Investigation of influence of an obstacle on granular flows by virtue of a depth-integrated theory

Abstract

Understanding granular flows past an obstacle is very important to most possibly avoid damage to human properties and infrastructures. The present paper investigates the influence of an obstacle on dry and fluid-saturated granular flows to gain insights into physics behind them. To this end, we extend the existing depth-integrated theory by considering additional effects from the pore fluid pressure and the granular dilatancy. We revisit a large-scale experiment to validate the extended theory. The good agreement between numerical results and experimental data reveals that the granular dilatancy plays a crucial role in the mobility and peak depth. Furthermore, we investigate the influence of obstacles on dynamics of dry granular flows by comparing numerical results with experimental data. It is shown that shock waves, dead zones and vacuum (grain-free zone) well observed in the experiments can be captured. Additionally, a fluid-saturated granular flow past the same obstacle is numerically simulated to interpret the role of the interstitial fluid, especially the pore fluid pressure, in the fluid-granular mixture causing distinct dynamic behaviours from those of a dry granular flow. It is also found that the granular dilatancy has a significant influence on the pore fluid pressure which can mitigate the granular friction. This is consistent with many experimental observations. Additionally, it is demonstrated that the pore fluid pressure is prone to elevate in front of a cuboid dam (but not in front of a forward-facing tetrahedral wedge), which in turn mitigates the granular friction. The findings are helpful to understand complex behaviours encountered in geophysical flows and industrial processes.