冰水沉积粉质黏土非饱和强度特征与细观机理研究

为弥补当前对非饱和粉质黏土细观结构研究的欠缺,基于Fredlund双应力变量理论、Fredlund-Xing土-水特征模型,通过室内试验从细观结构、矿物成分至非饱和力学特性方面展开对冰水沉积粉质黏土的系统研究,查明非饱和抗剪强度及参数变化特征,深入分析细观作用机理。研究表明:冰水沉积粉质黏土非饱和抗剪强度随基质吸力增大而提高,增长速率逐渐降低,内摩擦角φ′与含水率构成对数函数关系,内聚力c_total1具有峰值特征,峰值点含水率约为10.24%。土中的矿物组分遇水发生的水解、离子置换等作用对土体结构造成较大影响,在低基质吸力条件下造成宏观非饱和抗剪强度的损伤,根据其作用特征将非饱和抗剪强度随基质吸力的变化过程划分为3个阶段,建立了适用于冰水沉积粉质黏土的三维破坏包络面的概化模型。与此同时,分析发现材料参数φ^b在低基质吸力段并不为常数,以某一初始值逐渐减小,变化曲线呈反“S”形,最终无限趋近于0。

Unsaturated Strength Characteristics and Mesomechanism of Silty Clay Deposited in Ice Water

The mesostructure, mineral composition, and unsaturated mechanic properties of silty clay deposited in ice-water are investigated through laboratory test based on Fredlund’s double-stress variable theory and Fredlund-Xing’s soil-water characteristic model. The characteristics of unsaturated shear strength and parameter change are identified, and the mesomechanism of unsaturated shear strength varying with matric suction is revealed. Results demonstrate that the unsaturated shear strength of silty clay deposited in ice-water increases with the augment of matric suction; but the growth rate attenuates gradually. Internal friction angle φ′ is in a logarithmic function relation with water content; while cohesion c_total1 is of peak characteristic, with the water content reaching about 10.24% at peak cohesion. Hydrolysis and ion exchange of mineral components in soil encountered with water have great influence on soil structure and result in the damage of macro-unsaturated shear strength under low matric suction. The process of variation of unsaturated shear strength with matric suction is divided into three stages, and meanwhile a generalized three-dimensional failure envelope model of silty clay deposited in ice-water is established. In addition, the material parameter φ^b is not a constant in the segment of low matric suction, but rather declines gradually from an initial value to be approaching zero infinitely, with the change curve in an inversed “S” shape.