Laboratory test study on moisture migration and structural damage evolution of frozen unsaturated red clay

Heat transfer, moisture migration and water-ice phase change during the soil freezing process are important factors contributing to frost heave damage in geotechnical engineering. Firstly, the temperature variation characteristics of the samples were obtained using a temperature detection switch (TDS) acquisition system. Secondly, the NMR signal amplitude of the samples after one-dimensional unidirectional freezing under different initial conditions was measured using the GR-HSE sequence. Finally, the evolution of pore development and crack propagation in the samples before and after freezing was characterised using CT scanning technology. The results showed that there was no significant difference in temperature gradient between different regions of the samples, and the freezing depth increased with decreasing temperature. The redistribution characteristics of moisture in the samples after freezing were obtained through its correspondence with moisture content, which confirmed the phenomenon of moisture migration in frozen soil. The porosity of the samples significantly increased after freezing, and the damage in the laminar structure zone was more severe than that in the fibrous structure zone. There were significant differences in the quantity and volume contribution of pores at different particle sizes, and the proportion of pores with higher coordination number increased, promoting the degree of frost heave damage.