Influence of fines content and degree of saturation on the freezing deformation characteristics of unsaturated soils

In this study, a series of one-dimensional freezing deformation tests were conducted within a closed system to evaluate the influence of fines content and initial water content on the frost susceptibility of soils. Also, the pulsed nuclear magnetic resonance (P-NMR) method was adopted to investigate the pore water distribution and deformation mechanism of freezing soils. Results show that as soil temperature decreases, pore water freezes in two stages: the capillary (or free) water freezes first, followed by certain amounts of adsorbed water turned into pore ice. Soil specimens with higher fines content usually have higher unfrozen water content due to the more abundant adsorbed water from fine particles. The initial water content influences the soil-freezing characteristic curve significantly when the fines content is relatively high (e.g., FC = 50%), while this influence becomes negligible with lower fines content. In addition, the freezing deformation properties of soil within a closed system are affected by the initial water content. A higher degree of saturation (e.g., S r > 0.5) results in frost heave, and a lower degree of saturation (e.g., S r < 0.4) results in frost shrinkage. In fact, there is a critical degree of saturation (between 0.4 and 0.5) that separates soil's properties of frost heave and frost shrinkage. Frost heave or frost shrinkage of soil depends on which of the two, freezing of pore water or thinning of adsorbed water (i.e., dehydration), is predominant. • Pore water in soil freezes in two different stages as temperature decreases. • Soil becomes more sensitive to temperature with decreasing fines content. • A higher initial water content results in a higher super-cooling temperature. • A critical degree of saturation separates frost heave and frost shrinkage.