Freeze–Thaw Effects on the Mechanical Behavior of the Ice–Soil Interface in Cultivated Black Soils of Northeast China

Seasonal freeze–thaw cycles profoundly alter soil physical properties in cold-region agroecosystems, yet their effects on the mechanical behavior of the ice–soil interface remain poorly quantified. This interface plays a critical role in governing soil structural stability, detachment resistance, and subsequent erosion processes during thaw periods, particularly in the black soil region of Northeast China. In this study, controlled laboratory experiments were conducted to investigate the evolution of ice–soil interface mechanical properties under varying freeze–thaw conditions using cultivated black soils. Key parameters, including interface shear strength and bonding characteristics, were quantified across different freeze–thaw cycles. The results demonstrate that freeze–thaw action significantly weakens the mechanical integrity of the ice–soil interface, with pronounced reductions in shear strength observed after repeated cycles. This degradation is attributed to ice lens formation, pore structure disruption, and the redistribution of interfacial water films during freezing and thawing. Notably, the rate and magnitude of strength loss exhibit strong sensitivity to freeze–thaw frequency, highlighting the cumulative nature of freeze-induced damage at the interface scale. These findings provide mechanistic insights into how freeze–thaw processes modulate soil resistance to external forces during early thaw periods, offering an improved physical basis for understanding soil erosion vulnerability in cold agricultural regions. The results have direct implications for soil conservation strategies and erosion modeling under ongoing climate warming, which is expected to intensify freeze–thaw dynamics in seasonally frozen farmlands.