Effects of Freeze-Thaw Cycles on the Mechanical Properties of the Core-Wall Contact Clay of a Dam

In cold regions at high altitudes, freeze-thaw cycles due to diurnal temperature variation in the construction process in winter result in the core-wall soil materials of dams having varying mechanical properties. In this study, a series of consolidated undrained triaxial tests were performed on soil samples subjected to various numbers of freeze-thaw cycles to study the effects of freezing and thawing on the mechanical behaviors of contact clay. First, the samples were prepared with a dry density of 1.81 g/cm(3) and a moisture content of 16.8%, which was consistent with that in the in-site construction. The soil samples were subjected to freezing and thawing tests under supplementary water conditions. The freezing and thawing times were 0, 1, 3, and 5, respectively. Finally, consolidated undrained triaxial tests were conducted on the samples, and four levels of confining pressures were applied (50, 100, 200, and 400 kPa). The experimental results indicated that freezing and thawing significantly weakened the mechanical properties of contact clay. The modulus, strength, and internal friction angle decreased considerably with the increase in freeze-thaw cycles, particularly in the first three freeze-thaw cycles. After approximately five freeze-thaw cycles, these three parameters tended to stabilize. The cohesion decreased almost linearly as the number of freeze-thaw cycles increased. In addition, the double hardening constitutive model was employed to model the test results, in which the influence of freeze-thaw cycles was considered by varying the model parameters, and the evolution law of the yield surface with the freeze-thaw cycles was analyzed. A comparison between the test and computed results indicated that the deviatoric stress and pore pressure agreed relatively well.