Macro-micro mechanics of Fujian River sand under triaxial shear using X-ray micro-tomography

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Fujian River sand (FJS) is a complex mixture of minerals and rock fragments shaped by the dynamic geological history of Fujian province, China. The macro-micro mechanical responses of FJS under triaxial shear were carefully investigated through the X-ray tomography-based in-situ triaxial test. By utilizing the particle tracking strategy with the signature of histograms of orientation, both intact and crushed FJS particles can be successfully recognized and tracked at different stages of axial strain. It is found that a. smaller particles are more likely to crush than larger ones, and the crushed particles have more irregular particle shapes than the original set of particles; b. the coordination number, fabric anisotropy, 3D rose map, and particle displacement are found to highly correlate to the phase transition point from volumetric contraction to dilation; c. The sample deformation is found to be uniform at the early stage, and then it starts to spread from the boundaries to the inner part, and finally develops into an inclined shear band; d. locations of particle breakage within the granular assemblage show an overall sporadic and irregular pattern throughout the shearing process, which is not strongly correlated with the shear band developed, even at large strains.