Shear strength behavior of frozen unsaturated sands under thermal loads

Understanding the mechanical behavior of frozen unsaturated sand under thermal gradients is crucial for the design and maintenance of infrastructure in permafrost regions. In this study the shear strength of Ottawa sand under varying temperatures, degrees of saturation, and loading conditions is investigated. A series of laboratory experiments were performed to measure the shear strength of Ottawa sand using direct simple shear equipment placed in a temperature controlled environmental chamber. During the experiments, soil temperatures and stress–strain curves were recorded, and they were analyzed to determine the strength behavior. Results show that shear strength increases with decreasing temperature, increasing ice content, strain rate, and normal stress. A significant increase in strength was observed with increasing initial degree of saturation, attributed to higher ice content acting as a cementing agent within the soil matrix. A modified Mohr-Coulomb failure criterion was developed by integrating soil freezing curves to account for the effects of ice content on both cohesion and friction angle. The model exhibited strong predictive capability (R 2 = 0.98) for shear strength under thermal loads. These findings provide a robust framework for assessing the stability of geotechnical structures in cold regions and highlight the critical role of ice content in frozen soil behavior.