Nonsmooth simulations of 3D Drucker-Prager granular flows and validation against experimental column collapses

Testing advanced numerical hydro-mechanical models against well-controlled experiments is a critical step in improving our understanding of unsteady granular mass flows, and necessary to provide some domains of validity for any further risk assessment.
To this end, experimental granular collapses were performed to evaluate the sand6 numerical simulator introduced by Daviet & Bertails-Descoubes (2016), which represents the granular medium as an inelastic and dilatable continuum subject to the Drucker-Prager yield criterion in the dense regime, and computes its dynamics using a 3D material point method (MPM). A specificity of this numerical model is to solve such the Drucker-Prager nonsmooth rheology without any regularisation, by leveraging tools from nonsmooth optimisation.
This nonsmooth simulator, which relies on a constant friction coefficient, is able to reproduce with high fidelity various experimental granular collapses over inclined erodible beds, provided the friction coefficient is set to the avalanche angle - and not to the stop angle, as generally done. The results, obtained for two different granular materials and for bed inclinations ranging from 0° to 20°, suggest that a simple constant friction rheology choice remains reasonable for capturing a large variety of granular collapses up to aspect ratios in the order of 10.
Investigating the precise role of the frictional walls by performing experimental and simulated collapses with various channel widths, we find out that, unlike some assumptions formerly made in the literature, the channel width has lower influence than expected on the granular flow and deposit.
The constant coefficient model is extended with a hysteresis model, thereby improving the predictions of the early-stage dynamics of the collapse. This illustrates the potential effects of such phenomenology on transient granular flows, paving the way to more elaborate analysis.