冻融过程中未冻水含量对非饱和粉土抗剪强度的影响
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摘要
对含水率为18.3%的非饱和粉土进行了冻融过程中不同温度下的直剪试验,用核磁共振测定了冻融过程中孔隙水的相变过程,并分析了未冻水、孔隙冰对其力学性质的影响机制。试验结果表明:(1)非饱和粉土冻结可分为过冷段(>-1.15℃)、快速冻结阶段(-1.15℃～-2℃)和稳定冻结阶段(<-2℃),快速冻结阶段76%的孔隙水冻结,而稳定冻结阶段未冻水含量只减少7%;(2)冻融过程中黏聚力随温度发生显著变化,内摩擦角变化幅度很小;(3)冻结过程中抗剪强度的变化主要发生在稳定冻结阶段,快速冻结阶段黏聚力仅增大38.5%,内摩擦角基本无变化,而稳定冻结阶段黏聚力增大123.5%,内摩擦角降低12%。得到以下结论:(1)快速冻结阶段黏聚力增大主要是由于孔隙水冻结导致基质吸力增大,毛细黏聚作用增强;稳定冻结阶段黏聚力增大主要是由于冰对土颗粒胶结强度增大;(2)含冰量变化不大时,冻土抗剪强度主要受冰对土颗粒胶结强度的控制,而此胶结强度决定于未冻水膜的厚度;(3)稳定冻结阶段内摩擦角降低主要由孔隙中水冰相变发生体积膨胀时对土颗粒骨架的作用力导致。
A series of direct shear tests on unsaturated silt with a water content of 18.3% during freezing and thawing were conducted,and the phase composition of pore water was measured by NMR during the shear process.Effects of the unfrozen water content and the ice content on mechanical properties of the tested silt were analyzed.The results indicate that the freezing process of unsaturated silt can be divided into super-cooling stage>-1.15 ℃,no phase change),rapid freezing stage(-1.15 ℃–-2 ℃) where 76% of the pore water freezes,and stable freezing stage(<-2 ℃) where the unfrozen water content only decreases by 7%. The cohesion changes significantly with the temperature during the process of freezing and thawing while the friction angle varies slightly. The change of the shear strength of silt occurs primarily within the stable freezing stage,where the cohesion increases by 123.5% and the friction angle decreases by 12%. For the rapid freezing stage,the cohesion only ascends by 38.5% and the friction angle has no obvious change. It can be concluded that,within the rapid freezing phase,the freezing of the pore water drives the matrix suction to increase,which results in increasing of the cohesion,while that,within the stable freezing phase,the increase of the cementation strength between ice and soil particles leads to a rise of the cohesion. When the ice content changes slightly,the shear strength of frozen silt is mainly controlled by the cementation strength between ice and soil particles which depends on the thickness of the unfrozen water film. The decrease of the friction angle within the stable freezing phase is mainly caused by the force acting on the particle skeleton generated by volumetric expansion of the pore water upon freezing.
A series of direct shear tests on unsaturated silt with a water content of 18.3% during freezing and thawing were conducted,and the phase composition of pore water was measured by NMR during the shear process.Effects of the unfrozen water content and the ice content on mechanical properties of the tested silt were analyzed.The results indicate that the freezing process of unsaturated silt can be divided into super-cooling stage>-1.15 ℃,no phase change),rapid freezing stage(-1.15 ℃–-2 ℃) where 76% of the pore water freezes,and stable freezing stage(<-2 ℃) where the unfrozen water content only decreases by 7%. The cohesion changes significantly with the temperature during the process of freezing and thawing while the friction angle varies slightly. The change of the shear strength of silt occurs primarily within the stable freezing stage,where the cohesion increases by 123.5% and the friction angle decreases by 12%. For the rapid freezing stage,the cohesion only ascends by 38.5% and the friction angle has no obvious change. It can be concluded that,within the rapid freezing phase,the freezing of the pore water drives the matrix suction to increase,which results in increasing of the cohesion,while that,within the stable freezing phase,the increase of the cementation strength between ice and soil particles leads to a rise of the cohesion. When the ice content changes slightly,the shear strength of frozen silt is mainly controlled by the cementation strength between ice and soil particles which depends on the thickness of the unfrozen water film. The decrease of the friction angle within the stable freezing phase is mainly caused by the force acting on the particle skeleton generated by volumetric expansion of the pore water upon freezing.
引文
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[7]赖远明,程红彬,高志华,等.冻结砂土的应力-应变关系及非线性莫尔强度准则[J].岩石力学与工程学报,2007,6(8):1 612-1 617.(LAI Yuanming,CHENG Hongbin,GAO Zhihua,et al.Stress-strain relationships and nonlinear Mohr strength criterion of frozen sand clay[J].Chinese Journal of Rock Mechanics and Engineering,2007,6(8):1 612-1 617.(in Chinese))
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[11]李顺群,高凌霞,柴寿喜.冻土力学性质影响因素的显著性和交互作用研究[J].岩土力学,2012,33(4):1 173-1 177.(LI Shunqun,GAO Lingxia,CHAI Shouxi.Significance and interaction of factors on mechanical properties of frozen soil[J].Rock and Soil Mechanics,2012,33(4):1 173-1 177.(in Chinese))
[12]牛亚强,赖远明,王旭,等.初始含水率对冻结粉质黏土变形和强度的影响规律研究[J].岩土力学,2016,37(2):499-506.(NIUYaqiang,LAI Yuanming,WANG Xu,et al.Research on influences of initial water content on deformation and strength behaviors of frozen silty clay[J].Rock and Soil Mechanics,2016,37(2):499-506.(in Chinese))
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[14]刘振亚,刘建坤,李旭,等.非饱和粉质黏土冻结温度和冻结变形特性试验研究[J].岩土工程学报,2017,39(8):1 381-1 387.(LIUZhenya,LIU Jiankun,LI Xu,et al.Experimental study on freezing point and deformation characteristics of unsaturated silty clay subjected to freeze-thaw cycles[J].Chinese Journal of Geotechnical Engineering,2017,39(8):1 381-1 387.(in Chinese))
[15]TING J M,MARTIN R T,LADD C C.Mechanisms of strength for frozen sand[J].Journal of Geotechnical Engineering,1983,109(10):1 286-1 302.
[16]马巍,吴紫汪,张立新,等.高围压下冻土强度弱化的机理分析[J].冰川冻土,1999,21(1):28-32.(MA Wei,WU Ziwang,ZHANGLixin,et al.Mechanisms of strength weakening of frozen under high confining pressure[J].Journal of Glaciology and Geocryology,1999,21(1):28-32.(in Chinese))
[17]沈忠言,吴紫汪.冻土三轴强度破坏准则的基本形式及其未冻水含量的相关性[J].冰川冻土,1999,(1):22-26.(SHEN Zhongyan,WU Ziwang.Basic Form-of the failure criteria of triaxial strength of frozen and Its relativity to unfrozen water[J].Journal of Glaciology and Geocryology,1999,(1):22-26.(in Chinese))
[18]马玲,齐吉琳,余帆,等.冻结砂土三轴试验中颗粒破碎研究[J].岩土工程学报,2015,37(3):544-550.(MA Ling,QI Jilin,YU Fan,et al.Particle crushing of frozen sand under triaxial compression[J].Chinese Journal of Geotechnical Engineering,2015,37(3):544-550.(in Chinese))
[19]刘振亚.非饱和冻土力学特性及微观机理研究[博士学位论文][D].北京:北京交通大学,2018.(LIU Zhenya.Mechanical characteristics and microstructure mechanism of unsaturated soil subjected to freezing condition[Ph.D.Thesis][D].Beijing:Beijing Jiaotong University,2018.(in Chinese))
[20]中华人民共和国行业标准编写组.JTG E40-2007公路土工试验规程[S].北京:中华人民共和国交通部,2007.(The Professional Standards Compilation Group of People′s Republic of China.JTG E40-2007 Test method of soils for highway engineering[S].Beijing:Ministry of Transport,2007.(in Chinese))
[21]肖立志.核磁共振成像测井与岩石核磁共振及其应用[M].北京:科学出版社,1998:35-39.(XIAO Lizhi.NMR Imaging logging principles and applications[M].Beijing:Science Press,1998:35-39.(in Chinese))
[22]谭龙,韦昌富,田慧会,等.冻土未冻水含量的低场核磁共振试验研究[J].岩土力学,2015,36(6):1 566-1 572.(TAN Long,WEIChangfu,TIAN Huihui,et al.Experimental study of unfrozen water content of frozen soils by low-field nuclear magnetic resonance[J].Rock and Soil Mechanics,2015,36(6):1 566-1 572.(in Chinese))
[23]汪红志,张学龙,武杰.核磁共振成像技术试验教程[M].北京:科学出版社,2008:6-8.(WANG Hongzhi,ZHANG Xuelong,WUJie.NMR imaging technology test tutorial[M].Beijing:Science Press,2008:6-8.(in Chinese))
[24]TICE A R,OLIPHANT J L,ZHU Y L,et al.Relationship between the ice and unfrozen water phases in frozen soils as determined by pulsed nuclear resonance and physical desorption data[J].Journal of Glaciology and Geocryology,1983,5(2):37-39.
[25]李蒙蒙,牛永红,李先明,等.低含水率非饱和高温冻土模型[J].冰川冻土,2014,36(4):886-894.(LI Mengmeng,NIU Yonghong,LI Xianming,et al.Low moisture content unsaturated high temperature frozen soil model[J].Journal of Glaciology and Geocryology,2014,36(4):886-894.(in Chinese))
[26]路建国,张明义,张熙胤,等.冻融过程中未冻水含量及冻结温度的试验研究[J].岩石力学与工程学报,2017,36(7):1 803-1 812.(LU Jianguo,ZHANG Mingyi,ZHANG Xiyin,et al.Experimental study on the content and temperature of unfrozen water in freeze-thaw process[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(7):1 803-1 812.(in Chinese))
[27]MARTINEZ G A,DAVIS L A.Petrophysical measurements on shales using NMR[C]//Proceedings of the SPE/AAPG Western Regional Meeting.California:Society of Petroleum Engineers,2000:1-10.DOI:10.2118/62851-MS.
[28]COATES G R,MARSCHALL D,MARDON D,et al.A new characterization of bulk-volume irreducible using magnetic resonance[J].Log Analyst,1997,39(1):51-63.
[29]刘振亚,刘建坤,李旭,等.毛细黏聚与冰胶结作用对非饱和粉质黏土冻结强度及变形特性的影响[J].岩石力学与工程学报,2018,37(6):1 551-1 559.(LIU Zhenya,LIU Jiankun,LI Xu,et al.Effect of capillary cohesion and ice cementation on strength and deformation of unsaturated frozen silty clay[J].Chinese Journal of Rock Mechanics and Engineering,2018,37(6):1 551-1 559.(in Chinese))
[30]GILPIN R R.A model for the prediction of ice lensing and frost heave in soils[J].Water Resources Research,1980,16(5):918-930.
[31]张立新,徐学祖,张招祥,等.冻土未冻水含量与压力关系的实验研究[J],冰川冻土,1998,(2):28-31.(ZHANG Lixin,XU Xuezu,ZHANG Zhaoxiang,et al.Experimental study of the relationship between the unfrozen water content of frozen soil and pressure[J].Journal of Glaciology and Geocryology,1998,(2):28-31.(in Chinese))
[2]TSYTOVICH N A,SUMGIN M I.Principles of mechanics of frozen ground[R].Hanover:Cold Regions Research and Engineering Laboratory,1959.
[3]CHAMBERLAIN E,GROVES C,PERHAM J.The mechanism behavior of frozen earth materials under high pressure triaxial test conditions[J].Geotechnique,1972,22(3):469-483.
[4]JONES S J,PARAMESWARAN V R.Deformation behavior of frozen sand-ice materials under triaxial compression[C]//Proceedings of the4th International Conference on Permafrost.Fairbanks Alaska:TLPéwéand J.Brown,1983:17-22.
[5]HAYNES F D,KARALIUS J A.Effect of temperature on the strength of frozen silt[R].Hanover:Cold Regions Research and Engineering Laboratory,1977.
[6]SAYLES F H,CARBEE D L.Strength of frozen silt as a function of ice content and dry unit weight[J].Engineering Geology,1981,18(1-4):55-56.
[7]赖远明,程红彬,高志华,等.冻结砂土的应力-应变关系及非线性莫尔强度准则[J].岩石力学与工程学报,2007,6(8):1 612-1 617.(LAI Yuanming,CHENG Hongbin,GAO Zhihua,et al.Stress-strain relationships and nonlinear Mohr strength criterion of frozen sand clay[J].Chinese Journal of Rock Mechanics and Engineering,2007,6(8):1 612-1 617.(in Chinese))
[8]马小杰,张建明,常小晓,等.高温-高含冰量冻结黏土强度试验研究[J].岩土力学,2008,29(9):2 498-2 502.(MA Xiaojie,ZHANGJianming,CHANG Xiaoxiao,et al.Experimental research on strength of warm and ice-rich frozen clays[J].Rock and Soil Mechanics,2008,29(9):2 498-2 502.(in Chinese))
[9]谭玉才,李巍,陈孝兵.冻结粉质黏土强度同温度和含水率的关系[J].煤炭科技,2008,(1):42-44.(TAN Yucai,LI Wei,CHENXiaobin.Relation between strength of frozen powdered clay and percentage of moisture under different temperatures[J].Coal science and Technology Magazine,2008,(1):42-44.(in Chinese))
[10]亢锋,刘志伟.温度对冻土强度的影响研究[J].内蒙古公路与运输,2015,(4):22-25.(KANG Feng,LIU Zhiwei.Study on the effect of temperature on the strength of frozen soil[J].Highways and Transportation in Inner Mongolia,2015,(4):22-25.(in Chinese))
[11]李顺群,高凌霞,柴寿喜.冻土力学性质影响因素的显著性和交互作用研究[J].岩土力学,2012,33(4):1 173-1 177.(LI Shunqun,GAO Lingxia,CHAI Shouxi.Significance and interaction of factors on mechanical properties of frozen soil[J].Rock and Soil Mechanics,2012,33(4):1 173-1 177.(in Chinese))
[12]牛亚强,赖远明,王旭,等.初始含水率对冻结粉质黏土变形和强度的影响规律研究[J].岩土力学,2016,37(2):499-506.(NIUYaqiang,LAI Yuanming,WANG Xu,et al.Research on influences of initial water content on deformation and strength behaviors of frozen silty clay[J].Rock and Soil Mechanics,2016,37(2):499-506.(in Chinese))
[13]孙义强.粉质粘土负温抗剪强度试验研究[硕士学位论文][D].哈尔滨:哈尔滨工业大学,2017.(SUN Yiqiang.Experimental study on negative temperature shear strength of silty clay[M.S.Thesis][D].Harbin:Harbin Institute of Technology,2017.(in Chinese))
[14]刘振亚,刘建坤,李旭,等.非饱和粉质黏土冻结温度和冻结变形特性试验研究[J].岩土工程学报,2017,39(8):1 381-1 387.(LIUZhenya,LIU Jiankun,LI Xu,et al.Experimental study on freezing point and deformation characteristics of unsaturated silty clay subjected to freeze-thaw cycles[J].Chinese Journal of Geotechnical Engineering,2017,39(8):1 381-1 387.(in Chinese))
[15]TING J M,MARTIN R T,LADD C C.Mechanisms of strength for frozen sand[J].Journal of Geotechnical Engineering,1983,109(10):1 286-1 302.
[16]马巍,吴紫汪,张立新,等.高围压下冻土强度弱化的机理分析[J].冰川冻土,1999,21(1):28-32.(MA Wei,WU Ziwang,ZHANGLixin,et al.Mechanisms of strength weakening of frozen under high confining pressure[J].Journal of Glaciology and Geocryology,1999,21(1):28-32.(in Chinese))
[17]沈忠言,吴紫汪.冻土三轴强度破坏准则的基本形式及其未冻水含量的相关性[J].冰川冻土,1999,(1):22-26.(SHEN Zhongyan,WU Ziwang.Basic Form-of the failure criteria of triaxial strength of frozen and Its relativity to unfrozen water[J].Journal of Glaciology and Geocryology,1999,(1):22-26.(in Chinese))
[18]马玲,齐吉琳,余帆,等.冻结砂土三轴试验中颗粒破碎研究[J].岩土工程学报,2015,37(3):544-550.(MA Ling,QI Jilin,YU Fan,et al.Particle crushing of frozen sand under triaxial compression[J].Chinese Journal of Geotechnical Engineering,2015,37(3):544-550.(in Chinese))
[19]刘振亚.非饱和冻土力学特性及微观机理研究[博士学位论文][D].北京:北京交通大学,2018.(LIU Zhenya.Mechanical characteristics and microstructure mechanism of unsaturated soil subjected to freezing condition[Ph.D.Thesis][D].Beijing:Beijing Jiaotong University,2018.(in Chinese))
[20]中华人民共和国行业标准编写组.JTG E40-2007公路土工试验规程[S].北京:中华人民共和国交通部,2007.(The Professional Standards Compilation Group of People′s Republic of China.JTG E40-2007 Test method of soils for highway engineering[S].Beijing:Ministry of Transport,2007.(in Chinese))
[21]肖立志.核磁共振成像测井与岩石核磁共振及其应用[M].北京:科学出版社,1998:35-39.(XIAO Lizhi.NMR Imaging logging principles and applications[M].Beijing:Science Press,1998:35-39.(in Chinese))
[22]谭龙,韦昌富,田慧会,等.冻土未冻水含量的低场核磁共振试验研究[J].岩土力学,2015,36(6):1 566-1 572.(TAN Long,WEIChangfu,TIAN Huihui,et al.Experimental study of unfrozen water content of frozen soils by low-field nuclear magnetic resonance[J].Rock and Soil Mechanics,2015,36(6):1 566-1 572.(in Chinese))
[23]汪红志,张学龙,武杰.核磁共振成像技术试验教程[M].北京:科学出版社,2008:6-8.(WANG Hongzhi,ZHANG Xuelong,WUJie.NMR imaging technology test tutorial[M].Beijing:Science Press,2008:6-8.(in Chinese))
[24]TICE A R,OLIPHANT J L,ZHU Y L,et al.Relationship between the ice and unfrozen water phases in frozen soils as determined by pulsed nuclear resonance and physical desorption data[J].Journal of Glaciology and Geocryology,1983,5(2):37-39.
[25]李蒙蒙,牛永红,李先明,等.低含水率非饱和高温冻土模型[J].冰川冻土,2014,36(4):886-894.(LI Mengmeng,NIU Yonghong,LI Xianming,et al.Low moisture content unsaturated high temperature frozen soil model[J].Journal of Glaciology and Geocryology,2014,36(4):886-894.(in Chinese))
[26]路建国,张明义,张熙胤,等.冻融过程中未冻水含量及冻结温度的试验研究[J].岩石力学与工程学报,2017,36(7):1 803-1 812.(LU Jianguo,ZHANG Mingyi,ZHANG Xiyin,et al.Experimental study on the content and temperature of unfrozen water in freeze-thaw process[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(7):1 803-1 812.(in Chinese))
[27]MARTINEZ G A,DAVIS L A.Petrophysical measurements on shales using NMR[C]//Proceedings of the SPE/AAPG Western Regional Meeting.California:Society of Petroleum Engineers,2000:1-10.DOI:10.2118/62851-MS.
[28]COATES G R,MARSCHALL D,MARDON D,et al.A new characterization of bulk-volume irreducible using magnetic resonance[J].Log Analyst,1997,39(1):51-63.
[29]刘振亚,刘建坤,李旭,等.毛细黏聚与冰胶结作用对非饱和粉质黏土冻结强度及变形特性的影响[J].岩石力学与工程学报,2018,37(6):1 551-1 559.(LIU Zhenya,LIU Jiankun,LI Xu,et al.Effect of capillary cohesion and ice cementation on strength and deformation of unsaturated frozen silty clay[J].Chinese Journal of Rock Mechanics and Engineering,2018,37(6):1 551-1 559.(in Chinese))
[30]GILPIN R R.A model for the prediction of ice lensing and frost heave in soils[J].Water Resources Research,1980,16(5):918-930.
[31]张立新,徐学祖,张招祥,等.冻土未冻水含量与压力关系的实验研究[J],冰川冻土,1998,(2):28-31.(ZHANG Lixin,XU Xuezu,ZHANG Zhaoxiang,et al.Experimental study of the relationship between the unfrozen water content of frozen soil and pressure[J].Journal of Glaciology and Geocryology,1998,(2):28-31.(in Chinese))
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