Strength Evolution Characteristics of Frozen Soil Based on Laboratory Vane Shear Tests

【Objective】To elucidate the evolution of shear strength and the brittle failure characteristics of soil during freezing, laboratory vane shear tests were performed on fine-grained sandy soil collected from Nyingchi, Tibet.【Methods】Under a constant freezing temperature of −8°C, specimens with initial gravimetric water contents of 5%, 9%, and 13% were prepared. Different volumetric ice contents were achieved by controlling the freezing duration. The evolution of ice content was determined from monitored temperature and unfrozen water content, and peak strength, residual strength, and brittleness index were derived from the shear strength-rotation angle curves obtained from the vane shear tests.【Results】The shear strength of the specimens increased continuously with freezing time, corresponding to the increase in ice content. Peak strength increased significantly more than residual strength, resulting in a progressively wider gap between the two and increasingly pronounced post-peak softening. Accordingly, the failure mode evolved gradually from progressive deformation to a more distinct brittle response. The brittleness index exhibited an overall upward trend with increasing ice content, indicating that higher ice content markedly intensified post-peak strength degradation and brittle failure characteristics in frozen soil. Under the present test conditions, peak strength occurred predominantly within a rotation angle range of 20°~30°, which may provide a useful reference interval for peak-strength identification and result interpretation in laboratory vane shear tests on frozen soil.【Conclusion】Ice content is a key factor governing the evolution of shear strength, post-peak softening, and brittle failure characteristics of frozen soil. Laboratory vane shear tests can effectively characterize the full-process evolution of frozen-soil strength.