An investigation of the breakage behaviour of a pre-crushed carbonate sand under shear using X-ray micro-tomography

The breakage behaviour of a pre-crushed carbonate sand sheared within a miniature triaxial loading apparatus is investigated using high-spatial resolution X-ray micro-tomography. Full-field 3D CT images of the sand sample are acquired at different loading stages of the test. This enables the quantitative investigation of the temporal and spatial evolution of soil microstructures throughout the test, including particle size, particle shape and local strains. A particle tracking approach capable of identifying fragments of crushed particles is presented, which allows the identification of different particle crushing modes (i.e., chipping, major splitting and fragmentation) occurring during the shear. Particle breakage is found to exhibit clear localization around the shear band as it develops. Meanwhile, the failure modes of particles crushed during shear are found to be related to their particle-scale characteristics, which include particle size and particle shape. Specifically, particles with a smaller size are more likely to fail in the major splitting mode, while particles with highly irregular shapes tend to fail in the fragmentation mode. The image data and experimental findings presented in this study will be useful to develop and validate advanced approaches for discrete element modelling of crushable soils with realistic particle shape.