城市环境下黏性土的热力学行为及其微观响应机理研究

Thermal disasters related to temperature effect have become more and more serious with the speedup of the urbanization process. In this project, based on various macro, meso and micro tests, a thermal-mechanical coupling mechanism would be analyzed, aiming to gain an insight into thermal and mechanical behaviour of clayey soil in urban environment. This study is organized in the following way. Firstly, a new test equipment for borehole shear test was developed by adding temperature control system, in-situ thermal-mechanical tests at different temperatures are conducted for evaluating thermal stability and conductivity of clayey soil, and a method for obtaining in-situ parameters considering temperature effect is also proposed. Afterwards, thermal consolidation and static and dynamic triaxial test are conducted in three temperature path conditions, including constant temperature, rise temperature and up-down temperature cycle. The rule and influence of temperature to deformation and strength characteristics of clayey soil are studied, and the occurred conditions for heat softening or hardening are discussed. The material factors that lead to temperature effect and the temperature-sensitive physical or chemical composition are investigated. Furthermore, real-time tracing tests for microstructure are conducted for studying microstructure evolutionary process, using the environmental scanning electron microscope (ESEM) and temperature control stages. Finally, based on the experimental findings, a temperature-sensitive microstructure parameter is proposed in order to create the relationship between microstructure evolutionary and mechanical behavior, the mechanism for thermo-mechanical behaviour of clayey soil are revealed consequently. The results of this research project are helpful to offer the theoretical and technical support for controlling thermal urban disasters and promote urban sustainable development.

项目以城市发展产生温度升高引发的热灾害日益凸显为背景，以深化认知城市环境下黏性土的热力学行为及其微观机理为主线，采用“温度影响+宏、中、微观试验→机理分析→指导与应用”的研究思路，研制温控原位孔内剪切设备，开展变化温度场影响的原位力学试验，提出考虑温度效应的原位力学参数确定方法，评价黏性土的持热与导热性能;开展恒温、升温与升、降温循环三种热路径的热固结与动、静三轴试验，研究温度对黏性土变形规律与强度特性的控制影响，提出热硬化或热软化产生的温度条件；明晰温度效应产生的物质基础，提出主控温度效应的热敏组分；借助环境扫描电镜与温控热台，开展温度变化的微观结构动态跟踪测试，分析不同热路径下微观结构的演化规律，寻找到对温度最敏感的微结构参数，建立其与宏、中观力学参数的相关性与敏感性分析，阐明城市环境下黏性土热力学行为的微观响应机理，为科学治理和调控城市热灾害，实现城市的可持续发展提供理论技术支持。

项目以城市发展产生温度升高引发的热灾害日益凸显为背景，以深化认知城市环境下黏性土的热力学行为及其微观机理为主线。首先，研发了基于遥感数据和地温变化评价城市热岛效应时空特征的分析软件，从宏观尺度上研究区域气候与城市环境对黏性土力学行为与工程灾害的影响；研发了新型温控原位孔内剪切仪与原位地温测试方法，提出了黏性土持热能力与导热性能的试验方法与分析软件，以此研究了温度影响下黏性土的原位力学行为；开展了模拟炎热多雨、频降暴雨、干湿循环等气候变化影响下黏性土力学性能测试，调查了气候影响下土的强度与刚度衰减规律；通过恒温、升温与升、降温循环路径下的热固结、动三轴、静三轴试验，获得了一套系统的表征温度效应的黏性土力学性质数据，研究了温度效应对黏性土变形规律与强度特性的影响与作用；利用热重-差热试验、扫描电镜试验和纳米CT试验，找到了主控土的温度效应的热敏参数与微观结构参数；最后，建立了黏性土在温度作用下力学参数、热敏组分与微观结构参数的相关性与敏感性分析，获得了温度效应下黏性土力学行为的微观机理。研究表明，土体在温度作用下产生的变形与强度特征是结构连结、颗粒和孔隙等要素变化的综合结果，具有不同矿物组成和结构特性的土在相同温度变化下可能会产生热软化或热硬化不同的力学行为，而结构特性的演变是发生温度效应的重要体现，胶结程度和孔隙度是表征黏性土温度效应的最敏感参数。项目实施过程中发现黏性土在高频振动作用下具有特殊的力学特征，为此增加了爆破荷载作用下残积型黏性土的力学行为与机理的研究。本研究可为科学治理和调控城市热灾害提供理论基础，亦可为温度效应明显的热能贮存、地热资源开发、核废料处置、供热管道设计等领域提供借鉴参考。