饱和岩土介质的化学-力学耦合问题—理论模型与试验验证

Most of geomaterials, either natural or artificial, are composed of multispecies and electrically charged. When exposed to complex environmental impacts, such as thermal variation, chemical attack and/or mechanical actions, such materials show strong chemo-mechanical coupling effect and complex mechanical behavior. Proper characterization of the chemo-mechanical behavior of geomaterials plays a crucial role in resolving many significant scientific and engineering issues. This research is proposed to investigate the chemo-mechanical coupling effect and mechanical behavior of electrically-charged geomaterials under complex environmental loading conditions. Based on the continuum mechanics of porous media and classical Gibbsian thermodynamics, a continuum theory of geomaterials with multiphases and multispecies is developed; in particular, a general expression of electro-chemical potential is developed, and the effective stress equation for geomaterials is formulated that can effectively describe the chemo-mechanical coupling effect; with the newest findings from related experimental studies, a constitutive framework is developed based on the proposed theory, which can be effectively used to address the chemo-mechanical behavior of geomaterials under complex environmental loading conditions. Laboratory experiments are designed and performed to investigate the mechanical properties and responses of clayey soils under complex environmental loading conditions, and the experimental results obtained in this research and available in the literature are introduced to calibrate and validate the proposed theory. The significance of the proposed research is far-reaching, in that it will help foster the development of modern soil mechanics, while laying bare a solid theoretical foundation for analyzing the chemo-mechanical behavior of geomaterials under complex environmental impacts.

岩土介质均含有多种组份，通常具有电性。在温度变化、化学作用、物理扰动等环境荷载作用下，这类介质表现出强烈的化学-力学耦合效应以及复杂的工程力学行为，有效模拟这些复杂效应与行为是解决许多重大科学和工程问题所面临的关键难题之一。针对这一问题，本项目重点研究在复杂环境荷载作用下饱和多组份岩土介质化学-力学耦合作用效应及力学行为。基于多孔介质混合物理论与经典Gibbs热动力学，建立饱和多组份岩土介质的化学-力学耦合作用理论，并提出组份电化学势的一般表达式以及能考虑土颗粒间电化学作用的有效应力公式；结合国内外有关实验成果，建立能够有效描述复杂环境荷载作用下饱和岩土介质力学行为的本构关系模型；开展室内试验和物理模拟试验，研究在各种环境荷载作用下粘性土的力学特性及其变化规律，校正和验证所建理论模型。本研究将为模拟复杂环境荷载下岩土介质的力学行为提供理论基础，并对完善和发展岩土力学学科具有重要的理论意义。

岩土介质所具有的多相多组分特性以及带电性，使得其在温度变化、化学作用、物理扰动等环境荷载作用下，这类介质表现出强烈的化学-力学耦合效应以及复杂的工程力学行为，有效模拟这些复杂效应和行为是解决许多重大科学和工程问题所面临的关键难题之一，而现有的岩土力学理论在描述化学-力学耦合问题存在明显地局限性。针对这一问题，本项目基于多孔介质混合物理论和Gibbs热动力学，建立了岩土介质的化学-力学耦合理论。从理论上实现了对微观物理化学作用的宏观数学表征；给出了孔隙水各组份电化学势的一般表达式，揭示了多相多组份土体中孔隙水压力的组成结构，提出了考虑粒间物理化学效应的有效应力公式；并基于修正剑桥模型，建立了考虑粒间物理化学作用的非饱和土本构关系模型。通过开展不同水化学状态下液塑限和沉降试验，从宏观角度研究了化学作用对微观结构的影响，并采用压汞、扫描电镜和核磁共振技术，从微观角度观察了化学作用后微观孔隙结构的改变。通过开展固结试验、直接剪切试验和三轴试验研究化学作用对粘性土宏观力学性质的影响，表明化学作用对粘性土的变形和强度有较大影响，阐释了通过莫尔-库伦强度准则导出的土体粘聚力的有效组成；并基于所建立的模型较好的模拟了化学作用诱导的固结。通过开展温度-化学-力学耦合作用下一维固结试验，研究了温度和化学耦合作用对固结屈服应力的影响，同时揭示了温度变化作用下含盐分土体的体变特性。该项目还研究了不同水化学条件下的粘性土的渗透性和持水特性。这些研究成果将为地下环境保护、核废料地下填埋、CO2地质封存、高土石坝的沉降控制等重大工程实践的解决提供重要的理论依据，并对完善和发展土力学学科具有重要的理论意义