低剪应力水平主应力轴循环旋转对原状黏土性状影响研究
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摘要
为研究低剪应力水平主应力轴循环路径可能对黏土性状产生的影响,以杭州地区典型原状软黏土为对象开展试验研究。结果表明,试样在安全极限剪应力水平下进行剪应力恒定的多振次主应力轴循环旋转后(含单幅和双幅旋转),应变及孔隙水压力发展进入动态平衡,瞬时等效刚度和孔隙水压力值主要取决于剪应力中的扭剪应力分量,而轴向应力分量对两值亦有促进作用。进入主应力轴循环旋转动态平衡的试样在卸载后进行后续静态剪切时,应力–应变关系将表现出明显的刚度硬化特征,其中尤以三轴压缩过程中强度发挥程度提前的现象最为显著。同时,由于主应力轴循环旋转导致试样残余应变的积累及结构上的变化,使得试样在后续三轴压缩试验初期产生的主应变增量与主应力增量方向不共轴特性较为明显。但低于安全极限剪应力水平的主应力轴循环旋转未对试样的静态抗剪强度以及临界孔隙水压力产生显著影响。
In order to study the influence of principal stress axis cyclic rotation at low shear stress level on clay′s behavior,a series of experiments of Hangzhou typical intact soft clay were conducted. The experimental results reveal that the stress paths such as principal stress axis cyclic rotation with constant shear stress lower than the limit shear stress bring the variation of samples′ strain components and pore water pressure into dynamic equilibrium;the stable values of equivalent stiffness and pore water pressure at equilibrium are mainly decided by the tortional shear stress component;and the axial stress component also promotes these two values when the tortional shear stress components are the same. Meanwhile,such principal stress axis cyclic rotation causes the stiffness to be enhanced during the following static shear stage. Especially,when the following stage is triaxial compression one,the strength will arrive in advance observably,and the directions of principal stress increment and principal strain increment become obviously non-coaxial at the initial of triaxial compression,which are mainly caused by the residual strain and changes of soils′ structure generated in the previous cyclic principal stress axis cyclic rotation. But the static shear strength and critical pore water pressure in the following static shear stages are not greatly influenced by the previous principal stress axis cyclic rotation.
In order to study the influence of principal stress axis cyclic rotation at low shear stress level on clay′s behavior,a series of experiments of Hangzhou typical intact soft clay were conducted. The experimental results reveal that the stress paths such as principal stress axis cyclic rotation with constant shear stress lower than the limit shear stress bring the variation of samples′ strain components and pore water pressure into dynamic equilibrium;the stable values of equivalent stiffness and pore water pressure at equilibrium are mainly decided by the tortional shear stress component;and the axial stress component also promotes these two values when the tortional shear stress components are the same. Meanwhile,such principal stress axis cyclic rotation causes the stiffness to be enhanced during the following static shear stage. Especially,when the following stage is triaxial compression one,the strength will arrive in advance observably,and the directions of principal stress increment and principal strain increment become obviously non-coaxial at the initial of triaxial compression,which are mainly caused by the residual strain and changes of soils′ structure generated in the previous cyclic principal stress axis cyclic rotation. But the static shear strength and critical pore water pressure in the following static shear stages are not greatly influenced by the previous principal stress axis cyclic rotation.
引文
[1]ISHIHARA K,TOWHATA I.Sand response to cyclic rotation of principal stress directions as induced by wave loads[J].Soils and Foundations,1983,23(4):11–26.
[2]TOWHATA I,ISHIHARA K.Undrained strength of sand undergoing cyclic rotation of principal stress axes[J].Soils and Foundations,1985,25(2):135–147.
[3]SHIBUYA S,HIGHT D W.Paterns of cyclic principal stress rotation and liquefaction[C]//ISHIHARA K ed.Proceedings of the2nd International Symposium on Numerical Models in Geomechanics.[S.l.]:[s.n.],1986:265–268.
[4]付磊,王洪瑾,周景星.主应力偏转角对砂砾料动力特性影响的试验研究[J].岩土工程学报,2000,22(4):435–440.(FU Lei,WANG Hongjin,ZHOU Jingxing.Effect of the initial rotation angle of principal stress on the dynamic properties of soil[J].Chinese Journal of Geotechnical Engineering,2000,22(4):435–440.(in Chinese))
[5]郭莹,栾茂田,何杨,等.复杂应力条件下饱和松砂孔隙水压力增长特性的试验研究[J].地震工程与工程振动,2004,24(3):139–144.(GUO Ying,LUAN Maotian,HE Yang,et al.Experimental study on development pattern of shaking-induced pore water pressure of saturated loose sand under complex loading[J].Earthquake Engineering and Engineering Vibration,2004,24(3):139–144.(in Chinese))
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[7]ARTHUR J R F,CHUA K S,DUNSTAN T,et al.Principal stress rotation:a missing parameter[J].Journal of the Geotechnial Engineering Division,ASCE,1980,106(4):419–433.
[8]WONG R K S,ARTHUR J R F.Sand sheared by stresses with cyclic variations in direction[J].Geotechnique,1986,36(2):215–226.
[9]GR?BE P J.Resilient and permanent deformation of railway foundations under principal stress rotation[Ph.D.Thesis][D].Southampton:University of Southampton,2002.
[10]郭莹,栾茂田,许成顺,等.主应力方向变化对松砂不排水动强度特性影响[J].岩土工程学报,2003,25(6):666–670.(GUO Ying,LUAN Maotian,XU Chengshun,et al.Effect of variation of principal stress orientation on undrained dynamic strength behavior of loose sand[J].Chinese Journal of Geotechnical Engineering,2003,25(6):666–670.(in Chinese))
[11]栾茂田,许成顺,何杨,等.主应力方向对饱和松砂不排水单调剪切特性影响的试验研究[J].岩土工程学报,2006,28(9):1085–1089.(LUAN Maotian,XU Chengshun,HE Yang,et al.Experimental study on effect of orientation of the principal stress on undrained behavior of saturated loose sand under monotonic shearing[J].Chinese Journal of Geotechnical Engineering,2006,28(9):1085–1089.(in Chinese))
[12]HAN L.Three-dimensional static and dynamic behavior of Kaolin clay with controlled microfabric using combined axial-torsional testing[Ph.D.Thesis][D].Knoxville:The University of Tennessee,2003.
[13]沈扬,周建,龚晓南.空心圆柱仪(HCA)模拟恒定围压下主应力轴循环旋转应力路径能力分析[J].岩土工程学报,2006,28(3):281–287.(SHEN Yang,ZHOU Jian,GONG Xiaonan.Analysis of the ability of HCA to imitate cyclic principal stress rotation under constant confining pressure[J].Chinese Journal of Geotechnical Engineering,2006,28(3):281–287.(in Chinese))
[14]沈扬,周建,张金良,等.考虑主应力方向变化的原状黏土强度及超静孔压特性研究[J].岩土工程学报,2007,29(6):843–847.(SHEN Yang,ZHOU Jian,ZHANG Jinliang,et al.Research on characteristics of intact clay′s strength and pore pressure considering variable principal stress direction[J].Chinese Journal of Geotechnical Engineering,2007,29(6):843–847.(in Chinese))
[15]沈扬,周建,张金良,等.主应力轴循环旋转下原状软黏土临界性状试验研究[J].浙江大学学报(工学版),(待刊).(SHEN Yang,ZHOU Jian,ZHANG Jinliang,et al.Experimental study on critical properties of natural soft clay under cyclic principal stress rotation[J].Journal of Zhejiang University(Engineering Science),(to be pressed).(in Chinese))
[2]TOWHATA I,ISHIHARA K.Undrained strength of sand undergoing cyclic rotation of principal stress axes[J].Soils and Foundations,1985,25(2):135–147.
[3]SHIBUYA S,HIGHT D W.Paterns of cyclic principal stress rotation and liquefaction[C]//ISHIHARA K ed.Proceedings of the2nd International Symposium on Numerical Models in Geomechanics.[S.l.]:[s.n.],1986:265–268.
[4]付磊,王洪瑾,周景星.主应力偏转角对砂砾料动力特性影响的试验研究[J].岩土工程学报,2000,22(4):435–440.(FU Lei,WANG Hongjin,ZHOU Jingxing.Effect of the initial rotation angle of principal stress on the dynamic properties of soil[J].Chinese Journal of Geotechnical Engineering,2000,22(4):435–440.(in Chinese))
[5]郭莹,栾茂田,何杨,等.复杂应力条件下饱和松砂孔隙水压力增长特性的试验研究[J].地震工程与工程振动,2004,24(3):139–144.(GUO Ying,LUAN Maotian,HE Yang,et al.Experimental study on development pattern of shaking-induced pore water pressure of saturated loose sand under complex loading[J].Earthquake Engineering and Engineering Vibration,2004,24(3):139–144.(in Chinese))
[6]沈瑞福,王洪瑾,周景星.动主应力轴连续旋转下砂土的动强度[J].水利学报,1996,27(1):27–33.(SHEN Ruifu,WANG Hongjin,ZHOU Jingxing.Dynamic strength of sand under cyclic rotation of principal stress directions[J].Journal of Hydraulic Engineering,1996,27(1):27–33.(in Chinese))
[7]ARTHUR J R F,CHUA K S,DUNSTAN T,et al.Principal stress rotation:a missing parameter[J].Journal of the Geotechnial Engineering Division,ASCE,1980,106(4):419–433.
[8]WONG R K S,ARTHUR J R F.Sand sheared by stresses with cyclic variations in direction[J].Geotechnique,1986,36(2):215–226.
[9]GR?BE P J.Resilient and permanent deformation of railway foundations under principal stress rotation[Ph.D.Thesis][D].Southampton:University of Southampton,2002.
[10]郭莹,栾茂田,许成顺,等.主应力方向变化对松砂不排水动强度特性影响[J].岩土工程学报,2003,25(6):666–670.(GUO Ying,LUAN Maotian,XU Chengshun,et al.Effect of variation of principal stress orientation on undrained dynamic strength behavior of loose sand[J].Chinese Journal of Geotechnical Engineering,2003,25(6):666–670.(in Chinese))
[11]栾茂田,许成顺,何杨,等.主应力方向对饱和松砂不排水单调剪切特性影响的试验研究[J].岩土工程学报,2006,28(9):1085–1089.(LUAN Maotian,XU Chengshun,HE Yang,et al.Experimental study on effect of orientation of the principal stress on undrained behavior of saturated loose sand under monotonic shearing[J].Chinese Journal of Geotechnical Engineering,2006,28(9):1085–1089.(in Chinese))
[12]HAN L.Three-dimensional static and dynamic behavior of Kaolin clay with controlled microfabric using combined axial-torsional testing[Ph.D.Thesis][D].Knoxville:The University of Tennessee,2003.
[13]沈扬,周建,龚晓南.空心圆柱仪(HCA)模拟恒定围压下主应力轴循环旋转应力路径能力分析[J].岩土工程学报,2006,28(3):281–287.(SHEN Yang,ZHOU Jian,GONG Xiaonan.Analysis of the ability of HCA to imitate cyclic principal stress rotation under constant confining pressure[J].Chinese Journal of Geotechnical Engineering,2006,28(3):281–287.(in Chinese))
[14]沈扬,周建,张金良,等.考虑主应力方向变化的原状黏土强度及超静孔压特性研究[J].岩土工程学报,2007,29(6):843–847.(SHEN Yang,ZHOU Jian,ZHANG Jinliang,et al.Research on characteristics of intact clay′s strength and pore pressure considering variable principal stress direction[J].Chinese Journal of Geotechnical Engineering,2007,29(6):843–847.(in Chinese))
[15]沈扬,周建,张金良,等.主应力轴循环旋转下原状软黏土临界性状试验研究[J].浙江大学学报(工学版),(待刊).(SHEN Yang,ZHOU Jian,ZHANG Jinliang,et al.Experimental study on critical properties of natural soft clay under cyclic principal stress rotation[J].Journal of Zhejiang University(Engineering Science),(to be pressed).(in Chinese))
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