractal geometry. Rough surfaces are created using a method called fractional Brownian motion. When the surfaces are moved, the space in the fractures becomes uneven. By using a level-set method together with a fluid flow model, the study explores how the speed the fluid enters, the roughness of the surface, and the movement of the surfaces affect the change between bubble, slug, and ring-like flow. The results indicate that more roughness and movement make the flow less stable, which causes a reverse change from ring-like flow to slug and bubble flow. A framework based on pressure is built, showing that the outlet pressure decreases quickly with fluid speed, rises steadily with roughness, and changes in a square relation with movement. A single prediction formula is made with R2 = 0.98, allowing precise identification of the flow types using pressure change limits. This research gives insights into flow changes in fractured reservoirs and offers a way to predict flow in real-time.

The long-term stability of coal pillars in underground stopes and open-pit slopes depends critically on the creep behavior of coal–rock combinations, wherein the rock-to-coal height ratio ( K rc ) exerts a governing yet insufficiently characterized influence. In this study, stepwise creep tests, scanning electron microscopy observations, and acoustic emission tests were conducted on five types of specimens: pure coal (0:1), three composite specimens with height ratios of 1:3, 1:1, and 3:1, and pure rock (1:0). The influence of the K rc on creep deformation, long‑term strength, and Acoustic emission crack evolution was systematically investigated. Three principal findings emerged. First, irrespective of K rc , the creep failure stress consistently approached 90% of the peak uniaxial compressive strength across all specimen types, establishing a straightforward yet robust predictive relationship for long-term strength estimation. Second, the 1:1 composite configuration demonstrated the greatest creep longevity, along with the smallest instantaneous and time-dependent strains and the lowest steady-state creep rate among all composite specimens—collectively identifying this ratio as an optimal configuration for creep resistance. Third, as the proportion of rock increased, the relative contribution of shear cracking declined while tensile cracking became progressively dominant, reflecting a transition in failure mechanism from shear-controlled to tension-controlled behavior. Correspondingly, both the crack initiation stress and the crack damage stress thresholds followed a non-monotonic trend, reaching peak values at K rc = 1:1 before declining at higher rock fractions. Taken together, these results provide quantitative guidance for the rational design of coal pillar geometries and the assessment of long-term structural stability in underground mining operations.

However, its role in controlling damage accumulation rate, microcrack evolution pathway, and water-mediated deterioration mechanism remains insufficiently understood. In this study, weakly cemented sandstone from a cold-region open-pit mine slope was subjected to 100 freeze–thaw cycles at five initial water contents (0%, 1.22%, 2.58%, 3.91%, and 5.06%). Effective porosity, P-wave velocity, uniaxial compression tests, macroscopic failure observations, and site-specific scanning electron microscopy observations were combined to reveal the multiscale evolution mechanism of freeze–thaw damage regulated by initial water content. The results show that freeze–thaw cycling increases effective porosity, whereas P-wave velocity, uniaxial compressive strength, and elastic modulus decrease markedly, with deterioration increasing as initial water content increases. After 100 cycles, the effective porosity of initially saturated specimens increased from 11.9% to 20.3%, while P-wave velocity decreased from 2240 m/s to 980 m/s. The reductions in uniaxial compressive strength and elastic modulus reached 85.99% and 87.18%, respectively. High-water-content specimens exhibited rapid early-stage deterioration, whereas low-water-content specimens showed progressive damage accumulation. Site-specific SEM observations indicate that microcracks preferentially propagated along primary pores, grain-contact interfaces, and weakly cemented zones, and gradually coalesced into crack networks. Water forms a positive feedback mechanism through frost-heave-induced cracking, bond weakening, and crack-channel-enhanced water migration, controlling the transition from microcrack propagation to macroscopic structural deterioration. The findings provide a theoretical basis for freeze–thaw damage assessment and stability analysis of cold-region open-pit mine slopes.

Accurate identification of crack types in rock masses is critical for understanding damage mechanisms and ensuring the structural safety of rock engineering. This study presents a novel unsupervised classification framework based on Gaussian mixture modeling (GMM) for distinguishing acoustic emission (AE) signatures associated with different fracture modes in sandstone samples that contain prefabricated fissures at varying inclination angles. The frequency-domain characteristics of the AE signals were extracted using fast Fourier transform (FFT), while the RA–AF (rise time/amplitude versus average frequency) parameter space was employed to characterize the crack mechanisms. To increase classification accuracy and model robustness, the Bayesian information criterion (BIC) was introduced to determine the optimal number of Gaussian components. Experimental results from uniaxial compression tests reveal that fissure inclination significantly affects crack evolution behavior: low-angle fissures favor shear and hybrid cracks, whereas high-angle fissures cause tensile failure. The proposed GMM-based method effectively identifies tensile, shear, and hybrid cracks with increased objectivity and accuracy, outperforming traditional empirical RA–AF thresholding techniques. This research provides a reliable and generalizable approach for AE signal classification, which presents theoretical insights and practical support for real-time monitoring, early warning, and structural health assessment in fractured rock masses.

In a high-gas and rockburst combined coal mine, the effectiveness of long-borehole blasting in rock floors for rockburst elimination in ultra-thick coal seams is evaluated. The protective layer's failure in coal safety mining is analyzed, and a numerical model is developed to study the local accumulation of high-energy seismic events, considering the spatio-temporal relationship between the protective layer and the working faces in coal seam. A multi-round blasting scheme is designed using a gas-extraction roadway under the coal seam, with a blasting efficiency index (Se) proposed for assessment. The study compares blasting efficiency in the coal pillar area and solid coal area. Results show that the protective layer, compacted by long-term strong mining stress, loses its pressure relief function, leading to stress concentration and energy accumulation in the coal pillar, causing high-energy seismic events and damage to adjacent roadways. Floor blasting effectively prevents rockbursts by inducing high-energy seismic events that dissipate energy through coal and rock mass rupture. The initial local blasting reduces strain energy by 78 %, outperforming subsequent rounds; Se reaches 0.519-0.604 near thrust faults and stabilizes at 0.3-0.5 in solid coal areas. The local initial blasting outperforms subsequent rounds, the frequency of seismic events in the blasting treatment area increases, and the elastic energy accumulated in the coal and rock mass is released as low-energy seismic events. Se evaluates seismic induction, energy release, and pressure relief, reflecting the energy accumulation of coal and rock in different regions where Se is stable in areas with low mining disturbance, while areas with repeated high-energy seismic events show more complex energy re-accumulation processes. Multi-rounds for inducing seismic events and releasing strain energy should be adjusted based on monitoring results during mining.

Mechanical behavior degradation of sandstone due to long-term water immersion is critical when assessing the stability of rock masses in geothermal recovery systems from abandoned/closed mines. In this study, a macro/meso-scale experimental framework was employed to investigate the influence of water immersion on sandstone. The sandstone samples were subjected to uniaxial compression after being immersed in water for various days (0–150 days). X-ray computed tomography (CT) was employed to reveal structural evolution and mechanical degradation under water – rock interaction. The results show that the peak strength and elastic modulus decreased by 64

To address the Rockburst prevention challenges caused by the limitations of roof blasting in deep coal mines, the stress relief mechanism of floor strata was investigated through numerical simulations based on 195 field practices of cross-layer blasting in floor drainage roadways. Three real-time evaluation indices, namely the scalar seismic moment Bm, stress drop Bd and apparent stress Ba per unit charge, were proposed, and a four-level discriminant standard was established. Results show that the scheme effectively intercepts the horizontal stress transmission path by inducing rock mass damage in the floor. Under high tectonic stress conditions, the average vertical and horizontal stresses in key strata decrease by 29.38 and 12.30%, respectively. Simultaneously, the blasting induces the transfer of high-stress concentration zones into the deep surrounding rock, with the maximum offsets of vertical and horizontal stress peaks reaching 5.0 m and 6.0 m, respectively, achieving stress field reconstruction in both intensity and spatial distribution. Cross-validation with seismic wave computed tomography inversion confirms that Bm and Bd indices are highly sensitive in identifying ineffective stress relief events. Field engineering applications significantly reduce the frequency of high-energy microseismic events and stabilize seismic activity, validating the effectiveness of the evaluation system and providing a scientific basis for the quantitative assessment of deep dynamic disasters.

Gas–water displacement in fracture networks is governed by the coupled evolution of interfacial morphology, pressure forcing, gravity-assisted drainage, and network topology. However, how pressure forcing induces gas-phase fragmentation and how fracture-network topology controls residual gas trapping remain insufficiently understood. In this study, volume-of-fluid (VOF) simulations were performed to investigate gas–water displacement in symmetric fracture networks and discrete fracture networks under pressure drops of 3, 5, and 7 kPa and dip-angle combinations of 30°–150°, 45°–135°, and 60°–120°. The results show that increasing pressure forcing promotes the transition of the gas phase from connected bands to gas slugs and dispersed bubbles. As the pressure–capillary competition parameter Πp increases from 41.2 to 96.2, the representative velocity in the main displacement pathway increases from 0.58 to 1.17 m/s, with the capillary number Ca increasing from 7.97 × 10-3 to 1.61 × 10-2 and the Reynolds number Re increasing from 579 to 1168. These changes indicate enhanced interfacial shear and water-phase momentum, which drive viscous fragmentation, reduce gas-phase connectivity, and accelerate early water-saturation growth. Fracture orientation further regulates displacement through gravity-assisted drainage. As the vertical projection factor Φθ increases from 0.50 to 0.87, steeper fracture orientations improve the alignment among preferential pathways, pressure gradient, and gravity, thereby reducing hydraulic tortuosity and promoting faster water-front propagation. Compared with symmetric networks, discrete fracture networks retain more residual gas because dead-end branches, laterally shielded zones, and pressure-isolated pockets reduce the hydraulic accessibility of gas clusters. Under identical pressure and orientation conditions, the steady-state water saturation in discrete networks is 11.8%–20.6% lower than that in symmetric networks. These results reveal a competition between pressure-induced viscous fragmentation and topology-induced gas trapping: pressure forcing fragments gas along hydraulically active pathways, whereas network topology determines whether fragmented gas clusters can be removed. A conceptual displacement-regime map is proposed to summarize the transition from continuous gas bands to slug flow, bubble fragmentation, and topology-controlled residual trapping. This study provides physical insight into multiphase transport, displacement efficiency, and residual gas trapping in fractured subsurface systems.

The stability control of slope rock masses is a fundamental prerequisite for the safe and efficient extraction of coal resources in cold regions. However, the damage behavior of slope rock masses subjected to low-temperature freezing and high-intensity blasting poses significant challenges to stability control in cold-region open-pit mining. Therefore, investigating the dynamic failure mechanical properties of frozen rock and elucidating the coupled damage mechanisms under freezing conditions represent essential scientific issues that must be addressed. In this study, a Split Hopkinson tension bar (SHTB) system was employed to examine the macroscopic tensile failure behavior of water-saturated frozen sandstone. The experimental results demonstrate that, under the combined influence of low temperature and high strain rate, the sandstone exhibits increased strength and brittleness. At lower strain rates, the stress–strain curves display features of ductile deformation, whereas at higher strain rates, they exhibit typical brittle failure behavior. The dynamic tensile strength of coal-bearing sandstone increases progressively with decreasing freezing temperature and increasing strain rate. Similarly, the dynamic elastic modulus rises with decreasing temperature. In contrast, the dynamic peak strain decreases with either decreasing temperature or lower strain rate. High-speed camera imaging and scanning electron microscopy (SEM) analysis further reveal that decreasing temperature or increasing strain rate leads to more complex macroscopic failure patterns and rougher, more irregular fracture surfaces. The strain rate controls the development rate of the internal stress–strain state within the sandstone, directly influencing the dynamic fracture process. Furthermore, the micro-damage evolution is closely linked to freezing temperature, being affected by internal moisture conditions, the material’s brittle–ductile transition behavior, and its microstructural characteristics.

Understanding the dynamic tensile fracture mechanism of thermally damaged coal-rock media is crucial for developing scientific prevention and early warning systems in geotechnical engineering, particularly for high-temperature dynamic environments like underground coal gasification. This study employs a high-temperature loading system and a split Hopkinson tension bar (SHTB) experiment system to conduct dynamic direct tensile failure experiments on hightemperature thermally damaged coal sandstone. Three-dimensional cross-sectional scanners, scanning electron microscopy (SEM), and computed tomography are used to reveal the macroscopic and microscopic mechanisms of dynamic direct tensile fracture in thermally damaged coal sandstone. Experimental results show that temperature has a more significant effect on the macroscopic fracture characteristics of coal-rock media than impact velocity. As the impact velocity increases, the number of macroscopic debris gradually increases. However, the rise in temperature causes a deviation between the fracture plane normal and the tensile load direction and reduces the size of macroscopic debris. The macroscopic cross-sectional structural parameters of tensile failure exhibit an exponential change with increasing temperature and impact velocity. However, the change in cross-sectional structural parameters with temperature is significantly greater than with impact velocity. Additionally, the brittleness of the samples initially increases and then rapidly decreases with rising temperature, with the influence of high temperature on the rocks' brittle-ductile properties gradually intensifies. The evolutionary pattern of microcracks and microporous defects within the coal-rock media shows that the formation and expansion of microcracks and the decoupling of mineral interfaces due to temperature significantly influence the rock's physical and mechanical properties. At lower temperatures, the coal-rock media exhibits relatively smooth brittle fracture characteristics. However, under high-temperature conditions, the rock damage effect intensifies, and the cross-sectional morphological characteristics

The valorization of high-volume fly ash (HVFA) in cemented backfill is a critical strategy for sustainable mining but is often hindered by the technical trade-off between slurry fluidity and mechanical strength development. This study investigates the synergistic regulation of sodium lignosulfonate (SL) on HVFA backfill, employing a multi-scale approach that integrates rheological tests, mechanical testing with Digital Image Correlation (DIC), energy evolution analysis, and quantitative microstructural characterization via Thermogravimetric Analysis (TGA) and X-ray Diffraction (XRD). Results indicate that an optimal SL dosage of 0.3 % effectively balances workability and setting properties, increasing slump by 9.6 % while maintaining a controllable setting delay. Crucially, quantitative hydration kinetics analysis reveals a distinct reversal in performance over time: while SL retards early-age hydration, the 0.3 % dosage significantly enhances long-term reaction efficiency. At 28 days, this optimal dosage achieved the highest chemically bound water content of 16.17 % (surpassing the 15.83 % of the control group) and a similar to 22 % reduction in residual C3S peak intensity, providing robust evidence for enhanced cement hydration and pozzolanic activity. This microstructural densification directly dictates the macroscopic failure mechanism: DIC and energy analysis demonstrate a transition from ductile, energy-dissipating damage to a stable, energy-storage-dominant mode with localized fracture. We establish a clear process-structure-property relationship in SL-modified HVFA systems, providing a scientific basis for engineering high-performance, lowcarbon mining backfill.

The stability of slope rock masses under low-temperature conditions and dynamic impact loading is critical for ensuring the safety and operational efficiency of open-pit mining in cold regions. This study aims to investigate the direct tensile response characteristics, as well as the mesoscopic damage and failure mechanisms, of low-temperature frozen coal-bearing sandstone subjected to dynamic loading. A numerical model of the Split Hopkinson Tensile Bar (SHTB) was developed in this study, utilizing the coupled continuum-discrete element method. A three-dimensional equivalent grain-based model (GBM) was constructed based on the actual mineralogical composition of rock samples, and the freezing effect of water-saturated sandstone at low temperatures was simulated using the particle expansion method. The numerical results demonstrate that the simulation accurately captures the dynamic direct tensile mechanical behavior of frozen, damaged sandstone, as observed in experimental tests. A quantitative analysis was conducted on the trends, quantities, and contact forces of multi-level force chains and microcracks through the multi-level classification within the numerical model. Combined with Scanning Electron Microscope (SEM) observations, it was found that as the strain rate increased, the failure mode of the sample progressively shifted from ductile fracture to brittle fracture, exhibiting a pronounced strain rate effect. As the temperature decreased, the phase transition of water to ice led to the "consolidation" effect, gradually evolving into a degradation effect. The increase in strain rate sensitivity of the sample gradually diminished, and the internal structure tended toward stability.

Understanding nonlinear fluid flow in fractured rocks is critical for various geoengineering and geosciences. This study investigates the evolution of seepage behavior under varying fracture surface roughness, confining pressures, and shear displacements. A total of four sandstone fracture specimens were prepared using controlled splitting techniques, with surface morphology quantified by Joint Roughness Coefficient (JRC) values ranging from 2.8 to 17.7. Triaxial seepage tests were conducted under four confining pressures (3–9 MPa) and four shear displacements (0–1.5 mm). Experimental results reveal that permeability remains stable under low hydraulic gradients but transitions to nonlinear regimes as the flow rate increases, accompanied by significant energy loss and deviation from the cubic law. The onset of nonlinearity occurs earlier with higher roughness, stress, and displacement. A critical hydraulic gradient Jc was introduced to define the threshold at which inertial effects dominate. Forchheimer’s equation was employed to model nonlinear flow, and empirical regression models were developed to predict coefficients A, B, and Jc using hydraulic aperture and JRC as input variables. These models demonstrated high accuracy (R2 > 0.92). This work provides theoretical insights and predictive approaches for assessing nonlinear fluid transport in rock fracture. Future research will address mechanical–hydraulic coupling and incorporate additional factors such as scale effects and flow anisotropy.