Water accumulation unrelated to ice segregation near the freezing front during soil freezing: Implications for frost heave in high-speed railway embankments and ground ice formation

Abstract

Investigating water migration in frozen ground is crucial for understanding the hydrothermal dynamics of frozen soil, which is central to frozen soil engineering (e.g., frost heave) and permafrost environments (e.g., ground ice formation). Previous studies have mostly focused on water migration related to ice segregation in frost-susceptible soils, but less on water migration that is independent of ice segregation in non-frost-susceptible soils. Using a novel layer-scanning method based on the nuclear magnetic resonance (NMR) techniques, the water migration dynamic was observed during the freezing of non-frost-susceptible loess under different drainage conditions (with or without water drainage). Results showed an apparent phenomenon of water migration to the freezing front (TFF) (layer L7) (i.e., water accumulation that is independent of ice segregation) occurred in the early freezing stage of non-frost-susceptible soils under no draining water conditions. The traditional water migration mode is related to ice segregation, a new water migration (including upward and downward) mechanism was proposed to reveal this water accumulation unrelated to ice segregation at TFF. The water accumulation at the freezing front is independent of ice segregation, and is attributed to 9% volume expansion due to pore ice formation in the frozen zone, causing water migration downward TFF; while the decrease of the pore volume of the unfrozen zone (being compressed) accounts for the water migration upward TFF. Investigation into whether ice segregation exists and different modes of water migrations (depending on ice segregation or not) will be greatly helpful for exploring the mechanisms of micro frost heave in the high-speed railway embankments and the thick-layered ground ice formation.