Flow impact on granular force chains and induced instability

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; With today's fully coupled DEM/PFV simulations, the impact of an internal fluid flow on the mechanical stability of a granular material is assessed at the scale of a three-dimensional representative elementary volume. To isolate the specific impact of the fluid on the contact network, a granular sample in which rattlers have been initially removed is considered while a fluid pressure drop is applied under constant mechanical loading. Although the initial state is reputed to be unstable according to the second order work criterion, it is shown that i) an internal fluid flow is able to trigger the underlying instability on its own and ii) the flow direction has no influence because of local fluid force fluctuations. In addition, the microscale mechanisms occurring during the sample collapse are investigated and it is shown that the fluid perturbation induces a decrease in kinematic constraints around force chains, which is characteristic of a local loss of stability.