The effect of salinity on the freezing of coarse-grained sands

Unfrozen water is very important because it has a significant influence on the mechanical response of a frozen soil. It is particularly important to know if the water is available as free water or if it is bonded to the solid particles. A simple experimental setup was used to observe the freezing process of a coarse-grained soil under controlled freezing gradients and salinities. A fluorescent tracer helped to determine the location of the unfrozen water during freezing. Depending on the salinity and the thermal gradient, pockets of unfrozen water with a much higher salt concentration were trapped in pores under increased pore pressures. Even at salinities as low as 2 g/L, spicular ice crystals were identified with channels containing unfrozen water between the ice crystals. The experiments further indicate that the unfrozen water in coarse-grained frozen soils is in the middle of the pore space compared to the unfrozen water film that immediately surrounds fine-grained saline or non-saline soil particles.