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
This study aimed to assess pregnancy outcomes after high-quality D5- and D6-blastocyst transfer in frozen cycles of in vitro fertilization and embryo transfer and to further evaluate whether there was a difference in ...This study aimed to assess pregnancy outcomes after high-quality D5- and D6-blastocyst transfer in frozen cycles of in vitro fertilization and embryo transfer and to further evaluate whether there was a difference in blastocyst development potentials with different developmental speeds and in pregnancy outcomes. A retrospective analysis was conducted to analyze 247 frozen cycles in our center from September 2015 to July 2017, which were divided into two groups: a D5-FET group with 193 cycles of D5-blastocyst transfer, and a D6-FET group with 54 cycles of D6-blastocyst transfer. Hormone replacement method was utilized to prepare frozen-cycle endometria. Pregnancy outcomes were analyzed and compared between these two groups. The mean ages of the two groups were 31.45 ± 4.43 years and 31.98 ± 4.84 years, respectively, with no statistically significant differences (P > 0.05). The difference in the endometrial thickness during transfer was also not statistically significant. The implantation rate in the D5-FET group was 60.13%, significantly higher than that in the D6-FET group (31.58%, P P < 0.05). No statistically significant differences were found in the abortion rate and ectopic pregnancy rate between the two groups. The implantation, biochemical pregnancy, and clinical pregnancy rates of the blastocyst D5 were all superior to those of the blastocyst D6. In clinics, therefore, D5-blastocyst transfer could be prioritized for embryo transfer.展开更多
The clinical outcomes of five groups of infertility patients receiving frozen- thawed, cleavage-stage embryo transfers with exogenous hormone protocols with or without a depot gonadotropin-releasing hormone （GnRH） a...The clinical outcomes of five groups of infertility patients receiving frozen- thawed, cleavage-stage embryo transfers with exogenous hormone protocols with or without a depot gonadotropin-releasing hormone （GnRH） agonist were assessed. A retrospective cohort analysis was performed on 1003 cycles undergoing frozen-thawed, cleavage-stage embryo transfers from January 1, 2012 to June 31, 2015 in the Reproductive Medicine Center of Wuhan General Hospital of Guangzhou Military Region. Based on the infertility etiologies of the patients, the 1003 cycles were divided into five groups： tubal infertility, polycystic ovary syndrome （PCOS）, endometriosis, male infertility, and unexplained infertility. The main outcome was the live birth rate. Two groups were set up based on the intervention： group A was given a GnRH agonist with exogenous estrogen and progesterone, and group B （control group） was given exogenous estrogen and progesterone only. The results showed that the baseline serum hormone levels and basic characteristics of the patients were not significantly different between groups A and B. The live birth rates in groups A and B were 41.67% and 29.29%, respectively （P〈0.05）. The live birth rates in patients with PCOS in groups A and B were 56.25% and 30.61%, respectively （P〈0.05）. The clinical pregnancy, implantation and on-going pregnancy rates showed the same trends as the live birth rates between groups A and B. The ectopic pregnancy rate was significantly lower in group A than in group B. We concluded that the live birth rate was higher and other clinical outcomes were more satisfactory with GnRH agonist co- treatment than without GnRH agonist co-treatment for frozen-thawed embryo transfer. The GnRH agonist combined with exogenous estrogen and progesterone worked for all types of infertility tested, especially for women with PCOS.展开更多
Objectives:To assess the clinical outcomes of frozen-thawed blastocysts transfer in natural and hormonally controlled cycles.Methods:A retrospective analysis of natural and hormonally controlled cycle for 246 frozen-t...Objectives:To assess the clinical outcomes of frozen-thawed blastocysts transfer in natural and hormonally controlled cycles.Methods:A retrospective analysis of natural and hormonally controlled cycle for 246 frozen-thawed blastocyst transfer cycles,the clinical pregnancy rate,implantation rate,early abortion rate were compared.Results:Of the 192 hormonally controlled cycles,the cancel rate,clinical pregnancy rate per ET,implantation rate and abortion rate were 7.3%(14/192),53.9%(96/178),38.8%(131/338)and 11.5%(11/96)respectively,whereas in 54 natural cycles,these rates were 16.7%(9/54),68.9%(31/45),52.9%(45/85)and 16.1%(5/31)respectively.There was no significant difference between the two groups with regard to the clinical pregnancy and abortion rate per ET,but the cancel rate and implantation rate were higher in natural cycles.However,the pregnancy and implantation rates of patients without PCOS in hormonal control cycles(57.2%,40.9%)were similar with those in natural cycles(P>0.05).Conclusion:These findings suggested that both hormonally controlled and natural cycles had similar pregnancy outcomes in frozen-thawed blastocysts transfer.展开更多
Using a new low-temperature dynamic triaxial apparatus, the influence law of freezing-thawing cycles on clay shear strength is studied. In this research, the concept of correction coefficients of freezing-thawing cycl...Using a new low-temperature dynamic triaxial apparatus, the influence law of freezing-thawing cycles on clay shear strength is studied. In this research, the concept of correction coefficients of freezing-thawing cycles on clay static strength, cohesion and internal friction angles is proposed, and the change patterns, correction curves and regressive formulae of clay static strength, cohesion and internal friction angles under freezing-thawing cycles are given. The test results indicate that with increasing numbers of freezing-thawing cycles, the clay static strength and cohesion decrease exponentially but the internal friction angle increases exponentially. The performance of static strength, cohesion and internal friction angles are different with increasing numbers of freezing-thawing cycles, i.e., the static strength decreases constantly until about 30% of the initial static strength prior to the freezing-thawing cycling and then stays basically stable. After 5-7 freezing-thawing cycles, the cohesion decreases gradually to about 70% of the initial cohesion. The internal friction angle increases about 20% after the first freezing-thawing cycle, then increases gradually close to a stable value which is an increase of about 40% of the internal friction angle. The freezing-thawing process can increase the variation of the density of the soil samples; therefore, strict density discreteness standards of frozen soil sample preparation should be established to ensure the reliability of the test results.展开更多
Compacted loess is widely used as fills of road embankments in loess regions of northern China.Generally, densely-compacted loess can satisfy the requirements of embankment strength and postconstruction deformation. H...Compacted loess is widely used as fills of road embankments in loess regions of northern China.Generally, densely-compacted loess can satisfy the requirements of embankment strength and postconstruction deformation. However, uneven subsidence, pavement cracks and other related damages can affect the integrity of loess subgrade after several years of operation,and even cause some hazards, especially in North China, where the strong freeze-thaw erosion occurs. In this study, cyclic freeze-thaw tests for both densely and loosely compacted loess samples were performed to determine the variation in engineering properties such as volume, void ratio, collapsible settlement,microstructure, and the related mechanisms were addressed. The experimental results showed that an obvious water migration and redistribution occurred within the samples during freeze-thaw cycles. Ice lenses and fissures could be identified in the upper frozen layers of the samples. After freeze-thaw cycles,the dry densities of the upper layers of samples changed significantly due to strong freeze-thaw erosion. The dry densities decreased for the dense sample and increased for the loose sample. It can be found that dense samples become loose, while loose samples became dense with the increasing number of freeze-thaw cycles. Their related void ratios changed reversely. Both void ratios tended to fall into a certain range, which verified the concept of a residual void ratio proposed by Viklander. The loosening process of densely compacted samples involves the formation of large pores, volume increase and density reduction as well as the related changes in mechanical properties because freeze-thaw cycles may be important contribution to problems of loess road embankments.Adverse effects of freeze-thaw cycles, therefore,should be taken into account in selecting loess parameters for the stability evaluation of road embankment in seasonally frozen ground regions.展开更多
As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying tem...As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying temperature. A series of dynamic cyclic triaxial experiments were conducted through a cryogenic triaxial apparatus for exploring the influences of F-T cycles on the dynamic mechanical properties of frozen subgrade clay.According to the experimental results of frozen clay at the temperature of-10℃, the dynamic responses and microstructure variation at different times of F-T cycles(0, 1, 5, and 20 cycles) were explored in detail.It is experimentally demonstrated that the dynamic stress-strain curves and dynamic volumetric strain curves of frozen clay are significantly sparse after 20F-T cycles. Meanwhile, the cyclic number at failure(Nf) of the frozen specimen reduces by 89% after 20freeze-thaw cycles at a low ratio of the dynamic stress amplitude. In addition, with the increasing F-T cycles,the axial accumulative strain, residual deformation,and the value of damage variable of frozen clay increase, while the dynamic resilient modulus and dynamic strength decrease. Finally, the influence of the F-T cycles on the failure mechanisms of frozen clay was discussed in terms of the microstructure variation. These studies contribute to a better understanding of the fundamental changes in the dynamic mechanical of frozen soils exposed to F-T cycles in cold and seismic regions.展开更多
In order to determine the changing rule of long-term frozen soil strength and elucidate the connection between long-term strength and soil physical properties,frozen loess was subjected to 4,6,8,10,and 50 freeze-thaw ...In order to determine the changing rule of long-term frozen soil strength and elucidate the connection between long-term strength and soil physical properties,frozen loess was subjected to 4,6,8,10,and 50 freeze-thaw cycles,under closed-state conditions in a constant-temperature box.The frozen samples were tested on a spherical template indenter,and the results show that under the effect of repeated freeze-thaw cycles,the long-term strength of frozen loess decreased; changes in the mechanical property indices were highly unstable during the first 10 cycles; the soil strength and density were the greatest at the eighth cycle while the void ratio was the smallest; and after eight cycles all of the indices had less fluctuation and certain rising or falling tendencies.By converting the number of freeze-thaw cycles into elapsed time in the tests,three different forecasting methods of long-term soil strength could be assessed and the soil equivalent cohesive force after 10 years,20 years,or 30 years could be estimated.展开更多
Soil slope stability in seasonally frozen regions is a challenging problem for geotechnical engineers.The freezethaw process of soil slope caused by the temperature fluctuation increases the difficulty in predicting t...Soil slope stability in seasonally frozen regions is a challenging problem for geotechnical engineers.The freezethaw process of soil slope caused by the temperature fluctuation increases the difficulty in predicting the slope stability because the soil property is influenced by the freeze-thaw cycle.In addition,the frozen soil,which has ice crystal,ice lens and experienced freeze-thaw process,could present stronger heterogeneity.Previous research has not investigated the combined effect of soil heterogeneity and freeze-thaw cycle.This paper studies the influence of soil heterogeneity on the stability of frozen soil slope under freeze-thaw cycles.The local average subdivision(LAS)is utilized to model the soil heterogeneity.A typical slope geometry has been chosen and analysed as an illustrative example and the strength reduction method is used to calculate the factor of safety(FOS)of slope.It has been found that when the temperature is steady,the FOS of the frozen soil slope is influenced by the spatial variability of the thermal conductivity,but the influence is not significant.When the standard deviation and the SOF of the thermal conductivity increase,the mean of the FOS is equal to the FOS of the homogeneous case and the standard deviation of the FOS also increases.After the frozen soil goes through freeze-thaw process,the FOS of the frozen soil slope decreases due to the reduction in the cohesion and the internal friction angle caused by the freeze-thaw cycles.Furthermore,the decreasing ratio of the FOS becomes more scattered after the 5th freeze-thaw cycle compared to that of the FOS after the 1st freeze-thaw cycle.The larger variability of the FOS could induce inaccuracy in the prediction of the frozen soil slope stability.展开更多
Although the dynamic properties of subgrade soils in seasonally frozen areas have already been studied, few researchers have considered the influence of shallow groundwater during the freeze–thaw(F–T) cycles. So a m...Although the dynamic properties of subgrade soils in seasonally frozen areas have already been studied, few researchers have considered the influence of shallow groundwater during the freeze–thaw(F–T) cycles. So a multifunctional F–T cycle system was developed to imitate the groundwater recharge in the subgrade during the freezing process and a large number of dynamic triaxial experiments were conducted after the F–T cycles. Some significant factors including the F–T cycle number, compaction degree, confining pressure, cyclic deviator stress, loading frequency, and water content were investigated for the resilient modulus of soils. The experimental results indicated that the dynamic resilient modulus of the subgrade was negatively correlated with the cyclic deviator stress, F–T cycle number, and initial water content, whereas the degree of compaction, confining pressure, and loading frequency could enhance the resilient modulus. Furthermore, a modified model considering the F–T cycle number and stress state was established to predict the dynamic resilient modulus. The calculated results of this modified model were very close to the experimental results. Consequently, calculation of the resilient modulus for F–T cycles considering the dynamic load was appropriate. This study provides reference for research focusing on F–T cycles with groundwater supply and the dynamic resilient moduli of subgrade soils in seasonally frozen areas.展开更多
At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components o...At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components of PEMFC-membrane-electrode assembly (MEA) and seek feasible measures to avoid degradation. The effect of freeze/thaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freeze/thaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable performance under subzero temperature and gas purging is proved to be the effective operation.展开更多
With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at ...With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity;however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.展开更多
The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out. Based on the damage mechanics theory, the dsmage which reflects the alternation of intern...The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out. Based on the damage mechanics theory, the dsmage which reflects the alternation of internal state of material were introduced into the formula presented by Desayi and Krishman and the weighted twin-shear strength theory. As a nondestructive examination method in common use, the ultrasonic technique was adopted in the study, and the ultrasonic velocity was used to establish the damage variable. After that, the failure criterion and one-dimensional stress-strain relationship for deteriorated concrete were obtained. Eventually, tests were carried out to study the evolution laws on the damage. The results show that the more freezing and thawing cycles are, the more apparently the failure surface shrinks. Meanwhile, the comparison between theoretical data and experimental data verifies tile rationality of tile damage-based one-dimensional stress-strain relationship proposed.展开更多
Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing.Cracking can also occur in expansive clayey soils under freeze–thaw cycles,of which little attention ...Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing.Cracking can also occur in expansive clayey soils under freeze–thaw cycles,of which little attention has been paid on this issue.In this study,laboratory experiment and cracking analysis were performed on an expansive soil.Crack patterns were quantitatively analyzed using the fractal concept.The relationships among crack pattern,water loss,number of freeze–thaw cycles,and fractal dimension were discussed.It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level.Cracks induced by freeze–thaw cycles are shorter,more irregularly oriented,and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one;water loss,closely related to specimen thickness,plays a significant role in the process of soil cracking;crack development under freeze-thaw cycles are not only attributed to capillary effect,but also to expansion and absorption effects.展开更多
Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions.In this study,cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau to ...Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions.In this study,cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau to study the effect of cyclic freeze-thaw on their uniaxial mechanical properties.The soil specimens were remolded with three dry densities and three moisture contents.Then,after performing a series of freeze-thaw tests in a closed system without water supply,the soil specimens were subjected to a uniaxial compression test.The results showed that the stress-strain curves of the tested soils mainly performed as strain-softening.The softening feature intensified with the increasing dry density but weakened with an increase in freeze-thaw cycles and moisture content.The uniaxial compressive strength,resilient modulus,residual strength and softening modulus decreased considerably with the increase of freeze-thaw cycles.After more than nine freeze-thaw cycles,these four parameters tended to be stable.These parameters increased with the increase of dry density and decreased with the increasing moisture content,except for the residual strength which did not exhibit any clear variation with an increase in moisture content.The residual strength,however,generally increased with an increase in dry density.The soil structural damage caused by frozen water expansion during the freeze-thaw is the major cause for the changes in mechanical behaviors of cohesive coarse-grained soils.With results in this study,the deterioration effect of freeze-thaw cycles on the mechanical properties of soils should be considered during the slope stability analysis in high-altitude mountain regions.展开更多
This paper presents various deformation-monitoring technologies employed to monitor the frost heave and thaw settlement of two mounds along the Qinghai–Tibet Engineering Corridor(QTEC), China. The QTEC is known as a ...This paper presents various deformation-monitoring technologies employed to monitor the frost heave and thaw settlement of two mounds along the Qinghai–Tibet Engineering Corridor(QTEC), China. The QTEC is known as a critical infrastructure and passage connecting inland China and the Qinghai–Tibet Plateau(QTP). Three technologies—global navigation satellite system(GNSS), terrestrial laser scanning(TLS), and unmanned aerial vehicle(UAV)—were used to estimate the freeze/thaw–induced 3D surface deformation of two frost mounds. Our results showed that (1) the two frost mounds exhibited mainly thaw settlement in thawing periods and frost heave in the freezing period, but frost heave dominated after repeated freeze–thaw cycles;(2) different zones of the mounds showed different deformation characteristics;(3) active-layer thickness(ALT) and elevation changes were highly correlated during thaw periods;(4) integrated 3D-measurement technologies can achieve a better understanding and assessment of hazards in the permafrost area.展开更多
Highway frost heave and thawing settlement caused by water migration towards the freezing front and ice lens development is widespread in the alpine meadow area of the southeast QinghaiTibet Plateau(QTP).A laboratory ...Highway frost heave and thawing settlement caused by water migration towards the freezing front and ice lens development is widespread in the alpine meadow area of the southeast QinghaiTibet Plateau(QTP).A laboratory experiment on a highway reconstruction and expansion project in the QTP was carried out in this work to analyze the effects of fine particle content,initial water content,and the number of freeze-thaw cycles(FTCs)on frost depth,temperature gradient(Grad T),total water intake,and water intake flux.Based on the results of the laboratory experiment,a modified model of migration potential related to fine particle content,freeze-thaw history,and freezing time was established.The results show that,with the increase of fine particle content,the frost depth of soil decreases,the curve of total water intake over time is transformed from an Sshape to an arch,and the curve of water intake flux over time is transformed from a peak shape to descending shape.The variation trend of migration potential with freezing time and the freeze-thaw history is the same as that of water intake flux with freezing time and freeze-thaw history.The variation trend of soil intake flux can be used as a reference to determine the variation trend of soil migration potential.This study provides a reference for the design and construction of highway subgrade in the alpine meadow area of the QTP.展开更多
The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses ...The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses such as SEM, XRD and TGA measurements were performed on the selected samples after freeze-thaw cycles. The corrosion products of the concrete were distinguished and quantitatively compared by the thermal analysis. Besides, the damage mechanism considering the dynamic modulus of elastically of concrete under the coupling effect was also investigated. The experimental results show that, under the action of freeze-thaw cycles and sulfate attack, the main attack products in concrete are ettringite and gypsum. The corrosion products exposed to MgSO4 solution are more than those to Na2SO4 solution. Furthermore, the content of gypsum in concrete is less than that of ettringite in test, and some of gypsum can be observed only after a certain corrosion extent. It is also shown that MgSO4 solution has a promoting effect to the damage of concrete under freeze-thaw cycles. Whereas for Na：SO4 solution, the damage of concrete has restrained before 300 freeze-thaw cycles, but the sulfate attack accelerates the deterioration process in its further test period.展开更多
Nitrous oxide(N_2 O) is one of the most important greenhouse gases in the atmosphere; freeze–thaw cycles(FTCs) might strongly influence the emission of soil N_2 O on the Qinghai–Tibetan Plateau(QTP). However, there ...Nitrous oxide(N_2 O) is one of the most important greenhouse gases in the atmosphere; freeze–thaw cycles(FTCs) might strongly influence the emission of soil N_2 O on the Qinghai–Tibetan Plateau(QTP). However, there is a lack of in situ research on the characteristics of soil N_2 O concentration and flux in response to variations in soil properties caused by FTCs.Here, we report the effect of FTC-induced changes in soil properties on the soil N_2 O concentration and flux in the permafrost region of the higher reaches of the Shule River Basin on the northeastern margin of the QTP. We measured chemical properties of the topsoil, activities of soil microorganisms, and air temperature(AT), as well as soil N_2 O concentration and flux, over an annual cycle from July 31, 2011, to July 30, 2012. The results showed that soil N_2 O concentration was significantly affected by soil temperature(ST), soil moisture(SM), soil salinity(SS), soil polyphenol oxidase(SPO), soil alkaline phosphatase(SAP), and soil culturable actinomycetes(SCA), ranked as SM>SS>ST>SPO>SAP>SCA, whereas ST significantly increased soil N_2 O flux, compared with SS. Overall, our study indicated that the soil N_2 O concentration and flux in permafrost zone FTCs were strongly affected by soil properties, especially soil moisture, soil salinity, and soil temperature.展开更多
The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed...The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.展开更多
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.
文摘This study aimed to assess pregnancy outcomes after high-quality D5- and D6-blastocyst transfer in frozen cycles of in vitro fertilization and embryo transfer and to further evaluate whether there was a difference in blastocyst development potentials with different developmental speeds and in pregnancy outcomes. A retrospective analysis was conducted to analyze 247 frozen cycles in our center from September 2015 to July 2017, which were divided into two groups: a D5-FET group with 193 cycles of D5-blastocyst transfer, and a D6-FET group with 54 cycles of D6-blastocyst transfer. Hormone replacement method was utilized to prepare frozen-cycle endometria. Pregnancy outcomes were analyzed and compared between these two groups. The mean ages of the two groups were 31.45 ± 4.43 years and 31.98 ± 4.84 years, respectively, with no statistically significant differences (P > 0.05). The difference in the endometrial thickness during transfer was also not statistically significant. The implantation rate in the D5-FET group was 60.13%, significantly higher than that in the D6-FET group (31.58%, P P < 0.05). No statistically significant differences were found in the abortion rate and ectopic pregnancy rate between the two groups. The implantation, biochemical pregnancy, and clinical pregnancy rates of the blastocyst D5 were all superior to those of the blastocyst D6. In clinics, therefore, D5-blastocyst transfer could be prioritized for embryo transfer.
文摘The clinical outcomes of five groups of infertility patients receiving frozen- thawed, cleavage-stage embryo transfers with exogenous hormone protocols with or without a depot gonadotropin-releasing hormone （GnRH） agonist were assessed. A retrospective cohort analysis was performed on 1003 cycles undergoing frozen-thawed, cleavage-stage embryo transfers from January 1, 2012 to June 31, 2015 in the Reproductive Medicine Center of Wuhan General Hospital of Guangzhou Military Region. Based on the infertility etiologies of the patients, the 1003 cycles were divided into five groups： tubal infertility, polycystic ovary syndrome （PCOS）, endometriosis, male infertility, and unexplained infertility. The main outcome was the live birth rate. Two groups were set up based on the intervention： group A was given a GnRH agonist with exogenous estrogen and progesterone, and group B （control group） was given exogenous estrogen and progesterone only. The results showed that the baseline serum hormone levels and basic characteristics of the patients were not significantly different between groups A and B. The live birth rates in groups A and B were 41.67% and 29.29%, respectively （P〈0.05）. The live birth rates in patients with PCOS in groups A and B were 56.25% and 30.61%, respectively （P〈0.05）. The clinical pregnancy, implantation and on-going pregnancy rates showed the same trends as the live birth rates between groups A and B. The ectopic pregnancy rate was significantly lower in group A than in group B. We concluded that the live birth rate was higher and other clinical outcomes were more satisfactory with GnRH agonist co- treatment than without GnRH agonist co-treatment for frozen-thawed embryo transfer. The GnRH agonist combined with exogenous estrogen and progesterone worked for all types of infertility tested, especially for women with PCOS.
文摘Objectives:To assess the clinical outcomes of frozen-thawed blastocysts transfer in natural and hormonally controlled cycles.Methods:A retrospective analysis of natural and hormonally controlled cycle for 246 frozen-thawed blastocyst transfer cycles,the clinical pregnancy rate,implantation rate,early abortion rate were compared.Results:Of the 192 hormonally controlled cycles,the cancel rate,clinical pregnancy rate per ET,implantation rate and abortion rate were 7.3%(14/192),53.9%(96/178),38.8%(131/338)and 11.5%(11/96)respectively,whereas in 54 natural cycles,these rates were 16.7%(9/54),68.9%(31/45),52.9%(45/85)and 16.1%(5/31)respectively.There was no significant difference between the two groups with regard to the clinical pregnancy and abortion rate per ET,but the cancel rate and implantation rate were higher in natural cycles.However,the pregnancy and implantation rates of patients without PCOS in hormonal control cycles(57.2%,40.9%)were similar with those in natural cycles(P>0.05).Conclusion:These findings suggested that both hormonally controlled and natural cycles had similar pregnancy outcomes in frozen-thawed blastocysts transfer.
基金Scientific Research Fund of Institute of Engineering Mechanics,China Earthquake Administration under Grant No.2018D12National Natural Science Foundation of Heilongjiang Province under Grant No.E 2016045+1 种基金National Natural Science Foundation of China under Grant No.5137816451508140
文摘Using a new low-temperature dynamic triaxial apparatus, the influence law of freezing-thawing cycles on clay shear strength is studied. In this research, the concept of correction coefficients of freezing-thawing cycles on clay static strength, cohesion and internal friction angles is proposed, and the change patterns, correction curves and regressive formulae of clay static strength, cohesion and internal friction angles under freezing-thawing cycles are given. The test results indicate that with increasing numbers of freezing-thawing cycles, the clay static strength and cohesion decrease exponentially but the internal friction angle increases exponentially. The performance of static strength, cohesion and internal friction angles are different with increasing numbers of freezing-thawing cycles, i.e., the static strength decreases constantly until about 30% of the initial static strength prior to the freezing-thawing cycling and then stays basically stable. After 5-7 freezing-thawing cycles, the cohesion decreases gradually to about 70% of the initial cohesion. The internal friction angle increases about 20% after the first freezing-thawing cycle, then increases gradually close to a stable value which is an increase of about 40% of the internal friction angle. The freezing-thawing process can increase the variation of the density of the soil samples; therefore, strict density discreteness standards of frozen soil sample preparation should be established to ensure the reliability of the test results.
基金supported by the National Key Basic Research Program of China(973 Program)(Grant No.2012CB026106)National Natural Science Foundation of China(No.41672310)+3 种基金the Science and Technology Major Project of Gansu Province(Grant No.143GKDA007)National key research and development program(2016YFC0802103)the West Light Foundation of CAS for Dr.G.Y.Li,Project of the State Key Laboratory of Frozen Soils Engineering of CAS(Grant No.SKLFSE-ZY-16)the STS research project of the Cold and Arid Regions Environmental and Engineering Research Institute(HHS-TSS-STS-1502)
文摘Compacted loess is widely used as fills of road embankments in loess regions of northern China.Generally, densely-compacted loess can satisfy the requirements of embankment strength and postconstruction deformation. However, uneven subsidence, pavement cracks and other related damages can affect the integrity of loess subgrade after several years of operation,and even cause some hazards, especially in North China, where the strong freeze-thaw erosion occurs. In this study, cyclic freeze-thaw tests for both densely and loosely compacted loess samples were performed to determine the variation in engineering properties such as volume, void ratio, collapsible settlement,microstructure, and the related mechanisms were addressed. The experimental results showed that an obvious water migration and redistribution occurred within the samples during freeze-thaw cycles. Ice lenses and fissures could be identified in the upper frozen layers of the samples. After freeze-thaw cycles,the dry densities of the upper layers of samples changed significantly due to strong freeze-thaw erosion. The dry densities decreased for the dense sample and increased for the loose sample. It can be found that dense samples become loose, while loose samples became dense with the increasing number of freeze-thaw cycles. Their related void ratios changed reversely. Both void ratios tended to fall into a certain range, which verified the concept of a residual void ratio proposed by Viklander. The loosening process of densely compacted samples involves the formation of large pores, volume increase and density reduction as well as the related changes in mechanical properties because freeze-thaw cycles may be important contribution to problems of loess road embankments.Adverse effects of freeze-thaw cycles, therefore,should be taken into account in selecting loess parameters for the stability evaluation of road embankment in seasonally frozen ground regions.
基金the National Natural Science Foundation of China (NSFC)(Grant Nos.U22A20596 and 41771066)the Science and Technology Project of Qinghai-Tibet Railway Company (QZ2021-G03)。
文摘As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying temperature. A series of dynamic cyclic triaxial experiments were conducted through a cryogenic triaxial apparatus for exploring the influences of F-T cycles on the dynamic mechanical properties of frozen subgrade clay.According to the experimental results of frozen clay at the temperature of-10℃, the dynamic responses and microstructure variation at different times of F-T cycles(0, 1, 5, and 20 cycles) were explored in detail.It is experimentally demonstrated that the dynamic stress-strain curves and dynamic volumetric strain curves of frozen clay are significantly sparse after 20F-T cycles. Meanwhile, the cyclic number at failure(Nf) of the frozen specimen reduces by 89% after 20freeze-thaw cycles at a low ratio of the dynamic stress amplitude. In addition, with the increasing F-T cycles,the axial accumulative strain, residual deformation,and the value of damage variable of frozen clay increase, while the dynamic resilient modulus and dynamic strength decrease. Finally, the influence of the F-T cycles on the failure mechanisms of frozen clay was discussed in terms of the microstructure variation. These studies contribute to a better understanding of the fundamental changes in the dynamic mechanical of frozen soils exposed to F-T cycles in cold and seismic regions.
基金This project is supported in part by the Natural Science Foundation of China (Nos.41301070,41301071)the West Light Program for Talent Cultivation of the Chinese Academy of Sciences (2013-03)the project sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars of State Education Ministry,granted to Dr.Ze Zhang
文摘In order to determine the changing rule of long-term frozen soil strength and elucidate the connection between long-term strength and soil physical properties,frozen loess was subjected to 4,6,8,10,and 50 freeze-thaw cycles,under closed-state conditions in a constant-temperature box.The frozen samples were tested on a spherical template indenter,and the results show that under the effect of repeated freeze-thaw cycles,the long-term strength of frozen loess decreased; changes in the mechanical property indices were highly unstable during the first 10 cycles; the soil strength and density were the greatest at the eighth cycle while the void ratio was the smallest; and after eight cycles all of the indices had less fluctuation and certain rising or falling tendencies.By converting the number of freeze-thaw cycles into elapsed time in the tests,three different forecasting methods of long-term soil strength could be assessed and the soil equivalent cohesive force after 10 years,20 years,or 30 years could be estimated.
基金The research is supported by the Natural Science Foundation of Anhui Province(Grant No.1908085QE242)the Fundamental Research Funds for the Central Universities(Grant No.JZ2021HGTB0097)the Natural Science Foundation of China(NSFC)(Grant No.51908175).The financial support is gratefully acknowledged.
文摘Soil slope stability in seasonally frozen regions is a challenging problem for geotechnical engineers.The freezethaw process of soil slope caused by the temperature fluctuation increases the difficulty in predicting the slope stability because the soil property is influenced by the freeze-thaw cycle.In addition,the frozen soil,which has ice crystal,ice lens and experienced freeze-thaw process,could present stronger heterogeneity.Previous research has not investigated the combined effect of soil heterogeneity and freeze-thaw cycle.This paper studies the influence of soil heterogeneity on the stability of frozen soil slope under freeze-thaw cycles.The local average subdivision(LAS)is utilized to model the soil heterogeneity.A typical slope geometry has been chosen and analysed as an illustrative example and the strength reduction method is used to calculate the factor of safety(FOS)of slope.It has been found that when the temperature is steady,the FOS of the frozen soil slope is influenced by the spatial variability of the thermal conductivity,but the influence is not significant.When the standard deviation and the SOF of the thermal conductivity increase,the mean of the FOS is equal to the FOS of the homogeneous case and the standard deviation of the FOS also increases.After the frozen soil goes through freeze-thaw process,the FOS of the frozen soil slope decreases due to the reduction in the cohesion and the internal friction angle caused by the freeze-thaw cycles.Furthermore,the decreasing ratio of the FOS becomes more scattered after the 5th freeze-thaw cycle compared to that of the FOS after the 1st freeze-thaw cycle.The larger variability of the FOS could induce inaccuracy in the prediction of the frozen soil slope stability.
基金Projects(41672312, 41972294) supported by the National Natural Science Foundation of ChinaProject(2017CFA056) supported by the Outstanding Youth Foundation of Hubei Province, ChinaProject(KFJ170104) supported by the Changsha University of Science & Technology via Open Fund of National Engineering Laboratory of Highway Maintenance Technology, China。
文摘Although the dynamic properties of subgrade soils in seasonally frozen areas have already been studied, few researchers have considered the influence of shallow groundwater during the freeze–thaw(F–T) cycles. So a multifunctional F–T cycle system was developed to imitate the groundwater recharge in the subgrade during the freezing process and a large number of dynamic triaxial experiments were conducted after the F–T cycles. Some significant factors including the F–T cycle number, compaction degree, confining pressure, cyclic deviator stress, loading frequency, and water content were investigated for the resilient modulus of soils. The experimental results indicated that the dynamic resilient modulus of the subgrade was negatively correlated with the cyclic deviator stress, F–T cycle number, and initial water content, whereas the degree of compaction, confining pressure, and loading frequency could enhance the resilient modulus. Furthermore, a modified model considering the F–T cycle number and stress state was established to predict the dynamic resilient modulus. The calculated results of this modified model were very close to the experimental results. Consequently, calculation of the resilient modulus for F–T cycles considering the dynamic load was appropriate. This study provides reference for research focusing on F–T cycles with groundwater supply and the dynamic resilient moduli of subgrade soils in seasonally frozen areas.
基金Supported by the National Natural Science Foundation of China (No.20206030) and Ministry of Science and Technology 863 Hi-Technology Research and Development Program of China (2005AA501660).
文摘At subzero temperature, the startup capability and performance of polymer electrolyte membrane fuel cell (PEMFC) deteriorates markedly. The object of this work is to study the degradation mechanism of key components of PEMFC-membrane-electrode assembly (MEA) and seek feasible measures to avoid degradation. The effect of freeze/thaw cycles on the structure of MEA is investigated based on porosity and SEM measurement. The performance of a single cell was also tested before and after repetitious freeze/thaw cycles. The experimental results indicated that the performance of a PEMFC decreased along with the total operating time as well as the pore size distribution shifting and micro configuration changing. However, when the redundant water had been removed by gas purging, the performance of the PEMFC stack was almost resumed when it experienced again the same subzero temperature test. These results show that it is necessary to remove the water in PEMFCs to maintain stable performance under subzero temperature and gas purging is proved to be the effective operation.
基金supported by projects from the National Natural Science Foundation of China (41807298, 41702372, 41672211)the China Postdoctoral Science Foundation (2019M650788)+2 种基金National Key Research and Development Project of China (2016YFC0600310)the China Geological Survey (DD20160022, DD20190059)the Basic Research Funds (JYYWF201810) of the Institute of Geology, CAGS.
文摘With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity;however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.
文摘The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out. Based on the damage mechanics theory, the dsmage which reflects the alternation of internal state of material were introduced into the formula presented by Desayi and Krishman and the weighted twin-shear strength theory. As a nondestructive examination method in common use, the ultrasonic technique was adopted in the study, and the ultrasonic velocity was used to establish the damage variable. After that, the failure criterion and one-dimensional stress-strain relationship for deteriorated concrete were obtained. Eventually, tests were carried out to study the evolution laws on the damage. The results show that the more freezing and thawing cycles are, the more apparently the failure surface shrinks. Meanwhile, the comparison between theoretical data and experimental data verifies tile rationality of tile damage-based one-dimensional stress-strain relationship proposed.
基金supported by"the Fundamental Research Funds for the Central Universities"(Grant No.2015B25014)"the Practical Innovation Program for Postgraduate Students of Jiangsu Province,China"(Grant No.SJZZ15_0058)+1 种基金funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)(Grant No.3014–SYS1401)the organizing committee of"XI International Symposium on Permafrost Engineering(Magadan,Russia,Sept.5-8,2017)"for giving the opportunity to exchange this study
文摘Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing.Cracking can also occur in expansive clayey soils under freeze–thaw cycles,of which little attention has been paid on this issue.In this study,laboratory experiment and cracking analysis were performed on an expansive soil.Crack patterns were quantitatively analyzed using the fractal concept.The relationships among crack pattern,water loss,number of freeze–thaw cycles,and fractal dimension were discussed.It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level.Cracks induced by freeze–thaw cycles are shorter,more irregularly oriented,and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one;water loss,closely related to specimen thickness,plays a significant role in the process of soil cracking;crack development under freeze-thaw cycles are not only attributed to capillary effect,but also to expansion and absorption effects.
基金supported by the National Key R&D Program of China(Grant No.2018YFC1505001)the Key Scientific Research Project of China Gold Group(Grant No.2016ZGHJ/XZHTL-YQSC-26)+1 种基金the funding from the Department of Transportation of Gansu Province(Grant No.2017-008)the Fundamental Research Funds for the Central Universities,CHD(Grant No.300102268716)
文摘Freeze-thaw cycles are closely related to the slope instability in high-altitude mountain regions.In this study,cohesive coarse-grained soils were collected from a high-altitude slope in the Qinghai–Tibet Plateau to study the effect of cyclic freeze-thaw on their uniaxial mechanical properties.The soil specimens were remolded with three dry densities and three moisture contents.Then,after performing a series of freeze-thaw tests in a closed system without water supply,the soil specimens were subjected to a uniaxial compression test.The results showed that the stress-strain curves of the tested soils mainly performed as strain-softening.The softening feature intensified with the increasing dry density but weakened with an increase in freeze-thaw cycles and moisture content.The uniaxial compressive strength,resilient modulus,residual strength and softening modulus decreased considerably with the increase of freeze-thaw cycles.After more than nine freeze-thaw cycles,these four parameters tended to be stable.These parameters increased with the increase of dry density and decreased with the increasing moisture content,except for the residual strength which did not exhibit any clear variation with an increase in moisture content.The residual strength,however,generally increased with an increase in dry density.The soil structural damage caused by frozen water expansion during the freeze-thaw is the major cause for the changes in mechanical behaviors of cohesive coarse-grained soils.With results in this study,the deterioration effect of freeze-thaw cycles on the mechanical properties of soils should be considered during the slope stability analysis in high-altitude mountain regions.
基金supported by the National Natural Science Foundation of China (41301508, 41630636)
文摘This paper presents various deformation-monitoring technologies employed to monitor the frost heave and thaw settlement of two mounds along the Qinghai–Tibet Engineering Corridor(QTEC), China. The QTEC is known as a critical infrastructure and passage connecting inland China and the Qinghai–Tibet Plateau(QTP). Three technologies—global navigation satellite system(GNSS), terrestrial laser scanning(TLS), and unmanned aerial vehicle(UAV)—were used to estimate the freeze/thaw–induced 3D surface deformation of two frost mounds. Our results showed that (1) the two frost mounds exhibited mainly thaw settlement in thawing periods and frost heave in the freezing period, but frost heave dominated after repeated freeze–thaw cycles;(2) different zones of the mounds showed different deformation characteristics;(3) active-layer thickness(ALT) and elevation changes were highly correlated during thaw periods;(4) integrated 3D-measurement technologies can achieve a better understanding and assessment of hazards in the permafrost area.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.310821173701)Natural Science Basic Research Program of Shaanxi(Grant No.2020JQ-379)。
文摘Highway frost heave and thawing settlement caused by water migration towards the freezing front and ice lens development is widespread in the alpine meadow area of the southeast QinghaiTibet Plateau(QTP).A laboratory experiment on a highway reconstruction and expansion project in the QTP was carried out in this work to analyze the effects of fine particle content,initial water content,and the number of freeze-thaw cycles(FTCs)on frost depth,temperature gradient(Grad T),total water intake,and water intake flux.Based on the results of the laboratory experiment,a modified model of migration potential related to fine particle content,freeze-thaw history,and freezing time was established.The results show that,with the increase of fine particle content,the frost depth of soil decreases,the curve of total water intake over time is transformed from an Sshape to an arch,and the curve of water intake flux over time is transformed from a peak shape to descending shape.The variation trend of migration potential with freezing time and the freeze-thaw history is the same as that of water intake flux with freezing time and freeze-thaw history.The variation trend of soil intake flux can be used as a reference to determine the variation trend of soil migration potential.This study provides a reference for the design and construction of highway subgrade in the alpine meadow area of the QTP.
基金Funded by the Durability and Life Forecast of Shotcrete Tunnel Structure Fund(No.51278403)the Program for Changjiang Scholars and Innovative Research Team in University
文摘The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses such as SEM, XRD and TGA measurements were performed on the selected samples after freeze-thaw cycles. The corrosion products of the concrete were distinguished and quantitatively compared by the thermal analysis. Besides, the damage mechanism considering the dynamic modulus of elastically of concrete under the coupling effect was also investigated. The experimental results show that, under the action of freeze-thaw cycles and sulfate attack, the main attack products in concrete are ettringite and gypsum. The corrosion products exposed to MgSO4 solution are more than those to Na2SO4 solution. Furthermore, the content of gypsum in concrete is less than that of ettringite in test, and some of gypsum can be observed only after a certain corrosion extent. It is also shown that MgSO4 solution has a promoting effect to the damage of concrete under freeze-thaw cycles. Whereas for Na：SO4 solution, the damage of concrete has restrained before 300 freeze-thaw cycles, but the sulfate attack accelerates the deterioration process in its further test period.
基金supported by the National Science Foundation of China(41690142)the Key Project of Chinese Academy of Sciences(KJZD-EW-G03-04)+1 种基金the National Natural Science Foundation of China(41171054)the National Science&Technology Pillar Program(2014BAC05B02)
文摘Nitrous oxide(N_2 O) is one of the most important greenhouse gases in the atmosphere; freeze–thaw cycles(FTCs) might strongly influence the emission of soil N_2 O on the Qinghai–Tibetan Plateau(QTP). However, there is a lack of in situ research on the characteristics of soil N_2 O concentration and flux in response to variations in soil properties caused by FTCs.Here, we report the effect of FTC-induced changes in soil properties on the soil N_2 O concentration and flux in the permafrost region of the higher reaches of the Shule River Basin on the northeastern margin of the QTP. We measured chemical properties of the topsoil, activities of soil microorganisms, and air temperature(AT), as well as soil N_2 O concentration and flux, over an annual cycle from July 31, 2011, to July 30, 2012. The results showed that soil N_2 O concentration was significantly affected by soil temperature(ST), soil moisture(SM), soil salinity(SS), soil polyphenol oxidase(SPO), soil alkaline phosphatase(SAP), and soil culturable actinomycetes(SCA), ranked as SM>SS>ST>SPO>SAP>SCA, whereas ST significantly increased soil N_2 O flux, compared with SS. Overall, our study indicated that the soil N_2 O concentration and flux in permafrost zone FTCs were strongly affected by soil properties, especially soil moisture, soil salinity, and soil temperature.
基金the National Natural Science Foundation of China(No.50479059)
文摘The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.
