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Water migration in subgrade soil under seasonal freeze-thaw cycles in an alpine meadow on the Qinghai-Tibet Plateau

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Journal of Mountain Science 2022年第6期19卷 1767-1781页

作者： WU Guan-qing XIE Yong-li WEI Jin YUE Xia-bing School of Highway Chang'an UniversityXi'an 710064China

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.

关键词： Water migration Seasonally frozen ground freeze-thaw cycles Laboratory experiment Migration potential model Qinghai-Tibet Plateau

Effect of freeze-thaw cycles on mechanical behavior of clay-gravel mixtures

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Journal of Mountain Science 2022年第12期19卷 3615-3626页

作者： ZHANG Yong-gan LIU Si-hong DENG Gang FANG Bin-xin ZHANG Yan-yi LU Yang College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China Key Laboratory of Construction and Safety of Water Engineering of the Ministry of Water Resources China Institute of Water Resources and Hydropower ResearchBeijing 100048China

The use of clay-gravel mixtures(i.e.,adding excavated or natural gravel particles into clay soil matrix)as the main filling materials is increasing in the anti-seepage system of high Earth Core Rockfill Dams(ECRDs).With the continuous construction of high ECRDs in the Chinese plateaus and cold regions,it is of great urgency and importance to understand the physical and mechanical characteristics of compacted clay-gravel mixtures under freeze-thaw *** this end,laboratory freezing-thawing tests,computed tomography(CT),and triaxial compression tests were conducted to evaluate the effects of freezethaw cycles on moisture loss,pore structure characteristics,stress-strain behavior,failure strength,elastic modulus,cohesion,and internal friction angle of compacted clay-gravel *** results demonstrate that,1)the freeze-thaw cycle significantly changed the mechanical characteristics of the clay-gravel mixture samples,but the shape of the stress-strain curve is less sensitive to it.2)The failure strength of samples exhibits a significant decrease after the first freeze-thaw cycle,but shows a certain increase as the number of freeze-thaw cycles increases from 1 to 2.3)The elastic modulus of samples first decreases and then increases with increasing freeze-thaw cycle,and the most severe deterioration was observed after the first freeze-thaw cycle.4)Regardless of the number of freeze-thaw cycles,there is a linear relationship between failure strength and elastic modulus for a sample that has suffered freeze-thaw weathering.5)The cohesion of samples decreases firstly and then slightly increases with increasing freeze-thaw cycles,while the internal friction angle is hardly affected.

关键词： Earth core rockfill dam Clay-gravel mixtures freeze-thaw cycles Computed tomography Mechanical behavior

Mechanical and acoustic emission characteristics of anhydrite rock under freeze-thaw cycles

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Journal of Mountain Science 2023年第1期20卷 227-241页

作者： ZHANG Chi JIN Xiao-guang HOU Chao HE Jie School of Civil Engineering Chongqing UniversityChongqing400045China China Railway 14TH Bureau Group Fourth Engineering Corporation Limited Jinan250101China Key Laboratory of New Technology for Construction of Cities in Mountain Area of the Ministry of Education Chongqing UniversityChongqing400045China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing UniversityChongqing400045China

To study the damage mechanisms of anhydrite rock under freeze-thaw cycles, the physicalmechanical properties and the microcracking activities of anhydrite rock were investigated through mass variation, nuclear magnetic resonance, scanning electron microscope tests, and uniaxial compression combined with acoustic emission(AE) tests. Results show that with the increase of freeze-thaw processes,the mass, uniaxial compression strength, and elastic modulus of the anhydrite specimens decrease while the porosity and plasticity characteristics *** example, after 120 cycles, the uniaxial compression strength and elastic modulus decrease by 46.54% and 60.16%, and the porosity increase by 75%. Combined with the evolution trend of stressstrain curves and the detected events, three stages were labeled to investigate the AE characteristics in freeze-thaw weathered anhydrite rock. It is found that with the increase of freeze-thaw cycles, the proportions of AE counts in stage Ⅰ and stage Ⅱ show a decaying exponential trend. Contrarily, the proportion of AE counts in stage Ⅲ displays an exponential ascending trend. Meanwhile, as the freeze-thaw cycles increase, the low-frequency AE signals increase while the intermediate-frequency AE signals decrease. After 120 cycles, the proportion of low-frequency AE signals increases by 168.95%, and the proportion of intermediate-frequency AE signals reduces by 81.14%. It is concluded that the microtensile cracking events occupy a dominant position during the loading process. With the increase of freeze-thaw cycles, the b value of samples *** 120 cycles, b value decreases by 27.2%, which means that the proportion of cracking events in rocks with small amplitude decreases. Finally, it is proposed that the freeze-thaw damage mechanism of anhydrite is also characterized by the water chemical softening effect.

关键词： freeze-thaw cycles Anhydrite rock Physical and mechanical properties AE characteristics Damage mechanism

Dynamic mechanical characteristics of frozen subgrade soil subjected to freeze-thaw cycles

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Journal of Mountain Science 2023年第1期20卷 242-255页

作者： WANG Dan LIU En-long YANG Cheng-song LIU You-qian ZHU Sheng-xian YU Qi-hao Northwest Institute of Eco-Environment and Resources State Key Laboratory of Frozen Soil EngineeringChinese Academy of SciencesLanzhou730000China University of Chinese Academy of Sciences Beijing100049China State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resources and HydropowerSichuan UniversityChengdu610065China Qinghai-Tibet Railway Company Qinghai810000China

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 *** 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 *** 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.

关键词： freeze-thaw cycles Frozen clay Dynamic triaxial test Dynamic mechanical properties

Experimental studies on the pore structure and mechanical properties of anhydrite rock under freeze-thaw cycles

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第3期14卷 781-797页

作者： Chao Hou Xiaoguang Jin Jie He Hanlin Li School of Civil Engineering Chongqing UniversityChongqing400045China Key Laboratory of New Technology for Construction of Cities in Mountain Area of the Ministry of Education Chongqing UniversityChongqing400045China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing UniversityChongqing400045China

To study the deterioration mechanisms of anhydrite rock under the freeze-thaw weathering process,the physico-mechanical characteristics and microstructure evolutions of anhydrite samples were determined by a series of laboratory ***,a descriptive-behavioral model was used to measure the integrity loss in anhydrite samples caused by cyclic ***,the freeze-thaw damage mechanisms of anhydrite rock were revealed from the macro and micro *** results show that the pore size of the anhydrite rock is mainly concentrated in the range of 0.001-10μ*** the number of freeze-thaw cycles increases,there is a growth in the proportion of macropores and ***,the proportion of micropores shows a declining *** relations of the uniaxial compressive strength,triaxial compressive strength,cohesion,and elastic modulus versus freeze-thaw cycles can be fitted by a decreasing exponential function,while the internal friction angle is basically unchanged with freezethaw *** the increase of confining pressure,the disintegration rates of the compressive strength and the elastic modulus decrease,and the corresponding half-life values increase,which reveals that the increase of confining pressures could inhibit freeze-thaw damage to ***,it has been proven that the water chemical softening mechanism plays an essential role in the freeze-thaw damage to anhydrite ***,it is concluded that the freeze-thaw weathering process significantly influences the macroscopic and microscopic damages of anhydrite rock.

关键词： Anhydrite rock freeze-thaw cycles Physico-mechanical characteristics Microstructure evolution Deterioration mechanisms

Frost heaving force considering synchronous damage to tunnel lining and surrounding rocks under freeze—thaw cycles

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Journal of Mountain Science 2023年第4期20卷 1131-1146页

作者： LIU Wen-jun LING Tong-hua HE Wen-chao LIU Xian-jun School of Civil Engineering Changsha University of Science and TechnologyChangsha410114China Logistics and Infrastructure Department Huaihua UniversityHuaihua418099China

In areas with seasonal freezing,when the tunnel lining concrete is saturated with water infiltrating the interior,the lining and the surrounding rocks will simultaneously ***,the current calculation of the frost heaving force fails to consider the synchronous damage to the lining and surrounding rocks under freeze-thaw ***,as per the elastic calculation model of the frost heaving force and model of steady-state heat transfer of circular tunnels,this study introduces the frost heaving rate of lining and surrounding ***,the analytical solution of frost heaving force is obtained for simultaneous frost heaving of lining and surrounding rocks under any steady-state temperature ***,based on the fracture theory and meso-damage mechanics,the damage variables of lining and surrounding rocks under freeze-thaw cycles are extracted,representing their elastic modulus and ***,the formula of frost heaving force for synchronous damage to the lining and surrounding rocks at any steady-state temperature field is *** calculation results demonstrate that the lower the temperature inside the lining,the greater the frost heaving *** the increasing number of freeze-thaw cycles,frost heaving force tends to gradually increase initially,reaching a peak value at 85 freeze-thaw cycles,decreasing to 80%of the peak value at 140 cycles before reaching a constant *** lining participates in frost heaving,increasing the frost heaving *** initial increase rate of frost heaving force is 15.7%.Changing the fitting coefficients s1 and s2 of the lining and surrounding rocks can effectively control the magnitude of the frost heaving force in the tunnels.

关键词： freeze-thaw cycles Frost heaving force Concrete lining Tunnel surrounding rock Synchronous damage

The Influence of freeze-thaw cycles on Unconfined Compressive Strength of Lignin Fiber-Reinforced Loess

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Journal of Renewable Materials 2022年第4期10卷 1063-1080页

作者： Zhongnan Gao Xiumei Zhong Qian Wang Yongqi Su Jun Wang Lanzhou Institute of Seismology China Earthquake AdministrationLanzhou730000China Key Laboratory of Loess Earthquake Engineering China Earthquake Administration&Gansu ProvinceLanzhou730000China Gansu Bureau of Coal Geology Lanzhou730000China

In the seasonal permafrost region with loess distribution,the influence of freeze-thaw cycles on the engineering performance of reinforced loess must be paid attention *** studies have shown that the use of fiber materials can improve the engineering performance of soil and its ability to resist freeze-thaw *** the same time,as eco-environmental protection has become the focus,which has been paid more and more attention to,it has become a trend to find new environmentally friendly improved materials that can replace traditional chemical *** purpose of this paper uses new environmental-friendly improved materials to reinforce the engineering performance of loess,improve the ability of loess to resist freeze-thaw cycles,and reduce the negative impact on the ecological *** reinforce the engineering performance of loess and improve its ability to resist freeze-thaw cycles,lignin fiber is used as a reinforcing *** a series of laboratory tests,the unconfined compressive strength(UCS)of lignin fiber-reinforced loess under different freeze-thaw cycles was *** effects of lignin fiber content and freeze-thaw cycles on the strength and deformation modulus of loess were *** with the microstructure features,the change mechanism of lignin fiber-reinforced loess strength under freeze-thaw cycles was *** results show that lignin fiber can improve the UCS of loess under freeze-thaw cycles,but the strengthening effect no longer increases with the increase of fiber *** the fiber content is less than 1%,the UCS growth rate of loess is the fastest under freeze-thaw *** the UCS of loess with 1%fiber content is the most stable under freeze-thaw *** freeze-thaw cycles increase the deformation modulus of loess with 1%fiber content,and its ability to resist deformation is obviously better than loess with 1.5%,2%and 3%fiber *** fiber content over 1%will weaken the strengthening effect of

关键词： Fiber-reinforced loess freeze-thaw cycles unconfined compressive strength deformation modulus

Effect of High Temperature Curing on the Frost Resistance of Recycled Aggregate Concrete and the Physical Properties of Second-Generation Recycled Coarse Aggregate under freeze-thaw cycles

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Journal of Renewable Materials 2023年第6期11卷 2953-2967页

作者： Xintong Chen Pinghua Zhu Xiancui Yan Lei Yang Huayu Wang Changzhou City Key Laboratory of Building Energy-Saving Technology Department of Civil EngineeringChangzhou UniversityChangzhou213164China

With the emphasis on environmental issues,the recycling of waste concrete,even recycled concrete,has become a hot spot in the field of *** the repeated recycling of waste concrete used in harsh environments is still a complex *** paper discusses the durability and recyclability of recycled aggregate concrete(RAC)as a prefabricated material in the harsh environment,the effect of high-temperature curing(60℃,80℃,and 100℃)on the frost resistance of RAC and physical properties of the second generation recycled coarse aggregate(RCA_(2))of RAC after 300 freeze-thaw cycles were *** frost resistance of RAC was characterized by compressive strength,relative dynamic elastic modulus,and mass *** the physical properties of RCA_(2),the apparent density,water absorption,and crushing value were *** the SEM images of RAC after 300 freeze-thaw cycles were *** results indicated that the frost resistance of RAC cured at 80℃ for 7 days was comparable to that cured in the standard condition(cured for 28 days at 20℃±2℃ and 95%humidity),and the RAC cured at 100℃ was slightly ***,the frost resistance of RAC cured at 60℃ deteriorated *** RAC cured at 80℃ for 7 days is the *** after the freeze-thaw cycle or not,the RCA that curd at 60℃,80℃,and 100℃ for 7 days can also meet the requirements of Grade III RCA and be used as the aggregate of non-bearing part of prefabricated concrete ***_(2) which is cured at 80℃ for 7 days had the best physical properties.

关键词： freeze-thaw cycles curing condition recycled aggregate concrete second-generation recycled coarse aggregate

The Effect of Different freeze-thaw cycles on Mortar Gas Permeability and Pore Structure

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Fluid Dynamics & Materials Processing 2023年第6期19卷 1623-1636页

作者： Wei Chen Ao Xu Hejun Zhang Mingquan Sheng Yue Liang Frederic Skoczylas School of Civil Engineering Architecture and EnvironmentHubei University of TechnologyWuhanChina CNRS Centrale LilleUMR9013-LaMcube-Laboratoire de Mécanique Multiphysique et MultiéchelleUniversitéde LilleLilleFrance

Two different freeze-thaw cycles(FTC)are considered in this study to assess the related impact on gas permeability and micro-pore structure of a *** are the water-freezing/water-thawing(WF-WT)and the air-freezing/air-thawing(AF-AT)*** problem is addressed experimentally through an advanced nuclear magnetic resonance(NMR)technique able to provide meaningful information on the relationships among gas permeability,pore structure,mechanical properties,and the number of *** is shown that the mortar gas permeability increases with the number of FTCs,the increase factor being 20 and 12.83 after 40 cycles for the WF-WT and AF-AT,*** results also confirm that gas permeability hysteresis phenomena occur during the confining pressure loading and unloading process.

关键词： Mortar freeze-thaw cycles gas permeability pore structure NMR mechanical properties