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
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摘要
为探究毛细黏聚和冰胶结作用对冻土强度及变形特性的影响,通过室内试验测定不同饱和度、初始孔隙比情况下,压实、冻结和风干土样的强度及三维等温冻结变形和压缩特性。试验结果及数据分析表明:非饱和粉质黏土冻结强度的提高是基质吸力增加导致的毛细黏聚与冰胶结黏聚共同作用的结果。饱和度较低时,毛细黏聚作用占较大比重;随着饱和度的提高,冰胶结逐渐占主导作用。假定相同吸力条件下,冻土和非饱和土毛细黏聚力相当,发现冰胶结黏聚力和冻土体积含冰量之间存在线性关系。对于粉质黏土体变,当饱和度高(>0.75)时,土体表现为冻胀,当饱和度低(<0.75)时,土体表现为冻缩,说明冻土体变由黏聚力增加导致的体缩作用与冰水相变导致的体胀作用共同决定。当土样初始饱和度和孔隙比相同时,由黏聚力增加导致的体缩量和受到压力时产生的压缩量相当,可由压缩曲线预估土体的体缩量,体积含冰量与冰水相变导致的体胀量存在线性关系。
The strength increase and volume shrinkage during freezing of unsaturated soil may relate to the capillary cohesion and ice cementation. In this paper,shear strength,three dimensional deformation and compaction characteristics of compacted,frozen and air-dried samples were experimental studied using silty clay. The saturation degree and void ratio were considered as variable parameters. The contributions of ice cementation and capillary cohesion to strength were investigated experimentally. The experimental results demonstrate that the strength increase of unsaturated frozen silty clay is due to the capillary cohesion enhanced by suction increase and ice cementation. The capillary cohesion is remarkable in frozen soil with low initial degree of saturation,and the ice cementation is major source of cohesion in frozen soil with increasing of the initial degree of saturation. The volumetric ice content has a linear relationship with ice cementation on the assumption that capillary cohesion of frozen soil equals to that of unsaturated soil at the same matric suction. For the silty clay used,the samples with degree of saturation lower than 0.75 shrink upon frozen while the samples with degree of saturation higher than 0.75 swell. So,the sum of shrinkage induced by cohesion and expansion induced by icing are the total deformation of unsaturated frozen soil. Such shrinkage strain can be inferred from the curve of soil compression. The expansion induced by transformation from water to ice has a linear relationship with volumetric ice content on the assumption that compression caused by load equals to shrinkage caused by increasing of capillary cohesion.
The strength increase and volume shrinkage during freezing of unsaturated soil may relate to the capillary cohesion and ice cementation. In this paper,shear strength,three dimensional deformation and compaction characteristics of compacted,frozen and air-dried samples were experimental studied using silty clay. The saturation degree and void ratio were considered as variable parameters. The contributions of ice cementation and capillary cohesion to strength were investigated experimentally. The experimental results demonstrate that the strength increase of unsaturated frozen silty clay is due to the capillary cohesion enhanced by suction increase and ice cementation. The capillary cohesion is remarkable in frozen soil with low initial degree of saturation,and the ice cementation is major source of cohesion in frozen soil with increasing of the initial degree of saturation. The volumetric ice content has a linear relationship with ice cementation on the assumption that capillary cohesion of frozen soil equals to that of unsaturated soil at the same matric suction. For the silty clay used,the samples with degree of saturation lower than 0.75 shrink upon frozen while the samples with degree of saturation higher than 0.75 swell. So,the sum of shrinkage induced by cohesion and expansion induced by icing are the total deformation of unsaturated frozen soil. Such shrinkage strain can be inferred from the curve of soil compression. The expansion induced by transformation from water to ice has a linear relationship with volumetric ice content on the assumption that compression caused by load equals to shrinkage caused by increasing of capillary cohesion.
引文
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[9]刘文化,杨庆,唐小微,等.干湿循环条件下粉质黏土在循环荷载作用下的动力特性试验研究[J].水利学报,2015,46(4):425–432.(LIU Wenhua,YANG Qing,TANG Xiaowei,et al.Experimental study on the dynamic characteristics of silt clay subjected to drying-wetting cycles under cyclic loading[J].Journal of Hydraulic Engineering,2015,46(4):425–432.(in Chinese))
[10]何平,程国栋,杨成松,等.非饱和冻土的强度分析[J].冰川冻土,2002,(3):260–263.(HE Ping,CHENG Guodong,YANG Chengsong,et al.Analysis of strength of unsaturated frozen soil[J].Journal of Glaciology and Geocryology,2002,(3):260–263.(in Chinese))
[11]MORGENSTERN N R.Geotechnical engineering and frontier resource development[J].Géotechnique,1981,31(3):305–365.
[12]周家作,韦昌富,李东庆,等.饱和粉土冻胀过程试验研究及数值模拟[J].岩石力学与工程学报,2017,36(2):485–495.(ZHOU Jiazuo,WEI Changfu,LI Dongqing,et al.Experimental study and numerical simulation to the process of frost heave in saturated silt[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(2):485–495.(in Chinese))
[13]齐吉琳,马巍.冻融作用对超固结土强度的影响[J].岩土工程学报,2006,28(12):2 082–2 086.(QI Jilin,MA Wei.Influence of freezing-thawing on strength of over consolidated soils[J].Chinese Journal of Geotechnical Engineering,2006,28(12):2 082–2 086.(in Chinese))
[14]吴礼舟,许强,黄润秋.非饱和粘土的冻胀融沉过程分析[J].岩土力学,2011,32(4):1 025–1 028.(WU Lizhou,XU Qiang,HUANG Runqiu.Analysis of freezing-thawing test process of unsaturated clay[J].Rock and Soil Mechanics,2011,32(4):1 025–1 028.(in Chinese))
[15]OTHMAN M A,BENSON C H.Effect of freeze-thaw on the hydraulic conductivity and morphology of compacted clay[J].Canadian Geotechnical Journal,1983,30(2):236–246.
[16]KOOPMANS R W R,MILLER R D.Soil freezing and soil water characteristic curves[J].Soil Science Society of America Proceedings,1966,30(6):680–685.
[17]BLACK P B,TICE A R.Comparison of soil freezing curve and soil water curve data for Windsor sandy loam[J].Water Resources Research,1988,25(10):2 205–2 210.
[18]AZMATCH T F,SEGO D C,ARENSON L U,et al.Using soil freezing characteristic curve to estimate the hydraulic conductivity function of partially frozen soils[J].Cold Region Science and Technology,2012,83–84:103–109.
[19]徐斅祖,王家澄,张立新.冻土物理学[M].北京:科学出版社,2001:42–43.(XU Xiaozu,WANG Jiacheng,ZHANG Lixin.Physics of frozen soil[M].Beijing:Science Press,2001:42–43.(in Chinese))
[20]徐斅祖,邓友生.冻土中水分迁移的实验研究[M].北京:科学出版社,1991:27–28.(XU Xiaozu,DENG Yousheng.Experimental study on water migration in freezing and frozen soils[M].Beijing:Science Press,1991:27–28.(in Chinese))
[2]马小杰,张建明,常小晓,等.高温–高含冰量冻结粘土强度试验研究[J].岩土力学,2008,29(9):2 498–2 502.(MA Xiaojie,ZHANG Jianming,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))
[3]张俊兵,李海鹏,林传年,等.饱和冻结粉土在常应变率下的单轴抗压强度[J].岩石力学与工程学报,2003,22(增2):2 865–2 870.(ZHANG Junbing,LI Haipeng,LIN Chuannian,et al.Compressive strength of saturated frozen silt under constant strain rate[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(Supp.2):2 865–2 870.(in Chinese))
[4]肖海斌.人工冻土单轴抗压强度与温度和含水率的关系[J].岩土工程界,2008,11(4):62–63.(XIAO Haibin.Relationship of uniaxial compressive strength and temperature and moisture of artificial frozen soil[J].Geotechnical Engineering World,2008,11(4):62–63.(in Chinese))
[5]TSYTOVICH N A.The mechanics of frozen ground[M].Beijing:Science Press,1985:55–57.
[6]ANDER L O B,LADANYI B.Mechanical properties of frozen soils[M].New York:Springer,1994:121–150.
[7]许四法,王志健,胡琦,等.重塑非饱和粉质黏土抗剪强度特性试验研究[J].浙江工业大学学报,2015,43(2):227–231.(XU Sifa,WANG Zhijian,HU Qi,et al.An experimental study on the shear strength characteristics of remolded unsaturated silty clay[J].Journal of Zhejiang University of Technology,2015,43(2):227–231.(in Chinese))
[8]高登辉,陈正汉,郭楠,等.干密度和基质吸力对重塑非饱和黄土变形与强度特性的影响[J].岩石力学与工程学报,2017,36(3):736–744.(GAO Denghui,CHEN Zhenghan,GUO Nan,et al.The influence of dry density and matric suction on the deformation and the strength characteristics of the remolded unsaturated loess soils[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(3):736–744.(in Chinese))
[9]刘文化,杨庆,唐小微,等.干湿循环条件下粉质黏土在循环荷载作用下的动力特性试验研究[J].水利学报,2015,46(4):425–432.(LIU Wenhua,YANG Qing,TANG Xiaowei,et al.Experimental study on the dynamic characteristics of silt clay subjected to drying-wetting cycles under cyclic loading[J].Journal of Hydraulic Engineering,2015,46(4):425–432.(in Chinese))
[10]何平,程国栋,杨成松,等.非饱和冻土的强度分析[J].冰川冻土,2002,(3):260–263.(HE Ping,CHENG Guodong,YANG Chengsong,et al.Analysis of strength of unsaturated frozen soil[J].Journal of Glaciology and Geocryology,2002,(3):260–263.(in Chinese))
[11]MORGENSTERN N R.Geotechnical engineering and frontier resource development[J].Géotechnique,1981,31(3):305–365.
[12]周家作,韦昌富,李东庆,等.饱和粉土冻胀过程试验研究及数值模拟[J].岩石力学与工程学报,2017,36(2):485–495.(ZHOU Jiazuo,WEI Changfu,LI Dongqing,et al.Experimental study and numerical simulation to the process of frost heave in saturated silt[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(2):485–495.(in Chinese))
[13]齐吉琳,马巍.冻融作用对超固结土强度的影响[J].岩土工程学报,2006,28(12):2 082–2 086.(QI Jilin,MA Wei.Influence of freezing-thawing on strength of over consolidated soils[J].Chinese Journal of Geotechnical Engineering,2006,28(12):2 082–2 086.(in Chinese))
[14]吴礼舟,许强,黄润秋.非饱和粘土的冻胀融沉过程分析[J].岩土力学,2011,32(4):1 025–1 028.(WU Lizhou,XU Qiang,HUANG Runqiu.Analysis of freezing-thawing test process of unsaturated clay[J].Rock and Soil Mechanics,2011,32(4):1 025–1 028.(in Chinese))
[15]OTHMAN M A,BENSON C H.Effect of freeze-thaw on the hydraulic conductivity and morphology of compacted clay[J].Canadian Geotechnical Journal,1983,30(2):236–246.
[16]KOOPMANS R W R,MILLER R D.Soil freezing and soil water characteristic curves[J].Soil Science Society of America Proceedings,1966,30(6):680–685.
[17]BLACK P B,TICE A R.Comparison of soil freezing curve and soil water curve data for Windsor sandy loam[J].Water Resources Research,1988,25(10):2 205–2 210.
[18]AZMATCH T F,SEGO D C,ARENSON L U,et al.Using soil freezing characteristic curve to estimate the hydraulic conductivity function of partially frozen soils[J].Cold Region Science and Technology,2012,83–84:103–109.
[19]徐斅祖,王家澄,张立新.冻土物理学[M].北京:科学出版社,2001:42–43.(XU Xiaozu,WANG Jiacheng,ZHANG Lixin.Physics of frozen soil[M].Beijing:Science Press,2001:42–43.(in Chinese))
[20]徐斅祖,邓友生.冻土中水分迁移的实验研究[M].北京:科学出版社,1991:27–28.(XU Xiaozu,DENG Yousheng.Experimental study on water migration in freezing and frozen soils[M].Beijing:Science Press,1991:27–28.(in Chinese))