Evaluating the impact of debris flow: a coupled CFD/DEM approach

This paper presents a micromechanical study on the impacting behavior of debris flow. A coupled approach of Computational Fluid Dynamics and Discrete Element Method (CFD/DEM) is employed to capture the complicated interactions between granular particles and fluid in a debris flow. The coupling considers important interacting forces including the buoyancy force, the drag force and the virtual mass force. The calibrated CFD/DEM tool is used to simulate the following two cases. (a) A dry granular system runs down an inclined slope and impacts a water basin with check dam at the foot of the slope; (b) A mixing body of granular particles and water flows down an inclined slope and impacts on a rigid obstacle. For case (a), our study shows the presence of water in the basin can generally help to reduce the direct impact of the granular flow on the check dam, but may cause impulse surging wave travelling between the check dam and the slope surface for sustained period which exert rather high water pressure and overall impact force on the check dam. The overall impact to the check depends on both the initial releasing height and the water level in the basin where an optimal water level may exist to achieve minimized overall impact to the check dam. In Case (b) we aim to simulate the real behavior of debris flow and its impact on the barrier dam. A granular system with proper grain size distribution is treated by DEM to simulate the big-size boulders and gravels in a debris system, while a suitable fluid is handled by the CFD to model the viscous flow composed of water, fines and silts. Detailed analysis is made regarding all aspects of the flow behavior of the debris system, including its forefront speed, velocity profile, segregation, the impacting to the rigid barrier and the trajectory traveling beyond the barrier and final deposit. The results are compared to those obtained from a corresponding dry case