冻土的率相关超塑性损伤本构模型研究

With the development of cold region engineering，frozen soil is widely used as structures and foundation of cold regions engineering. The mechanical properties of frozen soil, such as strength and deformation behavior, are very important for the design and the construction of cold regions engineering. Thus, it is necessary to perform the mechanical tests of frozen soils under complex thermal-mechanical conditions according to the working conditions and further establish the constitutive models to simulate the thermal-mechanical behavior of frozen soil. In this investigation, the triaxial creep tests and CT scan tests for frozen soil under different temperature and stress conditions are carried to study the effect of temperature, stress path，stress level，and damage degradation in the rheological behavior. The hyperplasticity theory is furtherly developed in the application of constitutive model for the rate-dependent materials. A rate-dependent hyperplasticity constitutive model is proposed base on thermodynamic principles in order to simulate and predict the rheological behavior for frozen soils under complex thermal-mechanical conditions. The theoretical results of constitutive model will be compared with testing results in order to further verify and judge the capacity of constitutive model.

冻土作为寒区工程的地基和构筑物，其流变力学特性是冻土工程设计、施工和运营维护的重要基础与依据。开展复杂热力条件（不同温度和应力条件）下的冻土力学试验和建立起能够描述冻土自身流变力学特性的理论模型是目前冻土力学的重要研究方向。本项目将采用试验与理论相结合的方法，系统研究冻土流变行为的宏细观特征及其相应的本构理论模型；具体内容如下：开展不同温度下三轴压缩、蠕变试验和CT动态扫描试验，揭示温度、应力水平、应力路径、损伤劣化程度对冻土流变和破坏行为的影响机制；拓展超塑性理论在率相关岩土材料中的应用，从热力学基本原理出发构建考虑温变效应的率相关超塑性理论框架，基于试验结果建立冻土的超塑性损伤本构模型，并对模型的可靠性及其适用条件进行验证和评判。

本项目开展了一系列不同应力路径下的三轴剪切、蠕变、应力松弛试验以及对应的单级和多级加载试验，系统研究了冻土强度、刚度、粘度在不同温度、围压、应力路径、应力历史、应变速率、变形程度条件下的损伤演化律，并从上述试验中验证了冻土重结晶过程对强度、刚度和粘度的强化作用，并确定了影响重结晶过程的主要因素。结合冻融循环试验，确定了冻土强度包络面、刚度损伤过程、粘滞性参数损伤过程，应力-应变行为对冻融循环过程的响应。提出了一个考虑冻融过程的修正型邓肯-张模型来预测经历不同热力条件下冻结黄土的强度和变形行为。最后基于三轴蠕变试验及其加卸载试验，确定了土体剪切应变和体积应变随温度和应力水平的发展特征，拓展应用超塑性理论在冻土率相关行为中的应用，并耦合温度、时间效应相关参数建立了一个冻土超塑性率相关本构模型，基于多轴加卸载蠕变结果明确了其模型参数的试验确定方法，并通过不同温度和应力水平下的蠕变试验结果验证了该模型的预测能力。

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