非饱和土本构模型中应力变量选择研究

 应力变量是本构模型的基本要素之一，非饱和土本构模型中应力变量的选择目前仍有较大争议，各模型中应力变量的选择非常混乱，严重阻碍了理论研究的进一步发展。Bishop有效应力或其修正的应力形式，以及新提出的吸应力等，虽然可以较好地表示非饱和土强度，但不能模拟非饱和土浸湿后体积膨胀和坍塌现象。双应力变量目前应用较多，有考虑非饱和土中孔隙水对土体力学性质影响的骨架应力和毛细应力，有用得最多的净应力和吸力，或者两个应力变量一个是应力的函数，另一个是吸力(或饱和度)的函数等多种形式，可以较好地反映非饱和土的强度和变形特性，但目前双应力变量选择有很大的随意性，没有确凿的理论依据。重点指出建立本构模型时土体的应力变量不能随意选用，应满足Houlsby功率方程，同时还要注意与应力变量对应的应变变量的选择。旨在澄清目前的混淆概念，为非饱和土本构模型建立提出合理的应力变量。

RESEARCH ON SELECTION OF STRESS VARIABLES OF CONSTITUTIVE MODEL FOR UNSATURATED SOILS

Stress variable is one of the basic elements in constitutive modeling. The debates in choosing the appropriate stress variables of constitutive model severely hinder the development of unsaturated soils. A single stress variable，i.e. Bishop stress，and its modified expression，or the recently proposed suction stress，can be used to simulate the strength of unsaturated soil，but they are incapable of deformation simulating because of their incapability reflect swelling or collapse after being wetted. There are many different forms of double-stress variables，such as the skeleton stress(or modified net stress) or the meniscus stress，which considers the influences of pore water pressure on the mechanical behaviors of unsaturated soils. Net stress and suction are most frequently used. Other forms of variables are also adopted，the common used one is the function of stress，and the other is the function of suction(or saturation)，which can preferably simulate the characteristics of strength and deformation of unsaturated soils. They are often chosen randomly without any theoretical deduction. Therefore，it is noted that stress variables should satisfy the Houlsby power equation；meanwhile，the strain variables corresponding to the stress variables should be selected carefully. The confused concept is clarified；and suitable stress variables in establishing the constitutive model of unsaturated soils are proposed.