Strength of partially frozen sand under triaxial compression

To investigate the effect of the pore matrix (i.e., ice and unfrozen water) on the strength of partially frozen sand, a series of triaxial compression tests with internal pore water pressure (PWP) measurements were performed. Both dense and loose saline sand samples were prepared by rapidly freezing the samples and then slowly warming the samples to, and subsequently shearing at the temperature of −3 °C. Test results indicate the temperature only affects the effective cohesion, not the effective friction angle of sand. The pore ice stress was estimated using Ladanyi and Morel’s 1990 postulate on the internal stresses within frozen soil; the stress (hydrostatic) change in pore ice was reflected by an equal change in PWP in the partially frozen loose sand. Based on Ladanyi and Morel’s 1990 concept of internal confinement in frozen sand, a Mohr–Coulomb model that uses effective failure and residual friction angles from unfrozen sand to estimate the strength of partially frozen sand is presented. The proposed model reflects how the pore matrix contributes to the strength of partially frozen sand. For loose sand, the peak strength is enhanced by the internal confinement and cohesion resulting from the pore water (suction) and pore ice, respectively. For dense sand, only pore ice affects the peak strength by incorporating the internal confinement and cohesion.