Characterizing Influence of Salt and Freeze–Thaw Cycle on Strength Properties of Clay

Subsea tunnel construction is usually associated with high risk due to high water pressure. To ensure the safety of the tunnel during construction, artificial ground freezing (AGF) technology is typically adopted to freeze the surrounding soil of the tunnel. Previous researches reveal that the strength properties of clay vary significantly due to the coupling effect of salt and freeze–thaw. For this reason, the consolidated-undrained triaxial compression test was carried out on clay saturated with NaCl solution. The influences of freeze–thaw cycle, salt content, confining pressure, and strain rate on the strength were comprehensively evaluated. A statistical analysis was performed to distinguish the influence of these factors and their coupling effect. Test results reveal that a critical salt content exists at which the soil strength before and after a freeze–thaw cycle is the lowest. Similarly, instead of linearly increase with increasing strain rate, a critical strain rate exists at which the soil strength is the highest under undrained loading. In addition, a damage model with consideration of the coupling effect of freeze–thaw cycle and salt content was specially proposed to predict the stress–strain characteristic of clay with different salt contents before and after a freeze–thaw cycle.