Macro- and mesoscopic experimental study of the effects of water content on moisture migration in coarse-grained fillings under freeze–thaw cycles and loads

Freeze–thaw cycles and loads are key external factors affecting moisture migration features and frost deformation of coarse-grained fillings. The objective of this study was to clarify the moisture migration features and mesoscopic mechanism of coarse-grained fillings with different initial water contents in seasonal frozen regions under short-term freeze–thaw cycles in the spring thawing period. To this end, a series of experiments realized by mesoscopic observation with X-ray computed tomography (CT) were conducted with fluorescein as a tracer. We then investigated the trends in the temperature field, frost depth and water replenishment, final distribution of the water content, moisture migration images, and changes in the CT value of coarse-grained fillings with different initial water contents under freeze–thaw cycles and static/dynamic loads in a system with an open-water supply. The experimental results demonstrated that under the freeze–thaw cycles and loads, the temperature fields of samples with different water contents change regularly with the change in the external temperature, while the loading pattern has a negligible influence. During the entire process, the external moisture migrated upward, and the initial water content affected the migration process. Typically, the external water replenishment and migration height of the liquid water were inversely proportional to the initial water content, while the final overall water content was higher than the initial value. Under freeze–thaw cycles and dynamic loads, thaw settlement compression deformations were observed during thawing. CT scanning revealed that the pore filling induced by moisture migration leads to grain dislocations after multiple freeze–thaw cycles. Specifically, moisture concentrates in unfrozen areas, the sample density increases, and damage increments are typically negative, which reduces the porosity, thus resulting in thaw settlement compression deformations during thawing.