Research on Creep Characteristics of Freeze-Thaw Cemented-Soil Based on LF-NMR and SEM

In the development of underground space in coastal urban areas, artificial freezing is commonly used to reinforce soft soils to ensure engineering safety. However, the freeze-thaw deformation induced by the method can threaten the stability of surrounding buildings and structures. In practice, cement is used for improvement before freezing to enhance soil strength and limit deformation. However, after freeze-thaw cycles, the properties of cemented-soil degrade to some extent, and long-term loading may induce creep, leading to potential failures. Therefore, it is crucial to investigate the creep characteristics and microstructural evolution mechanisms of freeze-thaw cemented-soil. This study focuses on soft clay from Shanghai and employs low field-nuclear magnetic resonance (LF-NMR) and scanning electron microscope (SEM) to investigate the influence pattern of freezing temperature and cement reinforcement on the creep characteristics of freeze-thaw cemented-soil. The results indicate that, after creep, the pore volume of the unfrozen samples increases from 24.5% to 28.5%, and the particle size decreases. After freeze-thaw at −25 ℃, structural damage intensifies, with pore volume reaching 39.1% and particle size reducing to 4.50 μm, confirming that low temperature causes particle fragmentation. Freeze-thaw cycle causes a shift in the NMR T₂ spectrum of samples from a single peak to a double peak. Creep facilitates the conversion of large pores to small pores, resulting in a decrease in the average pore diameter but an increase in the total number of pores, which leads to an over-all rise in porosity. This study explains the mechanism by which freeze-thaw cycle causes microstructural damage of cemented-soil and consequently changes macroscopic creep, providing a theoretical basis for the long-term stability of engineering projects.