热-水力-力学耦合下超固结非饱和土的特性及其本构描述

Clays in the engineering are overconsolidated and unsaturated. Besides, clays are in natural conditions where temperature and humidity are both always changing with seasons. Because the changes of temperature and humidity will affect the characteristics of clays, it is significant to study the unsaturated and overconsolidated stress-strain behaviours of clays considering the influences of temperature and humidity. However, most of current researches focus on the influence of humidity on normally-consolidated unsaturated clays and that of temperature on overconsolidated saturated clays, and there are few studies on the coupling effects of both temperature and humidity on overconsolidated unsaturated clays. Moreover, current studies use the net stress-suction framework to describe the effect of humidity on unsaturated clays, which is limited. Therefore, this study would adopt the net stress-effective saturation framework to reflect the influence of humidity, and ascertain the stress-strain behaviour of overconsolidated unsaturated clays affected by temperature and humidity on the basis of numerous tests on clays at changing temperature and humidity. Then temperature and effective saturation will be taken into the UH model in order to build a thermo (temperature)-hydro(humidity)-mechanic(stress history) constitutive relation. The new model can be extended into the generalized three-dimensional stress space by the transformed stress method.Finally, the supposed model will be incorporated into the finite element software to simulate and analyze engineering problems.

天然土多处于超固结和非饱和状态，并随着季节的交替处在温度和湿度不断变化的环境中。而温度、湿度的变化会改变土的特性。因此，研究土在温度和湿度影响下的非饱和与超固结应力应变特性对岩土工程至关重要。然而，目前多数研究主要集中于湿度对正常固结非饱和土或温度对正常固结饱和土的影响，针对温度和湿度耦合作用下的超固结非饱和土特性的研究较少。而且已有研究在描述湿度对土的影响时所采用的净应力-基质吸力框架也存在局限性。所以，本项目拟采用净应力-有效饱和度框架描述湿度的影响，并基于超固结非饱和土在变温度和变湿度条件下的室内试验结果，探明超固结非饱和土在温度和湿度作用下的力学特性，将温度和有效饱和度两个自变量引入统一硬化模型，建立贴近工程实际的土的热(温度)-水力(湿度)-力学(应力历史)本构关系。再通过变换应力的三维化方法将之推广到三维应力空间。最后将所提本构模型嵌入到有限元软件以模拟工程实际。

天然土多处于超固结和非饱和状态，并随着季节的交替处在温度和湿度不断变化的环境中。温度、湿度的变化会改变土的特性，因此，研究土在温度和湿度影响下的非饱和与超固结应力应变特性对岩土工程至关重要。本项目进行了非饱和土的系列试验研究，得出了非饱和土温度影响下的水汽迁移规律、非饱和土围压-吸力-强度-变形间的关系、加载路径对重塑黄土一维长期变形特性的影响规律、核废料处置库的温度场演化规律等非饱和土的温度变形强度关系。从土材料的基本特性出发，结合非饱和土的等向压缩特性和强度特性，分别考虑非饱和土的吸力、饱和度、膨胀性等因素，建立了膨胀性非饱和土UH模型、考虑水-力耦合的超固结非饱和土的UH模型等三维非饱和土弹塑性本构模型，所提模型能合理地反映超固结非饱和土的湿化特性、等向压缩特性、剪切硬化和软化特性、剪胀特性、应力路径依赖性、临界状态线的唯一性等特性。结合SMP准则，采用变换应力的三维化方法将提出的超固结非饱和土的本构模型三维化，使模型能反映中主应力对超固结非饱和土变形和强度的影响。将已建立的非饱和土的力学耦合关系框架与超固结UH 模型嵌入到有限元软件以模拟工程实际，研究结果对于非饱和土强度、变形分析及工程稳定分析将起到积极作用。