花岗岩残积土扰动损伤规律及本构模型

Granite residual soils possess complex microstructures. Tunneling and deep excavation, however, will inevitably cause disturbance to surrounding soils. For granite residual soils, disturbance always lead to some microstructure damage and strength loss, therefore, result in large deformation/settlement, base/slope failure, and disaster chains in geotechnical practice. To date, the mechanisms of microstructure damage and its link to strength loss of granite residual soils is still unknown, and constitutive models that can bridge the gap between micro and macro are missing. Targeted at granite residual soils, therefore, this project launches a multiscale approach toward the microstructure evolution to the mechanical characteristics of granite residual soils under unloading conditions. The microstructure of granite residual soils including floc and soil pore distribution evolution during dynamic disturbance are firstly obtained. Based on the soil pore and floc distribution, soil structure state parameter and shear modulus, which could be used to predict the structure damaging and modulus reduction, are obtained. Through the rule of mixtures and poromechanics, a granite residual soil constitutive model is established based on the Adapted Modified Cam-Clay with Two Yield Surfaces model. The model is calibrated by triaxial compression test results and a unified parameter will be proposed to evaluate the structured soils’ disturbance degree. This research will provide valuable insights into foundation design and construction in granite residual soils.

花岗岩残积土是一种结构性很强的特殊土。在基坑开挖或盾构掘进过程中，由于开挖卸载的扰动，花岗岩残积土容易发生应变软化、结构破坏、刚度降低等工程问题。但是，目前对花岗岩残积土在卸载扰动下微观结构损伤的研究主要以定性描述为主，而且对其扰动后力学特性弱化的机理研究还处于探索阶段。因此，亟待清楚认识花岗岩残积土的扰动损伤规律并建立考虑其结构性的本构模型。本项目针对典型的花岗岩残积土展开微细观结构损伤和宏观力学特征分析与研究。通过量测残积土团粒粒径与孔隙结构在扰动前后及过程中的动态分布，建立损伤结构性参数与剪切刚度随扰动荷载弱化的函数表征残积土的结构损伤。基于混合物理论、双屈服面本构模型及孔隙介质力学的有效应力原理等，提出考虑残积土结构损伤的本构模型，揭示残积土结构损伤机理与力学特性弱化规律，并通过室内单元体实验验证本构模型的合理性。本项目研究将为结构性土地基设计施工提供技术支持。

本项目针对典型的花岗岩残积土展开微细观结构损伤和宏观力学特征分析与研究。在宏观尺度上，利用现场测试、室内固结试验、应力路径控制的三轴-弯曲元测试技术研究了残积土强度与小应变刚度力学特性与扰动规律。同时在不同应力水平和扰动状态下，选取了典型的残积土试样，利用SEM和TEM定性分析了结构性土的微观结构与组构特征，利用X-CT定量研究了土颗粒扰动前后的空间形态与分布，利用 NMR技术定量研究了土样扰动前后及过程中孔隙结构群分布的变化规律，利用DLS技术量测了扰动前后及过程中土团粒的粒径分布。建立了残积土宏观力学属性与其微观结构演化的定性关系。在理论分析方面，根据微观实验结果提出了孔隙群与颗粒粒径动态分布函数描述结构性土的结构扰动与损伤过程，通过量测残积土团粒粒径与孔隙结构在扰动前后及过程中的动态分布，建立了损伤结构性参数与剪切刚度随扰动荷载弱化的函数表征残积土的结构损伤。基于双屈服面本构模型及孔隙介质力学的有效应力原理，提出了考虑残积土结构损伤的本构模型，揭示了残积土结构损伤机理与力学特性弱化规律，并通过室内单元体实验验证本构模型的合理性。本项目研究将为结构性土地基设计施工提供技术支持。