非饱和结构性黄土三维宏微观本构理论研究

Natural loess, widely distributed in the north China, is a typical silt-sized structural soil characterized by microscopic interparticle cementation and open-structure that result in macroscopic collapsibility, to which many three-dimensional (3D) engineering problems and disasters are ascribed. Thus it is necessary to establish a suitable 3D constitutive model for unsaturated and structural loess, which can be used in numerical analyses in the engineering construction, and disaster prevention and reduction in loess regions. In the framework of macro and micro soil mechanics, this project will firstly establish a 3D bond contact model for loess by carrying out experiments on different bond materials between two spheres subjected to tension, compression, shear, bend, torsion and their combinations. Then, true triaxial tests and wetting tests under complex stress conditions will be simulated on unsaturated and structural loess by the improved Discrete Element Method (DEM) to obtain the macroscopic and microscopic mechanical responses. Next, the damage evolution laws will be investigated in the DEM loess samples under the different conditions to establish a suitable 3D constitutive model. Finally, the constitutive model will be incorporated into a finite element software to analyze typical boundary value problems in loess regions subjected to loading and wetting. This project will make geo-researchers in China on the cutting edge of macroscopic and microscopic constitutive models for unsaturated and structural loess.

我国是黄土分布大国，天然黄土是主要由粉粒构成的结构性土，微观上具有粒间胶结和大孔隙架空结构，宏观上表现出湿陷性，其湿陷性造成了各种工程地质三维空间灾害。故十分有必要建立合适的非饱和结构性黄土三维本构模型以用于工程数值分析并指导黄土地区工程建设和防灾减灾。本课题依循宏微观土力学思路，首先进行球体间不同胶结物承受拉压剪弯扭及复杂组合力的室内接触试验，建立黄土颗粒间三维微观胶结接触模型。然后，利用改进的离散单元法模拟非饱和结构性黄土真三轴试验和复杂应力状态增湿试验的宏观力学性质，并获取微观力学信息；接着分析结构性黄土在受荷和浸水条件下的空间破损演化规律，从而建立合理的非饱和结构性黄土三维宏观本构模型，并通过多种含水量人工结构性黄土的真三轴试验进行验证。最后将该宏观本构模型引入有限元程序并应用于黄土地区工程受荷和浸水变形及破坏边值问题的分析。本课题将使我国黄土宏微观本构模型研究处于国际领先地位。

课题依循宏微观土力学思路，以室内微观接触试验为依据建立黄土颗粒间三维胶结接触力学模型；利用离散元数值仿真试验获取非饱和结构性黄土真三轴复杂应力路径和增湿试验的宏观与微观力学变化规律；根据室内宏观力学试验和离散元模拟结果联合分析结构性黄土在受荷和浸水条件下的空间破损演化规律，建立非饱和结构性黄土的三维宏观本构模型；并将该宏观本构模型嵌入有限元软件，以分析黄土地区典型边值问题并指导黄土地区工程建设和防灾减灾。