Effect of the frozen layer on the stability of cut soil slopes during seasonal freezing and thawing

Research on the stability of soil slopes in seasonally frozen regions has mainly focused on slope failures during the thawing window. There are few studies on slope stability during the freezing window and its subsequent influence on slope failure in the next thawing window. In this paper, soil strength was tested during freezing and thawing to obtain temperature-dependent strength parameters for the simulation of slope stability. Then, the slope's temperature field over an entire year was accurately simulated so that characteristics of the frozen layer could be determined at any time. Based on the above results, the progressive failure modes of frozen soil slopes are discussed. The results show that: 1) during the freezing window, depth of the frozen soil layer increases, as does the slope's safety factor, while a yield zone propagates towards the slope shoulder. (2) During the thawing window, the frozen soil layer shrinks in depth while the yield zone continuously expands, which decreases the safety factor. Comprehensive analysis of these results indicate that the frozen layer provides a “toe-locking effect” that increases the safety factor during the freezing window, while it also provides a “dragging effect” that propagates the yield zone towards the slope shoulder. During the thawing window, the “toe-locking effect” gradually diminishes; a continuous sliding surface is formed, which lead to a landslide. The frozen soil layer of the freezing window accelerates the slope sliding in the thawing window.