Undrained Shear Strength of Frozen Unsaturated Silts

This study focuses on investigation of the undrained shear strength of unsaturated frozen silts prepared at varying initial thermal and hydraulic conditions. The initial degree of saturation controls ice and unfrozen water contents at temperatures below depression point. The strength properties of frozen soils are highly influenced by ice and water contents which is highly coupled with thermal state of the soils. To evaluate the strength properties of frozen silts, a series of direct simple shear experiments were performed using Bonny silt prepared at different initial degrees of saturation under monotonic shear loading. Compacted silt samples at varying degrees of saturation were subjected to artificial freezing before shear loading and stress-strain curves were recorded during loading. Identical samples were prepared and sheared at room temperatures for comparison. The stress-strain behavior of frozen silts was observed to be significantly different than those of obtained at room temperatures where on an average the shear strength of the saturated frozen soils was higher by 150% in comparison to the shear strength of the same soil in saturated unfrozen condition. The undrained shear strengths for frozen soils were also observed to be affected by initial degree of saturation where the strength was observed to increase by 142 % when the initial degree of saturation was increased from 0.51 to 1.00. The results obtained from this study will be used in ongoing investigations of capacity of deep foundations in warming permafrost.