季节冻土区重载车荷载下路基融土细观结构演化与变形特性

Taking the silty clay of subgrade in the Northeast area as research object in this proposal, laboratory tests, combined with CT scans, theoretical analysis and numerical simulation were used to understand the meco-structure evolution and deformation characteristics for silty clay under heavy truck loads. Firstly, dynamic triaxial tests and isotropic compression-expansion test were carried out based the thawed silty clay, the equation of meco-structure damage and hardening caused by stress were establish with the CT scan. Next, the boundary surface function of thawed silty clay was established through cyclic triaxial plus-unloading test. Based of these, the mesostructural evolution bounding surface plasticity model of thawed silty clay under heavy truck load were proposed in the framework of critical state soil mechanics theory. Finally, the model parameters were determined according to the test. Moreover, the reliability of the constitutive model can be calculated and verified by the returning algorithm of implicit graphics. These results can help to understand the mesostructural evolution laws, and develop the mechanism of deformation of the subgrade to evaluated the deformation stability, and the results also helps to develop the soil dynamics of subgrade in cold regions.

以东北地区公路路基中常见的粉质粘土为研究对象，拟基于室内试验，并结合CT扫描、理论分析与数值模拟手段，深入研究重载车荷载下融化粉质粘土细观结构演化规律及其变形特性。首先，对粉质粘土进行封闭体系的有压冻融循环后，开展其常规动三轴试验和等向压缩－膨胀试验，结合CT扫描数据，建立应力致细观结构损伤/硬化演化方程；通过三轴分级加－卸载试验，构造融化粉质粘土的边界面函数；据此，在临界状态土力学理论框架下，建立重载车荷载下融化粉质粘土细观结构演化边界面塑性模型。最后，通过室内试验确定模型参数与冻融后粉质粘土结构性之间的定量关系，并以此作为细观结构演化边界面塑性模型初始输入；利用隐式图形返回算法，求解建立的本构模型并验证模型的可靠性。通过本项目研究，有利于深入理解季节冻土区重载车荷载下路基融土细观结构演化规律及变形发展机制，为评价融土路基的变形稳定性奠定理论基础，对寒区路基土动力学的发展有一定促进作用。

本项目以东北季冻区公路路基为研究对象，着重关注冻融与行车荷载双重作用下路基土体的变形行为。首先，总结并分析了近十年来国内外学者关于冻融作用对土的工程性质影响的研究进展，研制了三轴冻融循环试验系统和剪切波速测试系统。其次，开展了大量的静动三轴试验、等向压缩－膨胀试验、静力蠕变试验和剪切波速测试试验，系统地分析了冻融循环作用对饱和黏土物理与力学性能的影响。进而，研究并建立了能够描述长期循环荷载下融化饱和黏土动态剪切模量、阻尼比、回弹模量和永久变形的经验公式。在此基础上，基于剑桥模型的理论框架，采用广义各向同性硬化准则，建立并验证了反映融化饱和黏土循环稳定的弹塑性边界面模型。最后，基于建立的基层－路基－地基有限元模型研究了汽车轴型、后轴轴重、行车速度和路基融化厚度对正常期和春融期路基应力比和永久变形的影响。该项目的研究成果为评价季冻区融土路基的变形稳定性奠定理论基础，而且对寒区公路路基土动力学的发展有一定促进作用。