Abstract: 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.

Key words: ice-water deposited silty clay, soil-water characteristic curve, unsaturated shear strength, mesostructure, mineral composition