冻土流变行为的热力学机制与理论模拟

This project will investigate the rheological characteristics of frozen soil under complex thermo-mechanical coupled conditions, clarify the its thermo-mechanical states of rheological behavior, reveal its thermo-mechanical mechanism of rheological deformation and failure, and propose a theoretical model with restrict logic and clear physical meaning to describe the rheological behavior of frozen soil. Based on the literature reviews of rheological experimental methods and constitutive theories for frozen soil, this project is aiming to: (1) Develop a rheological testing approach to reproduce the varying temperature and various stress path of frozen soil in the practical condition; (2) Verify failure rules for the rheological deformation of frozen soil under various and its influence factors thermo-mechanical conditions; (3) Directly correlate the thermo-mechanical state function and rheological deformation for frozen soil, and propose its thermo-mechanical characterization method; (4) Build a theoretical framework for modeling the rheological behavior of frozen soil on the basis of combining the constitutive axioms of rational mechanics, representation theory of tensor function, thermo-mechanical laws and experimental laws of frozen soil, and propose a modeling method to the determine the creep model and long-term strength function from thermo-mechanical state functions. The research achievements from this project would not only make a significant contribution on the rheological behavior of frozen soil by developing new experimental techniques, building a theoretical framework to systematically understand and propose a theoretical model to accurately describe its behavior. Moreover, it will have extensive application potential in cold region engineering practice in design, construction, and maintenance.

为考察复杂热力条件下冻土的流变特征，确定冻土流变行为的热力学状态，揭示冻土流变变形破坏的热力学机制，建立逻辑严密、物理意义清晰又可准确描述冻土流变行为的理论模型。本项目拟在调研分析现有冻土流变试验方法和流变本构理论的基础上，开发可模拟实际工况下变温和不同应力路径的冻土流变试验方法；探明不同热力条件下冻土的流变变形与破坏规律及其影响因素；建立冻土热力学状态函数与流变变形之间的直接联系，提出冻土流变行为的热力学表征方法；在理性力学本构公理、张量函数表示理论等基础上，结合热力学定律和冻土流变试验规律，建立模拟冻土流变行为的理论框架，给出由热力学状态函数确定冻土蠕变模型与长期强度方程的建模方法。本项目的研究成果既对发展新的冻土流变试验技术、系统认识冻土复杂流变行为并对其进行准确的理论模拟具有重要科学意义，又在寒区工程的设计、建设、维修加固等工程实践中具有广泛的应用前景。

为揭示冻土在实际工况中复杂热力条件下的蠕变特征，并获得其蠕变热力学函数，本项目研究了三类周期热边界条件下一维热传导方程的理论求解方法，采用击实曲线确定试样物理状态的方法研究了冻融过程中根河粉质黏土热特性，研究了可模拟实际工况热力状态的变温蠕变方法，开展了冻结根河粉质黏土的静态蠕变试验和冻结青藏黏土的动力循环荷载试验。主要研究结果有：构造了三类周期上边界条件下一维热传导方程的统一解析解形式，阐明了实际压实工况下含水率与干密度对冻结根河粉质黏土导热系数的作用机制，提出了变温蠕变试验方法，得到了不同热力条件下根河冻结粉质黏土的蠕变特性，揭示了蠕变耗散能随时间和蠕变应变的演化规律，建立了可同时考虑冻融循环、应力幅值、围压及动荷载循环次数的冻结青藏黏土累积变形模型，获得了冻结青藏粉质黏土在累积变形过程中动弹模量的演化规律，提出了冻结青藏粉质黏土破坏判别准则。研究成果为在热力学体系下同步考察冻土的动静蠕变特征提供了理论与试验方法。