Triaxial tests of soil–rock mixtures with different rock block distributions

Triaxial tests on three types of soil–rock mixture (S-RM) samples with the same rock block content, but different grain size distributions, were performed in this study. To better understand the meso-mechanical behavior of soil–rock mixtures, one set of samples containing “oversized rock blocks” was designed. The oversized rock blocks in the other two sets were handled using the equivalent weight replacement method and the similar translation method. On this basis, the effect of the grain size distribution on the mechanical properties of the soil–rock mixtures was explored. The interlocking and the breakage of the large rock blocks were found to be two of the controlling factors of the mechanical properties of soil–rock mixtures. The deviator stress and the volumetric strain correlated well with the uniformity coefficient of the particle size distribution curve and performed differently under different confining pressure levels. Based on X-ray computed tomography (CT) slices of samples taken during the triaxial tests, the interaction of the internal rock blocks and the evolution of the sample meso-structure in the loading process were observed and analyzed; the present analysis provides explanations for the macroscopic mechanical behavior of soil–rock mixtures.