土体干缩裂隙发育方向及演化特征的层间摩擦效应研究
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摘要
自然界中的土体通常成层分布,在干旱条件下,表层土体的干缩开裂过程极易受层间接触条件的制约。为了探究土层间摩擦效应对土体干缩裂隙发育方向及其演化特征的影响,开展了一系列室内干燥试验。试验共配置了3组初始饱和的泥浆样,在30℃的室温条件下干燥失水,通过在试样底部铺设不同粗糙度的砂纸来模拟不同土层间的摩擦效应。试验过程中对试样表面及侧面进行定时拍照,从不同角度记录了裂隙发育全过程,通过分析,获得了一些新发现:(1)干缩裂隙不仅能从土体表面向下发育,而且还可能率先从土体底部向上发育,这不同于以往的习惯性认识;(2)初始裂隙的发育位置受土质条件及基底摩擦条件的共同制约,对于非均质性比较严重或者表面存在明显"杂点"的土体而言,裂隙往往首先从表面"杂点"处产生并向下发育,而对均质性较好的土体而言,在基底摩擦效应的影响下裂隙可以率先从土体底部生成并逐渐向上发育,且土体底部的裂隙发育程度甚至会高于表面的裂隙发育程度;(3)底部生成的裂隙以斜向上发育居多,这可能与裂隙发育过程中受到的剪切应力作用有关;(4)干燥过程中,土体呈向心收缩,存在明显的收缩核现象;(5)基底摩擦效应能改变土体干缩开裂过程中内部应力场的演化,从而对土体的横向和纵向收缩应变及剖面含水率的空间分布产生影响,如基底摩擦越大,土体横向收缩应变越小,而纵向收缩应变越大。
As the soils in nature are distributed in layers, the desiccation cracking process of the top soil is easily constrained by the contact conditions between the soil layers under drought conditions. A series of laboratory desiccation tests are therefore conducted to investigate the influences of interfacial frictional effect between soil layers on the developing direction and evolution characteristics of soil desiccation cracking. In the tests, three slurry samples with the initial saturation are prepared and dried under a constant room temperature of 30℃. Different interfacial friction conditions are designed at the bottom of the samples to simulate the frictional effect between soil layers in nature. During drying, photos of the surface and side of the samples at regular intervals are taken to record the development process of soil cracks from different angles. Some new discoveries show:(1) The soil desiccation cracks can develop from the surface downwards and may be firstly generated from the bottom of the soil and gradually develop upwards, which is different from the previous habitual understanding;(2) During the drying process, the initial development position and development degree of cracks are constrained by both the soil properties and the substrate friction conditions. For the soils with severe inhomogeneous or obvious flaws on the surface, the cracks are generated and develop from the surface flaws of soils, while for the relatively homogeneous soils, the cracks can be firstly generated from the bottom of the soil and gradually develop upwards under the influences of the substrate friction. Moreover, after the drying is completed, the development degree of the bottom cracks of the soils is even higher than that of the surface cracks.(3) The bottom cracks mostly propagate in inclined direction, and they are probably related to the developed shear stress.(4) During drying, the soil shrinks concentrically, and noticeable shrinkage nucleus at the bottom of soil appears at the bottom of the soils.(5) The substrate friction effect can change the internal stress field during the desiccation cracking process of soils, and therefore affects the transverse and longitudinal strains and profile water content distribution of the soils. For example, the larger the substrate frictional degree, the smaller the transverse strain of soils, but the greater the longitudinal strain of soils.
As the soils in nature are distributed in layers, the desiccation cracking process of the top soil is easily constrained by the contact conditions between the soil layers under drought conditions. A series of laboratory desiccation tests are therefore conducted to investigate the influences of interfacial frictional effect between soil layers on the developing direction and evolution characteristics of soil desiccation cracking. In the tests, three slurry samples with the initial saturation are prepared and dried under a constant room temperature of 30℃. Different interfacial friction conditions are designed at the bottom of the samples to simulate the frictional effect between soil layers in nature. During drying, photos of the surface and side of the samples at regular intervals are taken to record the development process of soil cracks from different angles. Some new discoveries show:(1) The soil desiccation cracks can develop from the surface downwards and may be firstly generated from the bottom of the soil and gradually develop upwards, which is different from the previous habitual understanding;(2) During the drying process, the initial development position and development degree of cracks are constrained by both the soil properties and the substrate friction conditions. For the soils with severe inhomogeneous or obvious flaws on the surface, the cracks are generated and develop from the surface flaws of soils, while for the relatively homogeneous soils, the cracks can be firstly generated from the bottom of the soil and gradually develop upwards under the influences of the substrate friction. Moreover, after the drying is completed, the development degree of the bottom cracks of the soils is even higher than that of the surface cracks.(3) The bottom cracks mostly propagate in inclined direction, and they are probably related to the developed shear stress.(4) During drying, the soil shrinks concentrically, and noticeable shrinkage nucleus at the bottom of soil appears at the bottom of the soils.(5) The substrate friction effect can change the internal stress field during the desiccation cracking process of soils, and therefore affects the transverse and longitudinal strains and profile water content distribution of the soils. For example, the larger the substrate frictional degree, the smaller the transverse strain of soils, but the greater the longitudinal strain of soils.
引文
[1]KODIKARA J,COSTA S.Desiccation cracking in clayey soils:mechanisms and modelling[M]//Multiphysical Testing of Soils and Shales.Berlin:Springer,2013:21-32.
[2]HEWITT P J,PHILIP L K.Problems of clay desiccation in composite lining systems[J].Engineering Geology,1999,53(2):107-113.
[3]RAYHANI M H,YANFUL E K,FAKHER A.Desiccationinduced cracking and its effect on the hydraulic conductive[J].Canadian Geotechnical Journal,2007,44(3):276-283.
[4]NELSON J D,MILLER D J.Expansive soils:problems and practice in foundation and pavement engineering[M].New York:John Wiley,1992.
[5]AYAD R,KONRAD J M,SOULIéM.Desiccation of a sensitive clay:application of the model CRACK[J].International Zoo Yearbook,1997,34(34):943-951.
[6]LOZADA C,THOREL L,CAICEDO B.Effects of cracks and desiccation on the bearing capacity of soil deposits[J].Géotechnique Letters,2015,5(3):112-117.
[7]BAKER R.Tensile strength,tension cracks,and stability of slopes[J].Soils&Foundations,1981,21(2):1-19.
[8]陈守义.考虑入渗和蒸发影响的土坡稳定性分析方法[J].岩土力学,1997(2):8-12.(CHEN Shou-yi.A method of stability analysis taken effects of infiltration and evaporation into consideration for soil slopes[J].Rock and Soil Mechanics,1997(2):8-12.(in Chinese))
[9]姚海林,郑少河,陈守义.考虑裂隙及雨水入渗影响的膨胀土边坡稳定性分析[J].岩土工程学报,2001,23(5):606-609.(YAO Hai-lin,ZHENG Shao-he,CHEN Shou-yi,et al.Analysis on the slope stability of expansive soils considering cracks and infiltration of rain[J].Chinese Journal of Geotechnical Engineering,2001,23(5):606-609.(in Chinese))
[10]殷宗泽,袁俊平,韦杰,等.论裂隙对膨胀土边坡稳定的影响[J].岩土工程学报,2012,34(12):2155-2161.(YINZong-ze,YUAN Jun-ping,WEI Jie,et al.Influences of fissures on slope stability of expansive soil[J].Chinese Journal of Geotechnical Engineering,2012,34(12):2155-2161.(in Chinese))
[11]TANG C S,CUI Y J,TANG A M,et al.Experiment evidence on the temperature dependence of desiccation cracking behavior of clayey soils[J].Engineering Geology,2010,114(3/4):261-266.
[12]TANG C,SHI B,LIU C,et al.Influencing factors of geometrical structure of surface shrinkage cracks in clayey soils[J].Engineering Geology,2008,101(3):204-219.
[13]唐朝生,施斌,刘春.膨胀土收缩开裂特性研究[J].工程地质学报,2012,20(5):663-673.(TANG Chao-sheng,SHI Bin,LIU Chun.Study on desiccation cracking behavior of expansive soil[J].Journal of Engineering Geology,2012,20(5):663-673.(in Chinese))
[14]TOWNER G D.The mechanics of cracking of drying clay[J].Journal of Agricultural Engineering Research,1987,36(2):115-124.
[15]MITCHELL J K,SOGA K.Fundamentals of soil behavior[J].Soil Science Society of America Journal,1976,40(4):827-866.
[16]LAKSHMIKANTHAM R,PRATPERE C,LEDESMA-ALBERTO.Experimental evidence of size effect in soil cracking[J].Canadian Geotechnical Journal,2012,49(3):264-284.
[17]袁权,谢锦宇,任柯.边界约束对膨胀土干缩开裂的影响[J].工程地质学报,2016,24(4):604-609.(YUANQuan,XIE Jin-yu,REN Ke,et al.Effect of boundary constrains on desiccation crack of swelling soil[J].Journal of Engineering Geology,2016,24(4):604-609.(in Chinese))
[18]易顺民,黎志恒,张延中.膨胀土裂隙结构的分形特征及其意义[J].岩石工程学报,1999,21(3):294-298.(YIShun-min,LI Zhi-heng,ZHANG Yan-zhong.The fractal characteristics of fractures in expansion soil and its significance[J].Chinese Journal of Geotechnical Engineering,1999,21(3):294-298.(in Chinese))
[19]唐朝生,施斌,顾凯.土中水分的蒸发过程试验研究[J].工程地质学报,2011(6):875-881.(TANG Chao-sheng,SHI Bin,GU Kai.Experimental investigation on evaporation process of water in soil during drying[J].Journal of Engineering Geology,2011(6):875-881.(in Chinese))
[20]TANG C S,CUI Y J,SHI B,et al.Desiccation and cracking behaviour of clay layer from slurry state under wetting-drying cycles[J].Geoderma,2011,166(1):111-118.
[21]LIU C,TANG C S,SHI B,et al.Automatic quantification of crack patterns by image processing[J].Computers&Geosciences,2013,57(4):77-80.
[22]KODIKARA J,BARBOUR S L,FREDLUND D G.An idealized framework for the analysis of cohesive soils undergoing desiccation[J].Canadian Geotechnical Journal,1997,34(4):477-488.
[23]唐朝生,施斌,刘春.影响黏性土表面干缩裂缝结构形态的因素及定量分析[J].水利学报,2007,38(10):1186-1193.(TANG Chao-sheng,SHI Bin,LIU Chun.Factors affecting the surface cracking in clay due to drying shrinkage[J].Journal of Hydraulic Engineering,2007,38(10):1186-1193.(in Chinese))
[24]唐朝生,王德银,施斌.土体干缩裂隙网络定量分析[J].岩土工程学报,2013,33(12):2298-2305.(TANGChao-sheng,WANG De-yin,SHI Bin,et al.Quantitative analysis of soil desiccation crack network[J].Chinese Journal of Geotechnical Engineering,2013,33(12):2298-2305.(in Chinese))
[25]MORRIS P H,GRAHAM J,WILLIAMS D J.Cracking in drying soils[J].Canadian Geotechnical Journal,1992,29(2):263-277.
[26]FREDLUND D G,RAHARDJO H.Soil mechanics for unsaturated soils[M].New York:John Wiley&Sons,1993.
[27]YESILLER N,MILLER C J,INCI G,et al.Desiccation and cracking behavior of three compacted landfill liner soils[J].Engineering Geology,2000,57(1):105-121.
[28]AMARASIRI A L,COSTA S,KODIKARA J K.Determination of cohesive properties for mode I fracture from compacted clay beams[J].Canadian Geotechnical Journal,2011,48(8):1163-1173.
[29]曾浩,唐朝生,刘昌黎,等.控制厚度条件下土体干缩开裂的界面摩擦效应[J].岩土工程学报,2019,41(3):544-553.(ZENG Hao,TANG Chao-sheng,LIU Chang-li,et al.Effects of boundary friction and layer thickness on desiccation cracking behaviors of soils[J].Chinese Journal of Geotechnical Engineering,2019,41(3):544-553.(in Chinese))
[30]HUECKEL T.On effective stress concepts and deformation in clays subjected to environmental loads:discussion[J].Canadian Geotechnical Journal,1992,29(6):1120-1125
[31]刘昌黎,唐朝生,李昊达,等.界面粗糙度对土体龟裂影响的试验研究[J].工程地质学报,2017,25(5):1314-1321.(LIU Chang-li,TANG Chao-sheng,LI Hao-da,et al.Experimental study on the effect of interfacial roughness on desiccation cracking behavior of soil[J].Journal of Engineering Geology,2017,25(5):1314-1321.(in Chinese))
[32]SHORLIN K A,DE BRUYN J R,GRAHAM M,et al.Development and geometry of isotropic and directional shrinkage-crack patterns[J].Physical Review E Statistical Physics Plasmas Fluids&Related Interdisciplinary Topics,1999,61(6 Pt B):6950.
[33]GROISMAN A,KAPLAN E.An experimental study of cracking induced by desiccation[J].Europhysics Letters,2007,25(6):415.
[34]PERON H,HUECKEL T,LALOUI L,et al.Fundamentals of desiccation cracking of fine-grained soils:experimental characterisation and mechanisms identification.[J].Canadian Geotechnical Journal,2009,46(10):1177-1201.
[35]PERON H,LALOUI L,HU L,et al.Desiccation cracking of soils[J].Chemosphere,2009,13(7/8):869-888.
[36]唐朝生,施斌,崔玉军.土体干缩裂隙的形成发育过程及机理[J].岩土工程学报,2018:1415-1423.(TANGChao-sheng,SHI Bin,CUI Yu-Jun.Behaviors and mechanisms of desiccation cracking of soils[J].Chinese Journal of Geotechnical Engineering,2018:1415-1423.(in Chinese))
[37]TOLLENAAR R N,PAASSEN L A V,JOMMI C.Observations on the desiccation and cracking of clay layers[J].Engineering Geology,2017,230:23-31.
[38]LU N,LIKOS W J.Unsaturated soil mechanics[M].J.Wiley,2004.
[39]TANG C S,SHI B,LIU C,et al.Experimental characterization of shrinkage and desiccation cracking in thin clay layer[J].Applied Clay Science,2011,52(1):69-77.
[2]HEWITT P J,PHILIP L K.Problems of clay desiccation in composite lining systems[J].Engineering Geology,1999,53(2):107-113.
[3]RAYHANI M H,YANFUL E K,FAKHER A.Desiccationinduced cracking and its effect on the hydraulic conductive[J].Canadian Geotechnical Journal,2007,44(3):276-283.
[4]NELSON J D,MILLER D J.Expansive soils:problems and practice in foundation and pavement engineering[M].New York:John Wiley,1992.
[5]AYAD R,KONRAD J M,SOULIéM.Desiccation of a sensitive clay:application of the model CRACK[J].International Zoo Yearbook,1997,34(34):943-951.
[6]LOZADA C,THOREL L,CAICEDO B.Effects of cracks and desiccation on the bearing capacity of soil deposits[J].Géotechnique Letters,2015,5(3):112-117.
[7]BAKER R.Tensile strength,tension cracks,and stability of slopes[J].Soils&Foundations,1981,21(2):1-19.
[8]陈守义.考虑入渗和蒸发影响的土坡稳定性分析方法[J].岩土力学,1997(2):8-12.(CHEN Shou-yi.A method of stability analysis taken effects of infiltration and evaporation into consideration for soil slopes[J].Rock and Soil Mechanics,1997(2):8-12.(in Chinese))
[9]姚海林,郑少河,陈守义.考虑裂隙及雨水入渗影响的膨胀土边坡稳定性分析[J].岩土工程学报,2001,23(5):606-609.(YAO Hai-lin,ZHENG Shao-he,CHEN Shou-yi,et al.Analysis on the slope stability of expansive soils considering cracks and infiltration of rain[J].Chinese Journal of Geotechnical Engineering,2001,23(5):606-609.(in Chinese))
[10]殷宗泽,袁俊平,韦杰,等.论裂隙对膨胀土边坡稳定的影响[J].岩土工程学报,2012,34(12):2155-2161.(YINZong-ze,YUAN Jun-ping,WEI Jie,et al.Influences of fissures on slope stability of expansive soil[J].Chinese Journal of Geotechnical Engineering,2012,34(12):2155-2161.(in Chinese))
[11]TANG C S,CUI Y J,TANG A M,et al.Experiment evidence on the temperature dependence of desiccation cracking behavior of clayey soils[J].Engineering Geology,2010,114(3/4):261-266.
[12]TANG C,SHI B,LIU C,et al.Influencing factors of geometrical structure of surface shrinkage cracks in clayey soils[J].Engineering Geology,2008,101(3):204-219.
[13]唐朝生,施斌,刘春.膨胀土收缩开裂特性研究[J].工程地质学报,2012,20(5):663-673.(TANG Chao-sheng,SHI Bin,LIU Chun.Study on desiccation cracking behavior of expansive soil[J].Journal of Engineering Geology,2012,20(5):663-673.(in Chinese))
[14]TOWNER G D.The mechanics of cracking of drying clay[J].Journal of Agricultural Engineering Research,1987,36(2):115-124.
[15]MITCHELL J K,SOGA K.Fundamentals of soil behavior[J].Soil Science Society of America Journal,1976,40(4):827-866.
[16]LAKSHMIKANTHAM R,PRATPERE C,LEDESMA-ALBERTO.Experimental evidence of size effect in soil cracking[J].Canadian Geotechnical Journal,2012,49(3):264-284.
[17]袁权,谢锦宇,任柯.边界约束对膨胀土干缩开裂的影响[J].工程地质学报,2016,24(4):604-609.(YUANQuan,XIE Jin-yu,REN Ke,et al.Effect of boundary constrains on desiccation crack of swelling soil[J].Journal of Engineering Geology,2016,24(4):604-609.(in Chinese))
[18]易顺民,黎志恒,张延中.膨胀土裂隙结构的分形特征及其意义[J].岩石工程学报,1999,21(3):294-298.(YIShun-min,LI Zhi-heng,ZHANG Yan-zhong.The fractal characteristics of fractures in expansion soil and its significance[J].Chinese Journal of Geotechnical Engineering,1999,21(3):294-298.(in Chinese))
[19]唐朝生,施斌,顾凯.土中水分的蒸发过程试验研究[J].工程地质学报,2011(6):875-881.(TANG Chao-sheng,SHI Bin,GU Kai.Experimental investigation on evaporation process of water in soil during drying[J].Journal of Engineering Geology,2011(6):875-881.(in Chinese))
[20]TANG C S,CUI Y J,SHI B,et al.Desiccation and cracking behaviour of clay layer from slurry state under wetting-drying cycles[J].Geoderma,2011,166(1):111-118.
[21]LIU C,TANG C S,SHI B,et al.Automatic quantification of crack patterns by image processing[J].Computers&Geosciences,2013,57(4):77-80.
[22]KODIKARA J,BARBOUR S L,FREDLUND D G.An idealized framework for the analysis of cohesive soils undergoing desiccation[J].Canadian Geotechnical Journal,1997,34(4):477-488.
[23]唐朝生,施斌,刘春.影响黏性土表面干缩裂缝结构形态的因素及定量分析[J].水利学报,2007,38(10):1186-1193.(TANG Chao-sheng,SHI Bin,LIU Chun.Factors affecting the surface cracking in clay due to drying shrinkage[J].Journal of Hydraulic Engineering,2007,38(10):1186-1193.(in Chinese))
[24]唐朝生,王德银,施斌.土体干缩裂隙网络定量分析[J].岩土工程学报,2013,33(12):2298-2305.(TANGChao-sheng,WANG De-yin,SHI Bin,et al.Quantitative analysis of soil desiccation crack network[J].Chinese Journal of Geotechnical Engineering,2013,33(12):2298-2305.(in Chinese))
[25]MORRIS P H,GRAHAM J,WILLIAMS D J.Cracking in drying soils[J].Canadian Geotechnical Journal,1992,29(2):263-277.
[26]FREDLUND D G,RAHARDJO H.Soil mechanics for unsaturated soils[M].New York:John Wiley&Sons,1993.
[27]YESILLER N,MILLER C J,INCI G,et al.Desiccation and cracking behavior of three compacted landfill liner soils[J].Engineering Geology,2000,57(1):105-121.
[28]AMARASIRI A L,COSTA S,KODIKARA J K.Determination of cohesive properties for mode I fracture from compacted clay beams[J].Canadian Geotechnical Journal,2011,48(8):1163-1173.
[29]曾浩,唐朝生,刘昌黎,等.控制厚度条件下土体干缩开裂的界面摩擦效应[J].岩土工程学报,2019,41(3):544-553.(ZENG Hao,TANG Chao-sheng,LIU Chang-li,et al.Effects of boundary friction and layer thickness on desiccation cracking behaviors of soils[J].Chinese Journal of Geotechnical Engineering,2019,41(3):544-553.(in Chinese))
[30]HUECKEL T.On effective stress concepts and deformation in clays subjected to environmental loads:discussion[J].Canadian Geotechnical Journal,1992,29(6):1120-1125
[31]刘昌黎,唐朝生,李昊达,等.界面粗糙度对土体龟裂影响的试验研究[J].工程地质学报,2017,25(5):1314-1321.(LIU Chang-li,TANG Chao-sheng,LI Hao-da,et al.Experimental study on the effect of interfacial roughness on desiccation cracking behavior of soil[J].Journal of Engineering Geology,2017,25(5):1314-1321.(in Chinese))
[32]SHORLIN K A,DE BRUYN J R,GRAHAM M,et al.Development and geometry of isotropic and directional shrinkage-crack patterns[J].Physical Review E Statistical Physics Plasmas Fluids&Related Interdisciplinary Topics,1999,61(6 Pt B):6950.
[33]GROISMAN A,KAPLAN E.An experimental study of cracking induced by desiccation[J].Europhysics Letters,2007,25(6):415.
[34]PERON H,HUECKEL T,LALOUI L,et al.Fundamentals of desiccation cracking of fine-grained soils:experimental characterisation and mechanisms identification.[J].Canadian Geotechnical Journal,2009,46(10):1177-1201.
[35]PERON H,LALOUI L,HU L,et al.Desiccation cracking of soils[J].Chemosphere,2009,13(7/8):869-888.
[36]唐朝生,施斌,崔玉军.土体干缩裂隙的形成发育过程及机理[J].岩土工程学报,2018:1415-1423.(TANGChao-sheng,SHI Bin,CUI Yu-Jun.Behaviors and mechanisms of desiccation cracking of soils[J].Chinese Journal of Geotechnical Engineering,2018:1415-1423.(in Chinese))
[37]TOLLENAAR R N,PAASSEN L A V,JOMMI C.Observations on the desiccation and cracking of clay layers[J].Engineering Geology,2017,230:23-31.
[38]LU N,LIKOS W J.Unsaturated soil mechanics[M].J.Wiley,2004.
[39]TANG C S,SHI B,LIU C,et al.Experimental characterization of shrinkage and desiccation cracking in thin clay layer[J].Applied Clay Science,2011,52(1):69-77.
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