Effects of carbon nanotubes treatment on engineering properties of sandy fine-grained soils subject to freeze–thaw cycles

Freeze–thaw cycles (FTCs) are the significant factors that affect the bearing capacity of foundations and stability of structures in cold regions, posing challenges for the construction of water conservancy projects. Therefore, seeking improved materials that can enhance the engineering properties of soil is one of the hotspots in research. Until now, research on the improvement of soil properties by carbon nanotubes is still lacking, particularly regarding the evolution of macro and micro characteristics of the improved soil under FTCs. To clarify the above issues and provide scientific evidence for the application of multi-walled carbon nanotubes (MWCNTs) in engineering projects in cold regions, MWCNTs are utilized as the improvement material in this study, and a series of FTCs tests are conducted on the improved soil. The relationships between shear strength, particle gradation, pore structure, and FTCs are analyzed. Additionally, the optimal dosage of MWCNTs is determined, and the ability of the soil to resist FTCs is investigated under the optimal dosage conditions. The results show that 0.5 wt% MWCNTs can effectively improve the shear strength of soil. Moreover, FTCs reduce the shear strength by altering the particle gradation and pore structure, while the resistance of treated soil to FTCs is significantly enhanced. This study reveals the effects of MWCNTs in enhancing the engineering properties and freeze–thaw resistance of soils, providing a reference for the selection of materials for improving foundation soils in practical engineering. • Changes of macro and micro properties of soil under freeze–thaw cycles were studied. • Multi-walled carbon nanotubes (MWCNTs) were used as reinforcing agent in soil. • The soil's shear strength was significantly enhanced due to the MWCNTs addition. • The particle gradation and pore structure of the soil were improved by MWCNTs.