X-ray CT quantification of in situ fabric evolution and shearing behaviour of granular soils of different particle shapes

The role of particle shape on soil mechanical response has been studied extensively especially through numerical means. The underlying micromechanics of how particle shape may affect the soil mechanical responses at element scale remains unclear. Systematic micromechanical experiments that consider in situ tracking of the evolution of fabric during the shearing process is missing. Aided by a miniaturised triaxial apparatus and X-ray computed tomography (CT), this study presents a series of triaxial compression on four granular soils with different particle shapes yet the same mineralogy, grading, and initial density. Evolution of three-dimensional soil fabric quantifiers during shearing was captured based on 192 full-field CT images. The results revealed that the initial shearing reduced the packing density without changing the particle packing pattern, followed by particle sliding and particle rotation, which redistributed the force chains and formed a new packing pattern to resist shearing, causing strain localisation, and reductions in both the contact number and concentration of contacts direction. Fabric anisotropy increased before reaching the peak and attained the maximum value as the soil approached the critical state. Particle shape, especially when quantified by overall regularity or other combinations of descriptors, displayed more significant linear correlations with critical-state parameters than by local descriptor.