Effect of Silt Content on Mechanical Behavior of River Gravel Material

River gravel foundations are frequently encountered geological conditions during the construction of earth-rockfill dams. Despite pre-treatment, river gravel foundations inevitably contain some amount of silt, directly impacting their behavior. This paper conducts sixteen sets of large-scale triaxial experiment to study the influence of silt content on mechanical behavior of the river gravel material. The loess was used to simulate the silt. Triaxial experiments with four different silt contents (0%, 2%, 4%, 6%) and four different confining pressures were carried out. The results showed that the peak strength decreased with the increase of silt content. Under low confining pressure, the specimen initially exhibits contraction, followed by dilation. At high confining pressure, the specimen exhibit contraction. Due to the bonding and lubrication characteristic of silt, the cohesion c increased with the increase of silt content, and the internal friction angle φ decreases with the increase of silt content. The lubrication of silt reduced the specimen deformation resistance. The increase of silt content results in the decreases of the initial shear modulus E₁, especially at the high confining pressure condition. As silt increases the dry density, the material’s the failure poisson ratio v_if decreases, especially under low confining pressure conditions.