低应力及拉应力条件下非饱和土强度及剪胀特性
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摘要
利用宽广含水率变化范围内非饱和压实土低应力下的直剪试验和抗拉强度试验,研究非饱和土的强度及剪胀特性。试验结果表明:含水率低于塑限时,非饱和土剪切时出现应变软化型破坏和剪胀性;宽广含水率变化范围内,非饱和土峰值剪切强度、最小剪胀率及单轴抗拉强度均随着含水率的增加先增加后减小,变化趋势相同。基于试验结果,首先,对非饱和土拉应力区的Mohr-Coulomb强度包线进行修正。其次,验证修正的Bishop非饱和土抗剪强度模型预测性较差,并分析这种模型广为流行的原因。最后,得到吸力对非饱和土峰值抗剪强度的贡献来源于吸力引起的颗粒间的拉应力和剪胀作用两方面,其中吸力应区分毛细和吸附作用,并可用单轴抗拉强度近似表征拉应力的大小。
The strength and dilation behavior of unsaturated compacted soils was investigated via low-stress direct shear and direct tensile tests over a wide range of water contents. The results show that the unsaturated soils with the water content below the plastic limit exhibit the characteristics of strain softening and shear dilation. The peak shear strength,the minimum dilation rate and the uniaxial tensile strength of unsaturated soils over a wide range of water contents increase and then decrease with the increasing of water content similarly. A modified Mohr-Coulomb strength envelope in tensile stress regime for unsaturated soils is proposed based on the test results. It is verified that the revised Bishop's shear strength model predicts the effect of suction on the shear strength poorly,and the reason why this model is popular is analyzed. Finally,it is suggested that the contribution of suction on the peak shear strength can be described in terms of the effect of suction on interparticle tensile stress and shear dilation,in which the suction is the sum of capillary and adsorptive processes,and the interparticle tensile stress is approximated by the uniaxial tensile strength.
The strength and dilation behavior of unsaturated compacted soils was investigated via low-stress direct shear and direct tensile tests over a wide range of water contents. The results show that the unsaturated soils with the water content below the plastic limit exhibit the characteristics of strain softening and shear dilation. The peak shear strength,the minimum dilation rate and the uniaxial tensile strength of unsaturated soils over a wide range of water contents increase and then decrease with the increasing of water content similarly. A modified Mohr-Coulomb strength envelope in tensile stress regime for unsaturated soils is proposed based on the test results. It is verified that the revised Bishop's shear strength model predicts the effect of suction on the shear strength poorly,and the reason why this model is popular is analyzed. Finally,it is suggested that the contribution of suction on the peak shear strength can be described in terms of the effect of suction on interparticle tensile stress and shear dilation,in which the suction is the sum of capillary and adsorptive processes,and the interparticle tensile stress is approximated by the uniaxial tensile strength.
引文
[1]陈正汉.非饱和土与特殊土力学的基本理论研究[J].岩土工程学报,2014,36(2):201–275.(CHEN Zhenghan.On basic theories of unsaturated soils and special soils[J].Chinese Journal of Geotechnical Engineering,2014,36(2):201–275.(in Chinese))
[2]LU N,LIKOS W J.Suction stress characteristic curve for unsaturated soil[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(2):131–142.
[3]IKARI M J,KOPF A J.Cohesive strength of clay-rich sediment[J].Geophysical Research Letters,2011,38(16):239–255.
[4]IKARI M J,KOPF A J.The role of cohesion and over consolidation in submarine slope failure[J].Marine Geology,2015,369:153–161.
[5]凌华,殷宗泽.非饱和土强度随含水量的变化[J].岩石力学与工程学报,2007,26(7):1 499–1 503.(LING Hua,YIN Zongze.Variation of unsaturated soil strength with water contents[J].Chinese Journal of Rock Mechanics and Engineering,2007,26(7):1 499–1 503.(in Chinese))
[6]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))
[7]BOLTON M D.Strength and dilatancy of sands[J].Géotechnique,1986,36(1):65–78.
[8]SCHOFIELD A N.Interlocking,and peak and design strengths[J].Géotechnique,2006,56(5):357–358.
[9]SCHOFIELD A N.Disturbed soil properties and geotechnical design[M].London:Thomas Telford,2005:22–43.
[10]ZHAN L T,NG C W W.Shear strength characteristics of an unsaturated expansive clay[J].Canadian Geotechnical Journal,2006,43(7):751–763.
[11]HOSSAIN MD A,YIN J H.Shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil[J].Canadian Geotechnical Journal,2010,47(10):1 112–1 126.
[12]岳中琦,徐前.现今斜坡工程安全设计理论的根本缺陷与灾难后果[J].岩土工程学报,2014,36(9):1 602–1 606.(YUE Zhongqi,XU Qian.Fundamental drawbacks and disastrous consequences of current geotechnical safety design theories for slopes[J].Chinese Journal of Geotechnical Engineering,2014,36(9):1 602–1 606.(in Chinese))
[13]汤连生,桑海涛,罗珍贵,等.土体抗拉张力学特性研究进展[J].地球科学进展,2015,30(3):297–309.(TANG Liansheng,SANG Haitao,LUO Zhengui,et al.Advances in research on the mechanical behavior of the tensile strength of soils[J].Advances in Earth Science,2015,30(3):297–309.(in Chinese))
[14]LU N,LIKOS W J.Origin of cohesion and its dependence on saturation for granular media[C]//the Fifth Biot Conference on Poromechanics.Vienna:American Society of Civil Engineers,2014:1 669–1 675.
[15]赵成刚,李舰,刘艳,等.非饱和土力学中几个基本问题的探讨[J].岩土力学,2013,34(7):1 825–1 831.(ZHAO Chenggang,LI Jian,LIU Yan,et al.Discussion on some fundamental problems in unsaturated soil mechanics[J].Rock and Soil Mechanics,2013,34(7):1 825–1 831.(in Chinese))
[16]LU N.Generalized soil water retention equation for adsorption and capillarity[J].Journal of Geotechnical and Geoenvironmental Engineering,2016,142(10):04016051.
[17]张俊然,孙德安,姜彤,等.宽广吸力范围内弱膨胀土的抗剪强度及其预测[J].岩土工程学报,2016,38(6):1 064–1 070.(ZHANG Junran,SUN Dean,JIANG Tong,et al.Shear strength of weakly expansive soils and its prediction in a wide range of suction[J].Chinese Journal of Geotechnical Engineering,2016,38(6):1 064–1 070.(in Chinese))
[18]中华人民共和国行业标准编写组.SL237—1999土工试验规程[S].南京:中国水利水电出版社,1999.(The Professional Standards Compilation Group of People?s Republic of China.SL237—1999Specification of soil test[S].Beijing:China Water Power Press,1999.(in Chinese))
[19]LU N,LIKOS W J.Unsaturated soil mechanics[M].New York:John Wiley,2004:415–459.
[20]孙德安,刘文捷,吕海波.桂林红黏土的土–水特征曲线[J].岩土力学,2014,35(12):3 345–3 351.(SUN Dean,LIU Wenjie,LV Haibo.Soil-water characteristic curve of Guilin lateritic clay[J].Rock and Soil Mechanics,2014,35(12):3 345–3 351.(in Chinese))
[21]孙德安,张俊然,吕海波.全吸力范围南阳膨胀土的土–水特征曲线[J].岩土力学,2013,34(7):1 839–1 846.(SUN Dean,ZHANG Junran,LV Haibo.Soil-water characteristic curve of Nanyang expansive soil in full suction range[J].Rock and Soil Mechanics,2013,34(7):1 839–1 846.(in Chinese))
[22]LEONG E C,HE L,RAHARDJO H.Factors affecting the filter paper method for total and matric suction measurements[J].Geotechnical Testing Journal,2002,25(3):322–333.
[23]蔡国庆,车睿杰,孔小昂,等.非饱和砂土抗拉强度的试验研究[J].水利学报,2017,48(5):623–630.(CAI Guoqing,CHE Ruijie,KONG Xiaoang,et al.Experimental investigation on tensile strength of unsaturated fine sands[J].Journal of Hydraulic Engineering,2017,48(5):623–630.(in Chinese))
[24]KIM T H.Moisture-induced tensile strength and cohesion in sand[Ph.D.Thesis][D].Boulder:University of Colorado,2001.
[25]LU N,WU B,TAN C P.Tensile strength characteristics of unsaturated sands[J].Journal of Geotechnical and Geoenvironmental Engineering,2007,133(2):144–154.
[26]TANG C S,PEI X J,WANG D Y,et al.Tensile strength of compacted clayey soil[J].Journal of Geotechnical and Geoenvironmental Engineering,2014,141(4):04014122.
[27]SHENG D C,ZHOU A N,FREDLUND D G.Shear strength criteria for unsaturated soils[J].Geotechnical and Geological Engineering,2011,29(2):145–159.
[28]ALONSO E E,PEREIRA J-M,VAUNAT J,et al.A microstructurally based effective stress for unsaturated soils[J].Géotechnique,2010,60(12):913–925.
[29]KIM B S,SHIBUYA S,PARK S W,et al.Application of suction stress for estimating unsaturated shear strength of soils using direct shear testing under low confining pressure[J].Canadian Geotechnical Journal,2010,47(9):955–970.
[30]SHIBUYA S,MITACHI T,TAMATE S.Interpretation of direct shear box testing of sands as quasi-simple shear[J].Géotechnique,1997,47(4):769–790.
[31]TAYLOR D W.Fundamentals of soil mechanics[M].New York:John Wiley&Sons,1948:311–362.
[32]LU N,KIM T H,STURE S,et al.Tensile strength of unsaturated sand[J].Journal of Engineering Mechanics,2009,135(12):1 410–1 419.
[2]LU N,LIKOS W J.Suction stress characteristic curve for unsaturated soil[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(2):131–142.
[3]IKARI M J,KOPF A J.Cohesive strength of clay-rich sediment[J].Geophysical Research Letters,2011,38(16):239–255.
[4]IKARI M J,KOPF A J.The role of cohesion and over consolidation in submarine slope failure[J].Marine Geology,2015,369:153–161.
[5]凌华,殷宗泽.非饱和土强度随含水量的变化[J].岩石力学与工程学报,2007,26(7):1 499–1 503.(LING Hua,YIN Zongze.Variation of unsaturated soil strength with water contents[J].Chinese Journal of Rock Mechanics and Engineering,2007,26(7):1 499–1 503.(in Chinese))
[6]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))
[7]BOLTON M D.Strength and dilatancy of sands[J].Géotechnique,1986,36(1):65–78.
[8]SCHOFIELD A N.Interlocking,and peak and design strengths[J].Géotechnique,2006,56(5):357–358.
[9]SCHOFIELD A N.Disturbed soil properties and geotechnical design[M].London:Thomas Telford,2005:22–43.
[10]ZHAN L T,NG C W W.Shear strength characteristics of an unsaturated expansive clay[J].Canadian Geotechnical Journal,2006,43(7):751–763.
[11]HOSSAIN MD A,YIN J H.Shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil[J].Canadian Geotechnical Journal,2010,47(10):1 112–1 126.
[12]岳中琦,徐前.现今斜坡工程安全设计理论的根本缺陷与灾难后果[J].岩土工程学报,2014,36(9):1 602–1 606.(YUE Zhongqi,XU Qian.Fundamental drawbacks and disastrous consequences of current geotechnical safety design theories for slopes[J].Chinese Journal of Geotechnical Engineering,2014,36(9):1 602–1 606.(in Chinese))
[13]汤连生,桑海涛,罗珍贵,等.土体抗拉张力学特性研究进展[J].地球科学进展,2015,30(3):297–309.(TANG Liansheng,SANG Haitao,LUO Zhengui,et al.Advances in research on the mechanical behavior of the tensile strength of soils[J].Advances in Earth Science,2015,30(3):297–309.(in Chinese))
[14]LU N,LIKOS W J.Origin of cohesion and its dependence on saturation for granular media[C]//the Fifth Biot Conference on Poromechanics.Vienna:American Society of Civil Engineers,2014:1 669–1 675.
[15]赵成刚,李舰,刘艳,等.非饱和土力学中几个基本问题的探讨[J].岩土力学,2013,34(7):1 825–1 831.(ZHAO Chenggang,LI Jian,LIU Yan,et al.Discussion on some fundamental problems in unsaturated soil mechanics[J].Rock and Soil Mechanics,2013,34(7):1 825–1 831.(in Chinese))
[16]LU N.Generalized soil water retention equation for adsorption and capillarity[J].Journal of Geotechnical and Geoenvironmental Engineering,2016,142(10):04016051.
[17]张俊然,孙德安,姜彤,等.宽广吸力范围内弱膨胀土的抗剪强度及其预测[J].岩土工程学报,2016,38(6):1 064–1 070.(ZHANG Junran,SUN Dean,JIANG Tong,et al.Shear strength of weakly expansive soils and its prediction in a wide range of suction[J].Chinese Journal of Geotechnical Engineering,2016,38(6):1 064–1 070.(in Chinese))
[18]中华人民共和国行业标准编写组.SL237—1999土工试验规程[S].南京:中国水利水电出版社,1999.(The Professional Standards Compilation Group of People?s Republic of China.SL237—1999Specification of soil test[S].Beijing:China Water Power Press,1999.(in Chinese))
[19]LU N,LIKOS W J.Unsaturated soil mechanics[M].New York:John Wiley,2004:415–459.
[20]孙德安,刘文捷,吕海波.桂林红黏土的土–水特征曲线[J].岩土力学,2014,35(12):3 345–3 351.(SUN Dean,LIU Wenjie,LV Haibo.Soil-water characteristic curve of Guilin lateritic clay[J].Rock and Soil Mechanics,2014,35(12):3 345–3 351.(in Chinese))
[21]孙德安,张俊然,吕海波.全吸力范围南阳膨胀土的土–水特征曲线[J].岩土力学,2013,34(7):1 839–1 846.(SUN Dean,ZHANG Junran,LV Haibo.Soil-water characteristic curve of Nanyang expansive soil in full suction range[J].Rock and Soil Mechanics,2013,34(7):1 839–1 846.(in Chinese))
[22]LEONG E C,HE L,RAHARDJO H.Factors affecting the filter paper method for total and matric suction measurements[J].Geotechnical Testing Journal,2002,25(3):322–333.
[23]蔡国庆,车睿杰,孔小昂,等.非饱和砂土抗拉强度的试验研究[J].水利学报,2017,48(5):623–630.(CAI Guoqing,CHE Ruijie,KONG Xiaoang,et al.Experimental investigation on tensile strength of unsaturated fine sands[J].Journal of Hydraulic Engineering,2017,48(5):623–630.(in Chinese))
[24]KIM T H.Moisture-induced tensile strength and cohesion in sand[Ph.D.Thesis][D].Boulder:University of Colorado,2001.
[25]LU N,WU B,TAN C P.Tensile strength characteristics of unsaturated sands[J].Journal of Geotechnical and Geoenvironmental Engineering,2007,133(2):144–154.
[26]TANG C S,PEI X J,WANG D Y,et al.Tensile strength of compacted clayey soil[J].Journal of Geotechnical and Geoenvironmental Engineering,2014,141(4):04014122.
[27]SHENG D C,ZHOU A N,FREDLUND D G.Shear strength criteria for unsaturated soils[J].Geotechnical and Geological Engineering,2011,29(2):145–159.
[28]ALONSO E E,PEREIRA J-M,VAUNAT J,et al.A microstructurally based effective stress for unsaturated soils[J].Géotechnique,2010,60(12):913–925.
[29]KIM B S,SHIBUYA S,PARK S W,et al.Application of suction stress for estimating unsaturated shear strength of soils using direct shear testing under low confining pressure[J].Canadian Geotechnical Journal,2010,47(9):955–970.
[30]SHIBUYA S,MITACHI T,TAMATE S.Interpretation of direct shear box testing of sands as quasi-simple shear[J].Géotechnique,1997,47(4):769–790.
[31]TAYLOR D W.Fundamentals of soil mechanics[M].New York:John Wiley&Sons,1948:311–362.
[32]LU N,KIM T H,STURE S,et al.Tensile strength of unsaturated sand[J].Journal of Engineering Mechanics,2009,135(12):1 410–1 419.