This paper presents a numerical study of the effects of the particle's shape and its interaction with surrounding fluid on the mechanism of sandpiles formation in air and water, respectively. This study is motivated by the fact that seabed sediments are predominantly deposited in water and consist of non-spherical particles. In our study, a non-linear contact model is employed in the Discrete Element Method. At the same time, the void fraction model and drag force model of non-spherical particles with sharp corners are further improved. Based on the above two advancements, an extended computational fluid dynamics-discrete element method (CFD-DEM) approach coupled with the super-quadric model is developed. It can accurately simulate multi-collision and interlocking characteristics between non-spherical particles, as well as particle-fluid interactions. Subsequently, the validation and applicability of this extended CFD-DEM approach are proved by comparing the results of experiment and theory models for various cases. The discrepancies induced by particle shape are revealed in terms of repose angles, porosity, and stress distribution. This is due to non-spherical particles exhibiting a significant occlusal interlocking effect, which enhances inter-particle friction. Additionally, the influence of ambient water is non-negligible, as it supports a portion of the upward particle weight during the process of sandpiles formation. The above findings can be substantiated by analyzing the fabric structure of sandpiles. Such coupling of macro- with micro-scale insights into the fundamental geomechanical issues will further extend to wide fields, particularly sea-water-flow-induced seabed instability.
