Macro-meso freeze-thaw damage mechanism of soil-rock mixtures with different rock contents

Soil-rock mixture is a typical discontinuous material and often used as a roadbed filler. Rock content is a key factor in this mixture's properties. The damage pattern of soil-rock mixtures with different rock contents after freeze-thaw cycles is more complicated than that in normal state. The damage behaviour of soil-rock mixtures with different rock contents after freeze-thaw cycles is analysed in this study. Firstly, size-distributed subgrade coarse grained soil samples with different rock contents (35, 45, 55 and 65%) are prepared. The samples are subjected to freeze-thaw cycles periodically (24 h per cycle) for different times (0 and 10). Large-scale indoor triaxial tests are performed, and elastic modulus and shear strength are determined. Secondly, the macro-properties of the soil-rock mixtures with different rock contents are compared under normal and freeze-thaw states. Finally, indoor triaxial experiments are numerically simulated with Particle Flow Code software. Matched results are obtained, and the meso-mechanism of the soil-rock mixtures with different rock contents is elucidated. At the macroscale, the elastic modulus and shear strength of the soil-rock mixture decrease after the freeze-thaw cycles, and the decrement trends differ with different rock contents. At the mesoscale, the freeze-thaw cycles reduce the strength of soil-rock particles with different properties. The soil-rock mixture with 55% rock content exhibits the most severe damage among all mixtures; this mixture has the most soil-rock particle contacts because of its good compactness and skeleton structure.