Experimental study of the mechanical behavior of clay–aggregate mixtures

•Oedometer and triaxial tests were performed on clay mixed with coarse particles.•CT scans were performed to identify the microstructure of the soil mixtures.•Coarse particles led to extra inter-particle voids at the clay–particle interface.•The effective friction angle increased with the coarse aggregate content.

Clay–aggregate mixtures are widely distributed in nature and are often used in engineering applications. To improve the understanding of the effects of coarse particles on the mechanical behavior of clay–aggregate mixtures, a series of oedometer and triaxial tests were conducted on clay–steel bead and clay–fine gravel mixtures. Based on computed tomography scans, both the number and total volume of the inter-particle voids were observed to increase with the coarse aggregate content. Because of the combined effects of the inter-particle voids and clay–aggregate skeleton, the compression index of the mixture first increased and then decreased with the coarse aggregate content. During the undrained loading, the specimen with higher compressibility tended to generate a larger pore-water pressure and exhibit a smaller shear strength. The effective friction angle was observed to increase with the coarse aggregate content. For the clay specimens mixed with 33.3% 1-mm beads, 2-mm beads, and fine gravels, the increases in the effective friction angles were 4.4°, 3.4°, and 6.2°, respectively.