Effects of Triaxial Sample Scaling on the Mechanical Behavior of Alluvial Gravels

In practical engineering, mechanical characterization of coarse gravels is usually performed on small-scale specimens, where the maximum particle size is limited to fit the material in standard testing devices. This implies altering the original particle size distribution, which is known to influence the stress–strain behavior. However, most research on grading effects has been done after comprehensive testing on sands, and the impact of small-scaling on gravelly soils is still poorly understood. This paper presents an experimental study on the shearing response of coarse soil at different specimen scales. The main objective is to assess the impact of small-scaling methods on the stress–strain behavior of coarse alluvial soils. Scalping grading and truncation techniques were used to prepare scaled specimens. Several tests were performed using triaxial cells with specimens of 100, 150, and 800 mm diameter. The analyses indicate that volumetric dilatancy strongly decreases with specimen size, while the secant strain modulus and peak shear strength slightly increase in larger specimens. Differences are mainly related to particle size distributions and packing properties. The article discusses practical insights into the effects of small-scaling variations and their implications for characterizing gravelly materials.