饱和粉土液化的宏观及细观机理研究

Silt in the field is widely distributed and the damage of earthquake liquefaction is huge. It is intended to research silt dynamic triaxial combined test method on change of the microscopic structure. By scanning electron microscopy (SEM) tests of silt specimens, dynamic triaxial tests of liquefaction properties, static triaxial tests and static loading large deformation tests after liquefaction, static lateral shear shaking table tests of model foundation, and lateral shear shaking table tests of model foundation after liquefaction, the macroscopic and microscopic liquefaction mechanism of saturated silt is studied. The quantitative relationship among the content of fine particles, intergranular pore ratio, the dynamic strength, and the excess pore water pressure of silt is established. It is introduced the intergranular pore ratio, which can embody intergranular contacts of silt, to replace the existing void ratio (i.e. overall void ratio) from a microscopic mechanistic point of view and the plasticity of the fines in the specimen is considered. The microscopic constitutive model that can reflect the silt liquefaction strength and deformation characteristics will be built and quantitative method of silt liquefaction effect analysis will be proposed. The numerical simulation tests based on silt liquefaction properties are developed in order to verify the microscopic liquefaction mechanism. Silt macroscopic and microscopic liquefaction criterion will be proposed. The corresponding relationship between macroscopic and microscopic liquefaction evaluation index and liquefaction discrimination method will be established, which is a new idea for silt liquefaction discrimination and evaluation.

天然粉土分布广泛，其地震液化破坏危害性大。本项目拟研究动三轴与粉土细观结构动态变化联合测试方法，通过粉土试样扫描电镜测试、液化特性动三轴试验、静三轴及液化后静加载大变形试验、小型振动台模型地基静横向剪切和液化后横向剪切试验，研究粉土液化的宏细观机理，建立粉土细观层面的细粒含量、粒间孔隙比与宏观层面的抗液化强度、超静孔压的定量关系。引入能充分体现粉土颗粒间接触关系的粒间孔隙比概念，代替现有的孔隙比（即整体孔隙比）作为试验控制指标，并且考虑粉土中细粒的塑性对液化特性的影响，建立反映粉土抗液化强度和变形特性的细观本构模型，提出粉土液化效应分析的定量方法，开展基于粉土液化特性动三轴试验的数值仿真试验，验证粉土液化细观机理。以此为基础，提出粉土宏细观液化标准，建立液化判别宏细观指标间的对应关系和粉土宏细观液化判别方法，从而深入理解粉土液化机理，为粉土液化判别和评价提供新的思路和方法。

天然饱和粉土分布广泛，其地震液化破坏危害性大。因此，饱和粉土液化地基的地震安全性问题是岩土地震工程领域热点问题。本项目采用动三轴与粉土细观结构动态变化联合测试方法，通过粉土试样扫描电镜测试、液化特性动三轴试验、静三轴及液化后静加载大变形试验、振动台模型地基试验，研究粉土液化的宏细观机理。主要工作如下：（1）通过动三轴试验确定了细粒含量临界值的存在，且大小为30%。并采用分形特征法、孔隙比法及物理指标确定法对其结果进行了验证。（2）通过对饱和粉砂及粉土进行动三轴试验，分析讨论细粒含量和粗、细粒间孔隙比对其抗液化强度的影响。（3）对不同黏粒含量粉土试样的微观结构进行研究，从微观层面揭示了土体内部颗粒粒间接触方式及黏粒含量对土体微观结构的影响。通过对土体微观结构参数的测量，发现微观结构参数随黏粒含量的变化有一定的规律性。（4）从土体微观结构角度阐述粉土颗粒间接触方式，在前人基础上提出适用粉土的粒间孔隙比概念。对于不同的试验条件，各类饱和粉土在指定液化循环周数下的抗液化强度与粒间孔隙比之间存在良好的指数函数关系。并结合Seed和Idriss的“简化判别法”，提出以粒间孔隙比为指标的液化判别方法。（5）采用GCTS空心圆柱扭剪仪开展了含不同细粒饱和粉砂土动三轴试验研究，根据试验结果分析了不同黏土矿物（高岭土、伊利土、蒙脱土）、黏粒含量、密实程度和细粒塑性等因素对饱和粉砂抗液化强度影响规律。在此基础上，提出粉土宏细观液化标准，建立液化判别宏细观指标间的对应关系和粉土宏细观液化判别方法，从而深入理解粉土液化机理，为粉土液化判别和评价提供新的思路和方法。