Soil Freezing Characteristic Surface for Partially Frozen Soils

The soil freezing characteristic curve (SFCC), which relates unfrozen water content to temperature, is a fundamental constitutive relationship in frost heave simulations. However, the influence of soil suction, another critical state variable, is often neglected. This study highlights how the SFCC is significantly affected by suction conditions, with unfrozen water content varying markedly between saturated (suction = 0) and completely dried (suction = ∞) conditions at the same subfreezing temperature. Recognizing this limitation, the concept of the soil freezing characteristic surface (SFCS) is proposed to incorporate the impacts of both temperature and suction on unfrozen water content. After that a method is introduced to construct the SFCS using the boundary SFCC (suction = 0), the boundary soil water characteristic curve (SWCC, temperature = 0°C), and SWCC or SFCC under varying temperature or suction levels, all of which can be obtained through laboratory experiments. A mathematical expression for SFCS is developed to describe its behavior across the full range of temperatures and suctions, integrating the interdependence of SFCC and SWCC. Validation against experimental data from initially saturated red clay, Lanzhou silt, fine sand, and initially unsaturated silt confirms the accuracy and applicability of the proposed SFCS. The proposed SFCS systematically captures the characteristics between SFCC and SWCC: they are similar yet distinct, interacting rather than functioning independently.