Numerical study on dry and immersed granular collapse: Role of particle shape and initial particle orientation

The shape of natural rock and soil particles is distinct and their orientation may prefer a certain direction, and determining the influences of particle shape and initial particle orientation on dry and immersed granular collapse is of great significance to prevention of geological disasters such as subaerial and submarine landslides. Using the superquadric DEM and the coupled CFD-DEM, the dry and immersed collapse process of granular columns with different particle shapes (aspect ratio A and blockiness B) and different initial particle orientations o are simulated. The results show that, compared with the case of A = 1 (spherical), the collapse of particles with larger A (elongated) or smaller A (platy) results in a shorter final runout distance and a higher final deposit height. The collapse of particles with larger B (more angular) also results in a shorter final runout distance and a higher final deposit height. The collapse of particles with o = 0 (approximately horizontal) produces an obviously smaller final runout distance, and progresses in a particular way that some particles being first squeezed out from the lateral free surface followed by the gradual slide of particles in the upper parts. For platy ellipsoidal particles, the collapse of particles with o = 135 (leaning on the fixed wall) generates the longest final runout distance. Whereas, for elongated ellipsoidal particles, the collapse of particles with o = 90 (approximately upright) generates the longest final runout distance.