Migration mechanism of capillary-film water in frozen soil and its experimental verification

In view of the capillary theory and the film water theory only considering one kind of the water migration mechanisms, it is difficult to fully and reasonably reveal the frost heaving mechanism of the soil. According to the occurrence characteristics of capillary water and film water in the pores, the pore diameter 0.1 μm or the transverse relaxation time 2.5 ms is proposed as the criteria for determining the capillary water and film water. Based on the fluid dynamics and fundamental thermodynamics, a driving force model for water migration of film, a mechanical model for the generalized Clapeyron equation, and a driving force model for migration of capillary-film water are established, and the conversion coefficient between the pressure variable and the suction variable is given. The model analysis shows that the frozen macropore generates a concentrated suction at the curved ice-water interface, which drives the capillary water and film water in the unfrozen small pores to migrate into the frozen macropore. The migration path is as follows: the capillary water in the unfrozen small pores and the film water on the particle surface → curved ice-water interface → the film water on the wall of frozen macropore. Finally, the low-field NMR tests on silt during freezing are used to prove the boundary between the capillary water and the film water, and the correctness of the migration model and path of the capillary-film water is verified.