The unfrozenwater content(UWC)is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions.In this study,three diffe...The unfrozenwater content(UWC)is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions.In this study,three different methods were employed to test and estimate the UWC of saturated sandstones,including nuclear magnetic resonance(NMR),mercury intrusion porosimetry(MIP),and ultrasonic methods.The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay(FID).The MIP method was used to analyze the pore structures of sandstones,with the UWC subsequently calculated based on pore ice crystallization.Therefore,the MIP test constituted an indirect measurement method.Furthermore,a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory,which could be employed to estimate the UWC as an empirical method.All methods demonstrated that the UWC initially exhibited a rapid decrease from 0C to5C and then generally became constant beyond20C.However,these test methods had different characteristics.The NMR method was used to directly and accurately calculate the UWC in the laboratory.However,the cost and complexity of NMR equipment have precluded its use in the field.The UWC can be effectively estimated by the MIP test,but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution.The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory.This method may be more suitable in the field.All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process.The average hysteresis coefficient was approximately 0.538,thus validating the GibbseThomson equation.This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.展开更多
The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties.This study presented a model for calculating the unfrozen water content of rock durin...The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties.This study presented a model for calculating the unfrozen water content of rock during freezing and thawing process,considering the influence of unfrozen water film and rock pore structure,which can reflect the hysteresis and super-cooling effects.The pore size distribution cu rves of red sandsto ne and its unfrozen water conte nt under different temperatures during the freezing and thawing process were measured using nuclear magnetic resonance(NMR) to validate the proposed model.Comparison between the experimental and calculated results indicated that the theoretical model accu rately reflected the water content change law of red sandstone during the freezing and thawing process.Furthermore,the influences of Hamaker constant and surface relaxation parameter on the model results were examined.The results showed that the appropriate magnitude order of Hamaker constant for the red sandstone was 10J to 10J;and when the relaxation parameter of the rock surface was within 25-30 μm/ms,the calculated unfrozen water content using the proposed model was consistent with the experimental value.展开更多
Determining the mechanical properties of frozen rock is highly important in cold-area engineering.These properties are essentially correlated with the content of liquid water remaining in frozen rock.Therefore,accurat...Determining the mechanical properties of frozen rock is highly important in cold-area engineering.These properties are essentially correlated with the content of liquid water remaining in frozen rock.Therefore,accurate determination of unfrozen water content could allow rapid evaluation of mechanical properties of frozen rock.This paper investigates the hysteresis characteristics of ultrasonic waves applied to sandstone(in terms of the parameters of P-wave velocity,amplitude,dominant frequency and quality factor Q)and their relationships with unfrozen water content during the freeze-thaw process.Their correlations are analysed in terms of their potential for use as indicators of freezing state and unfrozen water content.The results show that:(1)During a freeze-thaw cycle,the ultrasonic parameters and unfrozen water content of sandstone have significant hysteresis with changes in temperature.(2)There are three clear stages of change during freezing:supercooled stage(0℃to-2℃),rapid freezing stage(-2℃to-3℃),and stable freezing stage(-3℃to-20℃).The changes in unfrozen water content and ultrasonic parameters with freezing temperature are inverse.(3)During a single freeze-thaw cycle,the ultrasonic parameters of sandstone are significantly correlated with its unfrozen water content,and this correlation is affected by the pore structure.For sandstones with mesopores greater than 50%,there are inflection points in the curves of ultrasonic parameters vs.unfrozen water content at-3℃during freezing and at-1℃during thawing.It was found that thermal deformation of the mineral-grain skeleton and variations in the phase composition of pore water change the propagation path of ultrasonic waves.The inflection point in the curve of dominant frequency vs.temperature clearly marks the end of the rapid freezing stage of pore water,in which more than 70%of the pore water freezes.Consequently,the dominant frequency can be used as an index to conveniently estimate the unfrozen water content of frozen rock and,hence,its mechanical properties.展开更多
The unfrozen water content(UWC)of rocks at low temperature is an important index for evaluating the stability of the rock engineering in cold regions and artificial freezing engineering.This study addresses a new meth...The unfrozen water content(UWC)of rocks at low temperature is an important index for evaluating the stability of the rock engineering in cold regions and artificial freezing engineering.This study addresses a new method to estimate the UWC of saturated sandstones at low temperature by using the ultrasonic velocity.Ultrasonic velocity variations can be divided into the normal temperature stage(20 to 0℃),quick phase transition stage(0 to-5℃)and slow phase transition stage(-5 to-25℃).Most increment of ultrasonic velocity is completed in the quick phase transition stage and then turns to be almost a constant in the slow phase transition stage.In addition,the UWC is also measured by using nuclear magnetic resonance(NMR)technology.It is validated that the ultrasonic velocity and UWC have a similar change law against freezing and thawing temperatures.The WE(weighted equation)model is appropriate to estimate the UWC of saturated sandstones,in which the parameters have been accurately determined rather than by data fitting.In addition,a linear relationship between UWC and ultrasonic velocity is built based on pore ice crystallization theory.It is evidenced that this linear function can be adopted to estimate the UWC at any freezing temperature by using P-wave velocity,which is simple,practical,and accurate enough compared with the WE model.展开更多
We herein studied a non-cryogenic cell preservation and transportation method. We found that astrocytes can be preserved in an unfrozen state at 4℃ (without medium exchange), while maintaining good condition in compa...We herein studied a non-cryogenic cell preservation and transportation method. We found that astrocytes can be preserved in an unfrozen state at 4℃ (without medium exchange), while maintaining good condition in comparison with cryopreservation for the periods of 5 - 7 days. The gelatin solidification method can also prevent decreases in survival rate by preventing damage to astrocytes during transportation. Therefore, the gelatin solidification method at 4℃ may be a useful choice for short-term preservation and transportation.展开更多
冻融过程岩石孔隙内未冻水含量变化是影响其力学特性的关键因素之一。以砂岩为研究对象,采用低场核磁共振系统(nuclear magnetic resonance,NMR)对岩石冻融过程(20、0、-2、-4、-6、-10、-15、-10、-6、-4、-2、0、20℃)孔隙水含量进行...冻融过程岩石孔隙内未冻水含量变化是影响其力学特性的关键因素之一。以砂岩为研究对象,采用低场核磁共振系统(nuclear magnetic resonance,NMR)对岩石冻融过程(20、0、-2、-4、-6、-10、-15、-10、-6、-4、-2、0、20℃)孔隙水含量进行监测,分析未冻水含量随温度的演化规律,并探讨岩石冻融过程未冻水含量演化对其力学特性的影响。研究结果表明:(1)冻融过程岩石中孔隙水受温度影响显著,共经过5个阶段,即过冷段、快速冻结阶段、缓慢冻结阶段、缓慢融化阶段和融化加速阶段。(2)岩石在解冻过程中有明显的滞后现象。在相同温度下,岩样冻结过程未冻水含量明显高于解冻过程。与之对应,解冻过程的峰值强度和弹性模量相对于冻结阶段显著提高。(3)冻融过程的单轴抗压强度以及岩石弹性模量与未冻水含量的关系可由指数函数表示。冻结初期,岩石力学参数的变化主要受孔隙冰含量的增长及孔隙冰对岩石颗粒的胶结作用影响,随温度进一步降低,吸附水膜厚度下降,吸附能力增强,使孔隙冰与对岩石颗粒之间的整体性增强,岩石力学参数进一步发生改变。展开更多
Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors ...Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during fracturing.The melting of pore ice is measured using nuclear magnetic resonance(NMR)method.The results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack coalescence.However,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical temperature.Next,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture parameters.From-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.展开更多
The formation and growth of segregation ice dominate the frost heave during soil freezing,which is closely related to water migration.To analyze segregation ice during soil freezing for different soils,a freezing-thaw...The formation and growth of segregation ice dominate the frost heave during soil freezing,which is closely related to water migration.To analyze segregation ice during soil freezing for different soils,a freezing-thawing experiment was conducted with Lanzhou loess(LZL)and Qinghai-Tibet Plateau silty clay(QSC)using a novel layered nuclear magnetic resonance approach.During LZL freezing,the unfrozen water content first increased and then decreased with decreasing temperature near the freezing front,but decreased with decreasing temperature in other layers,whereas during the freezing of QSC,the unfrozen water content in different layers(including the freezing front)decreased with decreased temperature.Notably,the increased liquid water near the freezing front during LZL freezing was primarily adsorbed water.In addition to the temperature gradient,the squeezing action during soil freezing was another important factor affecting water migration,especially at the early stage of soil freezing.However,which of the two factors,squeezing action and temperature gradient,was the dominant one causing water migration depended on soil structure.At the early stage of soil freezing,the squeezing action had a significant effect on the water migration of LZL,but no significant effect on that of QSC.Furthermore,water accumulation of LZL near the freezing front due to squeezing action at the early stage of freezing limited the formation and growth of segregation ice.This study provided an improved understanding for ice segregation and water migration during soil freezing.展开更多
As an essential property of frozen soils,change of unfrozen water content(UWC)with temperature,namely soil-freezing characteristic curve(SFCC),plays significant roles in numerous physical,hydraulic and mechanical proc...As an essential property of frozen soils,change of unfrozen water content(UWC)with temperature,namely soil-freezing characteristic curve(SFCC),plays significant roles in numerous physical,hydraulic and mechanical processes in cold regions,including the heat and water transfer within soils and at the land–atmosphere interface,frost heave and thaw settlement,as well as the simulation of coupled thermo-hydro-mechanical interactions.Although various models have been proposed to estimate SFCC,their applicability remains limited due to their derivation from specific soil types,soil treatments,and test devices.Accordingly,this study proposes a novel data-driven model to predict the SFCC using an extreme Gradient Boosting(XGBoost)model.A systematic database for SFCC of frozen soils compiled from extensive experimental investigations via various testing methods was utilized to train the XGBoost model.The predicted soil freezing characteristic curves(SFCC,UWC as a function of temperature)from the well-trained XGBoost model were compared with original experimental data and three conventional models.The results demonstrate the superior performance of the proposed XGBoost model over the traditional models in predicting SFCC.This study provides valuable insights for future investigations regarding the SFCC of frozen soils.展开更多
Oil leakages cause environmental pollution,economic losses,and even engineering safety accidents.In cold regions,researchers urgently investigate the movement of oil spill in soils exposed to freeze-thaw cycles.In thi...Oil leakages cause environmental pollution,economic losses,and even engineering safety accidents.In cold regions,researchers urgently investigate the movement of oil spill in soils exposed to freeze-thaw cycles.In this study,a series of laboratory model experiments were carried out on the migration of oil leakage under freeze-thaw action,and the distributions of the soil temperature,unfrozen water content,and displacement were analyzed.The results showed that under freeze-thaw action,liquid water in soils migrated to the freezing front and accumulated.After the pipe cracked,oil pollutants first gathered at one side of the leak hole,and then moved around.The pipe wall temperature affected the soil temperature field,and the thermal influence range below and transverse the pipe wall(35–40 cm)was larger than that above the pipe wall(8 cm)owing to the soil surface temperature.The leaked oil's temperature would make the temperature of the surrounding soil rise.Oil would inhibit the cooling of the soils.Besides,oil migration was significantly affected by the gravity and water flow patterns.The freeze-thaw action would affect the migration of the oil,which was mainly manifested as inhibiting the diffusion and movement of oil when soils were frozen.Unfrozen water transport caused by freeze-thaw cycles would also inhibit oil migration.The research results would provide a scientific reference for understanding the relationship between the movement of oil pollutants,water,and soil temperature,and for establishing a waterheat-mass transport model in frozen soils.展开更多
为探究冻融循环条件下粉煤灰对膨胀土未冻水含量的影响,利用低场核磁共振(nuclear magnetic resonance,NMR)技术对不同粉煤灰掺量(3%、6%、9%、12%和15%)的改性膨胀土进行T2谱测定,分析不同温度下改性膨胀土的孔隙结构变化特征,并得出...为探究冻融循环条件下粉煤灰对膨胀土未冻水含量的影响,利用低场核磁共振(nuclear magnetic resonance,NMR)技术对不同粉煤灰掺量(3%、6%、9%、12%和15%)的改性膨胀土进行T2谱测定,分析不同温度下改性膨胀土的孔隙结构变化特征,并得出不同粉煤灰掺量的改性膨胀土未冻水含量的变化规律。试验结果表明:改性膨胀土相较于原状土,微、小孔隙的孔径分布在掺灰比为9%的试样出现降低,其余掺灰比的试样出现增长,掺灰比为6%的试样最显著;中孔隙增幅最显著的是掺灰比为12%的试样,大孔隙增幅最显著的是掺灰比为3%的试样;在冻结过程中,掺灰比为9%的试样未冻水含量在下降阶段变化最快,在融化阶段变化速率最慢;掺入粉煤灰降低了土壤的相变温度,且抑制土体冻结过程中的未冻水含量。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42377191)Hubei Provincial Natural Science Foundation of China(Grant No.2021CFA094)“The 14th Five Year Plan”Hubei Provincial advantaged characteristic disciplines(groups)project of Wuhan University of Science and Technology(Grant No.2023A0303)。
文摘The unfrozenwater content(UWC)is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions.In this study,three different methods were employed to test and estimate the UWC of saturated sandstones,including nuclear magnetic resonance(NMR),mercury intrusion porosimetry(MIP),and ultrasonic methods.The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay(FID).The MIP method was used to analyze the pore structures of sandstones,with the UWC subsequently calculated based on pore ice crystallization.Therefore,the MIP test constituted an indirect measurement method.Furthermore,a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory,which could be employed to estimate the UWC as an empirical method.All methods demonstrated that the UWC initially exhibited a rapid decrease from 0C to5C and then generally became constant beyond20C.However,these test methods had different characteristics.The NMR method was used to directly and accurately calculate the UWC in the laboratory.However,the cost and complexity of NMR equipment have precluded its use in the field.The UWC can be effectively estimated by the MIP test,but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution.The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory.This method may be more suitable in the field.All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process.The average hysteresis coefficient was approximately 0.538,thus validating the GibbseThomson equation.This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.
基金the support of the Second Tibetan Plateau Scientific Expedition and Research Program (STEP)of China (Grant No.2019QZKK0904)the National Outstanding Youth Science Fund Project of National Natural Science Foundation of China (Grant No.51922104)+1 种基金Youth Innovation Promotion Association CASOpen Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences (Grant No.Z018014)。
文摘The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties.This study presented a model for calculating the unfrozen water content of rock during freezing and thawing process,considering the influence of unfrozen water film and rock pore structure,which can reflect the hysteresis and super-cooling effects.The pore size distribution cu rves of red sandsto ne and its unfrozen water conte nt under different temperatures during the freezing and thawing process were measured using nuclear magnetic resonance(NMR) to validate the proposed model.Comparison between the experimental and calculated results indicated that the theoretical model accu rately reflected the water content change law of red sandstone during the freezing and thawing process.Furthermore,the influences of Hamaker constant and surface relaxation parameter on the model results were examined.The results showed that the appropriate magnitude order of Hamaker constant for the red sandstone was 10J to 10J;and when the relaxation parameter of the rock surface was within 25-30 μm/ms,the calculated unfrozen water content using the proposed model was consistent with the experimental value.
基金the National Natural Science Foundation of China(Grant No.41702334).
文摘Determining the mechanical properties of frozen rock is highly important in cold-area engineering.These properties are essentially correlated with the content of liquid water remaining in frozen rock.Therefore,accurate determination of unfrozen water content could allow rapid evaluation of mechanical properties of frozen rock.This paper investigates the hysteresis characteristics of ultrasonic waves applied to sandstone(in terms of the parameters of P-wave velocity,amplitude,dominant frequency and quality factor Q)and their relationships with unfrozen water content during the freeze-thaw process.Their correlations are analysed in terms of their potential for use as indicators of freezing state and unfrozen water content.The results show that:(1)During a freeze-thaw cycle,the ultrasonic parameters and unfrozen water content of sandstone have significant hysteresis with changes in temperature.(2)There are three clear stages of change during freezing:supercooled stage(0℃to-2℃),rapid freezing stage(-2℃to-3℃),and stable freezing stage(-3℃to-20℃).The changes in unfrozen water content and ultrasonic parameters with freezing temperature are inverse.(3)During a single freeze-thaw cycle,the ultrasonic parameters of sandstone are significantly correlated with its unfrozen water content,and this correlation is affected by the pore structure.For sandstones with mesopores greater than 50%,there are inflection points in the curves of ultrasonic parameters vs.unfrozen water content at-3℃during freezing and at-1℃during thawing.It was found that thermal deformation of the mineral-grain skeleton and variations in the phase composition of pore water change the propagation path of ultrasonic waves.The inflection point in the curve of dominant frequency vs.temperature clearly marks the end of the rapid freezing stage of pore water,in which more than 70%of the pore water freezes.Consequently,the dominant frequency can be used as an index to conveniently estimate the unfrozen water content of frozen rock and,hence,its mechanical properties.
基金National Natural Science Foundation of China(Nos.42072300 and 41702291)the Project of Natural Science Foundation of Hubei Province(No.2021CFA094).
文摘The unfrozen water content(UWC)of rocks at low temperature is an important index for evaluating the stability of the rock engineering in cold regions and artificial freezing engineering.This study addresses a new method to estimate the UWC of saturated sandstones at low temperature by using the ultrasonic velocity.Ultrasonic velocity variations can be divided into the normal temperature stage(20 to 0℃),quick phase transition stage(0 to-5℃)and slow phase transition stage(-5 to-25℃).Most increment of ultrasonic velocity is completed in the quick phase transition stage and then turns to be almost a constant in the slow phase transition stage.In addition,the UWC is also measured by using nuclear magnetic resonance(NMR)technology.It is validated that the ultrasonic velocity and UWC have a similar change law against freezing and thawing temperatures.The WE(weighted equation)model is appropriate to estimate the UWC of saturated sandstones,in which the parameters have been accurately determined rather than by data fitting.In addition,a linear relationship between UWC and ultrasonic velocity is built based on pore ice crystallization theory.It is evidenced that this linear function can be adopted to estimate the UWC at any freezing temperature by using P-wave velocity,which is simple,practical,and accurate enough compared with the WE model.
文摘We herein studied a non-cryogenic cell preservation and transportation method. We found that astrocytes can be preserved in an unfrozen state at 4℃ (without medium exchange), while maintaining good condition in comparison with cryopreservation for the periods of 5 - 7 days. The gelatin solidification method can also prevent decreases in survival rate by preventing damage to astrocytes during transportation. Therefore, the gelatin solidification method at 4℃ may be a useful choice for short-term preservation and transportation.
文摘冻融过程岩石孔隙内未冻水含量变化是影响其力学特性的关键因素之一。以砂岩为研究对象,采用低场核磁共振系统(nuclear magnetic resonance,NMR)对岩石冻融过程(20、0、-2、-4、-6、-10、-15、-10、-6、-4、-2、0、20℃)孔隙水含量进行监测,分析未冻水含量随温度的演化规律,并探讨岩石冻融过程未冻水含量演化对其力学特性的影响。研究结果表明:(1)冻融过程岩石中孔隙水受温度影响显著,共经过5个阶段,即过冷段、快速冻结阶段、缓慢冻结阶段、缓慢融化阶段和融化加速阶段。(2)岩石在解冻过程中有明显的滞后现象。在相同温度下,岩样冻结过程未冻水含量明显高于解冻过程。与之对应,解冻过程的峰值强度和弹性模量相对于冻结阶段显著提高。(3)冻融过程的单轴抗压强度以及岩石弹性模量与未冻水含量的关系可由指数函数表示。冻结初期,岩石力学参数的变化主要受孔隙冰含量的增长及孔隙冰对岩石颗粒的胶结作用影响,随温度进一步降低,吸附水膜厚度下降,吸附能力增强,使孔隙冰与对岩石颗粒之间的整体性增强,岩石力学参数进一步发生改变。
基金We acknowledge the funding support from the National Natural Science Foundation of China(Grant No.42271148).
文摘Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during fracturing.The melting of pore ice is measured using nuclear magnetic resonance(NMR)method.The results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack coalescence.However,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical temperature.Next,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture parameters.From-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.
基金supported by the Key Project of the Natural Science Foundation of China(No.41630636)the National Natural Science Foundation of China(No.41501072)+1 种基金the Independent Foundation of State Key Laboratory of Frozen Soil Engineering,China(No.SKLFSE-ZT-202107)the Natural Science Foundation of Gansu,China(No.22JR5RA057).
文摘The formation and growth of segregation ice dominate the frost heave during soil freezing,which is closely related to water migration.To analyze segregation ice during soil freezing for different soils,a freezing-thawing experiment was conducted with Lanzhou loess(LZL)and Qinghai-Tibet Plateau silty clay(QSC)using a novel layered nuclear magnetic resonance approach.During LZL freezing,the unfrozen water content first increased and then decreased with decreasing temperature near the freezing front,but decreased with decreasing temperature in other layers,whereas during the freezing of QSC,the unfrozen water content in different layers(including the freezing front)decreased with decreased temperature.Notably,the increased liquid water near the freezing front during LZL freezing was primarily adsorbed water.In addition to the temperature gradient,the squeezing action during soil freezing was another important factor affecting water migration,especially at the early stage of soil freezing.However,which of the two factors,squeezing action and temperature gradient,was the dominant one causing water migration depended on soil structure.At the early stage of soil freezing,the squeezing action had a significant effect on the water migration of LZL,but no significant effect on that of QSC.Furthermore,water accumulation of LZL near the freezing front due to squeezing action at the early stage of freezing limited the formation and growth of segregation ice.This study provided an improved understanding for ice segregation and water migration during soil freezing.
基金supported by the National Natural Science Foundation of China(Grant No.42177291)Innovation Capability Support Program of Shaanxi Province(2023-JC-JQ-25 and 2021KJXX-11).
文摘As an essential property of frozen soils,change of unfrozen water content(UWC)with temperature,namely soil-freezing characteristic curve(SFCC),plays significant roles in numerous physical,hydraulic and mechanical processes in cold regions,including the heat and water transfer within soils and at the land–atmosphere interface,frost heave and thaw settlement,as well as the simulation of coupled thermo-hydro-mechanical interactions.Although various models have been proposed to estimate SFCC,their applicability remains limited due to their derivation from specific soil types,soil treatments,and test devices.Accordingly,this study proposes a novel data-driven model to predict the SFCC using an extreme Gradient Boosting(XGBoost)model.A systematic database for SFCC of frozen soils compiled from extensive experimental investigations via various testing methods was utilized to train the XGBoost model.The predicted soil freezing characteristic curves(SFCC,UWC as a function of temperature)from the well-trained XGBoost model were compared with original experimental data and three conventional models.The results demonstrate the superior performance of the proposed XGBoost model over the traditional models in predicting SFCC.This study provides valuable insights for future investigations regarding the SFCC of frozen soils.
基金the Science and Technology program of Gansu Province(Grant No.23ZDFA017)the National Natural Science Foundation of China(Grant Nos.U21A2012,42101136)the Program for Top Leading Talents of Gansu Province(Granted to Dr.MingYi Zhang).
文摘Oil leakages cause environmental pollution,economic losses,and even engineering safety accidents.In cold regions,researchers urgently investigate the movement of oil spill in soils exposed to freeze-thaw cycles.In this study,a series of laboratory model experiments were carried out on the migration of oil leakage under freeze-thaw action,and the distributions of the soil temperature,unfrozen water content,and displacement were analyzed.The results showed that under freeze-thaw action,liquid water in soils migrated to the freezing front and accumulated.After the pipe cracked,oil pollutants first gathered at one side of the leak hole,and then moved around.The pipe wall temperature affected the soil temperature field,and the thermal influence range below and transverse the pipe wall(35–40 cm)was larger than that above the pipe wall(8 cm)owing to the soil surface temperature.The leaked oil's temperature would make the temperature of the surrounding soil rise.Oil would inhibit the cooling of the soils.Besides,oil migration was significantly affected by the gravity and water flow patterns.The freeze-thaw action would affect the migration of the oil,which was mainly manifested as inhibiting the diffusion and movement of oil when soils were frozen.Unfrozen water transport caused by freeze-thaw cycles would also inhibit oil migration.The research results would provide a scientific reference for understanding the relationship between the movement of oil pollutants,water,and soil temperature,and for establishing a waterheat-mass transport model in frozen soils.
文摘为探究冻融循环条件下粉煤灰对膨胀土未冻水含量的影响,利用低场核磁共振(nuclear magnetic resonance,NMR)技术对不同粉煤灰掺量(3%、6%、9%、12%和15%)的改性膨胀土进行T2谱测定,分析不同温度下改性膨胀土的孔隙结构变化特征,并得出不同粉煤灰掺量的改性膨胀土未冻水含量的变化规律。试验结果表明:改性膨胀土相较于原状土,微、小孔隙的孔径分布在掺灰比为9%的试样出现降低,其余掺灰比的试样出现增长,掺灰比为6%的试样最显著;中孔隙增幅最显著的是掺灰比为12%的试样,大孔隙增幅最显著的是掺灰比为3%的试样;在冻结过程中,掺灰比为9%的试样未冻水含量在下降阶段变化最快,在融化阶段变化速率最慢;掺入粉煤灰降低了土壤的相变温度,且抑制土体冻结过程中的未冻水含量。
