Increased frost heave deformation of synthetic water repellent soil

Abstract Synthetic water repellent soil is often used to reduce water infiltration across different soil layers to mitigate frost heave hazards in cold regions. However, the freezing performance of water repellent soil itself remains unclear. Samples with different degrees of water repellency were prepared using octadecylamine. The contact angles, unfrozen water content, pore size distribution, and freezing deformation of the samples were measured. There is a positive correlation between the degree of water repellency and unfrozen water content, the growth rate of macropores, the duration of the rapid frost heave stage and the amount of stable frost heave. Increased water repellency caused an increase in the critical nucleation work for the water–ice phase transition and shifted the dominant heat transfer mode from solid–liquid conduction to air–liquid conduction. This led to an increased unfrozen water content and an extended duration of rapid frost heave. The increased water repellency also changed the ice crystal growth pattern on soil particle surfaces from attachment to detachment, leading to an increased proportion of large pores and frost heave deformation. These outcomes raise concerns about the durability of the protective effect of synthetic water repellent soil used in cold area geotechnical engineering practices.