非饱和土应力变量选取原则刍议

Discussion on selection principle of stress variables of unsaturated soil

在非饱和土本构模型研究中,所选取的变量是否是非饱和土合适的应力变量往往被研究人员所忽视,这会阻碍本构模型的进一步发展。从土体的微观结构、能量守衡及力学平衡这3方面对非饱和土应力变量进行研究,以此提出了非饱和土应力变量选取应遵循的3个原则,强调指出非饱和土应力变量与应力状态变量的区别,并对本构模型研究中常用的应力变量进行分析,发现基质吸力、净法向应力并非为非饱和土应力变量,而有效应力和吸应力为其应力变量。建议使用有效应力来建立本构关系,其除了能满足文中提出的选取原则外,还能与饱和土理论之间有很好的过渡。文中的非饱和土应力变量选取原则还不成熟,但其重要性不容忽视,该研究还有待进一步补充和完善。

Stress variable is one of the key issues in constitutive modelling for unsaturated soil. Unfortunately, this issue is often ignored and may impede the further development of constitutive modelling. This article investigates the stress variables from the viewpoint of soil microstructure, conservation of energy and mechanical equilibrium, on which the selection principle of stress variables of unsaturated soil is put forward based. The difference between stress variables and stress state variables is highly focused. The study results show that some variables, like matric suction and net normal stress, which have the units of stress, are insufficient to qualify them as stress variables on the scale of the air-water-solid REV, but they are the essential stress state variables, and the effective stress and the suction stress could be the stress variables of unsaturated soil. Finally, we prefer using effective stress to simulate constitutive unsaturated soil behaviour, not only because it can obey the above principles but also it can smoothly switch to the theory of saturated soil. It is illustrated that the principle of stress variables selection for unsaturated soil is still immature, but the attempt to develop this theory is requisite.