This study introduces superabsorbent polymers(SAP)into recycled concrete and,through freeze-thaw cycle tests,unconfined compressive strength tests,and nuclear magnetic resonance(NMR)analysis,evaluates the freeze-thaw ...This study introduces superabsorbent polymers(SAP)into recycled concrete and,through freeze-thaw cycle tests,unconfined compressive strength tests,and nuclear magnetic resonance(NMR)analysis,evaluates the freeze-thaw resistance and durability of recycled concrete samples under varying freeze-thaw cycles.The results indicate that an appropriate addition of SAP significantly enhances the freeze-thaw resistance of recycled concrete.After 200 freeze-thaw cycles,the RS0.6 sample retained good surface integrity,demonstrating the best performance.Compared to NAC,its mass loss decreased by 1.16%,the relative dynamic modulus improved by 7.01%,and the compressive strength loss rate decreased by 5.41%.Additionally,T2 spectrum analysis revealed that adding SAP optimized the pore structure of recycled concrete and mitigated pore development during freeze-thaw cycles.As the number of freeze-thaw cycles increased,the RS0.3 and RS0.6 samples demonstrated superior frost resistance compared to NAC.However,an excessive amount of SAP increased pore expansion during subsequent freeze-thaw cycles,ultimately weakening frost resistance.展开更多
Freeze-thaw(F-T)cycle is receiving increasing attention as a primary threat to the long-term stability of rock engineering in high-elevation regions.In this study,artificial F-T cycle tests are first conducted on pre-...Freeze-thaw(F-T)cycle is receiving increasing attention as a primary threat to the long-term stability of rock engineering in high-elevation regions.In this study,artificial F-T cycle tests are first conducted on pre-flawed sandstone specimens with real-time frost heave pressure(FHP)monitoring,followed by subsequent cyclic loading tests with different maximum stresses.Given the water-ice-sandstone interaction,the evolution process of FHP in flaws can be divided into six phases,i.e.initial,silence,eruption,reduction,second-arising,and dissipation phases.Its magnitude exhibits an exponential decrease with increasing F-T cycle number.The influences of F-T cycles and the maximum stress on the fatigue mechanical characteristics of flawed sandstone are revealed.Subjected to higher F-T cycles and maximum stress,larger irreversible strain and less dissipated energy are accumulated inside flawed sandstone specimens,leading to faster damage and lower fatigue life.The three-stage evolution characters of irreversible strain and dissipated energy are both weakened by repeated F-T treatment,i.e.the prolonged initial and accelerated stages and shortened stable stage.In addition,the repeated F-T cycles diminish the impact of prefabricated flaws on cracking behavior of flawed sandstone specimens,and the fatigue failure pattern changes from shear-dominated failure with a transfixion shear band to tensile-dominated failure with massive tensile cracks as the F-T cycle number increases.Employing the scanning electron microscopy(SEM),the underlying damage mechanisms of flawed rocks under the coupling effect of F-T treatment and cyclic loading are discussed.Finally,an F-T-fatigue damage model is proposed based on FHP evolution and irreversible strain,which possesses distinct physical significance and reasonably quantifies the F-T deterioration and fatigue damage accumulation of flawed rocks.展开更多
Freezing and thawing processes play a crucial role in causing significant deformation and damage to layered soft rocks in cold region due to daily and seasonal temperature fluctuations.However,the frost heave mechanis...Freezing and thawing processes play a crucial role in causing significant deformation and damage to layered soft rocks in cold region due to daily and seasonal temperature fluctuations.However,the frost heave mechanism of the rocks and their mechanical behaviors at the meso-scale still require further investigations.For this,we focused on carbonaceous slate reported in a high-altitude cold region,in terms of mineral composition,content,and microstructure.The strength and failure of mineral grain(MG)interfaces are studied using three-point-bending tests,in order to explore the evolution of mode I fracture toughness and tensile strength with the Dugdale-Barenblatt model and the Weibull distribution model.The results indicate that the damage of slate involves the initiation and propagation of microfracture networks at clay MG interfaces(bedding planes),driven by frost heave pressure at macroscopic and microscopic scales.This process causes the detachment of some MGs,resulting in fracture surfaces with a distinctive pulled-off planar structure.The hydrophilicity of clay MGs,interfacial strengths,and microfracture structures contribute to the freeze-thaw damage.As the number of freeze-thaw cycles increases,the effective area per unit decreases,leading to an exponentially decreasing in mode I fracture toughness and tensile strength at MG interfaces.Approximately 67%strength degradation occurs after 14 freeze-thaw cycles.This provides theoretical basis and experimental methods for better understanding the damage and deterioration behaviors of layered soft rocks in cold region under natural freeze-thaw cycles.展开更多
Freeze-thaw cycles(FTCs)have an important effect on soil aggregate stability by altering soil structures,thereby influencing soil wind and water erosion on the eastern Qinghai-Tibet Plateau.However,the effects of FTCs...Freeze-thaw cycles(FTCs)have an important effect on soil aggregate stability by altering soil structures,thereby influencing soil wind and water erosion on the eastern Qinghai-Tibet Plateau.However,the effects of FTCs on the stability of these soils remain unclear.Here,we conducted freeze-thaw simulations in laboratory to investigate the effects of FTCs(0 to 15 cycles)on the wet-and dry-sieving aggregate stability of undisturbed sandy loam from Maqu county,which was treated with different initial soil moisture contents(1%to 25%in increments of 4%)and initial aggregate diameters(<2,2-5,5-10,and 10-15 mm).Results show that soil aggregates with initial diameters larger than 2 mm exhibit higher soil organic carbon contents(1.45%-1.57%)and silt contents(34.63%-35.52%)than those smaller than 2 mm(0.93%and 31.38%,respectively).The stability of both wet-and dry-sieving aggregates increases with larger initial diameters.Increasing initial soil moisture content from 1%to 25%reduces aggregate stability,with reductions of 2.4%-88.0%for wet-sieving aggregates and 2.1%-25.5%for dry-sieving aggregates(>2 mm).With increasing FTCs,wet-sieving aggregate(>2 mm)stability exhibits a fluctuating upward trend,with increases of 79.2%-87.4%after 15 FTCs,while dry-sieving aggregate(>2 mm)stability decreases significantly(5.7%-21.7%)upon the first FTC and remains unchanged thereafter.The stability of both the wet-and dry-sieving aggregates smaller than 2 mm remains unchanged with increasing FTCs(p>0.05).SOC content decreases by 22.3%on average with increasing FTCs from 1 to 15 and shows no significant correlations with wet-and dry-sieving aggregate stability.Higher silt content(r=0.39,p<0.05)and lower sand content(r=-0.38,p<0.05)enhances the wet-sieving aggregate stability of sandy loam.Frequent FTCs tend to improve wet-sieving aggregate stability but reduce dry-sieving aggregate stability in the sandy loam.The findings provide certain guidance for preventing freeze-thaw-induced wind erosion.展开更多
In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical...In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.展开更多
Low porosity is very significant for cementitious composite materials(CCM)under freeze-thaw conditions.To reduce the porosity of CCM,we used wollastonite mineral fibers as a partial replacement for cement and aggregat...Low porosity is very significant for cementitious composite materials(CCM)under freeze-thaw conditions.To reduce the porosity of CCM,we used wollastonite mineral fibers as a partial replacement for cement and aggregate.The five combinations,in which 10%,32%,and 48%Wollastonite were added,were made for scanning using both scanning electron microscopy(SEM)and computed tomography scan technology(CT).Then,the 2D SEM pictures and the 3D pore distribution curves are obtained before and after the freezing and thawing processes,where the micro-pores in the CCM materials are shown.The fractal dimension is used to quantify the topography image in two dimensions,as well as the pore distribution in three dimensions.This method allows for the determination of both surface porosity and volume porosity,both of which show an increase in response to an escalation of freeze-thaw cycles.It is also found that the micro-damage in the concrete is of self-similarity,and in the context of the fractal dimension,the pore evolution can be quantitatively characterized across different sizes,ranging from local to global levels,before and after freezing and thawing.展开更多
Sulfate attack-induced expansion of cement-treated aggregates in seasonally frozen regions is a well-known issue which causes continuous expansion in railway subgrades,and particularly in high-speed railways.According...Sulfate attack-induced expansion of cement-treated aggregates in seasonally frozen regions is a well-known issue which causes continuous expansion in railway subgrades,and particularly in high-speed railways.Accordingly,we investigated the influence of material proportions,the number of freeze-thaw(FT)cycles,and temperature gradients on the expansion mechanism of sulfate attack on cement-treated aggregates subjected to FT cycles.The conditions,laws,and dominant factors causing the expansion of aggregates were analyzed through swelling tests.The results indicate that under FT cycles,3%content cement-treated graded macadam only experiences slight deformation.The maximum strain of graded macadam attacked by 1%sodium sulfate content in each FT cycle is significantly larger than that of 3%content cement-treated graded macadam attacked by 1%sodium sulfate content.Using scanning electron microscopy,needle-like crystals were observed during sulfate attack of cement-treated graded macadam.Through quantitative analysis,we determined the recoverable and unrecoverable deformations of graded macadam under FT cycles.For graded macadam under sulfate attack,the expansion is mainly induced by periodic frost heave and salt expansion,as well as salt migration.For cement-treated graded macadam under sulfate attack,the expansion is mainly induced by chemical attack and salt migration.This study can serve as a reference for future research on the mechanics of sulfate attack on cement-treated aggregates that experience FT cycles,and provide theoretical support for methods that remediate the expansion induced by sulfate attack.展开更多
To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requir...To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requires immediate investigation.In view of this phenomenon,the durability of unit lining concrete is predicted by analyzing three key indicators:carbonation depth,relative dynamic elastic modulus,and residual quality.This prediction is achieved by integrating the Entropy Weight Method,Grey theory life prediction model and BP artificial neural networks using data from tests and predictions of these indicators.Then,the Entropy Weight-Grey theory-BP Network Model is compared with other methods to analyze the predicted life.Finally,verify the sci-entificity of this model,and the optimum silica fume content of unit concrete lining is verified.The results showed,1)The addition of silica fume will accelerate the carbonization of unit concrete lining,and slow down the freeze-thaw cycle and sulfate erosion.2)The utilization of artificial neural networks is essential for enhancing the realism of the data,as it emphasizes the significance of silica fume content.3)Silica fume content of 10%results in the longest life and is the most suitable for lining construction.4)A comparison between single-factor and multi-factor predictions indicates that the multi-factor approach yields a longer maximum life.This improvement can be attributed to the inclusion of additional factors,such as freeze-thaw cycles and carbonation,which enhance the predicted life when employing these methods.In conclusion,the Entropy Weight-Grey Theory-BP Network life prediction Model is well-suited for tunnel lining in the alpine sulfate area of northwest China.展开更多
Aiming at challenges posed by rock freezethaw(FT)in cold regions rock mass engineering,it is of great significance to analyze its macro-and micromechanical properties and damage laws for the smooth progress of constru...Aiming at challenges posed by rock freezethaw(FT)in cold regions rock mass engineering,it is of great significance to analyze its macro-and micromechanical properties and damage laws for the smooth progress of construction.In this study,indoor freezethaw cycle(FTC)tests on sandstone were conducted to analyze the mass change rate,density change rate,longitudinal wave velocity change rate,microstructure change and mechanical properties of sandstone after FTC.A microscopic FT damage variable reflecting the FT damage was defined based on the changes of rock porosity before and after the FTC,enabling the derivation of the total damage variable under the coupled action of FTC and mechanical loading.A damage evolution equation and a microscopic damage constitutive model for rock under coupled FTC and confining pressure were established by using Lemaitre’s strain equivalence principle,the theory of continuous damage mechanics,and the assumption that the failure of rock micro-units follows the SMP criterion.The rationality and accuracy of the model were verified using triaxial compression test data for FT-damaged rock.The results show that both macroand micro-mechanical properties of sandstone are degraded under the action of FTC,resulting in significant damage.The developed microscopic damage constitutive model can reflect the stress-strain characteristics of the whole process of FT rock triaxial compression,with excellent agreement observed between experimental and theoretical curves.This validates the reliability of the model and the methodology for determining its parameters.Additionally,defining the microscopic FT damage variable based on rock porosity changes is demonstrated to be a feasible and highly accurate approach to reflect rock FT damage degree.This model expands the damage model for rock under the coupling effect of FTC and confining pressure,further illuminating the damage mechanism and failure law in such environments.The findings provide references for the construction of rock mass engineering in cold regions.展开更多
Red mud(RM) is an industrial solid waste produced during the extraction of alumina from bauxite.The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization.This paper proposes ...Red mud(RM) is an industrial solid waste produced during the extraction of alumina from bauxite.The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization.This paper proposes a method for dealkalization and chromium(Cr) removal by repeated freeze and thaw to enhance the comprehensive utilization rate of RM.This study focused on the Bayer RM and investigated the effects of freeze-thaw(FT)-acid washing(AW) for dealkalization and Cr removal.The variables were the eluent concentration and FT cycles.The results showed that the synergistic action of FT-AW significantly improved the efficiency of dealkalization and Cr removal.After five FT cycles with 0.5 mol/L oxalic acid,the dealkalization and Cr removal rates reached 97.5% and 65.38%,respectively,16.1% and 7.40% higher than those achieved at room temperature.The repeated FT disrupted the structure of the RM particles,leading to an increase in the pore space between the soil particles.This enables complete eluent contact and reaction with Cr and alkali,thereby enhancing the removal rate.The FT-AW process is suitable for practical engineering applications.It offers a novel method for RM dealkalization and Cr removal by using the FT alternation phenomena in seasonally frozen regions.展开更多
High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock inst...High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.展开更多
In cold-region environments,where complex stresses and mining disturbances occur,rock masses are frequently segmented into discontinuous bodies by fractured structural planes,leading to anisotropic physical and mechan...In cold-region environments,where complex stresses and mining disturbances occur,rock masses are frequently segmented into discontinuous bodies by fractured structural planes,leading to anisotropic physical and mechanical properties.To explore the evolution of microcracks,degradation characteristics,and failure modes of fractured rocks in cold regions under the influence of freeze-thaw cycles,integrating laboratory experiments with the damage mechanics of freeze-thaw cycles.A numerical model for freeze-thaw cycle damage in rocks with various fracture dip angles was developed.The study revealed that the freeze-thaw expansion force generated during the pore water-ice phase transition is the primary driving factor behind freeze-thaw cycle damage.The initiation and propagation of microcracks and micropores,the detachment of matrix particles,and the loosening of clay mineral structures result in the transformation of the rock from a dense to a porous state,causing significant degradation in macroscopic mechanical properties.As freeze-thaw cycles increase,both the uniaxial compressive strength and the deformation modulus of the rock decrease significantly,with the failure mode gradually shifting from brittle instability to brittle-plastic or plastic failure.The findings of this study offer a practical approach to uncovering the mechanical response mechanisms between freeze-thaw damage in fractured rocks and structural planes.展开更多
The mechanical properties of bedding rock in cold regions are frequently affected by freeze-thaw(F-T)cycles and ani-sotropy.Research on the mechanical characteristics of rock damage under the combined action of F-T an...The mechanical properties of bedding rock in cold regions are frequently affected by freeze-thaw(F-T)cycles and ani-sotropy.Research on the mechanical characteristics of rock damage under the combined action of F-T and bedding angles is limited,and most traditional rock damage models cannot accurately capture these characteristics.We performed axial compression tests to ex-plore the strength characteristics of bedding slates at the bedding angles ofβ=0°,30°,45°,60°,and 90°under various F-T cycles.The experimental findings suggest that the elastic modulus and uniaxial compressive strength of the slate declined exponentially as the number of F-T cycles increased.Axial compressive strength was characterized by a U-shaped tendency with the bedding angle.This study proposes a damage model for the uniaxial compressive strength of transversely isotropic rock,which integrates the F-T effect,utilizing the enhanced anisotropic Hoek-Brown strength criterion and a statistical damage model.This model was validated using experimental data.This statistical damage model can precisely capture the dual attributes of rock mass strength reduction with F-T cy-cles and variations arising from the loading direction.展开更多
Infrastructure construction in seasonally frozen regions,covering 23%of total land,faces challenges from freeze-thaw(F-T)induced damages.Expansive soils,as an important problematic soil undergo major hydromechanical p...Infrastructure construction in seasonally frozen regions,covering 23%of total land,faces challenges from freeze-thaw(F-T)induced damages.Expansive soils,as an important problematic soil undergo major hydromechanical properties changes influenced by F-T cycles.Sand-bentonite mixtures are extensively used for constructing earthen hydraulic barriers in cold regions.This study investigates the influence of F-T cycles on multi-directional strains and anisotropic hydraulic conductivity of different sand-bentonite mixtures prepared at optimum water content and experienced three distinct saturation levels.Results indicate that saturation level and bentonite content significantly influence volumetric strain under F-T cycles.The simultaneous effect of ice lens formation,expanding micro-voids,and suction generated by freezing processes cause different volumetric behaviors at varying saturation degrees.The dry specimen exhibits no strain under F-T cycles,while optimum and saturated specimens experienced final volumetric strains of 1.02%and 3.03%,respectively.Notably,during freezing,the specimen at optimumwater content shrank,while the saturated specimen expanded.Increasing bentonite content from 40%to 70%developed freezing-induced shrinkage,from 1.73%to 4.72%,with higher thaw strain attributed to increased specimen plasticity.Also,dimensional variations revealed the cross-anisotropic nature of specimens,highlighting direct influence of water content on the shrinkage ratio.F-T cycles also increased hydraulic conductivity along both orthogonal directions by two orders of magnitude,while the anisotropy ratio decreased by about 3 after 9 F-T cycles,indicating altered pore structures.F-T cycles induce reduced swelling potential and compressibility over subsequent cycles.Microstructural observations also confirmed the F-T effects on the enhancement of porosity.展开更多
Strong sensitivity of satellite microwave remote sensing to the change of surface dielectric properties,as well as the insensitivity to air pollution and solar illumination effects,makes it very suitable for monitorin...Strong sensitivity of satellite microwave remote sensing to the change of surface dielectric properties,as well as the insensitivity to air pollution and solar illumination effects,makes it very suitable for monitoring freeze-thaw conditions.The freeze-thaw cycle changes in the Qinghai-Xizang Plateau have an important impact on the ecological environment and infrastructure.Based on the Scanning Multi-channel Microwave Radiometer(SMMR)and other sensors of microwave satellite,the freeze-thaw cycle data of permafrost in the Qinghai-Xizang Plateau in the past 40 years from 1981 to 2020 was obtained.The changes of soil freeze-thaw conditions in different seasons of 2020 and in the same season of 1990,2000,2010 and 2020 were compared,and the annual variation trend of soil freeze-thaw area in the four years was analyzed.Further,the linear regression analysis was carried out on the duration of soil freezing/thawing/transition and the interannual variation trend under different area conditions from 1981 to 2020.The results show that the freeze-thaw changes in different years are similar.In winter,it is mainly frozen for about 110 days.Spring and autumn are transitional periods,lasting for 170 days.In summer,it is mainly thawed for about 80 days.From 1981 to 2020,the freezing period and the average freezing area of the Qinghai-Xizang Plateau decreased at a rate of 0.22 days and 1986 km^(2) per year,respectively,while the thawing period and the average thawing area increased at a rate of 0.07 days and 3187 km^(2) per year,respectively.The research results provide important theoretical support for the ecological environment and permafrost protection of the Qinghai-Xizang Plateau.展开更多
In the frost-thaw region,prolonged freezethaw weathering can induce fracture and weaken rock masses,threatening engineering stability.While interbedded rock masses are common in such projects,their failure mechanisms ...In the frost-thaw region,prolonged freezethaw weathering can induce fracture and weaken rock masses,threatening engineering stability.While interbedded rock masses are common in such projects,their failure mechanisms remain insufficiently investigated in freezing and thawing environments.Therefore,this research establishes a particle flow code(PFC2D)model of interlayered rock masses with particular emphasis on the role of thickness variation.The analysis focuses on displacement,crack evolution,contact forces,and uniaxial compressive strength.The findings indicate that:(i)Completing 8 freeze-thaw cycles significantly increases displacement and contact forces,with crack growth accelerating markedly after 16 cycles.As the soft rock layer thickness ratio(Hs/H)increases,the peak contact force decreases by 18.3%,while the number of cracks rises by 48%.Once Hs/H exceeded 0.5,the rate of crack development decelerates.This reflects progressive bond degradation and damage accumulation:microscopic bonds weaken and rupture to form microcracks.Increased soft rock thickness promotes micro-damage accumulation,altering contact forces and intensifying degradation.(ii)Compressive cracks predominantly initiate in soft rock(limestone).After 20 cycles,cracking extends into the hard rock regions.As the Hs/H rises,compressive cracks first increase and then decline,with an overall reduction of 10.8%,while the compressive contact force exhibits a consistent downward trend.This trend indicates that freeze-thaw cycles cause severe microscopic degradation in soft rock,weakening its macroscopic strength and influencing compressive crack development.Increased soft rock thickness alters the stress state,thereby modifying crack propagation.(iii)Uniaxial compressive strength experiences a marked deterioration after 15 freeze-thaw cycles.It follows an exponential decay with increasing Hs/H,culminating in a total strength reduction of 76.9%.This demonstrates that freeze-thaw-induced microscopic damage deteriorates interparticle cohesion,reducing rock mass strength.A higher Hs/H ratio accelerates microscopic damage in the soft rock,causing cohesion to decay nonlinearly and macroscopic strength to drop exponentially.These results provide a theoretical basis for assessing the deformation and failure behaviors of rock masses under cyclic freeze-thaw action.展开更多
Based on compressive strength analysis,ultrasonic velocity testing and microstructural damage of three groups of concrete sprayed with inorganic coatings with different mix ratios were carried out under the freeze and...Based on compressive strength analysis,ultrasonic velocity testing and microstructural damage of three groups of concrete sprayed with inorganic coatings with different mix ratios were carried out under the freeze and thaw cycles(F-T).The strength attenuations of three groups of concrete were investigated,and a linear regression model showing the relationship model between acoustic parameters of three groups of concrete and their physicomechanical properties were constructed,and the micro-mechanism behind the strength decay of concrete was explained via scanning electron microscopy.The results show that in case of the same F-T cycles concrete sprayed inorganic coating adding a polypropylene fibre leads to a good anti-freezing performance.The trend in ultrasonic velocity decay in concrete under the F-T cycles is consistent with the trend in compression strength change.The ultrasonic velocity(UV)of the concrete shows a great correlation with compression strength:the greater the compression strength of concrete,the higher the UV.The losses in compressive strength of concrete in the three kinds(A,B and C,A is with silica fume,B is plain concrete,C is with polypropylene fibres)after 300 freeze-thaw cycles are 54.55%,62.25%and 22.26%,respectively,which of ultrasonic compressive wave velocities are 13.81%,16.65%and 3.77%,respectively.Concrete strength decreases during the freeze-thaw process;this is microscopically manifested as large pores,an increase in cracks,and the development of scattered primary pores affecting the centralised connectivity.The cracks of A group have a width of 5-10μm,which of B group have a width of 5-20μm,which of C group have a width of 1-2μm.The whole process of F-T is the process of generating and enlarging cracks in the inner microstructure of the concrete,which results in a markedly reduction in the mechanical characteristics of concrete.展开更多
Dangerous rock masses in cold regions subjected to repeated freeze–thaw cycles can cause progressive deterioration in structural planes and rock mechanical properties,which significantly reduces the overall stability...Dangerous rock masses in cold regions subjected to repeated freeze–thaw cycles can cause progressive deterioration in structural planes and rock mechanical properties,which significantly reduces the overall stability and often triggers collapses or landslides.Existing studies focus mostly on singlescale or single-factor analyses but cannot fully capture the coupled mechanisms driving instability under freeze-thaw conditions.This study aimed to establish a theoretical framework to quantitatively characterize the evolution of rock mass stability,thereby providing a sound basis for hazard prediction and prevention.By integrating limit equilibrium theory with rock frost heave and circular hole expansion theory,mechanical models for sliding-and toppling-type dangerous rock masses were established.Three key factors were incorporated:frost heave forces acting on throughgoing structural planes,rock property deterioration in nonpenetrative sections,and progressive freezing depth development.A theoretical relationship between the stability coefficient and the number of freeze-thaw cycles was derived.By considering the Zimei Peaks rock masses in Gansu Province as the case study and conducting parametric analyses,the results revealed that the stability coefficient rapidly decreases during the initial cycles,followed by a slower decrease and eventual stabilization.The coefficient decreased 4.5 times more during the first 15 cycles than during the subsequent 15 cycles.Moreover,stability degradation was strongly influenced by the freezing temperature,initial porosity,and rock debris loss ratio,with critical thresholds determined at a 3.8%porosity and a 0.83 debris loss ratio.The findings indicated that stability deterioration is governed by the coupled effects of frost heave loading,microstructural damage accumulation,and freezing depth development,with clear stagedependent and threshold-driven patterns.This work provides not only a quantitative explanation of instability mechanisms in cold-region rock masses but also practical guidance for engineering stability assessment and disaster mitigation.展开更多
The deterioration of soft rocks caused by freeze-thaw(F-T)climatic cycles results in huge structural and financial loss for foundation systems placed on soft rocks prone to F-T actions.In this study,cementtreated sand...The deterioration of soft rocks caused by freeze-thaw(F-T)climatic cycles results in huge structural and financial loss for foundation systems placed on soft rocks prone to F-T actions.In this study,cementtreated sand(CTS)and natural soft shale were subjected to unconfined compression and splitting tensile strength tests for evaluation of unconfined compressive strength(UCS,qu),initial small-strain Young’s modulus(Eo)using linear displacement transducers(LDT)up to a small strain of 0.001%,and secant elastic modulus(E_(50))using linear variable differential transducers(LVDTs)up to a large strain of 6%before and after reproduced laboratory weathering(RLW)cycles(-20℃e-110℃).The results showed that eight F-T cycles caused a reduction in q_(u),E_(50) and E_(o),which was 8.6,15.1,and 14.5 times for the CTS,and 2.2,3.5,and 5.3 times for the natural shale,respectively.The tensile strength of the CTS and natural rock samples exhibited a degradation of 5.4 times(after the 8th RLW cycle)and 2.7 times(after the 15th RLW cycle),respectively.Novel correlations have been developed to predict Eo(response)from the parameters qu and E_(50)(predictors)using MATLAB software's curve fitter.The findings of this study will assist in the design of foundations in soft rocks subjected to freezing and thawing.The analysis of variance(ANOVA)indicated 95%confidence in data health for the design of retaining walls,building foundations,excavation in soft rock,large-diameter borehole stability,and transportation tunnels in rocks for an operational strain range of 0.1%e0.01%(using LVDT)and a reference strain of less than 0.001%(using LDT).展开更多
Rock subjected to freeze-thaw(F-T)cycles may experience alterations in structural integrity and potentially impact its strength.This study investigates the effects of F-T cycles on granite by analyzing the acoustic em...Rock subjected to freeze-thaw(F-T)cycles may experience alterations in structural integrity and potentially impact its strength.This study investigates the effects of F-T cycles on granite by analyzing the acoustic emission(AE)signals recorded during uniaxial compression tests,characterizing the damage responses of the granite influenced by repeated F-T cycles.The results indicate significant reductions in uniaxial compression strength(UCS)and P-wave velocity as the number of F-T cycles increases.AE analysis reveals progressive damage accumulation,characterized by distinct stages of microcrack development.A parameter,AE energy intensity,is introduced to describe the failure process,showing that the typical AE quiet period in the failure stage is absent in granite pretreated with F-T cycles.Using the superlet transform method,AE frequency and amplitude are analyzed,revealing amplitude evolutions across three frequency domains.The results show that decreasing portions of signals in the highfrequency domain for granite are influenced by F-T cycles.These findings enhance understanding of rock degradation under F-T cycles,offering valuable implications for rock engineering in cold regions.展开更多
基金Funded by the Science and Technology Program of Gansu Province(Nos.25JRRA497,23ZDFA017)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB0950000)High-level Talent Funding of Kashi。
文摘This study introduces superabsorbent polymers(SAP)into recycled concrete and,through freeze-thaw cycle tests,unconfined compressive strength tests,and nuclear magnetic resonance(NMR)analysis,evaluates the freeze-thaw resistance and durability of recycled concrete samples under varying freeze-thaw cycles.The results indicate that an appropriate addition of SAP significantly enhances the freeze-thaw resistance of recycled concrete.After 200 freeze-thaw cycles,the RS0.6 sample retained good surface integrity,demonstrating the best performance.Compared to NAC,its mass loss decreased by 1.16%,the relative dynamic modulus improved by 7.01%,and the compressive strength loss rate decreased by 5.41%.Additionally,T2 spectrum analysis revealed that adding SAP optimized the pore structure of recycled concrete and mitigated pore development during freeze-thaw cycles.As the number of freeze-thaw cycles increased,the RS0.3 and RS0.6 samples demonstrated superior frost resistance compared to NAC.However,an excessive amount of SAP increased pore expansion during subsequent freeze-thaw cycles,ultimately weakening frost resistance.
基金support from the National Natural Science Foundation of China(Grant Nos.42377144,52225904 and 52039007)supported by the New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Freeze-thaw(F-T)cycle is receiving increasing attention as a primary threat to the long-term stability of rock engineering in high-elevation regions.In this study,artificial F-T cycle tests are first conducted on pre-flawed sandstone specimens with real-time frost heave pressure(FHP)monitoring,followed by subsequent cyclic loading tests with different maximum stresses.Given the water-ice-sandstone interaction,the evolution process of FHP in flaws can be divided into six phases,i.e.initial,silence,eruption,reduction,second-arising,and dissipation phases.Its magnitude exhibits an exponential decrease with increasing F-T cycle number.The influences of F-T cycles and the maximum stress on the fatigue mechanical characteristics of flawed sandstone are revealed.Subjected to higher F-T cycles and maximum stress,larger irreversible strain and less dissipated energy are accumulated inside flawed sandstone specimens,leading to faster damage and lower fatigue life.The three-stage evolution characters of irreversible strain and dissipated energy are both weakened by repeated F-T treatment,i.e.the prolonged initial and accelerated stages and shortened stable stage.In addition,the repeated F-T cycles diminish the impact of prefabricated flaws on cracking behavior of flawed sandstone specimens,and the fatigue failure pattern changes from shear-dominated failure with a transfixion shear band to tensile-dominated failure with massive tensile cracks as the F-T cycle number increases.Employing the scanning electron microscopy(SEM),the underlying damage mechanisms of flawed rocks under the coupling effect of F-T treatment and cyclic loading are discussed.Finally,an F-T-fatigue damage model is proposed based on FHP evolution and irreversible strain,which possesses distinct physical significance and reasonably quantifies the F-T deterioration and fatigue damage accumulation of flawed rocks.
基金support of National Natural Science Foundation of China(Grant No.U24A20184)Science and Technology Planning Project of Xizang Autonomous Region,China(Grant Nos.XZ202201ZY0021G,XZ202401ZY0085).
文摘Freezing and thawing processes play a crucial role in causing significant deformation and damage to layered soft rocks in cold region due to daily and seasonal temperature fluctuations.However,the frost heave mechanism of the rocks and their mechanical behaviors at the meso-scale still require further investigations.For this,we focused on carbonaceous slate reported in a high-altitude cold region,in terms of mineral composition,content,and microstructure.The strength and failure of mineral grain(MG)interfaces are studied using three-point-bending tests,in order to explore the evolution of mode I fracture toughness and tensile strength with the Dugdale-Barenblatt model and the Weibull distribution model.The results indicate that the damage of slate involves the initiation and propagation of microfracture networks at clay MG interfaces(bedding planes),driven by frost heave pressure at macroscopic and microscopic scales.This process causes the detachment of some MGs,resulting in fracture surfaces with a distinctive pulled-off planar structure.The hydrophilicity of clay MGs,interfacial strengths,and microfracture structures contribute to the freeze-thaw damage.As the number of freeze-thaw cycles increases,the effective area per unit decreases,leading to an exponentially decreasing in mode I fracture toughness and tensile strength at MG interfaces.Approximately 67%strength degradation occurs after 14 freeze-thaw cycles.This provides theoretical basis and experimental methods for better understanding the damage and deterioration behaviors of layered soft rocks in cold region under natural freeze-thaw cycles.
基金supported by National Natural Science Foundation of China(Grant No.42201080)Young Scientific and Technological Talents Program of Shaanxi Province(Grant No.2025ZC-KJXX-57)Special Scientific Research Program of the Shaanxi Provincial Department of Education(Grant No.21JK0967)。
文摘Freeze-thaw cycles(FTCs)have an important effect on soil aggregate stability by altering soil structures,thereby influencing soil wind and water erosion on the eastern Qinghai-Tibet Plateau.However,the effects of FTCs on the stability of these soils remain unclear.Here,we conducted freeze-thaw simulations in laboratory to investigate the effects of FTCs(0 to 15 cycles)on the wet-and dry-sieving aggregate stability of undisturbed sandy loam from Maqu county,which was treated with different initial soil moisture contents(1%to 25%in increments of 4%)and initial aggregate diameters(<2,2-5,5-10,and 10-15 mm).Results show that soil aggregates with initial diameters larger than 2 mm exhibit higher soil organic carbon contents(1.45%-1.57%)and silt contents(34.63%-35.52%)than those smaller than 2 mm(0.93%and 31.38%,respectively).The stability of both wet-and dry-sieving aggregates increases with larger initial diameters.Increasing initial soil moisture content from 1%to 25%reduces aggregate stability,with reductions of 2.4%-88.0%for wet-sieving aggregates and 2.1%-25.5%for dry-sieving aggregates(>2 mm).With increasing FTCs,wet-sieving aggregate(>2 mm)stability exhibits a fluctuating upward trend,with increases of 79.2%-87.4%after 15 FTCs,while dry-sieving aggregate(>2 mm)stability decreases significantly(5.7%-21.7%)upon the first FTC and remains unchanged thereafter.The stability of both the wet-and dry-sieving aggregates smaller than 2 mm remains unchanged with increasing FTCs(p>0.05).SOC content decreases by 22.3%on average with increasing FTCs from 1 to 15 and shows no significant correlations with wet-and dry-sieving aggregate stability.Higher silt content(r=0.39,p<0.05)and lower sand content(r=-0.38,p<0.05)enhances the wet-sieving aggregate stability of sandy loam.Frequent FTCs tend to improve wet-sieving aggregate stability but reduce dry-sieving aggregate stability in the sandy loam.The findings provide certain guidance for preventing freeze-thaw-induced wind erosion.
基金funding support from the National Natural Science Foundation of China(Grant No.12172019).
文摘In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.
文摘Low porosity is very significant for cementitious composite materials(CCM)under freeze-thaw conditions.To reduce the porosity of CCM,we used wollastonite mineral fibers as a partial replacement for cement and aggregate.The five combinations,in which 10%,32%,and 48%Wollastonite were added,were made for scanning using both scanning electron microscopy(SEM)and computed tomography scan technology(CT).Then,the 2D SEM pictures and the 3D pore distribution curves are obtained before and after the freezing and thawing processes,where the micro-pores in the CCM materials are shown.The fractal dimension is used to quantify the topography image in two dimensions,as well as the pore distribution in three dimensions.This method allows for the determination of both surface porosity and volume porosity,both of which show an increase in response to an escalation of freeze-thaw cycles.It is also found that the micro-damage in the concrete is of self-similarity,and in the context of the fractal dimension,the pore evolution can be quantitatively characterized across different sizes,ranging from local to global levels,before and after freezing and thawing.
基金National Natural Science Foundation of China(Nos.42171130 and 42301158)Pilot Project of China’s Strength in Transportation for the Central Research Institute(No.QG2021-1-4-7)National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2021YFB2601200).
文摘Sulfate attack-induced expansion of cement-treated aggregates in seasonally frozen regions is a well-known issue which causes continuous expansion in railway subgrades,and particularly in high-speed railways.Accordingly,we investigated the influence of material proportions,the number of freeze-thaw(FT)cycles,and temperature gradients on the expansion mechanism of sulfate attack on cement-treated aggregates subjected to FT cycles.The conditions,laws,and dominant factors causing the expansion of aggregates were analyzed through swelling tests.The results indicate that under FT cycles,3%content cement-treated graded macadam only experiences slight deformation.The maximum strain of graded macadam attacked by 1%sodium sulfate content in each FT cycle is significantly larger than that of 3%content cement-treated graded macadam attacked by 1%sodium sulfate content.Using scanning electron microscopy,needle-like crystals were observed during sulfate attack of cement-treated graded macadam.Through quantitative analysis,we determined the recoverable and unrecoverable deformations of graded macadam under FT cycles.For graded macadam under sulfate attack,the expansion is mainly induced by periodic frost heave and salt expansion,as well as salt migration.For cement-treated graded macadam under sulfate attack,the expansion is mainly induced by chemical attack and salt migration.This study can serve as a reference for future research on the mechanics of sulfate attack on cement-treated aggregates that experience FT cycles,and provide theoretical support for methods that remediate the expansion induced by sulfate attack.
基金funded by the Technology Funding Scheme of China Construction Second Engineering Bureau LTD(2020ZX150002)the National Natural Science Foundation Project of China(12262018).
文摘To address the challenges posed by tunnel construction in the alpine region,silica fume mixed concrete is commonly used as a construction material.The correlation between silica fume content and the lining life requires immediate investigation.In view of this phenomenon,the durability of unit lining concrete is predicted by analyzing three key indicators:carbonation depth,relative dynamic elastic modulus,and residual quality.This prediction is achieved by integrating the Entropy Weight Method,Grey theory life prediction model and BP artificial neural networks using data from tests and predictions of these indicators.Then,the Entropy Weight-Grey theory-BP Network Model is compared with other methods to analyze the predicted life.Finally,verify the sci-entificity of this model,and the optimum silica fume content of unit concrete lining is verified.The results showed,1)The addition of silica fume will accelerate the carbonization of unit concrete lining,and slow down the freeze-thaw cycle and sulfate erosion.2)The utilization of artificial neural networks is essential for enhancing the realism of the data,as it emphasizes the significance of silica fume content.3)Silica fume content of 10%results in the longest life and is the most suitable for lining construction.4)A comparison between single-factor and multi-factor predictions indicates that the multi-factor approach yields a longer maximum life.This improvement can be attributed to the inclusion of additional factors,such as freeze-thaw cycles and carbonation,which enhance the predicted life when employing these methods.In conclusion,the Entropy Weight-Grey Theory-BP Network life prediction Model is well-suited for tunnel lining in the alpine sulfate area of northwest China.
基金supported by the National Natural Science Foundation of China(No.42107168).
文摘Aiming at challenges posed by rock freezethaw(FT)in cold regions rock mass engineering,it is of great significance to analyze its macro-and micromechanical properties and damage laws for the smooth progress of construction.In this study,indoor freezethaw cycle(FTC)tests on sandstone were conducted to analyze the mass change rate,density change rate,longitudinal wave velocity change rate,microstructure change and mechanical properties of sandstone after FTC.A microscopic FT damage variable reflecting the FT damage was defined based on the changes of rock porosity before and after the FTC,enabling the derivation of the total damage variable under the coupled action of FTC and mechanical loading.A damage evolution equation and a microscopic damage constitutive model for rock under coupled FTC and confining pressure were established by using Lemaitre’s strain equivalence principle,the theory of continuous damage mechanics,and the assumption that the failure of rock micro-units follows the SMP criterion.The rationality and accuracy of the model were verified using triaxial compression test data for FT-damaged rock.The results show that both macroand micro-mechanical properties of sandstone are degraded under the action of FTC,resulting in significant damage.The developed microscopic damage constitutive model can reflect the stress-strain characteristics of the whole process of FT rock triaxial compression,with excellent agreement observed between experimental and theoretical curves.This validates the reliability of the model and the methodology for determining its parameters.Additionally,defining the microscopic FT damage variable based on rock porosity changes is demonstrated to be a feasible and highly accurate approach to reflect rock FT damage degree.This model expands the damage model for rock under the coupling effect of FTC and confining pressure,further illuminating the damage mechanism and failure law in such environments.The findings provide references for the construction of rock mass engineering in cold regions.
基金supported by the National Natural Science Foundation of China (No. U2004181)State Key Laboratory of Frozen Soil Engineering (No. SKLFSE20191702)+2 种基金the key scientific and technological project of Henan Province (222102320226)Basic research expenses of Henan Polytechnic University (NSFRF230424)the Natural Science Foundation of Henan Province (242300421650)。
文摘Red mud(RM) is an industrial solid waste produced during the extraction of alumina from bauxite.The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization.This paper proposes a method for dealkalization and chromium(Cr) removal by repeated freeze and thaw to enhance the comprehensive utilization rate of RM.This study focused on the Bayer RM and investigated the effects of freeze-thaw(FT)-acid washing(AW) for dealkalization and Cr removal.The variables were the eluent concentration and FT cycles.The results showed that the synergistic action of FT-AW significantly improved the efficiency of dealkalization and Cr removal.After five FT cycles with 0.5 mol/L oxalic acid,the dealkalization and Cr removal rates reached 97.5% and 65.38%,respectively,16.1% and 7.40% higher than those achieved at room temperature.The repeated FT disrupted the structure of the RM particles,leading to an increase in the pore space between the soil particles.This enables complete eluent contact and reaction with Cr and alkali,thereby enhancing the removal rate.The FT-AW process is suitable for practical engineering applications.It offers a novel method for RM dealkalization and Cr removal by using the FT alternation phenomena in seasonally frozen regions.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972283 and 42277182).
文摘High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.
基金supported by the National Key Research and Development Program of China(No.2022YFC2903902)the National Natural Science Foundation of China(Nos.52374157 and 52174070)+1 种基金the Young Elite Scientists Sponsorship Program by CAST(No.2023QNRC001)the Key Science and Technology Project of Ministry of Emergency Management of the People’s Republic of China(No.2024EMST080802).
文摘In cold-region environments,where complex stresses and mining disturbances occur,rock masses are frequently segmented into discontinuous bodies by fractured structural planes,leading to anisotropic physical and mechanical properties.To explore the evolution of microcracks,degradation characteristics,and failure modes of fractured rocks in cold regions under the influence of freeze-thaw cycles,integrating laboratory experiments with the damage mechanics of freeze-thaw cycles.A numerical model for freeze-thaw cycle damage in rocks with various fracture dip angles was developed.The study revealed that the freeze-thaw expansion force generated during the pore water-ice phase transition is the primary driving factor behind freeze-thaw cycle damage.The initiation and propagation of microcracks and micropores,the detachment of matrix particles,and the loosening of clay mineral structures result in the transformation of the rock from a dense to a porous state,causing significant degradation in macroscopic mechanical properties.As freeze-thaw cycles increase,both the uniaxial compressive strength and the deformation modulus of the rock decrease significantly,with the failure mode gradually shifting from brittle instability to brittle-plastic or plastic failure.The findings of this study offer a practical approach to uncovering the mechanical response mechanisms between freeze-thaw damage in fractured rocks and structural planes.
基金supported by the Qingdao Postdoctoral Science Foundation(No.862205040054)the International Research Fellowship from the Japan Society for the Promotion of Science(Postdoctoral Fellowships for Research in Japan(Standard))the National Natural Science Foundation of China(No.52078093).
文摘The mechanical properties of bedding rock in cold regions are frequently affected by freeze-thaw(F-T)cycles and ani-sotropy.Research on the mechanical characteristics of rock damage under the combined action of F-T and bedding angles is limited,and most traditional rock damage models cannot accurately capture these characteristics.We performed axial compression tests to ex-plore the strength characteristics of bedding slates at the bedding angles ofβ=0°,30°,45°,60°,and 90°under various F-T cycles.The experimental findings suggest that the elastic modulus and uniaxial compressive strength of the slate declined exponentially as the number of F-T cycles increased.Axial compressive strength was characterized by a U-shaped tendency with the bedding angle.This study proposes a damage model for the uniaxial compressive strength of transversely isotropic rock,which integrates the F-T effect,utilizing the enhanced anisotropic Hoek-Brown strength criterion and a statistical damage model.This model was validated using experimental data.This statistical damage model can precisely capture the dual attributes of rock mass strength reduction with F-T cy-cles and variations arising from the loading direction.
基金The financial support provided by the Research Grant Office at Sharif University Technology(Grant Nos.G4010902 and QB020105)is gratefully acknowledged.
文摘Infrastructure construction in seasonally frozen regions,covering 23%of total land,faces challenges from freeze-thaw(F-T)induced damages.Expansive soils,as an important problematic soil undergo major hydromechanical properties changes influenced by F-T cycles.Sand-bentonite mixtures are extensively used for constructing earthen hydraulic barriers in cold regions.This study investigates the influence of F-T cycles on multi-directional strains and anisotropic hydraulic conductivity of different sand-bentonite mixtures prepared at optimum water content and experienced three distinct saturation levels.Results indicate that saturation level and bentonite content significantly influence volumetric strain under F-T cycles.The simultaneous effect of ice lens formation,expanding micro-voids,and suction generated by freezing processes cause different volumetric behaviors at varying saturation degrees.The dry specimen exhibits no strain under F-T cycles,while optimum and saturated specimens experienced final volumetric strains of 1.02%and 3.03%,respectively.Notably,during freezing,the specimen at optimumwater content shrank,while the saturated specimen expanded.Increasing bentonite content from 40%to 70%developed freezing-induced shrinkage,from 1.73%to 4.72%,with higher thaw strain attributed to increased specimen plasticity.Also,dimensional variations revealed the cross-anisotropic nature of specimens,highlighting direct influence of water content on the shrinkage ratio.F-T cycles also increased hydraulic conductivity along both orthogonal directions by two orders of magnitude,while the anisotropy ratio decreased by about 3 after 9 F-T cycles,indicating altered pore structures.F-T cycles induce reduced swelling potential and compressibility over subsequent cycles.Microstructural observations also confirmed the F-T effects on the enhancement of porosity.
基金National Natural Science foundation of China(No.42271432)Foundation of Shanxi Vocational University of Engineering Science and Technology(No.KJ 202426).
文摘Strong sensitivity of satellite microwave remote sensing to the change of surface dielectric properties,as well as the insensitivity to air pollution and solar illumination effects,makes it very suitable for monitoring freeze-thaw conditions.The freeze-thaw cycle changes in the Qinghai-Xizang Plateau have an important impact on the ecological environment and infrastructure.Based on the Scanning Multi-channel Microwave Radiometer(SMMR)and other sensors of microwave satellite,the freeze-thaw cycle data of permafrost in the Qinghai-Xizang Plateau in the past 40 years from 1981 to 2020 was obtained.The changes of soil freeze-thaw conditions in different seasons of 2020 and in the same season of 1990,2000,2010 and 2020 were compared,and the annual variation trend of soil freeze-thaw area in the four years was analyzed.Further,the linear regression analysis was carried out on the duration of soil freezing/thawing/transition and the interannual variation trend under different area conditions from 1981 to 2020.The results show that the freeze-thaw changes in different years are similar.In winter,it is mainly frozen for about 110 days.Spring and autumn are transitional periods,lasting for 170 days.In summer,it is mainly thawed for about 80 days.From 1981 to 2020,the freezing period and the average freezing area of the Qinghai-Xizang Plateau decreased at a rate of 0.22 days and 1986 km^(2) per year,respectively,while the thawing period and the average thawing area increased at a rate of 0.07 days and 3187 km^(2) per year,respectively.The research results provide important theoretical support for the ecological environment and permafrost protection of the Qinghai-Xizang Plateau.
基金supported by the National Natural Science Foundation of China(Grant Nos.52379100 and 42462030)。
文摘In the frost-thaw region,prolonged freezethaw weathering can induce fracture and weaken rock masses,threatening engineering stability.While interbedded rock masses are common in such projects,their failure mechanisms remain insufficiently investigated in freezing and thawing environments.Therefore,this research establishes a particle flow code(PFC2D)model of interlayered rock masses with particular emphasis on the role of thickness variation.The analysis focuses on displacement,crack evolution,contact forces,and uniaxial compressive strength.The findings indicate that:(i)Completing 8 freeze-thaw cycles significantly increases displacement and contact forces,with crack growth accelerating markedly after 16 cycles.As the soft rock layer thickness ratio(Hs/H)increases,the peak contact force decreases by 18.3%,while the number of cracks rises by 48%.Once Hs/H exceeded 0.5,the rate of crack development decelerates.This reflects progressive bond degradation and damage accumulation:microscopic bonds weaken and rupture to form microcracks.Increased soft rock thickness promotes micro-damage accumulation,altering contact forces and intensifying degradation.(ii)Compressive cracks predominantly initiate in soft rock(limestone).After 20 cycles,cracking extends into the hard rock regions.As the Hs/H rises,compressive cracks first increase and then decline,with an overall reduction of 10.8%,while the compressive contact force exhibits a consistent downward trend.This trend indicates that freeze-thaw cycles cause severe microscopic degradation in soft rock,weakening its macroscopic strength and influencing compressive crack development.Increased soft rock thickness alters the stress state,thereby modifying crack propagation.(iii)Uniaxial compressive strength experiences a marked deterioration after 15 freeze-thaw cycles.It follows an exponential decay with increasing Hs/H,culminating in a total strength reduction of 76.9%.This demonstrates that freeze-thaw-induced microscopic damage deteriorates interparticle cohesion,reducing rock mass strength.A higher Hs/H ratio accelerates microscopic damage in the soft rock,causing cohesion to decay nonlinearly and macroscopic strength to drop exponentially.These results provide a theoretical basis for assessing the deformation and failure behaviors of rock masses under cyclic freeze-thaw action.
基金provided by the Science for Earthquake Resilience Program of China Earthquake Administration(Grant No.XH24044A)the National Natural Science Foundation of China(Grant Nos.42330704,U1939209)+1 种基金the Scientific Research Fund of Institute of Earthquake Forecasting,China Earthquake Administration(Grant Nos.2022IESLZ03,2022 IESLZ01)the Natural Science Foundation of Gansu Province(Grant No.22JR5RA825).
文摘Based on compressive strength analysis,ultrasonic velocity testing and microstructural damage of three groups of concrete sprayed with inorganic coatings with different mix ratios were carried out under the freeze and thaw cycles(F-T).The strength attenuations of three groups of concrete were investigated,and a linear regression model showing the relationship model between acoustic parameters of three groups of concrete and their physicomechanical properties were constructed,and the micro-mechanism behind the strength decay of concrete was explained via scanning electron microscopy.The results show that in case of the same F-T cycles concrete sprayed inorganic coating adding a polypropylene fibre leads to a good anti-freezing performance.The trend in ultrasonic velocity decay in concrete under the F-T cycles is consistent with the trend in compression strength change.The ultrasonic velocity(UV)of the concrete shows a great correlation with compression strength:the greater the compression strength of concrete,the higher the UV.The losses in compressive strength of concrete in the three kinds(A,B and C,A is with silica fume,B is plain concrete,C is with polypropylene fibres)after 300 freeze-thaw cycles are 54.55%,62.25%and 22.26%,respectively,which of ultrasonic compressive wave velocities are 13.81%,16.65%and 3.77%,respectively.Concrete strength decreases during the freeze-thaw process;this is microscopically manifested as large pores,an increase in cracks,and the development of scattered primary pores affecting the centralised connectivity.The cracks of A group have a width of 5-10μm,which of B group have a width of 5-20μm,which of C group have a width of 1-2μm.The whole process of F-T is the process of generating and enlarging cracks in the inner microstructure of the concrete,which results in a markedly reduction in the mechanical characteristics of concrete.
基金the financial support provided by the Major Science and Technology Project of Xinjiang Uygur Autonomous Region(Grant NO.2024A01003)the National Natural Science Foundation of China(Grant NO.51508556)+3 种基金the Key Support Project of the National Natural Science Foundation of China Joint Fund(Grant No.U24B2039)the Natural Science Foundation of Jiangxi Province(Grant NO.20232BAB203079,20224BAB213045)Program of China Scholarship Council(Grant NO.202406430056)the Fundamental Research Funds for the Central Universities(Ph.D.Top Innovative Talents Fund of CUMTB)(Grant NO.BBJ2025081)。
文摘Dangerous rock masses in cold regions subjected to repeated freeze–thaw cycles can cause progressive deterioration in structural planes and rock mechanical properties,which significantly reduces the overall stability and often triggers collapses or landslides.Existing studies focus mostly on singlescale or single-factor analyses but cannot fully capture the coupled mechanisms driving instability under freeze-thaw conditions.This study aimed to establish a theoretical framework to quantitatively characterize the evolution of rock mass stability,thereby providing a sound basis for hazard prediction and prevention.By integrating limit equilibrium theory with rock frost heave and circular hole expansion theory,mechanical models for sliding-and toppling-type dangerous rock masses were established.Three key factors were incorporated:frost heave forces acting on throughgoing structural planes,rock property deterioration in nonpenetrative sections,and progressive freezing depth development.A theoretical relationship between the stability coefficient and the number of freeze-thaw cycles was derived.By considering the Zimei Peaks rock masses in Gansu Province as the case study and conducting parametric analyses,the results revealed that the stability coefficient rapidly decreases during the initial cycles,followed by a slower decrease and eventual stabilization.The coefficient decreased 4.5 times more during the first 15 cycles than during the subsequent 15 cycles.Moreover,stability degradation was strongly influenced by the freezing temperature,initial porosity,and rock debris loss ratio,with critical thresholds determined at a 3.8%porosity and a 0.83 debris loss ratio.The findings indicated that stability deterioration is governed by the coupled effects of frost heave loading,microstructural damage accumulation,and freezing depth development,with clear stagedependent and threshold-driven patterns.This work provides not only a quantitative explanation of instability mechanisms in cold-region rock masses but also practical guidance for engineering stability assessment and disaster mitigation.
文摘The deterioration of soft rocks caused by freeze-thaw(F-T)climatic cycles results in huge structural and financial loss for foundation systems placed on soft rocks prone to F-T actions.In this study,cementtreated sand(CTS)and natural soft shale were subjected to unconfined compression and splitting tensile strength tests for evaluation of unconfined compressive strength(UCS,qu),initial small-strain Young’s modulus(Eo)using linear displacement transducers(LDT)up to a small strain of 0.001%,and secant elastic modulus(E_(50))using linear variable differential transducers(LVDTs)up to a large strain of 6%before and after reproduced laboratory weathering(RLW)cycles(-20℃e-110℃).The results showed that eight F-T cycles caused a reduction in q_(u),E_(50) and E_(o),which was 8.6,15.1,and 14.5 times for the CTS,and 2.2,3.5,and 5.3 times for the natural shale,respectively.The tensile strength of the CTS and natural rock samples exhibited a degradation of 5.4 times(after the 8th RLW cycle)and 2.7 times(after the 15th RLW cycle),respectively.Novel correlations have been developed to predict Eo(response)from the parameters qu and E_(50)(predictors)using MATLAB software's curve fitter.The findings of this study will assist in the design of foundations in soft rocks subjected to freezing and thawing.The analysis of variance(ANOVA)indicated 95%confidence in data health for the design of retaining walls,building foundations,excavation in soft rock,large-diameter borehole stability,and transportation tunnels in rocks for an operational strain range of 0.1%e0.01%(using LVDT)and a reference strain of less than 0.001%(using LDT).
基金supported by the National Natural Science Foundation of China(Grant Nos.52179099 and U23A6018)The funding supported by the Natural Science Foundation of Hebei Province,China(Grant No.2020HBQZYC001)were also acknowledged.
文摘Rock subjected to freeze-thaw(F-T)cycles may experience alterations in structural integrity and potentially impact its strength.This study investigates the effects of F-T cycles on granite by analyzing the acoustic emission(AE)signals recorded during uniaxial compression tests,characterizing the damage responses of the granite influenced by repeated F-T cycles.The results indicate significant reductions in uniaxial compression strength(UCS)and P-wave velocity as the number of F-T cycles increases.AE analysis reveals progressive damage accumulation,characterized by distinct stages of microcrack development.A parameter,AE energy intensity,is introduced to describe the failure process,showing that the typical AE quiet period in the failure stage is absent in granite pretreated with F-T cycles.Using the superlet transform method,AE frequency and amplitude are analyzed,revealing amplitude evolutions across three frequency domains.The results show that decreasing portions of signals in the highfrequency domain for granite are influenced by F-T cycles.These findings enhance understanding of rock degradation under F-T cycles,offering valuable implications for rock engineering in cold regions.
