In cold-region high-speed railway (HSR) subgrade engineering, coarse-grained soils are commonly used as frost heave prevention fillers. However, coupled water-heat migration during freeze-thaw cycles still induces frost heave. This study innovatively employs a nuclear magnetic resonance (NMR) system to elucidate the hydro-thermal transport mechanisms in coarse-grained soils during freezing. The results reveal that under identical temperature and freezing duration, high-water-content soils release substantial latent heat from pore water freezing, resulting in higher freezing zone temperatures than low-water-content soils. During freezing, unfrozen water content decreases as a power function with freezing time at different depths of soil samples, with the frozen zone experiencing the fastest water reduction, followed by the freezing front and then the unfrozen zone. Both free and bound water progressively decrease in frozen and unfrozen zones. After freeze-thaw, the change in soil pore structure leads to a decrease in bound water and an increase in free water in frozen zones, while both decrease in unfrozen zones. Furthermore, higher initial water content results in more pronounced reductions of bound water and increases of free water in frozen zones. These findings advance the understanding of hydro-thermal coupling mechanisms and provide theoretical foundations for frost damage mitigation in high-speed railway subgrades.

It is known from the literature that the rheological behavior of soils is largely dependent on the water content in pastes and soil organic matter forming the basis of organomineral soil gels. With an increase in soil moisture, gels can swell. As a result, the viscosity of the soil paste should change. The objective of this study was to assess the effect of soil moisture on the viscosity of soil paste. Arable soil horizons were used in this work: sod-podzolic, gray forest, leached chernozem, and chestnut. During the experiments, the soil moisture was changed, whereas the water content in the pastes in each soil type remained unchanged. The viscosity of the soil paste was determined by vibration viscometry, and the size of organomineral particles in pastes was determined by laser diffractometry. Two paste viscosity peaks depending on the soil moisture were obtained for all samples studied. The paste viscosity peaks were explained from the perspective of changes in the structure of humic substances in organomineral gels upon reaching critical concentrations: micelles-supramolecular formations-fractal clusters. Apparently, the transition between structural forms of humic substances under mechanical action on pastes is accompanied by the disintegration of large gel particles and the formation of a more balanced form of humic substances at a given water content.

Changes in water content have a significant impact on the consolidation of peat soil. Through the water content test and thermogravimetric analysis test, the water content, and the free water, weakly bonded water and strongly bonded water content of peat soil with different organic content in Yunnan Province (China) at different load levels and consolidation times were studied. The results show that the free water in peat soil samples was discharged when the temperature was less than 60 degrees C; the weakly bound water was released at 60 - 110 degrees C; and the strongly bound water was dehydrated at 110 - 200 degrees C. During the consolidation of peat soil, the water content in different states changed significantly. In the primary consolidation stage, the proportion of free water in the peat soil samples decreased by approximately 20%, while the proportion of weakly bound water increased slightly. In the secondary consolidation stage, the proportion of water in different states did not change considerably. In the third consolidation stage, the proportion of free water increased, and the proportion of weakly bonded water causing creep decreased by approximately 11%. For the undisturbed and deformed peat soil, the contents of free water and bound water increased with increasing total water content, but the ratio of free water to bound water remained relatively stable at approximately 1:2.