Rapid freezing of saturated clays under large thermal gradients

Abstract

This study investigates the rapid freezing behaviour of saturated clays under large thermal gradients. Although the freezing characteristics of soils under natural/low thermal gradients such as ice lens formation and water migration have been extensively studied, the freezing of a saturated soil under a large thermal gradient is not understood. This study presents rapid freezing tests to examine the freezing behaviour of saturated fine-grained soils in a closed system under large thermal gradients using liquid nitrogen (LN). Temperatures are measured inside specimens during freezing and micro-CT visualised internally after freezing. The results show that large thermal gradients develop near the surfaces of specimens on their submersion in LN. The specimens freeze homogeneously, and no visible ice lenses form, due to the insufficient time for water migration and ice segregation under rapid freezing. The specimens fracture and split into major pieces, under no confining stresses in this study; freezing first occurs near the boundaries, and the freezing front propagates inward, creating temporal, differential volume changes between the outer and inner parts of the specimens, which leads to fractures in the unconfined state. The fractures affect subsequent temperature propagation and thermal gradients.