Based on the characteristics of microplastic strain and strain hardening during single loading process of rock materials, high-cycle and low-cycle fatigue damage models describing the characteristics of micro-plastic strain and strain hardening of rocks under freeze-thaw cycles were obtained; a fatigue life equation linking microplastic strain and strain hardening is established. According to the high cycle and low cycle fatigue damage models and freeze-thaw cycle experimental data, the fatigue life and other model parameters in the high cycle and low cycle fatigue damage models are determined under double logarithmic coordinate system. In view of the micro pore expansion and the stress increase caused in rocks due to freeze-thaw cycles, the coupled damage variables and its damage range under the combined action of freeze-thaw and stress were derived. The research results indicate that with the increase of freeze-thaw cycles, the coupled damage shows a high cycle fatigue damage followed by low cycle fatigue damage; when determining the damage value of freeze-thaw rock, low cycle fatigue damage can be equivalent to the increase of high cycle fatigue cycle number; the equivalent damage model based on the Lemaitre strain equivalence hypothesis and high-cycle fatigue damage model only describe the damage evolution within the microplastic strain range; whereas the low-cycle fatigue damage model can reveal the damage evolution from microplastic strain to strain hardening range; in the process of microplastic strain to strain hardening development, the damage evolution rate of freeze-thaw rock gradually decreases, showing brittle reduction and plastic increase.

Although researchers have proposed various dynamic strength criteria, they still fail to fully couple fragment size evolution, overlooking the closed-loop mechanism of crack propagation-fragment formation-strength variation. This paper systematically analyzes experimental results and existing theoretical models to propose and verify a strain-rate model for average fragment size (SRAFS model). The analysis indicates that average fragment size remains approximately constant at low strain-rates, decreases sharply nonlinearly, and finally converges to a constant value with increasing strain-rate. It is found that the SRAFS model accurately describes the nonlinear relationship between average fragment size and strain-rate. On this basis, a dynamic fracture mechanics (DFM) criterion considering the strain-rate effect of average fragment size is established, followed by parametric analysis and comprehensive validation against other criteria. The DFM criterion clarifies the strain-rate effect mechanism of quasi-brittle materials' dynamic unconfined compressive strength (USC): at the peak of the stressstrain curve, higher strain-rates induce more high-stress regions (uncracked tensile cracks) at defects tip to enhance strength; in the post-peak stage, they promote more tensile crack propagation, reducing average fragment size. Parametric analysis indicates that the model parameters collectively influence the medium-low strainrate strength associated with initial defects, the strain-rate threshold for significant strength growth, the steepness of the nonlinear relationship between dynamic USC and strain-rate, and the overall strength variation across the entire strain-rate range. Validated with experimental data of five quasi-brittle materials covering two classics dynamic UCS variation patterns, the DFM criterion achieves high determination coefficients (R2 = 0.8429-0.9992), and outperforms the Gebbeken-Greulich and NDUS criteria for ice, silicon carbide and aluminum oxide. Therefore, it reveals the intrinsic link between dynamic USC and average fragment size, demonstrating reliability and adaptability as a robust tool for dynamic load-related engineering applications.

The crushed-rock layer embankment (CRLE) has been widely used in road/railway construction in permafrost regions to maintain subgrade stability via natural convective heat transfer. However, its cooling capacity tends to degrade over time due to sand infilling, rock weathering, and climate warming, making it necessary to enhance the convection process in a non-excavation manner for in-service CRLEs. This study proposes a novel nonexcavation reinforcement method by inserting thermosyphons into the upper part of the embankment, and laboratory model tests were conducted to investigate the underlying enhancement mechanism. Under identical testing conditions, comparative experiments involving a conventional CRLE and a thermosyphon-enhanced CRLE were carried out over four freeze-thaw cycles. Based on monitored temperature, air velocity, and heat flux data, the following key findings were obtained: the thermosyphon achieved a peak heat drainage flux of -90.79 W/m2 and a net heat drainage of 27.53 MJ/m2 per cycle; it reduced the temperature at the crushed-rock layer (CRL) surface by up to 7.29 degrees C, thereby increasing the temperature difference across the CRL and enhancing the natural convection driving force, which resulted in a 42% increase in the maximum porous air velocity and a 19.2% extension of the natural convection active duration. In addition, the thermosyphon not only intensified the cooling magnitude of the CRL but also expanded the cooling area toward the central part of the embankment, increasing the heat released from the underlying soil during cold periods by 96.5% on average. The results validate that thermosyphon insertion is an effective non-excavation technique to actively enhance the cooling performance of in-service CRLEs, offering a rapid and low-impact solution for ensuring the long-term stability of transportation infrastructure built on permafrost.

In order to achieve the effective utilization of biomass ash (BA) as a potential cementitious component, the present work explores the influence of BA, employed as a supplementary cementitious material, on the properties of cement paste. Meanwhile, the mechanism by which various BA replacement levels affect the mechanical strength of cement paste is analyzed via a series of microscopic characterization techniques. In this experimental program, BA was applied as a silica-rich admixture, and cement paste specimens were manufactured by substituting Portland cement with BA at mass ratios ranging from 0% to 50%According to the macroscopic test results, the fluidity of the fresh paste exhibits a slight decreasing trend with the elevation of BA substitution content. In terms of strength development, an initial increasing trend is observed, followed by a gradual reduction, and the optimal overall performance is achieved at a 20% replacement level; under the water-to-binder ratio of 0.6, the 28-day compressive strength reaches 36.11 MPa, showing a 29.6% increase compared with the control group (pure cement paste, 27.86 MPa), and the strength remains above 95% of the control group even at a 30% replacement level. Microscopic analytical results verify that BA possesses noticeable pozzolanic reactivity and is capable of participating in partial hydration reactions. During the hydration procedure, the silica-bearing mineral phases in BA are incorporated into the silicate chains and interlayer structures of C-S-H gels. Furthermore, the relative content of silicate phases within C-S-H gels and their polymerization degree are both remarkably enhanced with increasing BA replacement ratios. The impact of BA content on the pore structure of cement paste differs under varying water-to-binder (w/b) ratios, among which gel pores and mesopores are identified as the dominant factors responsible for the evolution of the overall pore system.

Asphalt pavements impose spatially heterogeneous thermal boundaries that alter the thermal regime of frozensoil subgrades. However, the scale-dependent effects of partial asphalt overlays remain insufficiently understood. This study combines controlled laboratory experiments with a unified thermal-response framework to quantify how overlay diameter regulates heat-transfer pathways and cumulative thermal disturbance. Partial coverage reorganizes subsurface heat-transfer pathways: small overlays enhance lateral diffusion, whereas larger overlays suppress radial loss and form a convergent vertical conduction channel, increasing deep-layer warming by up to 13.4 degrees C. At 10 cm depth, cumulative heat flux exhibits a pronounced non-monotonic response, reaching a minimum of 0.274 MJ/m2 at 11 cm and a maximum of 0.567 MJ/m2 at 15 cm. A dimensionless structuralresponse model generalizes these findings and predicts an optimal thermal-influence width of approximately 4.5 m, at which cumulative disturbance is minimized (1.009 MJ/m2). Both narrower and wider coverage scales increase disturbance by 13-15%. These findings clarify scale-dependent thermal disturbance mechanisms and provide a quantitative basis for optimizing overlay width in cold-region pavement engineering.

Natural rock contains irregular and randomly distributed micropores and microcracks. Under the action of freeze-thaw cycles, the pore water in these microdefects generates a frost heave force during the water-ice phase transition, leading to pore expansion and damage and the formation of cracks in the rock. This study establishes a microplastic freeze-thaw damage model based on the Clausius-Duhem inequality and an orthogonal rule based on irreversible thermodynamics. We determine the fatigue life that conforms to the characteristics of microplastic damage and the model parameters that satisfy the microplastic fatigue equation. To characterize the heterogeneity of rock materials at the mesoscopic scale and the randomness of initial microdefect distribution, a statistical damage model that conforms to strain-softening characteristics and model parameters that reflect the correlation between the microelement strength and the stress state of rocks are proposed based on the damage variable defined by the defect density ratio and probability density distribution under microelement. A direct correlation between axial strain and stress state is achieved. Based on the damage range and nonnegativity of individual damage variables and considering the increased damage caused by micropore expansion and stress changes, a freeze-thaw stress coupling model is derived to estimate fatigue life and characterize the strength of rock microelements. The damage variables and value range under the coupling state are also estimated. The fatigue, statistical, and freeze-thaw stress coupling damage models of freeze-thawed rocks are verified. The coupled damage evolution model is a power function that directly reflects the axial strain of the stress-strain state and the number of freeze-thaw cycles as independent variables. The model expresses the damage evolution of rocks in the initial compaction, postcompaction, and rapid damage stages. Furthermore, it describes the stochasticity, accumulation process, and regional sensitivity of microelement damage failure, revealing the correlation between the number of freeze-thaw cycles and material brittleness.

The freeze-thaw (FT) damage evolution of water-saturated fractured rocks in cold regions is a key cause of engineering disasters, such as rock slope instability and tunnel lining failure. Existing studies mainly focus on single-fracture systems and rely on post-test macroscopic characterization, making it difficult to capture the dynamic mesoscopic damage evolution during FT cycles. In particular, the damage mechanism of double parallel open fractures containing a rock bridge remains insufficiently understood. To address this issue, a Discrete Element Method (DEM)-based numerical model is developed for FT damage in water-filled rock with double parallel open fractures. The particle expansion method and effective volume expansion method are employed to simulate the frost heave effects of pore water and fracture water, respectively, together with a heat-pipe thermal conduction model. The predicted peak strengths under five representative fracture dip angles (0 degrees, 38 degrees, 45 degrees, 63 degrees, and 90 degrees) agree well with laboratory results, with relative errors below 30%. The mesoscopic damage evolution mechanism is systematically investigated through dynamic tracking of displacement fields, force-chain structures, tension-compression contact transformation, circumferential stress redistribution, and microcrack evolution. Results show that tensile failure is the dominant FT damage mode in rocks containing open fractures, with tensile cracks consistently far exceeding shear cracks. The fracture dip angle plays a decisive role in FT deterioration, exhibiting a staged migration of the dominant damage angle: 38 degrees specimens show the most severe damage in the early FT stage (<= 20 cycles), while 0 degrees horizontal fractures become dominant in the late stage (>40 cycles). Meanwhile, the frost heave force progressively migrates from fracture tips toward the rock bridge center, ultimately causing the loss of rock-bridge load-bearing capacity.

Based on the test data of rock material under different confining pressure and freeze-thaw cycle, the statistical damage model parameters related to the confining pressure level are determined, and the microelement strength of rock can be directly measured by axial strain; Using the inflection points in the damage evolution process of freeze-thaw rocks, the strain hysteresis factor, which characterizes the peak strain and model parameters, was obtained, the variation characteristics of axial strain of rock material from peak strength to residual strength in the post-peak region are revealed, and the definition of rock brittleness and plasticity and their value ranges were achieved by the model parameters; The inflection point strain is defined as the axial strain when the peak stress drops to the residual strength, the damage value at the inflection point strain is defined as the ultimate damage, a ultimate damage model under the coupled action of freeze-thaw and stress is established. The research results indicate that axial strain is sensitive to the brittle characteristics and ultimate damage of rocks under low confining pressure, and the inhibitory effect of low confining pressure on the ultimate damage of rocks subjected to different numbers of freeze-thaw cycles is not obvious; Under the action of low freeze-thaw cycle, increasing confining pressure has a significant effect on inhibiting the development of rock damage or the expansion of pores and fractures; Under the influence of high confining pressure and numerous freeze-thaw cycles, rock materials gradually exhibit the accumulation of freeze-thaw damage, the weakening of confining pressure constraint and the damage threshold effects.

The stability of rock engineering in cold regions is significantly influenced by the coupled effects of freeze-thaw (FT)cycles and dynamic loading, with the geometry of rock bridges playing a key role. This study investigates the dynamic crack propagation and fracture behavior of sandstone containing prefabricated fissures under combined FT cycles and impact loading, considering different rock bridge inclination angles (alpha = 48 degrees, 66 degrees, 90 degrees). Full-field strain evolution and crack development were quantitatively characterized using digital image correlation (DIC) and high-speed photography. Changes in pore structure and dynamic mechanical responses were further analyzed through nuclear magnetic resonance (NMR) and split Hopkinson pressure bar (SHPB) tests. DIC results indicate that crack initiation location, propagation path, and velocity are strongly controlled by the rock bridge inclination angle: As alpha increases, cracks tend to propagate along the bridge direction, leading to rapid penetration and a reduction in dynamic strength. FT cycles exacerbate damage, transforming crack patterns from localized to dispersed and shifting failure modes from tensile-dominated to tension-shear mixed. A macro-mesoscopic coupled constitutive model incorporating FT damage and fissure geometry was established. Model predictions show excellent agreement with experimental data, with coefficients of determination R2 greater than 0.93, average peak strength relative error below 2.29 %, and most peak strain errors within 10 %. This study provides both experimental and theoretical support for the stability assessment of rock structures in cold regions

ObjectivesDuring the tunnel construction， layered rock structures are prone to problems such as vault collapse and initial support cracking. Therefore， it is of great engineering value to deeply analyze the mechanical characteristics of layered rock.Carbonaceous slate， as a typical rock mass of layered metamorphic rock， exhibits poor interlayer cementation and is easily broken， which can lead to serious structural damage when tunneling through it， significantly reducing rock mass strength and altering its mechanical properties. This study aims to analyze the mechanical properties and clarify the disintegration mechanism of carbonaceous slate.MethodsStatic disintegration tests， uniaxial compression tests and triaxial compression tests were carried out on carbonaceous slate. The mechanical properties of slate under different water content states and different bedding plane angles were analyzed， and the deformation failure modes and disintegration mechanisms of rock samples were discussed.ResultsThe results show that： （1） The peak strength of dry samples is higher， the pre-peak stress-strain curve is approximately linear， and plastic failure occurs suddenly. The elastic modulus of the dry samples is higher than that of natural and saturated samples. After the peak strength， dry and natural samples exhibit different degrees of brittle drop， while the post-peak strength of the saturated samples （23.02 MPa） can still be maintained at approximately 21 MPa. （2） After multiple disintegration cycles， the disintegration degree of weakly weathered slate is low. For moderately weathered rock， water molecules entering the rock mass destroy cementation bonds and promote the formation of broken blocks， leading to disintegration. For fully weathered and strongly weathered slate， water absorption and swelling generate uneven stress， driving complete disintegration of the rock samples.ConclusionsThe research results can provide a reference for controlling large deformation and failure in soft rock tunnel construction under similar conditions.

The entire process of damage and weakening of heterogeneous rock materials was described using the number of freeze–thaw cycles as a randomly distributed variable. The characteristic points and lower limit values of rock damage evolution were determined. The post-buckling behavior of freeze–thaw layered slopes was explored using the initial post-buckling theory, and the critical buckling load and bifurcation buckling load of the slope rock mass were given. A stability criterion for the equilibrium configuration of the rock mass structure was established. The results show that the critical load of the slope rock mass decreased monotonically with the Weibull distribution density function, and the increment of bifurcation load decreased exponentially with the density function. Under the Weibull statistical model with freeze–thaw cycles as the random distribution variable, the fatigue damage residual modulus of the rock material could be determined using the number of freeze–thaw cycles to reach the fatigue damage life of the rock material. The evolution characteristics of heterogeneous layered slope rock masses in cold regions, from initial buckling under critical load to bifurcation buckling under bifurcation load, and then to structural buckling and failure caused by material damage and weakening, express the mutual influence and coupling between structural stability and material degradation under the combined action of freeze–thaw cycles and defect loads.

Clarifying the mechanical properties of cellulose-based materials is essential to ensure their safe use and service. However, current studies have not adequately addressed how specimen size influences their mechanical properties. To address this gap, the kraft paper is selected to conduct a uniaxial tensile test with different widths. Subsequently, the variation patterns of mechanical properties and their fluctuation with respect to specimen width are identified. Through examining the failure characteristics, the mechanism behind the size-dependent mechanical properties is elucidated. Finally, a size effect model considering edged and internal fracture process zones (FPZs) is established. The results indicate that the nominal peak stress (tensile strength) and the corresponding nominal strain of kraft paper increase initially and then decrease with increasing width. The mechanism behind this phenomenon is that the cutting-off fibers reduce the stress and strain capacities of the specimens' edges. The fluctuation of mechanical properties decreases with increasing width. The Logistic CDF provides a more accurate description of the fluctuation of kraft paper's mechanical properties compared to the Weibull CDF. The size effect model that we established can not only describe the “increase-then-decrease” size effect in kraft paper, but can also describe the “decrease-then-increase-then-decrease” size effect of the tensile strength of wood scrimber.

To investigate the disturbance caused by blasting in the excavation process of tunnel and coal mine surrounding rock, it is urgent to clarify the mechanical response, failure mode and energy dissipation characteristics of red sandstone under dynamic load under confining pressure. In this study, the split Hopkinson pressure bar (SHPB) test system with a self-developed active confining pressure control device was used to carry out dynamic compression tests on red sandstone specimens under different confining pressure levels, to explore the dynamic mechanical response, failure mode and energy dissipation mechanism of red sandstone under impact load. The test results show that the stress-strain curve presents a “two stages” characteristics under unconfined condition. and the stress-strain curve changes from a “two stages” to a “three stages” pattern with the increase of confining pressure. The confining pressure significantly enhances the dynamic compressive strength and peak strain of red sandstone, both of which show significant strain rate effect and confining pressure effect. In terms of failure mode and energy dissipation, the rock specimen is crushed when subjected to higher strain rate at unconfined condition. Under confining pressure, the damage degree of the sample is significantly reduced, and finally resulting in compression-shear failure. Under the same confining pressure, the reflection energy and reflectivity increase with the increase of strain rate, while the transmission energy increases with the increase of strain rate and the transmittance decreases with the increase of strain rate. Under the same strain rate, with the increase of confining pressure, the rock reflection energy and reflectivity decrease, the transmission energy and transmittance increase. When the specimen is dynamically damaged, the dissipation energy is regulated by strain rate and confining pressure. When the confining pressure is constant, the dissipation energy and dissipation rate increase with the increase of strain rate. When the strain rate is constant, both the dissipation energy and dissipation rate decrease with the increase of confining pressure.

It is challenging to control the concealability and roughness of the fracture grouting process in a water-rich environment, which makes it difficult to directly observe the grout diffusion and deposition process as well as evaluate the sealing effect. Consequently, the water-blocking mechanism remains unclear. To address this issue, this paper utilized 3D printing technology to create a transparent rough fracture model based on the random midpoint displacement method and fractal theory. Additionally, an independent water grouting test system was developed to perform dynamic water grouting tests under various working conditions. The computational fluid dynamics and two-phase flow approach (CFD-TFM) is employed for numerical simulation to ascertain the slurry diffusion patterns and deposition effects at various time intervals throughout the grouting operation. Uniaxial compression and direct shear tests were conducted to evaluate the mechanical behavior of the grout-consolidated specimens. The results indicate that the rough fracture produced by the 3D printing process exhibits effective visibility, allowing for the observable trend of grouting flow. The experimental phenomena categorize the distribution pattern of dynamic water grouting into three types: cross-section water plugging pattern, comet type, and elongated streamline type. The slurry flow trend and particle deposition effect described by the CFD-TFM Technology (2026) method are consistent with experimental observations, and all three forms-cross-section type, comet type, and slender streamline-are evident. The concrete results indicate that the particle deposition effect follows the order: cross-section type > comet type > slender streamline. Pressure monitoring data reveal a decreasing trend from the moving water inlet to the outlet boundary. As the distance from the grouting hole increases, the drop in sensor pressure values becomes less pronounced, resulting in reduced grouting deposition. These research findings provide a theoretical basis for the design of grouting reinforcement engineering.

Three-dimensional spatial effects in deep excavations critically govern the mechanical response of retaining structures and adjacent soils, yet their quantitative characterization remains a challenge. This study systematically investigates the spatial behavior of row-pile-supported foundation pits through an integrated approach combining model tests, theoretical analysis, and numerical simulations. A novel formulation for the spatial effect influence coefficient K is derived from limit equilibrium principles and subsequently validated via ABAQUS-based finite element simulations. Model test results reveal pronounced spatial heterogeneity in earth pressure and bending moment distributions along the pit perimeter: lateral earth pressure at corner regions exceeds that at mid-side locations at equivalent depths, whereas bending moments in mid-side piles are substantially larger than those at corners. Displacement field measurements further demonstrate that corner zones, constrained bidirectionally, undergo minimal deformation, while maximum displacement occurs at the midpoints of the long sides. These observations collectively confirm the existence of a marked corner effect and a subdued side-midpoint effect under three-dimensional confinement. Complementary numerical analyses indicate that the coefficient K decreases monotonically with increasing half-angle corners and distance from the corner, thereby quantitatively capturing the decay of spatial constraint intensity. Together, these findings establish a theoretical framework for assessing excavation-induced spatial effects and provide actionable guidance for the rational design of deep foundation pit support systems.

Engineers face significant challenges in determining the grouting parameters and evaluation criteria for environments with flowing water, which has become an urgent matter of concern. Due to the intricate nature of grouting flow and diffusion in practical grouting engineering, numerous fluid-related issues cannot be effectively resolved solely through theoretical analysis or the direct application of fundamental equations. Therefore, it is necessary to employ experimental methods to visually assess and explain these phenomena. In this study, a unique dynamic water grouting test equipment based on 3D printing was designed to evaluate the dynamic grouting travel in cracked rock with flowing water. The influences of fractal dimension, water flow rate, grouting flow rate, and water–cement ratio on the grouting diffusion properties of fractured rock with flowing water were extensively explored. The test demonstrates that the migration and diffusion of grout in the finite boundary fracture can be split into two stages, namely, the circumferent diffusion stage without lateral boundary and the boundary diffusion stage. According to each working circumstance, the diffusion patterns in the process of grouting water plugging are categorized into three types: cross-section, comet, and elongated streamline. A stagnant flow zone was developed in the valley region of the fracture, in which additional particles were deposited. High shear stress was distributed toward the apex area, where few particles were deposited. The experimental results corroborated these observations. The study of the range of grouting diffusion and transport patterns in 3D rough fissures can provide useful insights and guidance for the selection of grouting parameters in grouting engineering practice.

In the loess-filling project, the original structural loess under the filling will produce creep deformation under the isometric consolidation stress state, affecting the upper building’s safe construction and later operation. Therefore, studying the creep deformation characteristics of structural loess under different consolidation coefficients is significant. In this paper, the following results are obtained by combining test and theoretical analysis. In view of the structural loess under the filling, the triaxial creep test of undisturbed loess under different isometric consolidation coefficients, confining pressures and shear stress levels was completed, and the creep deformation law of structural loess was obtained. The creep characteristics of undisturbed loess are found to be diversified under different coefficients, confining pressures, and shear stresses, including initial instantaneous deformation, subsequent creep attenuation deformation, and final stable creep deformation. The damage creep constitutive model of undisturbed loess is established, taking the binary medium model as the framework, the cementation element adopts the Nishihara model, the friction element introduces the overstress model and considers the isometric consolidation effect, and the damage creep constitutive model of undisturbed loess is established. The theoretical model is obtained by determining the relevant parameters of the constitutive model. The theoretical curve is compared with the experimental curve and shows that the damage creep model established in this paper can better reflect the creep of structural loess under isometric consolidation conditions well. The research results can provide systematic theoretical support and an experimental basis for the deformation problems involved in the filling project in the loess area.

The study of the compression characteristics of loess in seasonal regions involves analyzing the mechanical properties and mesoscale damage evolution of intact loess subjected to dry–wet freeze–thaw cycles. This study meticulously examines the evolution of the stress–strain curve at the macroscale and the pore structure at the mesoscale of loess by consolidation and drainage triaxial shear tests, as well as nuclear magnetic resonance (NMR), under varying numbers of dry–wet freeze–thaw cycles. Then, utilizing the Duncan–Chang model (D-C), the damage model for intact loess is derived based on the principles of equivalent strain and Weibull distribution, with testing to verify its applicability. The results indicate that the stress–strain curve of undisturbed loess exhibits significant strain softening during the initial stage of the freeze–thaw dry–wet cycle. As the number of cycles increases, the degree of strain softening weakens and gradually exhibits a strain-hardening morphology; the volume strain also changes from dilatancy to shear contraction. According to the internal pore test data analysis, the undisturbed loess contributes two components to shear strength: cementation and friction during the shear process. The cementation component of the aggregate is destroyed after stress application, resulting in a gradual enlargement of the pore area, evidenced by the change from tiny pores into larger- and medium-sized pores. After 10 cycles, the internal pore area of the sample expands by nearly 35%, indicating that the localized damage caused by the dry–wet freeze–thaw cycle controls the macroscopic mechanical properties. Finally, a damage constitutive model is developed based on the experimental phenomena and mechanism analysis, and the model’s validity is verified by comparing the experimental data with theoretical predictions.

In order to solve the problems of instability and disturbance collapse of roadway surrounding rock in the process of coal mining, a splitting grouting reinforcement method is proposed. The splitting coal samples were grouted with cement-based slurry and epoxy resin with different water-cement ratios, and uniaxial compression experiments were carried out. Combined with acoustic emission and VIC3D monitoring system, the compressive strength and macroscopic failure characteristics of coal samples reinforced with different grouting materials were discussed. The experimental results show that: the compressive strength of grouting reinforcement increases with the decrease of water-cement ratio, and the strength of epoxy resin to the consolidation body is significantly improved, but the reinforcement effect is basically the same as that when the water-cement ratio is 0.6; in the aspect of the failure characteristics of the reinforced body, the stress concentration first occurs at the joints of the coal sample, with the extension of the loading time, the cracks are finally destroyed after initiation, expansion and penetration. The failure positions all occur in the non-reinforced zone, indicating that the splitting grouting reinforcement can improve the integrity of the coal rock.

The pore structure of foam concrete (FC) predominantly governs its performance, with frost resistance being a critically dependent property. This study aims to elucidate the mechanism by which aeolian sand influences the pore structure and frost resistance of FC. Through integrated characterization employing ultrasonic non-destructive testing, image analysis, and scanning electron microscopy (SEM), we analyze the correlation between pore characteristics and frost resistance, along with the degradation mechanisms under freeze-thaw (F-T) cycles. The results indicate that the addition of aeolian sand enhances the frost resistance of FC. The optimal dosage of aeolian sand was determined to be a sand-binder ratio of 0.25. After 80 F-T cycles, the mass loss rate and strength loss rate were reduced by 0.93 % and 12.87 %, respectively, compared to the control group. The porosity was only 56.8 %, representing a 5.5 % reduction relative to the control group. Additionally, the pore size distribution became more uniform, with the proportion of pores in the 100-300 mu m range increasing by 4.1 %, while the proportion of pores larger than 800 mu m decreased by 2.56 %. The micro-filling effect of aeolian sand effectively optimizes the pore structure of FC by reducing the number of interconnected pores and decreasing pore size, thereby enhancing its frost resistance. However, excessive incorporation leads to insufficient cementitious materials, resulting in poor paste coating capability. This subsequently causes an increase in porosity and structural loosening, ultimately reducing frost resistance.