中文摘要：

自然界所存在的原状土具有一定的结构性，与室内重塑土在加载过程中所表现出的力学特性（如变形和强度）具有明显的差异．本文以复合体损伤理论为基础，建立了适用于非饱和原状土的弹塑性损伤本构模型，并给出了损伤变量A的演化规律．其主要思想是把土材料看作由相对完整的土和相对破碎土两部分混合而成，二者的力学性能不同，且在受力过程中，相对完整的土逐渐转化为相对破碎的土，故分别采用弹性和弹塑性模型描述．该模型所采用的参数（除结构性参数β、α以外）均可以直接通过实验确定．结果表明，该模型能够较好描述非饱和原状土的应力．应变特性，尤其是应变软化现象，且所给出的扰动变量演化规律也能够较好描述土结构性退化规律．

英文摘要：

The structured natural soils are widely distributed in nature, whose mechanical properties, such as deformation and strength characteristics, are completely different from the reconstituted soils,. This paper builds up an elasto-plastic damage constitutive model of unsaturated natural soils based on the damage theory of composite substance. The influence of soil structure characteristics on stressstrain behavior is considered in the model, and the evolution law of damage variable）,is given. The main idea is to divide a soil body into two relatively intact soil body and relatively broken soil body, and the relatively intact soil body can be transformed into the relatively broken soil body during loading. In this paper, the deformation characteristics are described by elastic and elasto-plastic constitutive models, respectively. The parameters of model can be calibrated through experiments except the structural parameters β,α. By making comparisons of predictions with experimental data of unsaturated natural expansive soil and by conducting the parametric study, it is demonstrated that the new model captures the essential behaviors of the unsaturated natural soils, especially strain-softening behavior.