非饱和土力学中几个基本问题的探讨

近些年非饱和土力学的研究非常活跃，但对一些基本问题的认识并不一致，有时甚至概念混淆。针对非饱和土力学的几个基本问题：非饱和土状态变量的选择、非饱和土有效应力变量的选择、吸力概念的界定和轴平移技术的局限性、非饱和土的结构的表征方法等问题进行了分析和探讨。其中非饱和土状态变量和有效应力的选择对于非饱和土力学的理论和相应本构模型的建立具有重要影响，因此，首先深入讨论了这一问题，概括论述了非饱和土有效应力的演变并深入探讨了目前各种形式有效应力的优缺点。其次，指出由于受负压孔隙水气化（液-气相变化）的影响，在实际场地中大于某一界限值的基质吸力是不存在的；目前被广泛使用的轴平移试验技术却掩盖了这一情况，而基于此所建立的非饱和土强度和变形理论的适用性需要进一步的研究和论证。再次，指出非饱和土的结构除了包括组构和颗粒之间作用力的综合效应外，还建议增加孔隙水和孔隙气的分布以及各相之间的相互作用和物理-化学作用。最后对一些容易混淆的概念进行了梳理。其目的是希望国内同行在今后的研究中对这些问题加以关注，并建立正确的认识，促进非饱和土力学沿着正确的方向发展。

Discussion on some fundamental problems in unsaturated soil mechanics

Unsaturated soil mechanics has become an active researching area in recent years. However the understanding of some fundamental problems is inconsistent and some basic concepts are confusing. This paper aims at the fundamental problems, e.g. the choices of state variables and effective stress of unsaturated soils, the definition of suction, the limitation of axis-translation technique and the characterization of unsaturated soil structure. In these problems, the choices of state variables and effective stress of unsaturated soils play an important role in the theory of unsaturated soil mechanics and constructing constitutive models. Firstly, this paper briefly reviews expressions of effective stress of unsaturated soils and discusses their advantages and disadvantages. Secondly, this paper points out that there does not exist such matric suction beyond a certain limit in real site because of cavitation of capillary water. However the laboratory axis-translation technique conceals the possibility of cavitation and modifies soil behavior. Thus the validity of theories of shear strength and deformation of unsaturated soils based on it is a question worth study. Thirdly, the paper suggests that the characterization of unsaturated soil structure should include the distributions of pore water and pore air, the interaction among all phases (e.g. capillary and physical-chemical forces), except for the elements of saturated soil structure, e.g. fabric and inter-particle actions. Finally, this paper further combs the confusable concepts. The purposes of these discussions are to attract attention of domestic scholars on these problems, to set up correct understanding about them, and to promote development of unsaturated soil mechanics.