The formation of thawed interlayer beneath embankment can result in embankment settlement in permafrost regions. Based on the data on ground temperatures and deformations beneath the embankment, observed in-situ along...The formation of thawed interlayer beneath embankment can result in embankment settlement in permafrost regions. Based on the data on ground temperatures and deformations beneath the embankment, observed in-situ along the QinghaiTibet Railway in permafrost regions from 2006 to2013, characteristics of the thawed interlayer beneath the embankment and its influence on the embankment settlement are studied. The results indicate that the thawed interlayer hardly forms beneath the natural field, and beneath the embankments from the Qinghai-Tibet Railway the thawed interlayer develops widely, and it can be refrozen totally in the regions with lower mean annual ground temperature, and developed further in the regions with higher mean annual ground temperature.The thawed interlayer is closely related to the embankment settlement. The ice content of permafrost underlying the thawed interlayer influences the settlement of embankment. The higher the ice content is, the larger the settlement is, and vice versa. The increase in thickness of thawed interlayer mainly results from the decline of artificial permafrost table in high-temperature permafrost regions.展开更多
Thawed permafrost could cause a serious stability problem for foundations and oil-wells in cold regions. A non-damage testing procedure, employing the Bender Element Method, was used for permafrost samples collected f...Thawed permafrost could cause a serious stability problem for foundations and oil-wells in cold regions. A non-damage testing procedure, employing the Bender Element Method, was used for permafrost samples collected from a continuous frozen core obtained from the North Slope of Alaska, USA. The wave velocity and modulus of thawed permafrost were investigated on various isotropic confining pressure from 0 kPa to 400 kPa per 100 kPa. The received shear wave propagation was recorded, and the elastic wave theory was used to calculate shear modulus. Finally, the shear modulus affected by confining pressure, water content and dry density were analyzed and discussed, and a regression formulation of shear modulus based on the Janbu Model for thawed silty and sandy permafrost were proposed and validation.展开更多
The influence of inner cell mass （ICM） and trophectoderm （TE） score on pregnancy out- comes in frozen-thawed blastocyst transfer cycles was analyzed. A retrospective analysis of 741 cycles of frozen-thawed blastos...The influence of inner cell mass （ICM） and trophectoderm （TE） score on pregnancy out- comes in frozen-thawed blastocyst transfer cycles was analyzed. A retrospective analysis of 741 cycles of frozen-thawed blastosysts transfer was performed. All cycles were divided into four groups based on the number and morphological score of blastocysts： S-ICM B/TE B group （n=91）, the single blastocyst transfer oflCM B and TE B; D-ICM B/TE B group （n=579）, double blastocysts transfer oflCM B/TE B; D-1CM B/TE C group （n=35）, double blastocysts transfer of ICM B/TE C; and D-ICM C/TE B group （n=36）, double blastocysts transfer ofTE B/ICM C. The pregnancy outcomes were compared among the four groups. As compared with D-ICM B/TE C group, the clinical pregnancy rate, implantation rate and multiple pregnancy rate were increased in D-ICM B/TE B group （74.96% vs. 57.14%, 57.43% vs. 37.14%, and .48.62% vs. 25%, respectively, P〈0.05 for all）. Clinical pregnancy rate and implantation rate in D-ICM B/TE B group were also higher than in D-ICM C/TE B group （74.96% vs. 50%, and 57.43% vs. 33.33%, both P〈0.05）. Multivariable Logistic regression analysis indicated that ICM score was a better predictive parameter for clinical pregnancy （OR=3.05, CI 1.70-5.46, P〈0.001）, while the trophectoderm score was a better one for early abortion （OR=0.074, CI 0.03-0.19, P〈0.001）. Clinical pregnancy rate and multiple pregnancy rate in S-ICM B/TE B group were significantly lower than those in D-ICM B/TE B group （46.15% vs. 74.96%, and 2.38% vs. 48.62%, both P〈0.05）, but there was no si~,,niflcant difference in the implantation rate between the two groups. It was suggested that the higher score of ICM and TE may be indicative of the better pregnancy outcomes. The ICM score is a better predictor of clinical pregnancy than TE, while TE score is a better one in predicting early abortion. Sin- gle ICM B/TE B blastocyst transfer in frozen-thawed cycles can also get satisfactory pregnancy out- comes.展开更多
Based on ground temperatures and deformations monitored at the Xieshuihe site along the Qinghai-Tibet Highway(QTH)in permafrost regions from 2004 to 2015,variation of artificial permafrost table(APT),maximum frozen de...Based on ground temperatures and deformations monitored at the Xieshuihe site along the Qinghai-Tibet Highway(QTH)in permafrost regions from 2004 to 2015,variation of artificial permafrost table(APT),maximum frozen depth(MFD),thawed interlayer thickness(TIT)and ground temperature beneath embankment is analyzed,respectively.The results indicate that under the embankment,the change of APT occurred from October to December of that year and presented a deepening trend.The change of MFD occurred from April to June of that year with no obvious change trend,and TIT had an increasing trend year by year,which mainly resulted from the deepening artificial permafrost table.Mean annual ground temperature at 0.5 m depth was 3.91°C higher beneath the embankment center than that under the natural field.The rising ground temperature at shallow layer of embankment resulted in the development of thawed interlayer beneath the embankment and warming of underlying permafrost.Embankment settlement is closely associated with TIT.Greater settlement easily occurs when permafrost with higher ice content exists under the thawed interlayer,and in turn the settlement is smaller when permafrost with lower ice content exists under the thawed interlayer.展开更多
The endometrial condition is a significant factor for successful pregnancy. To regulate endometrial function in fertility treatment, prednisolone (PSL) is administered for suppression of increased natural killer cells...The endometrial condition is a significant factor for successful pregnancy. To regulate endometrial function in fertility treatment, prednisolone (PSL) is administered for suppression of increased natural killer cells and stimulation of endometrium embryo transfer (SEET) to enhance communication between embryo and maternal tissues. We attempted to improve the endometrial condition by PSL administration and SEET during frozen–thawed blastocyst transfer (FBT). Patients took PSL (5 mg) 3 times daily for 3 days after ovulation during the FBT cycle. To analyse effects of PSL combined with SEET, we determined rates of chemical pregnancy, clinical pregnancy, foetal heart movement (FHM) and live birth. Rates of chemical pregnancy, clinical pregnancy and FHM were significantly higher in the PSL(+)/SEET(+) (57.7%, 50.0% and 46.2%, respectively) and PSL(+)/SEET(-) (53.3%, 46.7% and 46.7%, respectively) groups than in the PSL(-)/SEET(+) (30.3%, 18.2% and 18.2%, respectively) and PSL(-)/SEET(-) (22.4%, 22.4% and 18.4%;P = 0.0043, 0.0081 and 0.0055, respectively) groups. The live birth rate was significantly higher in the PSL(+)/SEET(+) group than in the PSL(+)/SEET(-), PSL(-)/SEET(+) and PSL(-)/SEET(-) groups (42.3%, 26.7%, 18.2% and 12.2%, respectively;P = 0.0237). PSL combined with SEET may be a useful adjunct to assisted reproductive technology in women who repeatedly fail to conceive by infertility treatment.展开更多
Objective： The aim of our study was to observe the survival and morphological changes of thawed ovarian tis- sues after heterotopic transplantation. Methods： Twenty SPF-SD female rats （5-6 weeks old） were equally ...Objective： The aim of our study was to observe the survival and morphological changes of thawed ovarian tis- sues after heterotopic transplantation. Methods： Twenty SPF-SD female rats （5-6 weeks old） were equally randomized into the control group and experimental group. In control group, the freshly isolated ovaries were fixed in formalin. In experimental group, the freshly isolated ovaries were vitrified immediately and cut into thin slices. After stored in liquid nitrogen for 21 days, the tissues of experimental group were rapidly thawed and transplanted into back muscles of rats for 2 or 4 weeks, respectively. After that, all rats in experimental group were sacrificed and the ovarian tissues were collected and fixed in 4% formaldehyde solution. Then the ovarian tissues were stained with HE and observed under the light confocal microscope. Re- suits： With the naked eyes, there was no specific alteration except the size reduction with color changing. Under microscopy, we found normal cortex and medulla in the ovary, and the primordial follicles and follicles in various stages were observed in the cortex. The normal oocytes in ovarian tissues of experimental group were significant decreased than in the control group. Conclusion： The ovarian tissues survive well in experimental group and there is no significant difference in the proportion of follicles between different times （2 and 4 weeks） after grafting. Our results suggest that thawed ovarian tissues could survive after heterotopic transplantation into back muscles of rat models and maintain their morphology and function.展开更多
Objective To analyse factors influencing the outcome of frozen-thawed embryo transfer （FET）. Method A retrospective analysis was performed in our center on 129 thawing cycles from March 2001 to April 2003. The relat...Objective To analyse factors influencing the outcome of frozen-thawed embryo transfer （FET）. Method A retrospective analysis was performed in our center on 129 thawing cycles from March 2001 to April 2003. The related parameters were compared between conceived and non-conceived cycles. Results There were totally 129 clinical pregnancies in these transfers （pregnancy rate： 27.1%）. Frozen-thawed embryos were transferred to natural cycles and CC cycling and hormone replacement treatment had equal success. Groups of IVF and ICSI did not differ significantly in pregnancy rates （P〉0.05）. The pregnancy rates for one, two, three and four pre-embryos transfer were 0, 20.0%,44.1% and 75.0%, respectively （P〈0.05）. There were statistical differences between pregnancy group or non- pregnancy group in the endometrial thickness, CES, CES/No. of embryo. A higher pregnancy rate was observed in embryo transfers which had at least one 4-cell grade I embryo （d 2）（P〈0.01）. Conclusions The most important factors influencing the implantation rate and pregnancy rate of frozen-thawed embryo transfer are age, endometrium thickness, and the number, morphology and growth rate of transferred frozen embryos of women participants.展开更多
The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the roll...The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained.展开更多
Soil erosion by snow or ice melt waterflow is an important type of soil erosion in many high-altitude and high-latitude regions and is further aggravated by climate warming.The snowmelt waterflow erosion process is af...Soil erosion by snow or ice melt waterflow is an important type of soil erosion in many high-altitude and high-latitude regions and is further aggravated by climate warming.The snowmelt waterflow erosion process is affected by soil freeze-thaws and is highly dynamically variable.In this study,a methodology was developed to conduct in situ field experiments to investigate the effects of the thawed depth of the frozen soil profile on snowmelt waterflow erosion.The method was implemented on an alpine meadow soil slope at an altitude of 3700 m on the northeastern Tibetan Plateau.The erosion experiments involved five thawed soil depths of 0,10,30(35),50,and 80(100)mm under two snowmelt waterflow rates(3 and 5 L/min).When the topsoil was fully frozen or shallow-thawed(≤10 mm),its hydrothermal and structural properties caused a significant lag in the initiation of runoff and delayed soil erosion in the initial stage.The runoff and sediment concentration curves for fully frozen and shallow-thawed soil showed two-stage patterns characteristic of a sediment supply limited in the early stage and subject to hydrodynamic-controlled processes in the later stage.However,this effect did not exist where the thawed soil depth was greater than 30 mm.The deep-thawed cases(≥30 mm)showed normal hydrograph and sedigraph patterns similar to those of the unfrozen soil.The findings of this study are important for understanding the erosion rates of partially thawed soil and for improving erosion simulations in cold regions.展开更多
The Qinghai-Xizang Plateau of China faces challenges like thaw slumping,threatening slope stability and infrastructure.Understanding the mechanical properties of the roots of the dominant herbaceous plant species in t...The Qinghai-Xizang Plateau of China faces challenges like thaw slumping,threatening slope stability and infrastructure.Understanding the mechanical properties of the roots of the dominant herbaceous plant species in the alpine meadow layer of the permafrost regions on the Qinghai-Xizang Plateau is essential for evaluating their role in enhancing soil shear strength and mitigating slope deformation in these fragile environments.In this study,the roots of four dominant herbaceous plant species—Kobresia pygmaea,Kobresia humilis,Carex moorcroftii,and Leontopodium pusillum—that are widely distributed in the permafrost regions of the Qinghai-Xizang Plateau were explored to determine their mechanical properties and effects in enhancing soil shear strength.Through indoor single root tensile and root group tensile tests,we determined the root diameter,tensile force,tensile strength,tensile ratio,and strength frequency distributions.We also evaluated their contributions to inhibiting slope deformation and failure during the formation and development of thermal thaw slumps in the alpine meadow.The results showed that the distribution of the root diameter of the dominant plant species is mostly normal,while the tensile strength tends to be logarithmically normally distributed.The relationship between the root diameter and root tensile strength conforms to a power function.The theoretical tensile strength of the root group was calculated using the Wu-Waldron Model(WWM)and the Fiber Bundle Model(FBM)under the assumption that the cumulative single tensile strength of the root bundle is identical to the tensile strength of the root group in the WWM.The FBM considers three fracture modes:FBM-D(the tensile force on each single root is proportional to its diameter relative to the total sum of all the root diameters),FBM-S(the cross-sectional stress in the root bundle is uniform),and FBM-N(each tensile strength test of individual roots experiences an equal load).It was found that the model-calculated tensile strength of the root group was 162.60%higher than the test value.The model-derived tensile force of the root group from the FBM-D,FBM-S,and FBM-N was 73.10%,28.91%,and 13.47%higher than the test values,respectively.The additional cohesion of the soil provided by the roots was calculated to be 25.90-45.06 kPa using the modified WWM,67.05-38.15 kPa using the FBM-S,and 57.24-32.74 kPa using the FBM-N.These results not only provide a theoretical basis for further quantitative evaluation of the mechanical effects of the root systems of herbaceous plant species in reinforcing the surface soil but also have practical significance for the effective prevention and control of thermal thaw slumping disasters in the permafrost regions containing native alpine meadows on the Qinghai-Xizang Plateau using flexible plant protection measures.展开更多
During the thawing process of a railway subgrade,bidirectional thawing complicates water-heat transfer,leading to serious thaw settlement issues under train loads.Focusing on the severely frozen section of the Shuozho...During the thawing process of a railway subgrade,bidirectional thawing complicates water-heat transfer,leading to serious thaw settlement issues under train loads.Focusing on the severely frozen section of the Shuozhou-Huanghua port heavy-haul railway,this study conducted indoor soil-column laterally-limited compression tests on thawing fine-grained soil specimens to analyze the cumulative deformation during thawing.The deformation evolution was examined from both macroscopic and microscopic perspectives.The test results revealed a sig-nificant increase in the water content at the frozen interlayer during thawing,with minimal thaw settlement under no-load conditions.However,under dynamic loads,the thawing soil exhibited rapid settlement during the initial stages of the process.Increasing the dynamic load amplitude did not result in significant additional thaw settlement compression.Particle image velocimetry revealed substantial thaw settlement and compression at the top of thawing soil.Microscopically,the porosity at the top of the specimens significantly decreased,whereas the porosity in the frozen interlayer remained largely unchanged.Under dynamic loading,the specimens exhibited a concentrated distribution of large pores with scattered smaller pores.The phase change from ice to water,combined with dynamic loading,induced particle movement and expanded the inter-particle pore space,leading to macroscopic thaw settlement and soil compression.The findings can provide a theoretical foundation for maintaining and ensuring the safety of railway subgrades in cold regions.展开更多
The thawing of ice-rich permafrost leads to the formation of thermokarst landforms.Precise mapping of retrogressive thaw slumps(RTSs)is imperative for assessing the degradation and carbon exchange of permafrost at bot...The thawing of ice-rich permafrost leads to the formation of thermokarst landforms.Precise mapping of retrogressive thaw slumps(RTSs)is imperative for assessing the degradation and carbon exchange of permafrost at both local and regional scales on the Tibetan Plateau(TP).However,previous methods for RTSs mapping rely on a large number of samples and complex classifiers with low automation level or unnecessary complexity.We propose an automatic mapping network(AmRTSNet)for producing decimeter-level RTSs maps from GaoFen-7 images based on deep learning.Both the quantitative metrics and qualitative evaluations show that AmRTSNet trained in the Beiluhe offers significant advantages over previous methods.Without further fine-tuning,we conducted RTSs automatic mapping based on AmRTSNet in the Wulanwula,Chumarhe,and Gaolinggo.Over 141,312 ha on the TP have been automatically mapped,comprising 926 RTS regions with a total RTS area of 2318.72 ha.The average statistics of the mapped RTSs show low roundness(0.38),moderate rectangularity(0.61),and high convexity(0.79).About 90%of the RTSs are smaller than 6 ha.The average aspect ratio is 2.18.RTSs are unevenly distributed in belt-like aggregations with dominant density peaks.RTSs often concentrate in hillslopes and along lateral streams,with more dense areas more likely to have larger RTSs.展开更多
Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration...Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration and freeze–thaw(FT) cycles is a significant factor causing slope failure. This study aims to investigate the transmedia seepage characteristics at slope–concrete stabilizing pile interface systems by using silty clay and concrete with varying microstructure characteristics under FT cycles. To this end, a self-developed indoor test device for transmedia water migration, combined with a macro-meso-micro multiscale testing approach, was used to analyze the laws and mechanisms of transmedia seepage at the interface systems. The effect of the medium's microstructure characteristics on the transmedia seepage behavior at the interface systems under FT cycles was also assessed. Results indicated that the transmedia water migration exhibited particularity due to the migration of soil particles and the low permeability characteristics of concrete. The water content in the media increased significantly within the range of 1/3–2/3 of the height from the interface for soil and within 5 mm from the interface for concrete.FT cycles promoted the increase and penetration of cracks within the medium, enhancing the permeability of the slope-concrete stabilizing pile interface systems.With the increase in FT cycles, the porosity inside the medium first decreased and then increased, and the porosity reached the minimum after 25 FT cycles and the maximum after 75 FT cycles, and the water content of the medium after water migration was positively correlated with the porosity. FT cycles also significantly influenced the temporal variation characteristics of soil moisture and the migration path of water in concrete. The study results could serve as a reference for related research on slope stability assessment.展开更多
The pile-plate structure has proven highly effective support for high-speed railway subgrades,particularly in poor geological conditions.Although its efficacy in non-frozen regions is well-established,its potential in...The pile-plate structure has proven highly effective support for high-speed railway subgrades,particularly in poor geological conditions.Although its efficacy in non-frozen regions is well-established,its potential in frozen regions remains underexplored.In seasonally frozen areas,F-T(freeze-thaw)cycles threaten subgrade stability,necessitating research on pile-plate structure’s behavior under such conditions.To address this challenge,a scaled model experiment was conducted on a silty sand foundation,simulating F-T cycles using temperature control devices.Key parameters,including soil temperature,frozen depth,and displacement,were systematically monitored.Results indicate that the bearing plate functions as an effective insulation layer,significantly reducing sub-zero temperature penetration.Additionally,the anchoring action of the piles mitigates frost heave in the foundation soil,while the plate middle restrains soil deformation more effectively due to increased constraint.The thermal insulation provided by the plate maintains higher soil temperatures,delaying the onset of freezing.By the end of each freezing stage,the vertical displacement in the natural subgrade is approximately 4 times greater than that beneath the pile-plate structure.Furthermore,the frost depth is about 1.3-1.4 times and 1.6-4.9 times greater than that measured below the plate edge and middle,respectively.These insights contribute to the development of more resilient designs for high-speed railway subgrades in seasonally frozen regions,offering engineers a robust,scientifically-backed foundation for future infrastructure projects.展开更多
The freeze-thaw(FT)behavior of porous materials(PMs)involves the coupling of the thermo-hydromechanical(THM)processes and is significantly influenced by the microstructure.However,modeling FT in unsaturated PMs remain...The freeze-thaw(FT)behavior of porous materials(PMs)involves the coupling of the thermo-hydromechanical(THM)processes and is significantly influenced by the microstructure.However,modeling FT in unsaturated PMs remains an open issue,and the influence of microstructure is not yet fully understood.To address these challenges,we propose a THM model for FT in PMs that considers microstructure and variable air content.In this work,a non-equilibrium thermodynamic approach is proposed to capture ice formation/melting,the microstructure is accounted for utilizing micromechanics,and the FT processes in air-entrained PMs are formulated within the proposed THM model.This model incorporates variable air void characteristics,e.g.air content,spacing factor,specific surface area,and supercooled water-filled regimes,and distinguishes the roles of air voids between freezing and thawing.The FT behaviors,including deformation,ice formation/melting,spacing factor,and pore water pressure evolutions,are focused.Comparisons with experimental results,confirm the capability of the present model.The results demonstrate the effects of variable air voids on the FT behavior of air-entrained PMs.The findings reveal that assuming fixed air void characteristics can lead to underestimation of pore pressure and deformation,particularly at low air content.Additionally,air voids act as cryo-pumps during freezing and when the cooling temperature stabilizes.During thawing,air voids supply gas to the melting sites(i.e.“gas escape”),preventing further significant deformation reduction.These results can provide novel insights for understanding the frost damage of PMs.展开更多
Freezing–thawing indices serve as a comprehensive indicator of both the duration of the freezing/thawing periods and the degree of cold and heat in a given region.In-depth analysis of the freezing-thawing indices not...Freezing–thawing indices serve as a comprehensive indicator of both the duration of the freezing/thawing periods and the degree of cold and heat in a given region.In-depth analysis of the freezing-thawing indices not only enables the prediction of permafrost distribution and its dynamic changes,but also facilitates the assessment of damage risk to infrastructure under freeze-thaw action.In this paper,the air/ground freezing–thawing indices from 1987 to 2017,based on daily temperature observations from meteorological stations along the China–Nepal Highway(CNH),were calculated,and their spatial and temporal variation patterns were analyzed.The results showed that:(1)Both mean annual air temperature and mean annual ground surface temperature along the CNH fluctuated upward,with climate tendency rates of 0.43 and 0.52.C·(10a)~(-1),respectively;(2)The number of days with negative air temperature and ground temperature showed fluctuated downward,with change rates of-8.6 and-8.3 d·(10a)~(-1),respectively;(3)The ranges of air freezing index,air thawing index,ground freezing index,and ground thawing index over the years were 157.05-458.88°C·d,2034.20-2560.73°C·d,108.78-396.83°C·d,and 3515.25-4288.67°C·d,respectively.The climate tendency rates were-5.42,10.22,-6.79,and 12.14.C·d·a-1,respectively,showing a general warming trend;(4)The air freezing index,ground freezing index,and ground thawing index changed abruptly in 1999,2000,and 2002,respectively,evincing significant changes after 2002.The research results can provide a basis for the risk assessment of freezing–thawing erosion and the prevention and control of permafrost engineering diseases along the CNH.展开更多
The seasonal change in depths of the frozen and thawed soils within their active layer is reduced to a moving boundary problem, which describes the dynamics of the total ice content using an independent mass balance e...The seasonal change in depths of the frozen and thawed soils within their active layer is reduced to a moving boundary problem, which describes the dynamics of the total ice content using an independent mass balance equation and treats the soil frost/thaw depths as moving (sharp) interfaces governed by some Stefan-type moving boundary conditions, and hence simultaneously describes the liquid water and solid ice states as well as the positions of the frost/thaw depths in soil. An adaptive mesh method for the moving boundary problem is adopted to solve the relevant equations and to determine frost/thaw depths, water content and temperature distribution. A series of sensitivity experiments by the numerical model under the periodic sinusoidal upper boundary condition for temperature are conducted to validate the model, and to investigate the effects of the model soil thickness, ground surface temperature, annual amplitude of ground surface temperature and thermal conductivity on frost/thaw depths and soil temperature. The simulated frost/thaw depths by the model with a periodical change of the upper boundary condition have the same period as that of the upper boundary condition, which shows that it can simulate the frost/thaw depths reasonably for a periodical forcing.展开更多
In the section of fine-grained soil of regions with perennial and deep seasonally frozen ground, a crux to protect railroad, highway, water conservancy and other buildings from, frost damages is to reveal the laws of ...In the section of fine-grained soil of regions with perennial and deep seasonally frozen ground, a crux to protect railroad, highway, water conservancy and other buildings from, frost damages is to reveal the laws of water migration in the frozen, freezing and thawing soil. Most of the previous works on this subject have been concentrated on solving the problem of water migration from the unfrozen part of freezing ground towards the freezing front.展开更多
To explore the effects of freeze‒thaw cycles on the mechanical properties and crack evolution of fissured sandstone,biaxial compression experiments were carried out on sandstone subjected to freeze‒thaw cycles to char...To explore the effects of freeze‒thaw cycles on the mechanical properties and crack evolution of fissured sandstone,biaxial compression experiments were carried out on sandstone subjected to freeze‒thaw cycles to characterize the changes in the physical and mechanical properties of fissured sandstone caused by freeze‒thaw cycles.The crack evolution and crack change process on the surface of the fissured sandstone were recorded and analysed in detail via digital image technology(DIC).Numerical simulation was used to reveal the expansion process and damage mode of fine-scale cracks under the action of freeze‒thaw cycles,and the simulation results were compared and analysed with the experimental data to verify the reliability of the numerical model.The results show that the mass loss,porosity,peak stress and elastic modulus all increase with increasing number of freeze‒thaw cycles.With an increase in the number of freeze‒thaw cycles,a substantial change in displacement occurs around the prefabricated cracks,and a stress concentration appears at the crack tip.As new cracks continue to sprout at the tips of the prefabricated cracks until the microcracks gradually penetrate into the main cracks,the displacement cloud becomes obviously discontinuous,and the contours of the displacement field in the crack fracture damage area simply intersect with the prefabricated cracks to form an obvious fracture.The damage patterns of the fractured sandstone after freeze‒thaw cycles clearly differ,forming a symmetrical"L"-shaped damage pattern at zero freeze‒thaw cycles,a symmetrical"V"-shaped damage pattern at 10 freeze‒thaw cycles,and a"V"-shaped damage pattern at 20 freeze‒thaw cycles.After 20 freeze‒thaw cycles,a"V"-shaped destruction pattern and"L"-shaped destruction pattern are formed;after 30 freeze‒thaw cycles,an"N"-shaped destruction pattern is formed.This shows that the failure mode of fractured sandstone gradually becomes more complicated with an increasing number of freeze‒thaw cycles.The effects of freeze‒thaw cycles on the direction and rate of crack propagation are revealed through a temperature‒load coupled model,which provides an important reference for an in-depth understanding of the freeze‒thaw failure mechanisms of fractured rock masses.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41571064,41630636 and 41471061)the Independent Research of the State Key Laboratory of Frozen Soil Engineering(SKLFSE-ZT-09)
文摘The formation of thawed interlayer beneath embankment can result in embankment settlement in permafrost regions. Based on the data on ground temperatures and deformations beneath the embankment, observed in-situ along the QinghaiTibet Railway in permafrost regions from 2006 to2013, characteristics of the thawed interlayer beneath the embankment and its influence on the embankment settlement are studied. The results indicate that the thawed interlayer hardly forms beneath the natural field, and beneath the embankments from the Qinghai-Tibet Railway the thawed interlayer develops widely, and it can be refrozen totally in the regions with lower mean annual ground temperature, and developed further in the regions with higher mean annual ground temperature.The thawed interlayer is closely related to the embankment settlement. The ice content of permafrost underlying the thawed interlayer influences the settlement of embankment. The higher the ice content is, the larger the settlement is, and vice versa. The increase in thickness of thawed interlayer mainly results from the decline of artificial permafrost table in high-temperature permafrost regions.
基金the financial support from Conoco Phillips Alaska, Inc., BP Alaska, Exxon Mobil and Chevron
文摘Thawed permafrost could cause a serious stability problem for foundations and oil-wells in cold regions. A non-damage testing procedure, employing the Bender Element Method, was used for permafrost samples collected from a continuous frozen core obtained from the North Slope of Alaska, USA. The wave velocity and modulus of thawed permafrost were investigated on various isotropic confining pressure from 0 kPa to 400 kPa per 100 kPa. The received shear wave propagation was recorded, and the elastic wave theory was used to calculate shear modulus. Finally, the shear modulus affected by confining pressure, water content and dry density were analyzed and discussed, and a regression formulation of shear modulus based on the Janbu Model for thawed silty and sandy permafrost were proposed and validation.
文摘The influence of inner cell mass （ICM） and trophectoderm （TE） score on pregnancy out- comes in frozen-thawed blastocyst transfer cycles was analyzed. A retrospective analysis of 741 cycles of frozen-thawed blastosysts transfer was performed. All cycles were divided into four groups based on the number and morphological score of blastocysts： S-ICM B/TE B group （n=91）, the single blastocyst transfer oflCM B and TE B; D-ICM B/TE B group （n=579）, double blastocysts transfer oflCM B/TE B; D-1CM B/TE C group （n=35）, double blastocysts transfer of ICM B/TE C; and D-ICM C/TE B group （n=36）, double blastocysts transfer ofTE B/ICM C. The pregnancy outcomes were compared among the four groups. As compared with D-ICM B/TE C group, the clinical pregnancy rate, implantation rate and multiple pregnancy rate were increased in D-ICM B/TE B group （74.96% vs. 57.14%, 57.43% vs. 37.14%, and .48.62% vs. 25%, respectively, P〈0.05 for all）. Clinical pregnancy rate and implantation rate in D-ICM B/TE B group were also higher than in D-ICM C/TE B group （74.96% vs. 50%, and 57.43% vs. 33.33%, both P〈0.05）. Multivariable Logistic regression analysis indicated that ICM score was a better predictive parameter for clinical pregnancy （OR=3.05, CI 1.70-5.46, P〈0.001）, while the trophectoderm score was a better one for early abortion （OR=0.074, CI 0.03-0.19, P〈0.001）. Clinical pregnancy rate and multiple pregnancy rate in S-ICM B/TE B group were significantly lower than those in D-ICM B/TE B group （46.15% vs. 74.96%, and 2.38% vs. 48.62%, both P〈0.05）, but there was no si~,,niflcant difference in the implantation rate between the two groups. It was suggested that the higher score of ICM and TE may be indicative of the better pregnancy outcomes. The ICM score is a better predictor of clinical pregnancy than TE, while TE score is a better one in predicting early abortion. Sin- gle ICM B/TE B blastocyst transfer in frozen-thawed cycles can also get satisfactory pregnancy out- comes.
基金supported by the National Natural Science Foundation of China (No. 41571064)the Key Program of National Natural Science Foundation of China (No. 41630636)the Independent Research of the State Key Laboratory of Frozen Soil Engineering (No. SKLFSE-ZT-09)
文摘Based on ground temperatures and deformations monitored at the Xieshuihe site along the Qinghai-Tibet Highway(QTH)in permafrost regions from 2004 to 2015,variation of artificial permafrost table(APT),maximum frozen depth(MFD),thawed interlayer thickness(TIT)and ground temperature beneath embankment is analyzed,respectively.The results indicate that under the embankment,the change of APT occurred from October to December of that year and presented a deepening trend.The change of MFD occurred from April to June of that year with no obvious change trend,and TIT had an increasing trend year by year,which mainly resulted from the deepening artificial permafrost table.Mean annual ground temperature at 0.5 m depth was 3.91°C higher beneath the embankment center than that under the natural field.The rising ground temperature at shallow layer of embankment resulted in the development of thawed interlayer beneath the embankment and warming of underlying permafrost.Embankment settlement is closely associated with TIT.Greater settlement easily occurs when permafrost with higher ice content exists under the thawed interlayer,and in turn the settlement is smaller when permafrost with lower ice content exists under the thawed interlayer.
文摘The endometrial condition is a significant factor for successful pregnancy. To regulate endometrial function in fertility treatment, prednisolone (PSL) is administered for suppression of increased natural killer cells and stimulation of endometrium embryo transfer (SEET) to enhance communication between embryo and maternal tissues. We attempted to improve the endometrial condition by PSL administration and SEET during frozen–thawed blastocyst transfer (FBT). Patients took PSL (5 mg) 3 times daily for 3 days after ovulation during the FBT cycle. To analyse effects of PSL combined with SEET, we determined rates of chemical pregnancy, clinical pregnancy, foetal heart movement (FHM) and live birth. Rates of chemical pregnancy, clinical pregnancy and FHM were significantly higher in the PSL(+)/SEET(+) (57.7%, 50.0% and 46.2%, respectively) and PSL(+)/SEET(-) (53.3%, 46.7% and 46.7%, respectively) groups than in the PSL(-)/SEET(+) (30.3%, 18.2% and 18.2%, respectively) and PSL(-)/SEET(-) (22.4%, 22.4% and 18.4%;P = 0.0043, 0.0081 and 0.0055, respectively) groups. The live birth rate was significantly higher in the PSL(+)/SEET(+) group than in the PSL(+)/SEET(-), PSL(-)/SEET(+) and PSL(-)/SEET(-) groups (42.3%, 26.7%, 18.2% and 12.2%, respectively;P = 0.0237). PSL combined with SEET may be a useful adjunct to assisted reproductive technology in women who repeatedly fail to conceive by infertility treatment.
文摘Objective： The aim of our study was to observe the survival and morphological changes of thawed ovarian tis- sues after heterotopic transplantation. Methods： Twenty SPF-SD female rats （5-6 weeks old） were equally randomized into the control group and experimental group. In control group, the freshly isolated ovaries were fixed in formalin. In experimental group, the freshly isolated ovaries were vitrified immediately and cut into thin slices. After stored in liquid nitrogen for 21 days, the tissues of experimental group were rapidly thawed and transplanted into back muscles of rats for 2 or 4 weeks, respectively. After that, all rats in experimental group were sacrificed and the ovarian tissues were collected and fixed in 4% formaldehyde solution. Then the ovarian tissues were stained with HE and observed under the light confocal microscope. Re- suits： With the naked eyes, there was no specific alteration except the size reduction with color changing. Under microscopy, we found normal cortex and medulla in the ovary, and the primordial follicles and follicles in various stages were observed in the cortex. The normal oocytes in ovarian tissues of experimental group were significant decreased than in the control group. Conclusion： The ovarian tissues survive well in experimental group and there is no significant difference in the proportion of follicles between different times （2 and 4 weeks） after grafting. Our results suggest that thawed ovarian tissues could survive after heterotopic transplantation into back muscles of rat models and maintain their morphology and function.
文摘Objective To analyse factors influencing the outcome of frozen-thawed embryo transfer （FET）. Method A retrospective analysis was performed in our center on 129 thawing cycles from March 2001 to April 2003. The related parameters were compared between conceived and non-conceived cycles. Results There were totally 129 clinical pregnancies in these transfers （pregnancy rate： 27.1%）. Frozen-thawed embryos were transferred to natural cycles and CC cycling and hormone replacement treatment had equal success. Groups of IVF and ICSI did not differ significantly in pregnancy rates （P〉0.05）. The pregnancy rates for one, two, three and four pre-embryos transfer were 0, 20.0%,44.1% and 75.0%, respectively （P〈0.05）. There were statistical differences between pregnancy group or non- pregnancy group in the endometrial thickness, CES, CES/No. of embryo. A higher pregnancy rate was observed in embryo transfers which had at least one 4-cell grade I embryo （d 2）（P〈0.01）. Conclusions The most important factors influencing the implantation rate and pregnancy rate of frozen-thawed embryo transfer are age, endometrium thickness, and the number, morphology and growth rate of transferred frozen embryos of women participants.
文摘The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained.
基金This study is financially supported by the National Natural Science Foundation of China(Grant No.42271142,42101130)the Belt and Road Special Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering(2020490311).
文摘Soil erosion by snow or ice melt waterflow is an important type of soil erosion in many high-altitude and high-latitude regions and is further aggravated by climate warming.The snowmelt waterflow erosion process is affected by soil freeze-thaws and is highly dynamically variable.In this study,a methodology was developed to conduct in situ field experiments to investigate the effects of the thawed depth of the frozen soil profile on snowmelt waterflow erosion.The method was implemented on an alpine meadow soil slope at an altitude of 3700 m on the northeastern Tibetan Plateau.The erosion experiments involved five thawed soil depths of 0,10,30(35),50,and 80(100)mm under two snowmelt waterflow rates(3 and 5 L/min).When the topsoil was fully frozen or shallow-thawed(≤10 mm),its hydrothermal and structural properties caused a significant lag in the initiation of runoff and delayed soil erosion in the initial stage.The runoff and sediment concentration curves for fully frozen and shallow-thawed soil showed two-stage patterns characteristic of a sediment supply limited in the early stage and subject to hydrodynamic-controlled processes in the later stage.However,this effect did not exist where the thawed soil depth was greater than 30 mm.The deep-thawed cases(≥30 mm)showed normal hydrograph and sedigraph patterns similar to those of the unfrozen soil.The findings of this study are important for understanding the erosion rates of partially thawed soil and for improving erosion simulations in cold regions.
基金supported by the Qinghai Science and Technology Department Project(2025-QY-225)the National Natural Science Foundation of China(42267024)the Second Comprehensive Scientific Investigation and Research Project of the Qinghai-Xizang Plateau(2019QZKK0905).
文摘The Qinghai-Xizang Plateau of China faces challenges like thaw slumping,threatening slope stability and infrastructure.Understanding the mechanical properties of the roots of the dominant herbaceous plant species in the alpine meadow layer of the permafrost regions on the Qinghai-Xizang Plateau is essential for evaluating their role in enhancing soil shear strength and mitigating slope deformation in these fragile environments.In this study,the roots of four dominant herbaceous plant species—Kobresia pygmaea,Kobresia humilis,Carex moorcroftii,and Leontopodium pusillum—that are widely distributed in the permafrost regions of the Qinghai-Xizang Plateau were explored to determine their mechanical properties and effects in enhancing soil shear strength.Through indoor single root tensile and root group tensile tests,we determined the root diameter,tensile force,tensile strength,tensile ratio,and strength frequency distributions.We also evaluated their contributions to inhibiting slope deformation and failure during the formation and development of thermal thaw slumps in the alpine meadow.The results showed that the distribution of the root diameter of the dominant plant species is mostly normal,while the tensile strength tends to be logarithmically normally distributed.The relationship between the root diameter and root tensile strength conforms to a power function.The theoretical tensile strength of the root group was calculated using the Wu-Waldron Model(WWM)and the Fiber Bundle Model(FBM)under the assumption that the cumulative single tensile strength of the root bundle is identical to the tensile strength of the root group in the WWM.The FBM considers three fracture modes:FBM-D(the tensile force on each single root is proportional to its diameter relative to the total sum of all the root diameters),FBM-S(the cross-sectional stress in the root bundle is uniform),and FBM-N(each tensile strength test of individual roots experiences an equal load).It was found that the model-calculated tensile strength of the root group was 162.60%higher than the test value.The model-derived tensile force of the root group from the FBM-D,FBM-S,and FBM-N was 73.10%,28.91%,and 13.47%higher than the test values,respectively.The additional cohesion of the soil provided by the roots was calculated to be 25.90-45.06 kPa using the modified WWM,67.05-38.15 kPa using the FBM-S,and 57.24-32.74 kPa using the FBM-N.These results not only provide a theoretical basis for further quantitative evaluation of the mechanical effects of the root systems of herbaceous plant species in reinforcing the surface soil but also have practical significance for the effective prevention and control of thermal thaw slumping disasters in the permafrost regions containing native alpine meadows on the Qinghai-Xizang Plateau using flexible plant protection measures.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.52078312,52478461,and 52408379)the Natural Science Foundation of Hebei Province(E2024210134)+2 种基金the Innovative Research Group Project of the Natural Science Foundation of Hebei Province(Grant No.E2021210099)CCCC Science and Technology R&D Project(Grant No.2021-ZJKJ-01)the S&T Program of Hebei(Grant No.225A0802D).
文摘During the thawing process of a railway subgrade,bidirectional thawing complicates water-heat transfer,leading to serious thaw settlement issues under train loads.Focusing on the severely frozen section of the Shuozhou-Huanghua port heavy-haul railway,this study conducted indoor soil-column laterally-limited compression tests on thawing fine-grained soil specimens to analyze the cumulative deformation during thawing.The deformation evolution was examined from both macroscopic and microscopic perspectives.The test results revealed a sig-nificant increase in the water content at the frozen interlayer during thawing,with minimal thaw settlement under no-load conditions.However,under dynamic loads,the thawing soil exhibited rapid settlement during the initial stages of the process.Increasing the dynamic load amplitude did not result in significant additional thaw settlement compression.Particle image velocimetry revealed substantial thaw settlement and compression at the top of thawing soil.Microscopically,the porosity at the top of the specimens significantly decreased,whereas the porosity in the frozen interlayer remained largely unchanged.Under dynamic loading,the specimens exhibited a concentrated distribution of large pores with scattered smaller pores.The phase change from ice to water,combined with dynamic loading,induced particle movement and expanded the inter-particle pore space,leading to macroscopic thaw settlement and soil compression.The findings can provide a theoretical foundation for maintaining and ensuring the safety of railway subgrades in cold regions.
基金The Second Tibetan Plateau Scientific Expedition and Research,No.2022QZKK0101National Natural Science Foundation of China,No.42271427。
文摘The thawing of ice-rich permafrost leads to the formation of thermokarst landforms.Precise mapping of retrogressive thaw slumps(RTSs)is imperative for assessing the degradation and carbon exchange of permafrost at both local and regional scales on the Tibetan Plateau(TP).However,previous methods for RTSs mapping rely on a large number of samples and complex classifiers with low automation level or unnecessary complexity.We propose an automatic mapping network(AmRTSNet)for producing decimeter-level RTSs maps from GaoFen-7 images based on deep learning.Both the quantitative metrics and qualitative evaluations show that AmRTSNet trained in the Beiluhe offers significant advantages over previous methods.Without further fine-tuning,we conducted RTSs automatic mapping based on AmRTSNet in the Wulanwula,Chumarhe,and Gaolinggo.Over 141,312 ha on the TP have been automatically mapped,comprising 926 RTS regions with a total RTS area of 2318.72 ha.The average statistics of the mapped RTSs show low roundness(0.38),moderate rectangularity(0.61),and high convexity(0.79).About 90%of the RTSs are smaller than 6 ha.The average aspect ratio is 2.18.RTSs are unevenly distributed in belt-like aggregations with dominant density peaks.RTSs often concentrate in hillslopes and along lateral streams,with more dense areas more likely to have larger RTSs.
基金financially supported by Jilin Provincial Natural Science Foundation (No.20220101164JC)。
文摘Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration and freeze–thaw(FT) cycles is a significant factor causing slope failure. This study aims to investigate the transmedia seepage characteristics at slope–concrete stabilizing pile interface systems by using silty clay and concrete with varying microstructure characteristics under FT cycles. To this end, a self-developed indoor test device for transmedia water migration, combined with a macro-meso-micro multiscale testing approach, was used to analyze the laws and mechanisms of transmedia seepage at the interface systems. The effect of the medium's microstructure characteristics on the transmedia seepage behavior at the interface systems under FT cycles was also assessed. Results indicated that the transmedia water migration exhibited particularity due to the migration of soil particles and the low permeability characteristics of concrete. The water content in the media increased significantly within the range of 1/3–2/3 of the height from the interface for soil and within 5 mm from the interface for concrete.FT cycles promoted the increase and penetration of cracks within the medium, enhancing the permeability of the slope-concrete stabilizing pile interface systems.With the increase in FT cycles, the porosity inside the medium first decreased and then increased, and the porosity reached the minimum after 25 FT cycles and the maximum after 75 FT cycles, and the water content of the medium after water migration was positively correlated with the porosity. FT cycles also significantly influenced the temporal variation characteristics of soil moisture and the migration path of water in concrete. The study results could serve as a reference for related research on slope stability assessment.
基金The authors express their gratitude to the financial support from National Key R&D Program of China(No.2023YFB2604001)National Natural Science Foundation of China(No.52478475,No.52378463 and No.52168066).
文摘The pile-plate structure has proven highly effective support for high-speed railway subgrades,particularly in poor geological conditions.Although its efficacy in non-frozen regions is well-established,its potential in frozen regions remains underexplored.In seasonally frozen areas,F-T(freeze-thaw)cycles threaten subgrade stability,necessitating research on pile-plate structure’s behavior under such conditions.To address this challenge,a scaled model experiment was conducted on a silty sand foundation,simulating F-T cycles using temperature control devices.Key parameters,including soil temperature,frozen depth,and displacement,were systematically monitored.Results indicate that the bearing plate functions as an effective insulation layer,significantly reducing sub-zero temperature penetration.Additionally,the anchoring action of the piles mitigates frost heave in the foundation soil,while the plate middle restrains soil deformation more effectively due to increased constraint.The thermal insulation provided by the plate maintains higher soil temperatures,delaying the onset of freezing.By the end of each freezing stage,the vertical displacement in the natural subgrade is approximately 4 times greater than that beneath the pile-plate structure.Furthermore,the frost depth is about 1.3-1.4 times and 1.6-4.9 times greater than that measured below the plate edge and middle,respectively.These insights contribute to the development of more resilient designs for high-speed railway subgrades in seasonally frozen regions,offering engineers a robust,scientifically-backed foundation for future infrastructure projects.
基金the funding support from the National Natural Science Foundation of China(Grant Nos.52350004 and 51925903).
文摘The freeze-thaw(FT)behavior of porous materials(PMs)involves the coupling of the thermo-hydromechanical(THM)processes and is significantly influenced by the microstructure.However,modeling FT in unsaturated PMs remains an open issue,and the influence of microstructure is not yet fully understood.To address these challenges,we propose a THM model for FT in PMs that considers microstructure and variable air content.In this work,a non-equilibrium thermodynamic approach is proposed to capture ice formation/melting,the microstructure is accounted for utilizing micromechanics,and the FT processes in air-entrained PMs are formulated within the proposed THM model.This model incorporates variable air void characteristics,e.g.air content,spacing factor,specific surface area,and supercooled water-filled regimes,and distinguishes the roles of air voids between freezing and thawing.The FT behaviors,including deformation,ice formation/melting,spacing factor,and pore water pressure evolutions,are focused.Comparisons with experimental results,confirm the capability of the present model.The results demonstrate the effects of variable air voids on the FT behavior of air-entrained PMs.The findings reveal that assuming fixed air void characteristics can lead to underestimation of pore pressure and deformation,particularly at low air content.Additionally,air voids act as cryo-pumps during freezing and when the cooling temperature stabilizes.During thawing,air voids supply gas to the melting sites(i.e.“gas escape”),preventing further significant deformation reduction.These results can provide novel insights for understanding the frost damage of PMs.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2021QZKK0202)Shaanxi Provincial Youth Science and Technology Rising Star Project(No.2022KJXX-85)+3 种基金Key Scientific Research Project of Shaanxi Provincial Department of Education(No.22JS041)Youth Innovation Team Research Project of Shaanxi Provincial Department of Education(Nos.22JP099,21JP137)The Youth Innovation Team of Shaanxi Universitiesthe Support Program for Outstanding Young Talents of Shaanxi Universities(Dr.Tao Luo)。
文摘Freezing–thawing indices serve as a comprehensive indicator of both the duration of the freezing/thawing periods and the degree of cold and heat in a given region.In-depth analysis of the freezing-thawing indices not only enables the prediction of permafrost distribution and its dynamic changes,but also facilitates the assessment of damage risk to infrastructure under freeze-thaw action.In this paper,the air/ground freezing–thawing indices from 1987 to 2017,based on daily temperature observations from meteorological stations along the China–Nepal Highway(CNH),were calculated,and their spatial and temporal variation patterns were analyzed.The results showed that:(1)Both mean annual air temperature and mean annual ground surface temperature along the CNH fluctuated upward,with climate tendency rates of 0.43 and 0.52.C·(10a)~(-1),respectively;(2)The number of days with negative air temperature and ground temperature showed fluctuated downward,with change rates of-8.6 and-8.3 d·(10a)~(-1),respectively;(3)The ranges of air freezing index,air thawing index,ground freezing index,and ground thawing index over the years were 157.05-458.88°C·d,2034.20-2560.73°C·d,108.78-396.83°C·d,and 3515.25-4288.67°C·d,respectively.The climate tendency rates were-5.42,10.22,-6.79,and 12.14.C·d·a-1,respectively,showing a general warming trend;(4)The air freezing index,ground freezing index,and ground thawing index changed abruptly in 1999,2000,and 2002,respectively,evincing significant changes after 2002.The research results can provide a basis for the risk assessment of freezing–thawing erosion and the prevention and control of permafrost engineering diseases along the CNH.
基金the National Basic Research Program(Grant No.2005CB321703)the Knowledge Innovation Project of Chinese Academy of Sciences(Grant Nos.KZCX2-yw-126-2,KZCX2-yw-217)the Chinese Coordinated Observation and Prediction of the Earth System project(Grant No.GYHY20070605)
文摘The seasonal change in depths of the frozen and thawed soils within their active layer is reduced to a moving boundary problem, which describes the dynamics of the total ice content using an independent mass balance equation and treats the soil frost/thaw depths as moving (sharp) interfaces governed by some Stefan-type moving boundary conditions, and hence simultaneously describes the liquid water and solid ice states as well as the positions of the frost/thaw depths in soil. An adaptive mesh method for the moving boundary problem is adopted to solve the relevant equations and to determine frost/thaw depths, water content and temperature distribution. A series of sensitivity experiments by the numerical model under the periodic sinusoidal upper boundary condition for temperature are conducted to validate the model, and to investigate the effects of the model soil thickness, ground surface temperature, annual amplitude of ground surface temperature and thermal conductivity on frost/thaw depths and soil temperature. The simulated frost/thaw depths by the model with a periodical change of the upper boundary condition have the same period as that of the upper boundary condition, which shows that it can simulate the frost/thaw depths reasonably for a periodical forcing.
文摘In the section of fine-grained soil of regions with perennial and deep seasonally frozen ground, a crux to protect railroad, highway, water conservancy and other buildings from, frost damages is to reveal the laws of water migration in the frozen, freezing and thawing soil. Most of the previous works on this subject have been concentrated on solving the problem of water migration from the unfrozen part of freezing ground towards the freezing front.
基金supported by the National Natural Science Foundation of China(Project No.52074123).
文摘To explore the effects of freeze‒thaw cycles on the mechanical properties and crack evolution of fissured sandstone,biaxial compression experiments were carried out on sandstone subjected to freeze‒thaw cycles to characterize the changes in the physical and mechanical properties of fissured sandstone caused by freeze‒thaw cycles.The crack evolution and crack change process on the surface of the fissured sandstone were recorded and analysed in detail via digital image technology(DIC).Numerical simulation was used to reveal the expansion process and damage mode of fine-scale cracks under the action of freeze‒thaw cycles,and the simulation results were compared and analysed with the experimental data to verify the reliability of the numerical model.The results show that the mass loss,porosity,peak stress and elastic modulus all increase with increasing number of freeze‒thaw cycles.With an increase in the number of freeze‒thaw cycles,a substantial change in displacement occurs around the prefabricated cracks,and a stress concentration appears at the crack tip.As new cracks continue to sprout at the tips of the prefabricated cracks until the microcracks gradually penetrate into the main cracks,the displacement cloud becomes obviously discontinuous,and the contours of the displacement field in the crack fracture damage area simply intersect with the prefabricated cracks to form an obvious fracture.The damage patterns of the fractured sandstone after freeze‒thaw cycles clearly differ,forming a symmetrical"L"-shaped damage pattern at zero freeze‒thaw cycles,a symmetrical"V"-shaped damage pattern at 10 freeze‒thaw cycles,and a"V"-shaped damage pattern at 20 freeze‒thaw cycles.After 20 freeze‒thaw cycles,a"V"-shaped destruction pattern and"L"-shaped destruction pattern are formed;after 30 freeze‒thaw cycles,an"N"-shaped destruction pattern is formed.This shows that the failure mode of fractured sandstone gradually becomes more complicated with an increasing number of freeze‒thaw cycles.The effects of freeze‒thaw cycles on the direction and rate of crack propagation are revealed through a temperature‒load coupled model,which provides an important reference for an in-depth understanding of the freeze‒thaw failure mechanisms of fractured rock masses.
