Evolution of deformation, strength, and permeability of compacted clay under freeze-thaw cycles for levee engineering

Seasonal freeze-thaw cycling significantly affects the deformation, mechanical, and hydraulic performance of compacted clay used in cold-region levees. In this study, a series of laboratory tests was conducted to investigate the coupled evolution of volumetric deformation, shear strength, stiffness, and anisotropic hydraulic conductivity of compacted levee clay under repeated freeze-thaw cycles. Specimens with degrees of compaction ranging from 0.86 to 0.94 were subjected to up to 10 freeze-thaw cycles under a multidirectional closed-system condition. Moisture content, volumetric deformation, consolidated-drained triaxial shear behavior, and vertical and horizontal hydraulic conductivities were systematically analyzed. The results show that freeze-thaw cycling caused progressive moisture loss and irreversible volumetric deformation. Low-compaction specimens exhibited greater accumulated expansion and more severe surface deterioration, whereas highly compacted specimens showed better volumetric stability. The shear strength and elastic modulus decreased with increasing freeze-thaw cycles, with cohesion and stiffness being more sensitive to freeze-thaw damage than the frictional component. Additional triaxial tests after ten cycles showed that increasing the degree of compaction improved post-freeze-thaw shear strength, cohesion, internal friction angle, and elastic modulus. Hydraulic conductivity increased with cycle number and exhibited marked anisotropy, with horizontal conductivity consistently higher than vertical conductivity. Although higher compaction reduced the absolute hydraulic conductivity, the relative increase in conductivity after cycling was more pronounced in highly compacted specimens. These findings indicate that deformation, strength, stiffness, and permeability are interrelated but non-equivalent indicators of freeze-thaw deterioration, and that cold-region levee performance should be evaluated using an integrated deformation-strength-permeability framework.