主应力轴旋转对土体性状影响的试验进展研究

对目前国内外主应力轴旋转条件（包括单向旋转和循环旋转）下土体性状研究的室内试验进行系统的分析与总结，得到以下结论：土体在不排水主应力轴旋转条件下产生孔压积累，这在主应力轴循环旋转中特别显著，且通常大于等剪应力幅度的动三轴或扭剪试验产生的孔压，并可建立与某种应变增量的函数关系，此外孔压开展的速率与程度受到土体原生各向异性的影响，但当试样所受剪应力水平较低时，上述影响的程度减弱。而在主应力轴循环旋转过程中，孔压还与主应力轴的转幅或循环次数等因素有关；主应力轴循环旋转并没有导致有效内摩擦角的显著变化。相当一部分试验结果表明，不论主应力轴旋转时的排水条件如何，只要采用归一化的强度标准，土体后续的抗剪强度并不受主应力轴旋转的影响，但也有一些试验表明，排水条件下主应力轴旋转引起原生各向异性轴的同步旋转，导致同一方向旋转前后的定向抗剪强度不尽相同；土体在主应力轴旋转条件下的主应变增量方向往往介于主应力增量和主应力方向之间，而旋转过程对土体后续加载路径中的应力一应变关系是否产生影响主要依赖于主应力轴旋转过程中产生的应变积累水平。此外，还建议可从孔压、强度、应力-应变关系3个角度出发，进行高剪应力水平、高频率主应力轴旋转试验，并深入研究各个应力因素对主应力轴旋转下土性的影响。

EXPERIMENTAL PROGRESS RESEARCH ON INFLUENCE OF PRINCIPAL STRESS ROTATION ON SOILS' CHARACTERISTICS

The experiments used to detect the characteristics of soil under the condition of principal stress rotation are analyzed systematically.Some conclusions have been drawn as follows.Under the condition of undrained principal stress rotation the pore pressure is generated and accumulated,which is especially obvious in the cyclic rotation;and the pore pressure is usually larger than that in the dynamic triaxial or torsion shear test at the same level of the shear stress.Besides,the mode of the pore pressure accumulation has a certain functional relationship with some kinds of strains,and is influenced by the inherent anisotropy of soil,but this influence is also inhibited at the low level of the shear stress.During cyclic rotation the pore pressure is also influenced by the rotation amplitude,frequency and cycle times.The cyclic stress rotation does not obviously change the effective internal friction angle of soil,and quite a few tests show that whether the soil has experienced principal stress rotation or not,the normalized shear strength criterion is same.But some results convince that the axis of inherent anisotropy can rotate with the rotation of the principal stress under drained condition,which leads to the different shear strengths before and after rotation.During the principal stress rotation the direction of the principal strain increment is between those of the principal stress and the principal stress increment.The degree to which stress-strain relationship influenced by the principal stress rotation as stress history is mainly dependent on the strain level having accumulated during principal stress rotation.The suggestions to bring pore pressure,strength,and stress-strain relationship into consideration on the further experimental study are also put forward.The higher shear stress level is,the higher frequency tests should be taken and the influences of specified stress factors on the properties of the soil under principal stress rotation need to be further investigated.