The stress-strain behavior of calcareous sand is significantly influencedby particle breakage(B)and initial relative density(Dri),but few constitutive models consider their combined effects.To bridge this gap,we condu...The stress-strain behavior of calcareous sand is significantly influencedby particle breakage(B)and initial relative density(Dri),but few constitutive models consider their combined effects.To bridge this gap,we conducted a series of triaxial tests on calcareous sand with varying Dri and stress paths,examining particle breakage and critical state behavior.Key findingsinclude:(1)At a constant stress ratio(η),B follows a hyperbolic relationship with mean effective stress(p'),and for a given p',B increases proportionally withη;(2)The critical state line(CSL)moves downward with increasing Dri,whereas the critical state friction angle(φcs)decreases with increasing B.Based on these findings,we propose a unifiedbreakage evolution model to quantify particle breakage in calcareous sand under various loading conditions.Integrating this model with the Normal Consolidation Line(NCL)and CSL equations,we successfully simulate the steepening of NCL and CSL slopes as B increases with the onset of particle breakage.Furthermore,we quantitatively evaluate the effect of B onφcs.Finally,within the framework of Critical State Soil Mechanics and Hypoplasticity theory,we develop a hypoplastic model incorporating B and Dri.The model is validated through strong agreement with experimental results across various initial relative densities,stress paths and drainage conditions.展开更多
Hard carbon is a vital anode material for sodium-ion batteries;however,the nonuniform growth of solid electrolyte interphase(SEI)film substantially diminishes its initial coulombic efficiency(ICE)and cycle life.The ch...Hard carbon is a vital anode material for sodium-ion batteries;however,the nonuniform growth of solid electrolyte interphase(SEI)film substantially diminishes its initial coulombic efficiency(ICE)and cycle life.The chemical and morphological properties of surface highly influence the electrode/electrolyte interfacial reactions.In this study,we have tuned orbital hybridization states forming an interface enriched with sp^(2) hybridized carbon(sp^(2)-C),which decreases the binding energy to solvent molecules and inhibits excessive solvent decomposition during SEI formation.Benefiting from successfully constructed inorganic-rich SEI,the ICE increased to 91%and sodium storage capacity reached 346 mAh/g.Besides,the capacity retention rate was 90.7%after 700 cycles at 1 A/g higher than pristine electrode(83.8%).展开更多
This paper deals with homogeneous Dirichlet boundary value problem to a class of porous medium equations with viscoelastic term ∂u/∂t-Δu^(m)+∫^(t)_(0)g(t-s)Δu^(m)(x,s)ds=u^(p),x∈Ω,t≥0,where p>m(m>0).We pro...This paper deals with homogeneous Dirichlet boundary value problem to a class of porous medium equations with viscoelastic term ∂u/∂t-Δu^(m)+∫^(t)_(0)g(t-s)Δu^(m)(x,s)ds=u^(p),x∈Ω,t≥0,where p>m(m>0).We prove that the weak solutions of the above problem blow up in finite time when the initial energy is positive and the function g satisfies suitable conditions.Our result generalizes that of S.A.Messaoudi in[1].展开更多
To investigate the long-term stability of soft-hard interbedded rock masses with initial damage induced by earthquakes and periodic drying and wetting,this study prepared samples with different initial damage through ...To investigate the long-term stability of soft-hard interbedded rock masses with initial damage induced by earthquakes and periodic drying and wetting,this study prepared samples with different initial damage through cyclic loading and unloading(CLU)experiments followed by cyclic drying and wetting(CDW)experiments,and finally conducted creep experiments.The study analyzed the effects of initial damage on creep mechanical behavior,crack evolution,and explored failure precursor information,revealing the damage failure mechanisms.The results show that the structural characteristics of the rock mass control its macroscopic failure mode.Initial damage promotes microcrack development,influences the fracture mode,and increases the proportion of high-frequency(200−280 kHz)acoustic emission events during creep.Meanwhile,initial damage exacerbates creep characteristics,increasing the creep rate,shortening total creep failure time,and reducing long-term strength.The damage failure is attributed to:the generation of internal cracks and pores in the rock caused by CLU;mineral hydrolysis and expansion-contraction due to CDW,resulting in weakened intergranular cementation;and full development of cracks and pores under creep stress.Additionally,the deformation difference coefficient and the coefficient of variation of RA/AF values can serve as precursor indicators for creep failure.展开更多
After coal seam mining,the overlying rock strata above the goaf are subjected to long-term stress and eventually undergo failure.Under mining-induced disturbances,the strata develop fractures at various angles,which s...After coal seam mining,the overlying rock strata above the goaf are subjected to long-term stress and eventually undergo failure.Under mining-induced disturbances,the strata develop fractures at various angles,which significantly influence failure modes and the morphology of gas flow channels.This study employed multistage loading experiments,numerical simulations,three-dimensional reconstruction,and image recognition to investigate the fragmentation process of rocks with different initial fracture angles under multistage loading.The results show that variations in the initial fracture angle affect the transmission of contact forces among rock particles.As the angle increases,the transmission pattern shifts from a uniform distribution to one extending along the direction of the fracture.Rocks with small initial fracture angles tend to experience tensile-dominated failure,with most of the material subjected to longitudinal loading,resulting in reduced strength.Fractures propagate from the central region of the initial fracture,producing a complex internal fracture network.The proportion of fracture channels varies considerably across regions,creating multiple zones of velocity variation in the gas flow.In contrast,rocks with large initial fracture angles are more susceptible to shear failure,with the primary load-bearing zones aligned along the inclined fracture direction.As a result,the influence on surrounding regions is limited,improving the rock's load-bearing capacity under multistage loading.In these cases,the distribution and proportion of fracture channels become more uniform,promoting more stable gas flow within the channels.Overall,these findings provide theoretical insights into how initial fracture angles govern rock failure patterns and gas flow characteristics.展开更多
The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of...The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of the initial spin direction,the spin dynamics of the electron beam are found to depend on the self-injection mechanism.The effects of wakefields and laser fields are studied using test particle dynamics and particle-in-cell simulations based on the Thomas-Bargmann-Michel-Telegdi equation.Compared with transverse injection,longitudinal injection is found to be preferable for obtaining a highly polarized electron beam.展开更多
The cemented tailings backfill(CTB)with initial defects is more prone to destabilization damage under the influence of various unfavorable factors during the mining process.In order to investigate its influence on the...The cemented tailings backfill(CTB)with initial defects is more prone to destabilization damage under the influence of various unfavorable factors during the mining process.In order to investigate its influence on the stability of underground mining engineering,this paper simulates the generation of different degrees of initial defects inside the CTB by adding different contents of air-entraining agent(AEA),investigates the acoustic emission RA/AF eigenvalues of CTB with different contents of AEA under uniaxial compression,and adopts various denoising algorithms(e.g.,moving average smoothing,median filtering,and outlier detection)to improve the accuracy of the data.The variance and autocorrelation coefficients of RA/AF parameters were analyzed in conjunction with the critical slowing down(CSD)theory.The results show that the acoustic emission RA/AF values can be used to characterize the progressive damage evolution of CTB.The denoising algorithm processed the AE signals to reduce the effects of extraneous noise and anomalous spikes.Changes in the variance curves provide clear precursor information,while abrupt changes in the autocorrelation coefficient can be used as an auxiliary localization warning signal.The phenomenon of dramatic increase in the variance and autocorrelation coefficient curves during the compression-tightening stage,which is influenced by the initial defects,can lead to false warnings.As the initial defects of the CTB increase,its instability precursor time and instability time are prolonged,the peak stress decreases,and the time difference between the CTB and the instability damage is smaller.The results provide a new method for real-time monitoring and early warning of CTB instability damage.展开更多
The high efficiency particulate air filter(HEPA)in exhaust system of high-level biosafety laboratory must be disinfected to kill harmful microorganisms before being replaced or tested.In-situ fumigation by vaporized h...The high efficiency particulate air filter(HEPA)in exhaust system of high-level biosafety laboratory must be disinfected to kill harmful microorganisms before being replaced or tested.In-situ fumigation by vaporized hydrogen peroxide(VHP)is the most commonly used disinfection method for HEPA unit.The disinfection effect of HEPA unit is affected by the internal environment,but the influence of initial internal environment on VHP penetration during the fumigation process is still rarely studied.In this paper,a numerical model was established based on a physical HEPA box unit and field measurement.According to the simulated VHP flow field during in-situ fumigation process,the influence of initial internal temperature and relative humidity on the VHP penetration effect in HEPA was discussed with the indicators of penetration rate and velocity distribution.The results showed that the VHP concentration in the upstream section of HEPA was relatively uniform,while the maximum and minimum concentrations in the downstream section showed great difference and located at the top and bottom,respectively.The distributions of VHP penetration and upstream velocity were both vertically uneven.The VHP penetration rates in the middle of HEPA remained around 73%.The initial temperature of 32℃or 36℃,or the initial relative humidity of 18%were the suitable initial internal environment for HEPA in-situ fumigation,which could keep the VHP penetration rates of the upper and lower parts of HEPA at about 76%and 61%,respectively.In the suitable initial environment,the penetration and disinfection effect could be promoted by appropriately extending the rapid injection duration.This study provides a reference for optimizing the initial environment setting of HEPA in-situ fumigation.展开更多
Typhoon Bebinca in 2024 experienced a nearshore outbreak(a rapid intensification(RI)near the coast),making accurate forecasting of unpredictable tracks and intensities highly challenging.The AI model is superior to th...Typhoon Bebinca in 2024 experienced a nearshore outbreak(a rapid intensification(RI)near the coast),making accurate forecasting of unpredictable tracks and intensities highly challenging.The AI model is superior to the numerical model for typhoon track prediction but performs worse for intensity forecasting.Vortex initialization is an effective approach to further improve numerical prediction via cycle assimilation,accounting for multiple relocating TC centers and adjusting the typhoon initial structure.In addition,by integrating numerical runs with an AI weather model through real-time dynamic weight correction of the forecast,the predictive skill is further improved.For example,it can reduce the deviation of 72-h track forecasting by 25%compared with the numerical model and decrease the intensity deviation by 2%and 56%relative to the numerical run and AI forecasts,respectively.On the basis of the best-performing forecasting,the inner-core convective burst(CB)characteristics are illuminated.The attributions of the nearshore outbreak and RI of Typhoon Bebinca are examined.From the viewpoint of bottom-up convection growth,the CB is associated with the energy supply from the high-boundarylayer CAPE,the following upward-developing secondary circulation,and accompanying latent heat release of hydrometeors.The contracted radius of maximum winds(RMW)and increased inertial stability within the inner core region effectively prevent the escape of the high-energy atmosphere and favor rapid intensification and maintenance of the offshore burst of a typhoon.The intensifying secondary circulation further promotes the primary circulation of the TC and RI processes through the gradient wind balance.展开更多
In position-sensorless brushless direct current(DC)motors(BLDCMs)fed by a four-switch three-phase(FSTP)inverter,only two phases are fully controlled,while the remaining phase is tied to the midpoint of the split DC-li...In position-sensorless brushless direct current(DC)motors(BLDCMs)fed by a four-switch three-phase(FSTP)inverter,only two phases are fully controlled,while the remaining phase is tied to the midpoint of the split DC-link capacitors.The voltage pulses required by inductance-based initial position detection can cause unequal discharge of the series capacitors,shifting the neutral-point voltage away from half of DC-link voltage(U_(dc)/2).This neutral-point drift breaks the spatial symmetry of the inverter voltage vectors,so the 360°electrical period can no longer be evenly partitioned into six sectors during initial rotor position detection.To address this issue,this paper proposes a detection-pulse injection sequence that explicitly accounts for the asymmetric voltage vectors of the FSTP inverter.With the proposed sequence,the initial rotor position can be identified within a 30°electrical sector.The method requires no additional voltage or current sensors,and experimental results confirm its feasibility.展开更多
The operational Tropical Regional Atmospheric Model System(TRAMS)often underestimates initial typhoon intensity when using the global analysis field as the initial condition.The TRAMS tropical cyclone(TC)initializatio...The operational Tropical Regional Atmospheric Model System(TRAMS)often underestimates initial typhoon intensity when using the global analysis field as the initial condition.The TRAMS tropical cyclone(TC)initialization scheme,developed based on the incremental analysis updates(IAU)technique,effectively reduces initial bias.However,the original IAU-based TC initialization scheme only adjusts the wind field at the analysis moment,with other variables adjusted implicitly under the model's constraints according to a gradually inserted wind increment(named“univariate adjustment scheme”hereafter).The univariate adjustment scheme requires approximately 3 h to reach a dynamic equilibrium state,which constrains the assimilation of hourly TC observations and causes excessive dissipation of meaningful short-wave information in adjustment increments.To address this limitation,this study develops a multivariate adjustment IAU-based TC initialization scheme that incorporates gradient wind balance and hydrostatic balance as its largescale constraints.Numerical experiments with TC Hato(2017)demonstrate that the multivariate adjustment scheme reduces the IAU relaxation time to 1 h while marginally improving forecast skill.These findings are consistently replicated across 12 additional TC cases.The development of the IAU-based multivariate adjustment initialization scheme establishes a foundation for 4-D initialization using hourly TC observations.展开更多
During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial...During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial damage on mechanical behavior and acoustic emission(AE)characteristics of coal under TCLU.Initial damage variables(IDVs)of coal specimens were quantified using preloading,followed by TCLU experiments to assess the deformation,energy distribution,and fracture development.The results revealed that the increase in IDVs significantly reduced the structural integrity of coal specimens,increased the cumulative irreversible strain,and enhanced the dissipated energy owing to microfracture expansion.Moreover,AE monitoring showed earlier activation of fractures and a higher occurrence of large-scale rupture events of coal specimens with high IDVs,which correlated with decreasing AE b values(reflecting the different scales of fracture within specimens)and increasing S values(reflecting the AE activity within specimens).Additionally,computed tomography analysis revealed intensified fracture networks and increasing three-dimensional fractal dimensions of coal specimens with higher IDVs.Finally,the coupling effect of TCLU and initial damage on the weakening mechanism of coal was investigated.Initial damage significantly reduced the structural integrity of coal by increasing the number of weak planes within coal specimens,contributing to the earlier activation and rapid expansion of fractures at low stress levels under TCLU and eventually accelerating the weakening process of coal.This study provides a scientific basis and theoretical support for the prevention and control of dynamic disasters in deep coal mining.展开更多
During the initial impoundment period of a canyon-shaped reservoir,the water body fluctuated violently regarding water level,hydrological condition,and thermal stratification.These variations may alter the structure o...During the initial impoundment period of a canyon-shaped reservoir,the water body fluctuated violently regarding water level,hydrological condition,and thermal stratification.These variations may alter the structure of phytoplankton community,resulting in algal blooms and seriously threatening the ecological security of the reservoir.It is of great significance to understand the continuous changes of phytoplankton in the initial impoundment period for the protection of reservoir water quality.Therefore,a two-year in-situ monitoring study was conducted on water quality and phytoplankton in a representative canyonshaped reservoir named Sanhekou and the interannual changes of phytoplankton community and its response to environmental changes during the initial impoundment period were discussed at taxonomic versus functional classification levels.The results showed that the total nitrogen and permanganate index levels were relatively high in the first year due to rapid water storage and heavy rainfall input,and the more stable hydrological conditions in the second year promoted the increase of algae density and the transformation of community,and the proportion of cyanobacteria increased significantly.The succession order of phytoplankton in the first year of the initial impoundment periodwas Chlorophyta-Bacillariophyta-Chlorophyta,or J/F/X1-P/MP/W1-A/X1/MP,respectively.And the succession order in the second year was Cyanobacteria/Chlorophyta-Bacillariophyta-Chlorophyta,or L_(M)/G/P-P/A/X1-X1/J/G.Water temperature,relativewater column stability,mixing depth,and pHwere crucial factors affecting phytoplankton community succession.This study revealed the interannual succession law and driving factors of phytoplankton in the initial impoundment period and provided an important reference for the operation management and ecological protection of canyon-shaped reservoirs.展开更多
Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have en...Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.展开更多
We study the two-dimensional(2D)Cauchy problem of nonhomogeneous Boussinesq system for magnetohydrodynamics convection without heat diffusion in the whole plane.Based on delicate weighted estimates,we derive the globa...We study the two-dimensional(2D)Cauchy problem of nonhomogeneous Boussinesq system for magnetohydrodynamics convection without heat diffusion in the whole plane.Based on delicate weighted estimates,we derive the global existence and uniqueness of strong solutions.In particular,the initial data can be arbitrarily large and the initial density may contain vacuum states and even have compact support.展开更多
Extensive oedometer tests and physical tests have been conducted on remolded and reconstituted marine soils with different initial water contents and liquid limits. The oedometer test data can be well fitted with a st...Extensive oedometer tests and physical tests have been conducted on remolded and reconstituted marine soils with different initial water contents and liquid limits. The oedometer test data can be well fitted with a straight line in the bilogarithmic ln(1+ e ) ～ lg p plot. The initial effective stress corresponding to the initial void ratio is determined by extrapolation of the bilogarithmic compression line. This new way of extrapolating oedometer test data to the initial void ratio overcomes the difficulty of measuring the residual effective stress of soils in the remolded state. The initial stable compression line of ocean floor deposits under different deposition environments corresponds to the compression line at the sensitivity equal to one. This initial stable compression line obtained in this study is consistent with the available compression line at the sensitivity equal to one which is proposed based on the experimental data of remolded undrained strength and the theoretical concept of Cam clay critical state line.展开更多
The microstructure evolution and mechanical properties of a Fe-0.12C-0.2Si-1.6Mn-0.3Cr-0.0025B(wt.%)steel with different initial microstructures,i.e.,hot rolled(HR)and cold rolled-annealed(CRA),were studied through op...The microstructure evolution and mechanical properties of a Fe-0.12C-0.2Si-1.6Mn-0.3Cr-0.0025B(wt.%)steel with different initial microstructures,i.e.,hot rolled(HR)and cold rolled-annealed(CRA),were studied through optical microscopy,scanning electron microscopy,electron channeling contrast imaging,microhardness and room temperature uniaxial tensile tests.After water quenching from 930℃ to room temperature,a fully martensitic microstructure was obtained in both as-quenched HR and CRA specimens,which shows a microhardness of 480±5 HV,and no significant difference in microstructure and microhardness was observed.Tensile test results show that the product of tensile strength and total elongation(UTS×TE)of the as-quenched HR specimen,i.e.,24.1 GPa%,is higher than that of the as-quenched CRA specimen,i.e.,18.9 GPa%.While,after being tempered at 300℃,the martensitic microstructures and mechanical properties of the two as-quenched specimens change significantly due to the synergy role of the matrix phase softening and the precipitation strengthening.Concerning the maximum UTS×TE,it is 18.9 GPa%obtained in the as-quenched CRA one,while that is 24.4 GPa%obtained in the HR specimen after tempered at 300℃ for 5 min.展开更多
Pangu-Weather(PGW),trained with deep learning–based methods(DL-based model),shows significant potential for global medium-range weather forecasting.However,the interpretability and trustworthiness of global medium-ra...Pangu-Weather(PGW),trained with deep learning–based methods(DL-based model),shows significant potential for global medium-range weather forecasting.However,the interpretability and trustworthiness of global medium-range DLbased models raise many concerns.This study uses the singular vector(SV)initial condition(IC)perturbations of the China Meteorological Administration's Global Ensemble Prediction System(CMA-GEPS)as inputs of PGW for global ensemble prediction(PGW-GEPS)to investigate the ensemble forecast sensitivity of DL-based models to the IC errors.Meanwhile,the CMA-GEPS forecasts serve as benchmarks for comparison and verification.The spatial structures and prediction performance of PGW-GEPS are discussed and compared to CMA-GEPS based on seasonal ensemble experiments.The results show that the ensemble mean and dispersion of PGW-GEPS are similar to those of CMA-GEPS in the medium range but with smoother forecasts.Meanwhile,PGW-GEPS is sensitive to the SV IC perturbations.Specifically,PGWGEPS can generate realistic ensemble spread beyond the sub-synoptic scale(wavenumbers≤64)with SV IC perturbations.However,PGW's kinetic energy is significantly reduced at the sub-synoptic scale,leading to error growth behavior inconsistent with CMA-GEPS at that scale.Thus,this behavior indicates that the effective resolution of PGW-GEPS is beyond the sub-synoptic scale and is limited to predicting mesoscale atmospheric motions.In terms of the global mediumrange ensemble prediction performance,the probability prediction skill of PGW-GEPS is comparable to CMA-GEPS in the extratropic when they use the same IC perturbations.That means that PGW has a general ability to provide skillful global medium-range forecasts with different ICs from numerical weather prediction.展开更多
The impact of various initial states on the ultimate mechanical properties of medium Mn steel(MMnS)following the hot stamping process is revealed.MMnS blanks with three typical initial states were prepared separately,...The impact of various initial states on the ultimate mechanical properties of medium Mn steel(MMnS)following the hot stamping process is revealed.MMnS blanks with three typical initial states were prepared separately,including hot-rolled,cold-rolled and cold-rolled and annealed(CRA).Their microstructures were observed and analyzed by scanning electron microscopy and electron backscatter diffraction,and their mechanical properties were measured by tensile tests following hot stamping and baking treatments.The results reveal that the microstructure of martensite and residual austenite characterizes the hot-stamped MMnS across different rolling conditions,with CRA state exhibiting a clearly higher residual austenite content compared to the other two states.Meanwhile,CRA state boasts not only the highest tensile strength but also the greatest elongation post-hot stamping treatment.The superior comprehensive mechanical properties are attributed to its unique biphase structure of Mn-rich austenite and Mn-poor ferrite,which emerges in CRA state following a 12 h intercritical annealing and can be partially preserved during the hot stamping process.This structure is instrumental in achieving a higher level of residual austenite,consequently leading to enhanced elongation.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
基金support to this study from the National Natural Science Foundation of China,NSFC(Grant No.52278367)The Belt and Road Special Foundation of the National Key Laboratory ofWater Disaster Prevention(Grant No.2024nkms08).
文摘The stress-strain behavior of calcareous sand is significantly influencedby particle breakage(B)and initial relative density(Dri),but few constitutive models consider their combined effects.To bridge this gap,we conducted a series of triaxial tests on calcareous sand with varying Dri and stress paths,examining particle breakage and critical state behavior.Key findingsinclude:(1)At a constant stress ratio(η),B follows a hyperbolic relationship with mean effective stress(p'),and for a given p',B increases proportionally withη;(2)The critical state line(CSL)moves downward with increasing Dri,whereas the critical state friction angle(φcs)decreases with increasing B.Based on these findings,we propose a unifiedbreakage evolution model to quantify particle breakage in calcareous sand under various loading conditions.Integrating this model with the Normal Consolidation Line(NCL)and CSL equations,we successfully simulate the steepening of NCL and CSL slopes as B increases with the onset of particle breakage.Furthermore,we quantitatively evaluate the effect of B onφcs.Finally,within the framework of Critical State Soil Mechanics and Hypoplasticity theory,we develop a hypoplastic model incorporating B and Dri.The model is validated through strong agreement with experimental results across various initial relative densities,stress paths and drainage conditions.
基金support from the Heilongjiang Province"Double First Class"Discipline Collaborative Innovation Project(No.LJGXCG2023-061).
文摘Hard carbon is a vital anode material for sodium-ion batteries;however,the nonuniform growth of solid electrolyte interphase(SEI)film substantially diminishes its initial coulombic efficiency(ICE)and cycle life.The chemical and morphological properties of surface highly influence the electrode/electrolyte interfacial reactions.In this study,we have tuned orbital hybridization states forming an interface enriched with sp^(2) hybridized carbon(sp^(2)-C),which decreases the binding energy to solvent molecules and inhibits excessive solvent decomposition during SEI formation.Benefiting from successfully constructed inorganic-rich SEI,the ICE increased to 91%and sodium storage capacity reached 346 mAh/g.Besides,the capacity retention rate was 90.7%after 700 cycles at 1 A/g higher than pristine electrode(83.8%).
基金Supported by Scientific Research Project of Jilin Provincial Department of Education(JJKH20250464KJ)。
文摘This paper deals with homogeneous Dirichlet boundary value problem to a class of porous medium equations with viscoelastic term ∂u/∂t-Δu^(m)+∫^(t)_(0)g(t-s)Δu^(m)(x,s)ds=u^(p),x∈Ω,t≥0,where p>m(m>0).We prove that the weak solutions of the above problem blow up in finite time when the initial energy is positive and the function g satisfies suitable conditions.Our result generalizes that of S.A.Messaoudi in[1].
基金Project(U22A20603)supported by the National Natural Science Foundation of ChinaProject(2023YFC3008300)supported by the National Key Research and Development Program of China。
文摘To investigate the long-term stability of soft-hard interbedded rock masses with initial damage induced by earthquakes and periodic drying and wetting,this study prepared samples with different initial damage through cyclic loading and unloading(CLU)experiments followed by cyclic drying and wetting(CDW)experiments,and finally conducted creep experiments.The study analyzed the effects of initial damage on creep mechanical behavior,crack evolution,and explored failure precursor information,revealing the damage failure mechanisms.The results show that the structural characteristics of the rock mass control its macroscopic failure mode.Initial damage promotes microcrack development,influences the fracture mode,and increases the proportion of high-frequency(200−280 kHz)acoustic emission events during creep.Meanwhile,initial damage exacerbates creep characteristics,increasing the creep rate,shortening total creep failure time,and reducing long-term strength.The damage failure is attributed to:the generation of internal cracks and pores in the rock caused by CLU;mineral hydrolysis and expansion-contraction due to CDW,resulting in weakened intergranular cementation;and full development of cracks and pores under creep stress.Additionally,the deformation difference coefficient and the coefficient of variation of RA/AF values can serve as precursor indicators for creep failure.
基金supported by the National Natural Science Foundation of China(Grant No.52522405)Key R&D Project of Sichuan Province of China(Regional Innovation Coop-eration)(Grant No.2025YFHZ0314).
文摘After coal seam mining,the overlying rock strata above the goaf are subjected to long-term stress and eventually undergo failure.Under mining-induced disturbances,the strata develop fractures at various angles,which significantly influence failure modes and the morphology of gas flow channels.This study employed multistage loading experiments,numerical simulations,three-dimensional reconstruction,and image recognition to investigate the fragmentation process of rocks with different initial fracture angles under multistage loading.The results show that variations in the initial fracture angle affect the transmission of contact forces among rock particles.As the angle increases,the transmission pattern shifts from a uniform distribution to one extending along the direction of the fracture.Rocks with small initial fracture angles tend to experience tensile-dominated failure,with most of the material subjected to longitudinal loading,resulting in reduced strength.Fractures propagate from the central region of the initial fracture,producing a complex internal fracture network.The proportion of fracture channels varies considerably across regions,creating multiple zones of velocity variation in the gas flow.In contrast,rocks with large initial fracture angles are more susceptible to shear failure,with the primary load-bearing zones aligned along the inclined fracture direction.As a result,the influence on surrounding regions is limited,improving the rock's load-bearing capacity under multistage loading.In these cases,the distribution and proportion of fracture channels become more uniform,promoting more stable gas flow within the channels.Overall,these findings provide theoretical insights into how initial fracture angles govern rock failure patterns and gas flow characteristics.
基金supported by the National Natural Science Foundation of China(Grant Nos.11804348,11775056,11975154,12225505,and 12405281)the Science Challenge(Project No.TZ2018005)+2 种基金supported by the Shanghai Pujiang Program(Grant No.23PJ1414600)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0890203)supported by the Accelerator Technology Helmholtz Infrastructure consortium ATHENA.
文摘The effects of initial spin orientation on the final electron beam polarization in laser wakefield acceleration in a pre-polarized plasma are investigated theoretically and numerically.From the results of variation of the initial spin direction,the spin dynamics of the electron beam are found to depend on the self-injection mechanism.The effects of wakefields and laser fields are studied using test particle dynamics and particle-in-cell simulations based on the Thomas-Bargmann-Michel-Telegdi equation.Compared with transverse injection,longitudinal injection is found to be preferable for obtaining a highly polarized electron beam.
基金Projects(52374138,51764013)supported by the National Natural Science Foundation of ChinaProject(20204BCJ22005)supported by the Training Plan for Academic and Technical Leaders of Major Disciplines of Jiangxi Province,China+1 种基金Project(2019M652277)supported by the China Postdoctoral Science FoundationProject(20192ACBL21014)supported by the Natural Science Youth Foundation Key Projects of Jiangxi Province,China。
文摘The cemented tailings backfill(CTB)with initial defects is more prone to destabilization damage under the influence of various unfavorable factors during the mining process.In order to investigate its influence on the stability of underground mining engineering,this paper simulates the generation of different degrees of initial defects inside the CTB by adding different contents of air-entraining agent(AEA),investigates the acoustic emission RA/AF eigenvalues of CTB with different contents of AEA under uniaxial compression,and adopts various denoising algorithms(e.g.,moving average smoothing,median filtering,and outlier detection)to improve the accuracy of the data.The variance and autocorrelation coefficients of RA/AF parameters were analyzed in conjunction with the critical slowing down(CSD)theory.The results show that the acoustic emission RA/AF values can be used to characterize the progressive damage evolution of CTB.The denoising algorithm processed the AE signals to reduce the effects of extraneous noise and anomalous spikes.Changes in the variance curves provide clear precursor information,while abrupt changes in the autocorrelation coefficient can be used as an auxiliary localization warning signal.The phenomenon of dramatic increase in the variance and autocorrelation coefficient curves during the compression-tightening stage,which is influenced by the initial defects,can lead to false warnings.As the initial defects of the CTB increase,its instability precursor time and instability time are prolonged,the peak stress decreases,and the time difference between the CTB and the instability damage is smaller.The results provide a new method for real-time monitoring and early warning of CTB instability damage.
基金supported by the Natural Science Foundation of Hebei Province(Project no.E2023202232)Science and Technology Research Project for Colleges and Universities in Hebei Province(Project no.CXY2024026).
文摘The high efficiency particulate air filter(HEPA)in exhaust system of high-level biosafety laboratory must be disinfected to kill harmful microorganisms before being replaced or tested.In-situ fumigation by vaporized hydrogen peroxide(VHP)is the most commonly used disinfection method for HEPA unit.The disinfection effect of HEPA unit is affected by the internal environment,but the influence of initial internal environment on VHP penetration during the fumigation process is still rarely studied.In this paper,a numerical model was established based on a physical HEPA box unit and field measurement.According to the simulated VHP flow field during in-situ fumigation process,the influence of initial internal temperature and relative humidity on the VHP penetration effect in HEPA was discussed with the indicators of penetration rate and velocity distribution.The results showed that the VHP concentration in the upstream section of HEPA was relatively uniform,while the maximum and minimum concentrations in the downstream section showed great difference and located at the top and bottom,respectively.The distributions of VHP penetration and upstream velocity were both vertically uneven.The VHP penetration rates in the middle of HEPA remained around 73%.The initial temperature of 32℃or 36℃,or the initial relative humidity of 18%were the suitable initial internal environment for HEPA in-situ fumigation,which could keep the VHP penetration rates of the upper and lower parts of HEPA at about 76%and 61%,respectively.In the suitable initial environment,the penetration and disinfection effect could be promoted by appropriately extending the rapid injection duration.This study provides a reference for optimizing the initial environment setting of HEPA in-situ fumigation.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDB0760300)the National Natural Science Foundation of China (Grant Nos.42175010 and 41875079)。
文摘Typhoon Bebinca in 2024 experienced a nearshore outbreak(a rapid intensification(RI)near the coast),making accurate forecasting of unpredictable tracks and intensities highly challenging.The AI model is superior to the numerical model for typhoon track prediction but performs worse for intensity forecasting.Vortex initialization is an effective approach to further improve numerical prediction via cycle assimilation,accounting for multiple relocating TC centers and adjusting the typhoon initial structure.In addition,by integrating numerical runs with an AI weather model through real-time dynamic weight correction of the forecast,the predictive skill is further improved.For example,it can reduce the deviation of 72-h track forecasting by 25%compared with the numerical model and decrease the intensity deviation by 2%and 56%relative to the numerical run and AI forecasts,respectively.On the basis of the best-performing forecasting,the inner-core convective burst(CB)characteristics are illuminated.The attributions of the nearshore outbreak and RI of Typhoon Bebinca are examined.From the viewpoint of bottom-up convection growth,the CB is associated with the energy supply from the high-boundarylayer CAPE,the following upward-developing secondary circulation,and accompanying latent heat release of hydrometeors.The contracted radius of maximum winds(RMW)and increased inertial stability within the inner core region effectively prevent the escape of the high-energy atmosphere and favor rapid intensification and maintenance of the offshore burst of a typhoon.The intensifying secondary circulation further promotes the primary circulation of the TC and RI processes through the gradient wind balance.
基金supported in part by the National Natural Science Foundation of China under Grant 52477060in part by the Tianjin Natural Science Foundation Project under Grant 24JCZDJC00250in part by the Zhejiang Leading Innovation and Entrepreneurship Team Project under Grant 2024R01012.
文摘In position-sensorless brushless direct current(DC)motors(BLDCMs)fed by a four-switch three-phase(FSTP)inverter,only two phases are fully controlled,while the remaining phase is tied to the midpoint of the split DC-link capacitors.The voltage pulses required by inductance-based initial position detection can cause unequal discharge of the series capacitors,shifting the neutral-point voltage away from half of DC-link voltage(U_(dc)/2).This neutral-point drift breaks the spatial symmetry of the inverter voltage vectors,so the 360°electrical period can no longer be evenly partitioned into six sectors during initial rotor position detection.To address this issue,this paper proposes a detection-pulse injection sequence that explicitly accounts for the asymmetric voltage vectors of the FSTP inverter.With the proposed sequence,the initial rotor position can be identified within a 30°electrical sector.The method requires no additional voltage or current sensors,and experimental results confirm its feasibility.
基金supported by the National University of Defense Technology(NUDT)Research Initiation Funding for High-Level Scientific and Technological Innovative Talents(202402-YJRC-LJ-001)the National Natural Science Foundation of China(Grant No.U2142213)+1 种基金the Basic and Applied Basic Research Foundation of Guangdong Province(Grants 2025A1515011835,2022A1515011870)the National Natural Science Foundation of China(Grant No.42305167)。
文摘The operational Tropical Regional Atmospheric Model System(TRAMS)often underestimates initial typhoon intensity when using the global analysis field as the initial condition.The TRAMS tropical cyclone(TC)initialization scheme,developed based on the incremental analysis updates(IAU)technique,effectively reduces initial bias.However,the original IAU-based TC initialization scheme only adjusts the wind field at the analysis moment,with other variables adjusted implicitly under the model's constraints according to a gradually inserted wind increment(named“univariate adjustment scheme”hereafter).The univariate adjustment scheme requires approximately 3 h to reach a dynamic equilibrium state,which constrains the assimilation of hourly TC observations and causes excessive dissipation of meaningful short-wave information in adjustment increments.To address this limitation,this study develops a multivariate adjustment IAU-based TC initialization scheme that incorporates gradient wind balance and hydrostatic balance as its largescale constraints.Numerical experiments with TC Hato(2017)demonstrate that the multivariate adjustment scheme reduces the IAU relaxation time to 1 h while marginally improving forecast skill.These findings are consistently replicated across 12 additional TC cases.The development of the IAU-based multivariate adjustment initialization scheme establishes a foundation for 4-D initialization using hourly TC observations.
基金supported by the National Key R&D Program of China(Grant No.2022YFC3004704)the National Natural Science Foundation of China(Grant No.52174166)Graduate Research and Innovation Foundation of Chongqing,China(Grant No.CYB23031),which were gratefully acknowledged.
文摘During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial damage on mechanical behavior and acoustic emission(AE)characteristics of coal under TCLU.Initial damage variables(IDVs)of coal specimens were quantified using preloading,followed by TCLU experiments to assess the deformation,energy distribution,and fracture development.The results revealed that the increase in IDVs significantly reduced the structural integrity of coal specimens,increased the cumulative irreversible strain,and enhanced the dissipated energy owing to microfracture expansion.Moreover,AE monitoring showed earlier activation of fractures and a higher occurrence of large-scale rupture events of coal specimens with high IDVs,which correlated with decreasing AE b values(reflecting the different scales of fracture within specimens)and increasing S values(reflecting the AE activity within specimens).Additionally,computed tomography analysis revealed intensified fracture networks and increasing three-dimensional fractal dimensions of coal specimens with higher IDVs.Finally,the coupling effect of TCLU and initial damage on the weakening mechanism of coal was investigated.Initial damage significantly reduced the structural integrity of coal by increasing the number of weak planes within coal specimens,contributing to the earlier activation and rapid expansion of fractures at low stress levels under TCLU and eventually accelerating the weakening process of coal.This study provides a scientific basis and theoretical support for the prevention and control of dynamic disasters in deep coal mining.
基金supported by the National Key R&D Program of China(No.2022YFC3203602)the Natural Science Foundation of China(No.52370018)+1 种基金Shaanxi Provincial Youth Innovation Team Project(No.22JP040)Shaanxi Provincial Key Scientific and Technological Innovation Team(No.2023-CX-TD-32).
文摘During the initial impoundment period of a canyon-shaped reservoir,the water body fluctuated violently regarding water level,hydrological condition,and thermal stratification.These variations may alter the structure of phytoplankton community,resulting in algal blooms and seriously threatening the ecological security of the reservoir.It is of great significance to understand the continuous changes of phytoplankton in the initial impoundment period for the protection of reservoir water quality.Therefore,a two-year in-situ monitoring study was conducted on water quality and phytoplankton in a representative canyonshaped reservoir named Sanhekou and the interannual changes of phytoplankton community and its response to environmental changes during the initial impoundment period were discussed at taxonomic versus functional classification levels.The results showed that the total nitrogen and permanganate index levels were relatively high in the first year due to rapid water storage and heavy rainfall input,and the more stable hydrological conditions in the second year promoted the increase of algae density and the transformation of community,and the proportion of cyanobacteria increased significantly.The succession order of phytoplankton in the first year of the initial impoundment periodwas Chlorophyta-Bacillariophyta-Chlorophyta,or J/F/X1-P/MP/W1-A/X1/MP,respectively.And the succession order in the second year was Cyanobacteria/Chlorophyta-Bacillariophyta-Chlorophyta,or L_(M)/G/P-P/A/X1-X1/J/G.Water temperature,relativewater column stability,mixing depth,and pHwere crucial factors affecting phytoplankton community succession.This study revealed the interannual succession law and driving factors of phytoplankton in the initial impoundment period and provided an important reference for the operation management and ecological protection of canyon-shaped reservoirs.
文摘Evaluation of hydromechanical shear behavior of unsaturated soils is still a challenging issue. The time and cost needed for conducting precise experimental investigation on shear behavior of unsaturated soils have encouraged several investigators to develop analytical, empirical, or semi-empirical models for predicting the shear behavior of unsaturated soils. However, most of the previously proposed models are for specimens subjected to the isotropic state of stress, without considering the effect of initial shear stress. In this study, a hydromechanical constitutive model is proposed for unsaturated collapsible soils during shearing, with consideration of the effect of the initial shear stress. The model implements an effective stress-based disturbed state concept (DSC) to predict the stress-strain behavior of the soil. Accordingly, material/state variables were defined for both the start of the shearing stage and the critical state of the soil. A series of laboratory tests was performed using a fully automated unsaturated triaxial device to verify the proposed model. The experimental program included 23 suction-controlled unsaturated triaxial shear tests on reconstituted specimens of Gorgan clayey loess wetted to different levels of suctions under both isotropic and anisotropic stress states. The results show excellent agreement between the prediction by the proposed model and the experimental results.
文摘We study the two-dimensional(2D)Cauchy problem of nonhomogeneous Boussinesq system for magnetohydrodynamics convection without heat diffusion in the whole plane.Based on delicate weighted estimates,we derive the global existence and uniqueness of strong solutions.In particular,the initial data can be arbitrarily large and the initial density may contain vacuum states and even have compact support.
文摘Extensive oedometer tests and physical tests have been conducted on remolded and reconstituted marine soils with different initial water contents and liquid limits. The oedometer test data can be well fitted with a straight line in the bilogarithmic ln(1+ e ) ～ lg p plot. The initial effective stress corresponding to the initial void ratio is determined by extrapolation of the bilogarithmic compression line. This new way of extrapolating oedometer test data to the initial void ratio overcomes the difficulty of measuring the residual effective stress of soils in the remolded state. The initial stable compression line of ocean floor deposits under different deposition environments corresponds to the compression line at the sensitivity equal to one. This initial stable compression line obtained in this study is consistent with the available compression line at the sensitivity equal to one which is proposed based on the experimental data of remolded undrained strength and the theoretical concept of Cam clay critical state line.
基金Chongqing Natural Science Foundation(No.CSTB2022NSCQ-MSX1394)Graduate Research and Innovation Foundation of Chongqing,China(Grant No.CYS22008)+2 种基金Open Project of State Key Laboratory of Advanced Special Steel,Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University(SKLASS 2023-10)the Science and Technology Commission of Shanghai Municipality(No.19DZ2270200)the Open Project of the Large Casting and Forging Manufacturing Technology Engineering Center of Shanghai Institute of Mechanical and Electrical Engineering,State Key Laboratory of Vanadium and Titanium Resources Open Fund(No.2022P4FZG04A).
文摘The microstructure evolution and mechanical properties of a Fe-0.12C-0.2Si-1.6Mn-0.3Cr-0.0025B(wt.%)steel with different initial microstructures,i.e.,hot rolled(HR)and cold rolled-annealed(CRA),were studied through optical microscopy,scanning electron microscopy,electron channeling contrast imaging,microhardness and room temperature uniaxial tensile tests.After water quenching from 930℃ to room temperature,a fully martensitic microstructure was obtained in both as-quenched HR and CRA specimens,which shows a microhardness of 480±5 HV,and no significant difference in microstructure and microhardness was observed.Tensile test results show that the product of tensile strength and total elongation(UTS×TE)of the as-quenched HR specimen,i.e.,24.1 GPa%,is higher than that of the as-quenched CRA specimen,i.e.,18.9 GPa%.While,after being tempered at 300℃,the martensitic microstructures and mechanical properties of the two as-quenched specimens change significantly due to the synergy role of the matrix phase softening and the precipitation strengthening.Concerning the maximum UTS×TE,it is 18.9 GPa%obtained in the as-quenched CRA one,while that is 24.4 GPa%obtained in the HR specimen after tempered at 300℃ for 5 min.
基金supported by the joint funds of the Chinese National Natural Science Foundation(NSFC)(Grant No.U2242213)the funds of the NSFC(Grant No.42341209)+2 种基金the National Key Research and Development(R&D)Program of the Ministry of Science and Technology of China(Grant No.2021YFC3000902)the National Science Foundation for Young Scholars(Grant No.42205166)the Joint Research Project for Meteorological Capacity Improvement(Grant No.22NLTSQ008)。
文摘Pangu-Weather(PGW),trained with deep learning–based methods(DL-based model),shows significant potential for global medium-range weather forecasting.However,the interpretability and trustworthiness of global medium-range DLbased models raise many concerns.This study uses the singular vector(SV)initial condition(IC)perturbations of the China Meteorological Administration's Global Ensemble Prediction System(CMA-GEPS)as inputs of PGW for global ensemble prediction(PGW-GEPS)to investigate the ensemble forecast sensitivity of DL-based models to the IC errors.Meanwhile,the CMA-GEPS forecasts serve as benchmarks for comparison and verification.The spatial structures and prediction performance of PGW-GEPS are discussed and compared to CMA-GEPS based on seasonal ensemble experiments.The results show that the ensemble mean and dispersion of PGW-GEPS are similar to those of CMA-GEPS in the medium range but with smoother forecasts.Meanwhile,PGW-GEPS is sensitive to the SV IC perturbations.Specifically,PGWGEPS can generate realistic ensemble spread beyond the sub-synoptic scale(wavenumbers≤64)with SV IC perturbations.However,PGW's kinetic energy is significantly reduced at the sub-synoptic scale,leading to error growth behavior inconsistent with CMA-GEPS at that scale.Thus,this behavior indicates that the effective resolution of PGW-GEPS is beyond the sub-synoptic scale and is limited to predicting mesoscale atmospheric motions.In terms of the global mediumrange ensemble prediction performance,the probability prediction skill of PGW-GEPS is comparable to CMA-GEPS in the extratropic when they use the same IC perturbations.That means that PGW has a general ability to provide skillful global medium-range forecasts with different ICs from numerical weather prediction.
基金supported by the National Key R&D Program of China(No.2022YFE0196600)the National Natural Science Foundation of China(No.52175349)the Shanghai Oriental Talent Program(No.BJKJ2024016).
文摘The impact of various initial states on the ultimate mechanical properties of medium Mn steel(MMnS)following the hot stamping process is revealed.MMnS blanks with three typical initial states were prepared separately,including hot-rolled,cold-rolled and cold-rolled and annealed(CRA).Their microstructures were observed and analyzed by scanning electron microscopy and electron backscatter diffraction,and their mechanical properties were measured by tensile tests following hot stamping and baking treatments.The results reveal that the microstructure of martensite and residual austenite characterizes the hot-stamped MMnS across different rolling conditions,with CRA state exhibiting a clearly higher residual austenite content compared to the other two states.Meanwhile,CRA state boasts not only the highest tensile strength but also the greatest elongation post-hot stamping treatment.The superior comprehensive mechanical properties are attributed to its unique biphase structure of Mn-rich austenite and Mn-poor ferrite,which emerges in CRA state following a 12 h intercritical annealing and can be partially preserved during the hot stamping process.This structure is instrumental in achieving a higher level of residual austenite,consequently leading to enhanced elongation.
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.
