考虑细观结构演化的非饱和Q_3原状黄土弹塑性本构模型

An elastic-plastic constitutive model for unsaturated Q_3 undisturbed loess considering meso-structured evolution

Q_3原状黄土是典型的非饱和土,具有明显的结构性,其力学变形特征与结构性密切相关。建立黄土的本构模型有必要考虑加载和湿陷过程中结构演化特征,才能真实地反映原状黄土的固有特性。假设原状黄土的屈服应力是重塑黄土与结构性两者的耦合,基于细观结构演化规律,考虑吸力和结构性的影响,提出了一个非饱和Q_3原状黄土的弹塑性本构模型。模型包括土骨架变形与水量变化两个方面,土骨架变形方面以修正Barcelona非饱和土弹塑性模型为基础,引入通过CT三轴试验获得的Q_3原状黄土加载-湿陷过程中的结构演化方程,分别得到描述土骨架在加载和湿陷过程的本构模型,以突出加载和湿陷过程中结构性对变形的影响;水量变化方面则采用广义土-水特征曲线描述,以反映净平均应力和偏应力对持水性的影响。模型总计22个材料参数,均可由试验确定。通过对比若干试验数据与模型计算结果,初步验证了模型的合理性。建立的考虑结构性的弹塑性本构模型为深化认识黄土力学特性提供了可能,并为有效分析黄土地基湿陷变形提供了一定借鉴。

Undisturbed Q3 loess is a typical unsaturated soil and has obvious structure which is closely related with its mechanical and deformation properties. The elastic-plastic constitutive model for undisturbed Q3 loess would consider structured evolution in the loading and collapsing process, which would meet the inherent characteristics of the mechanical deformation of undisturbed loess. Assuming that the yielding response of undisturbed loess is the coupling of remolded loess and structure of undisturbed loess, a new elastic-plastic constitutive model of undisturbed Q3 loess considering the influence of suction and structure is established based on meso-structured evolution in this paper. The new elastic-plastic constitutive model has two aspects including soil skeleton deformation and water changes, loading and loading-collapsing process are described, respectively. For soil skeleton deformation, the structured evolution equations obtained by CT triaxial tests of undisturbed Q3 loess in the process of loading and loading-collapsing are introduced into Barcelona unsaturated soil elastic-plastic modified model, respectively. The generalized soil-water characteristic curve is used to describe the aspect of water content considering influence of net mean stress and deviator stress. All of 22 material parameters of the new proposed elastic-plastic constitutive model can be determined by the unsaturated soil tests. The validity of elastic-plastic constitutive model is verified preliminarily by comparison of computation results and test data in this paper. The establishment of elastic-plastic constitutive model deepens the understanding of mechanical characteristics of unsaturated undisturbed Q3 loess, which will provide the gateway to reasonably analyze collapsible deformation coupling problems of loess foundation.