Effect of freeze-thaw cycles on mechanical behavior of clay-gravel mixtures

The use of clay-gravel mixtures (i.e., adding excavated or natural gravel particles into clay soil matrix) as the main filling materials is increasing in the anti-seepage system of high Earth Core Rockfill Dams (ECRDs). With the continuous construction of high ECRDs in the Chinese plateaus and cold regions, it is of great urgency and importance to understand the physical and mechanical characteristics of compacted clay-gravel mixtures under freeze-thaw action. To this end, laboratory freezing-thawing tests, computed tomography (CT), and triaxial compression tests were conducted to evaluate the effects of freeze-thaw cycles on moisture loss, pore structure characteristics, stress-strain behavior, failure strength, elastic modulus, cohesion, and internal friction angle of compacted clay-gravel mixtures. The results demonstrate that, 1) the freeze-thaw cycle significantly changed the mechanical characteristics of the clay-gravel mixture samples, but the shape of the stress-strain curve is less sensitive to it. 2) The failure strength of samples exhibits a significant decrease after the first freeze-thaw cycle, but shows a certain increase as the number of freeze-thaw cycles increases from 1 to 2. 3) The elastic modulus of samples first decreases and then increases with increasing freeze-thaw cycle, and the most severe deterioration was observed after the first freeze-thaw cycle. 4) Regardless of the number of freeze-thaw cycles, there is a linear relationship between failure strength and elastic modulus for a sample that has suffered freeze-thaw weathering. 5) The cohesion of samples decreases firstly and then slightly increases with increasing freeze-thaw cycles, while the internal friction angle is hardly affected.