3D evolution of sand fracture under 1D compression

Abstract

Three-dimensional (3D) synchrotron microtomography (SMT) and the discrete-element method (DEM) were used to investigate the evolution of particle fracture and deformation behaviour of a granular assembly subjected to the k0-loading condition. A series of one-dimensional (1D) compression laboratory experiments were first conducted to better understand the effect of specimen aspect ratio (height-to-diameter ratio, H/D) on deformation behaviour, which demonstrated that changing the specimen aspect ratio influences the stress–strain response of sand. 1D compression was simulated using a 3D DEM model by mapping particle positions from SMT images. Crushable sand particles were modelled in DEM using agglomerates of spherical sub-particles that were bonded by parallel bonds. The DEM model successfully predicted the compressive behaviour of specimens with different aspect ratios. The experimental and DEM results show that the onset of particle fracture and specimen yielding occur at the same strain level. The evolution and distribution of particle fracture were analysed non-destructively at the particle and specimen scales using SMT images and the DEM model. The SMT images revealed that the majority of the particle fracture occurred in particles close to the loading platen. The onset of the fracture pattern of individual sand particles within the granular assembly was also examined at consecutive strain levels using SMT images and DEM simulation results. The development and collapse of force chains were investigated using the DEM model and it was observed that the agglomerates that are part of a strong force chain mostly experience bond breakages. Combining SMT imaging technique and DEM simulations provided valuable insight into complex micromechanical processes occurring during the compression of crushable granular materials.