考虑温度与相变效应的冻土热力学本构模型研究

The strength and deformation failure problems existed in continuously developed cold region engineering require higher advance in the research of frozen soil mechanics. For this, it is primarily important to conduct mechanical experiments on frozen soil under complex thermal-mechanical conditions which can simulate actual engineering situation, and to further establish suitable theoretical models to describe the constitutive mechanics behavior of frozen soil under complex thermal-mechanical conditions. Therefore, through combined theoretical analysis and laboratory experiment, the mechanical characteristics and the constitutive models under complicated thermal-mechanical conditons for frozen soil will be investigated in this study. The detailed content includes the following parts: mechanical experimental study for frozen soil under different temperature and stress conditions to investigate the effect of temperature and stress conditions on the deformational properties and mechanical indexes, and the temperature effect will be quantified in the constitutive models for frozen soil based on mechanical experiment results; research on the quantitative influence of phase-change effect on the mechanical behavior of frozen soil through analyzing the phase equilibrium equation which was determined by thermophysical properties; research on the thermodynamic constitutive theory that can describe the effect of the temperature and phase change based on thermodynamic functions containing temperature variable for frozen soil, and based on coupling thermodynamic function with phase equilibrium equations. The research result will have important value on the study of complicated thermal-mechanical behavior for frozen soil and will provide an uniform theoretical framework for establishing strict and logical constitutive models. It will have broad perspectives in both academic progress and engineering application.

寒区工程建设的不断发展和已建冻土工程中存在的强度与变形失效问题对冻土力学的研究提出了更高的要求。为此，需要开展模拟实际工程中复杂热力条件的冻土力学试验和建立能描述复杂热力条件下冻土力学行为的理论模型。本项目采用试验与理论相结合的办法，研究复杂热力条件下的冻土力学特征和本构模型。具体内容包括：开展不同温度和应力条件下的冻土力学试验(包括整理和分析已有的试验数据)，探明温度和应力条件对冻土各力学指标的影响，为在本构模型中量化温度效应提供试验依据；开展热物理试验确定冻土的相平衡方程，定量研究相变效应对冻土力学行为的影响；应用热力学理论和传热学导出含有温度参量的冻土热力学函数，耦合冻土热力学函数与相平衡方程，建立能描述温度与相变效应的冻土热力学本构模型。本项目的研究成果对揭示冻土的复杂力学行为具有重要价值，并为建立逻辑严密、结构紧凑的冻土本构模型提供统一的理论工具，具有广阔的学术价值和应用前景。

冻土中由于冰的存在，不但使冻土的力学行为对温度敏感，同时在受荷变形过程中产生温度变化、冰的压融压碎而使冻土力学性质发生劣化的复杂热力特征。在冻土工程设计和计算中，深入认识冻土的复杂热力响应并建立能准确描述和预测其力学行为的本构模型是冻土力学与冻土工程研究的重点。本项目在可以同时描述力学过程和热学过程的不可逆热力学体系下开展了冻土的本构模型研究、冻土力学试验方法研究和冻土力学性质研究。在不可逆热力学的基础上，将温度变量和克拉伯龙方程引入冻土热力学函数，给出了可以描述冻土变温和相变效应的冻土本构模型一般形式，提出了由热力学函数确定本构模型的系统方法，根据试验资料确定了冻结兰州黄土的热力学函数，推出了其双屈服面本构模型，给出了模型参数的确定方法，模型验证结果表明，该模型能很好的描述冻结兰州黄土在不同应力路径下的变形行为。应用冻土三轴仪实现了冻土的加卸载循环试验、等p试验、各向等压试验和等斜率应力路径试验等多种应力条件下的冻土力学试验，基于这些试验方法，发现了冻结兰州黄土塑性应变增量方向随应力路径改变的新现象，初步认识了冻土在变形过程中的能量耗散与损伤行为。对冻结兰州黄土、冻结和林黄土、含盐冻结青藏粉砂等土质的冻土进行了不同含水率、应变速率、含盐量、温度和围压下的力学试验，根据试验数据，建立了冻土力学指标与影响因素之间的定量关系，对比分析了不同冻土变形指标取值标准，证实了现有冻土力学试验规范中的冻土弹性模量取值标准合理性，提出了根据冻土刚度和强度随围压变化规律的差异性确定压融应力值的方法，由此给出了冻结兰州黄土中的应力集中系数。本项目的研究成果对进一步认识冻土的复杂力学响应并对其进行本构模拟提供了试验方法和理论工具。