Exploring particle breakage in sand under triaxial shearing using combined X-ray tomography and particle tracking method

In this paper, a novel investigation of the particle breakage behaviour of sands is made using combined techniques of X-ray micro-computed tomography (μCT) and sand particle tracking. First, an in situ μCT triaxial test on a miniature sand specimen is conducted to allow the visualisation of particle-scale morphology and movement. Then a two-step particle tracking method is developed and applied to track the sand particles that experience a zero or slight degree of particle breakage. Making use of the power of the particle tracking method, the individual intact particles within a sheared sand specimen containing a mixture of crushed and uncrushed particles were tracked for the first time. The results show that the degree of particle breakage in the consolidation stage is very low, and before the peak stress is reached, more than half of the particles were crushed for the first time; also significant particle breakage occurred at the centre of the specimen during the post-peak stage. The particle shape and gradation analyses reveal that larger grains with lower values of sphericity and convexity are prone to breakage, with the angularities of the crushed particles being closely related to their mother particles.