基于扰动变量的非饱和原状土本构模型

A CONSTITUTIVE MODEL FOR UNSATURATED NATURAL SOILS BASED ON DISTURBING VARIABLE

该文根据复合材料均匀化理论的思想建立了考虑水的滞后性与应力-应变特性相耦合的非饱和原状土本构模型。复合材料均匀化理论的主要思想是将变形的岩土材料视为由相对完整状态土(RISP)和完全调整状态土(FASP)混合而成的复合材料,RISP和FASP的力学性能分别与原状土和重塑土的力学性能相同。另外,在土体的变形过程中,RISP将逐渐转变成FASP,故二者的变形特性应分别采用不同的本构模型描述。该文则分别采用了弹性和弹塑性本构关系描述,土材料的总体应力-应变本构关系即可通过均匀化理论得到。该文对水滞后性的描述则采用了Wei给出的边界面模型。非饱和原状土结构性的退化采用扰动变量D来描述,该文已给出了其随变形变化的演化规律。该文模型共有16个参数,其中新引入的结构性参数衰减指数α和峰值因子β则主要描述了结构性对土材料力学性能的影响,该文对二者的影响分别进行了分析。通过对比模型预测结果和实验结果以及结构性参数分析发现,该模型能够较好的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的描述土结构性的退化规律。

Based on the homogenization theory of composite materials, a constitutive model for unsaturated natural soils considering the coupling of hydraulic hysteresis and stress-strain behaviour is proposed. The main idea of the homogenization theory is to consider the deforming unsaturated natural soil as a mixture of two parts in relative intact （RISP） and fully adjusted states （FASP）, whose mechanical properties are the same as those of natural and reconstituted soils, respectively. As the deformation progresses, RISP will gradually transform into FASP. Therefore, the deformation characteristics of them should be described by different models respectively. If elastic and elasto-plastic constitutive relations are applied, the total constitutive relation for unsaturated natural soils could be obtained according to the homogenization theory. The hydraulic hysteresis behaviours of RISP and FASP are described by the bounding surface model of Wei. The evolution equation of disturbing variable D, describing the degradation law of unsaturated natural soil structure characteristics, is proposed. There are sixteen parameters in the present model, in which two structural parameters attenuation index a and peak factor fl are introduced to describe the influence of structure on the mechanical behaviour of soil, and the influences of them are investigated. 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 behaviours of the unsaturated natural soils, especially the strain-softening behaviour. Besides, the degradation law of soil structure can be well described by the proposed evolution equation of disturbing variable.