PhD research by Xavier Garcia included development of a clustered sphere model for representing irregular particles for DEM simulations of packing and flow. Here we show a DEM simulation of avalanching where the grain shape is of an irregular but rounded shape, therefore considered well-suited to DEM simulation in terms of computational resources and accuracy.

The static angle of repose was studied by Garcia to look at the sensitivity of an important emergent property as a function of shape resolution. This study is informative because building DEM models with anything other than quite rounded particles using clustered spheres becomes very expensive. The number of spheres used to represent an irregular particle was increased in order to study the resolution needed to achieve consistent results for the angle of repose using clustered spheres and DEM, see Garcia et al. 2009.

Reference

Garcia, X., Latham, J.-P., Xiang, J., Harrison., J. 2009. A clustered overlapping sphere algorithm to represent real particles in discrete element modelling, Geotechnique, 59, No. 9, 779-784 doi:10.1680/geot.8.T.037

The figure shows a 60m high rock slope with a wide valley and a massive rock block perched on a 45 degree slope.  The block is restrained only by basal fiction and with μ = 0.95  it begins to slide.

Strong rock sliding (top) Weak rock sliding (bottom)

Heterogeneous strains during sliding lead to fracture and fragmentation. The avalanche process is found to be very different for the two cases modelled where the tensile strength is set to 5MPa (strong rock) and 1MPa (weak rock). The stress fluctuations and cracking are shown side by side for each case. The comminution leads to a much wider size distribution for the stronger rock as large boulders remain on the valley floor.

The entire avalanche process with fragmenting boulders strewn across the valley floor, seen in the videos, lasts about 15 seconds in real time.

References

Xiang, J., Latham, J.P., Munjiza, A., Mindel., J. 2008. Applications of the combined finite-discrete element method. Proceedings, Beijing DEM’08. p223-231.

Munjiza, A., Andrews, K.R.F., White, J.K. 1999. Combined single and smeared crack model in combined finite-discrete element analysis. International Journal for Numerical Methods in Engineering, 44, 41-57.