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

RESEARCH ON INFLUENCE OF PRINCIPAL STRESS AXIS CYCLIC ROTATION AT LOW SHEAR STRESS LEVEL ON BEHAVIOR OF INTACT CLAY

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.