Super-large-scale triaxial tests to study the effects of particle size on the monotonic stress–strain response of rockfill materials

Owing to the lack of super-large-scale triaxial apparatuses, the prediction of field behaviour involving rockfill materials is commonly based on laboratory test data, which are often unreliable due to size scaling. In this work, a newly developed super-large-scale triaxial apparatus able to accommodate a sample diameter of up to 1000 mm was introduced to analyse the effects of particle size on the monotonic stress–strain response of rockfill materials. A series of triaxial tests was conducted with maximum particle sizes d_max of 200 mm, 160 mm, and 60 mm in parallel grading to investigate the effects of particle size on the strength and deformation behaviour of Rumei rockfill materials. The results indicated that the peak friction angle ϕ_p, peak dilation angle ψ_p and secant modulus at 50% of the peak strength E₅₀ decreased with increasing d_max and the particle breakage was enhanced as d_max increased. A unified linear relationship between ϕ_p and ψ_p was observed, regardless of d_max, and an equation considering d_max and the confining pressure was proposed to simulate E₅₀. These rare super-large-scale triaxial data can provide a valuable reference for assessing the effects of particle size on the strength and deformation behaviour of rockfill materials.