脱吸附机理对膨胀土自收缩自固结变形及力学特性的表征

Expansive soil has been known to its complicated swelling/shrinkage behavior due to the interaction with water during drying and wetting. It brings potential geo-hazards to geotechnical, environmental and energy related geo-systems. Currently, researchers start to explore the micro-scale mechanism of mineral-water interaction to understand the shrinkage or swelling behavior associated with drying or wetting. However, the detailed physical processes are not identified yet. A unified theoretical framework is still lacking to effectively illustrate the complexity of the moisture-induced deformation for expansive soils by up-scaling from molecules to bulk soils. This proposal will work on nano-scale level to elucidate the physical process of mineral-water interaction based on water isotherms, together with the various techniques to analyze the variation of crystal spacing and the amount of adsorptive water content. Meanwhile, this proposal will design a comprehensive experimental program covering all spectrums of expansive soils saturated with different type of cations. The experimental study will use Drying/Wetting Cake method to measure the soil shrinkage curve (SSC) and self-consolidation curve (SCC) for soil specimens under free-confining condition during drying and wetting, and analyze the shrinkage rate at adsorption water retention regime and compression index of self-consolidation at high suction stress by bridging the fundamental soil properties and practical geotechnical indices. Inspired by these correlations, a new method of determination of swelling pressure for expansive soils and a soil-water retention-based classification system will be proposed. This research will provide effective tools and solid theoretical background for engineers to deal with practical challenges of expansive soils.

膨胀土与水相互作用的同时有着复杂的干缩湿胀变形行为，也为涉及到膨胀土的岩土、环境和能源工程带来巨大的灾害隐患。目前，人们开始从膨胀土矿物颗粒与水相互作用的细观机理来了解膨胀土脱吸湿变形特性，但具体物理过程还未明确，仍缺乏有效的关联方法将微观行为上升到宏观表现。本项目将从膨胀土细观吸附脱附机理为出发点，重点考察宏观土体在不受外力作用下的自身固有变形特征。结合多尺度不同试验方法研究矿物晶体与水分子相互作用的物理化学过程，并运用土饼脱湿吸湿法量测各类膨胀土在不同饱和阳离子和不同初始密实度情况下的自收缩特征曲线和自固结特征曲线，将吸附段收缩率和自固结压缩系数等特征变量与膨胀土的基本属性相关联，建立基于微观吸附机理的膨胀土变形特性的数学模型。并以此相关性为启发，提出基于自收缩特征的膨胀力计算准则，和基于土水特征的新型膨胀土分类判别标准及测试方法，为解决膨胀土工程问题提供可靠的理论基础和分析手段。

膨胀土在干湿循环条件下的变形及刚度、强度等力学特性的演化与诸多工程应用难题，例如路基边坡等土工构筑物的稳定性、核废料等固体废弃物的阻隔材料的渗滤及力学稳定性都密切相关。当前，人们开始关注黏土矿物颗粒与水的相互作用的微细观机理，并运用于揭示膨胀土的脱吸湿变形特性，但是具体的物理过程仍未明确，也缺乏合理有效的升尺方法将微观行为与宏观表现相关联。本项目从膨胀土细观吸附脱附机理出发，重点考察宏观土体在不受外力作用下脱吸湿过程中的自身固有变形特征。开展了不同尺度的矿物晶体与水分子相互作用的试验研究，考察不同吸附水含量条件下的水密度变化特征；并运用土饼脱湿吸湿法量测各类膨胀土的收缩特征曲线和自固结特征曲线；同时测试并分析了不同类型土体的刚度随含水量的变化规律，研究了土体非饱和状态下无侧限弹性模量和微米压痕弹性力学响应；结合各类土体脱吸湿路径下的变形和刚度演化，反演了土体内部粒间应力的发展，并以此相关性为启发，提出基于自收缩特征的膨胀力计算准则，和基于土水特征的新型膨胀土分类判别标准及测试方法。