温度对非饱和黄土变形和强度特性影响的试验和理论研究

Many infrastructures constructed in loess region are subjected to variations of both temperature and water content, such as subgrade, energy foundation and landfill barriers. The deformation and strength behavior of unsaturated loess are closely related to the settlement and stability problems encountered in these infrastructures. Based on the conceptual analysis from the viewpoint of micro-structure and preliminary experimental results, the deformation and strength behavior of unsaturated loess are dominated by both temperature and suction. So far, the suction effects on the behavior of loess have been widely investigated while effects of temperature on the deformation and strength behavior of unsaturated loess are still not clear. In this program, the thermal effects on the deformation and strength behavior of unsaturated loess will be studied through a modified suction and temperature controlled triaxial apparatus. Micro-structure analysis will be carried out through Environmental Scanning Electron Microscope (ESEM), Mercury Intrusion Porosimetry (MIP) and Computed tomography (CT) to assist in the interpretation of triaxial results. A new constitutive model will be proposed to consider both thermal and suction effects on the deformation and strength behavior of loess. This program is expected to provide scientific guidance for analyzing the settlement and stability of infrastructures in loess region subjected to various temperature and suction conditions.

建立于黄土之上的诸多工程构筑物涉及热-水耦合作用的服役环境，如黄土路基、地热能源基础和生活垃圾填埋场屏障系统等。这类工程构筑物的不均匀沉降和失稳破坏问题与非饱和黄土的变形和强度特性密切相关。从微观机理和初步的单元试验可知，黄土的变形和强度特性受温度和吸力耦合支配。然而，目前国内外研究黄土变形和强度时，多集中在考虑吸力变化的影响，对温度引起的非饱和黄土变形和强度变化规律及其量化描述尚不清楚。本项目基于非饱和土力学的理论和测试手段，利用自主设计的可独立控制温度和吸力的三轴仪开展三轴试验，揭示温度对非饱和黄土变形和强度特性的影响规律。并利用环境扫描仪、计算机断层扫描仪和压汞仪开展试验，从微观角度定性解释三轴试验结果。基于三轴试验结果，建立可同时考虑温度和吸力作用的黄土本构模型。本项目研究成果可为我国黄土地区涉及热-水耦合服役环境的工程构筑物的沉降控制和稳定性分析提供科学指导。

建立于黄土之上的诸多工程构筑物涉及热-水-力服役环境，如路基、地热能源基础和生活垃圾填埋场屏障系统等。这类工程构筑物的不均匀沉降和失稳与黄土力学特性密切相关。本项目基于非饱和土力学理论和测试手段，利用可控制温度-吸力-应力的三轴仪和压力板仪开展试验，研究了热-水-力作用对黄土变形和强度的影响规律。利用扫描电镜仪、计算机断层扫描仪和压汞仪开展微观分析，定性和定量研究了黄土微观结构及其演化规律。基于单元体试验和微观分析结果，建立了结构性黄土的本构模型，并进行了不同热-水-力路径下的验证。主要获得以下四个结果：（1）黄土结构性显著影响温度和吸力作用下的变形特性，在不同应力状态下压实黄土较原状黄土变形可大30%左右。（2）黄土微观结构主要包括胶结和大孔隙，胶结又可分为与含水状态相关的黏土颗粒胶结以及与含水状态无关的矿物胶结。上述微观结构的分类可较好的用于解释黄土持水、压缩、湿陷以及抗剪强度特性。（3）以Bishop有效应力、偏应力和基质吸力为状态变量，基于严格的非饱和土弹塑性理论，建立了结构性黄土本构模型。该模型可用一套参数模拟不同结构性的黄土力学特性（如：矿物胶结主导、黏土胶结主导、矿物和黏土胶结共同主导）。（4）建立了简化的黄土湿陷系数计算方法，可实现黄土湿陷性的原位快速评价。基于文献中已有数据的验证表明，该简化方法判定黄土湿陷程度（如轻微、中等和强烈湿陷）的正确率高达90%以上。上述研究成果可为我国黄土地区涉及热-水-力服役环境构筑物的服役性能设计和稳定性分析提供科学指导。