Impact of Rheology and Aspect Ratio of Dislodged Debris Mass on the Depositional Characteristics of Debris Flow

Debris flow is a gravity-driven phenomenon comprising a soil-fluid mixture of high mobility, which causes a serious threat to the living population and infrastructure owing to the high velocity and long runout. Hence, for the purpose of risk reduction, it becomes imperative to examine the depositional features of debris flow, e.g., runout, flow height, velocity, etc. The rheological properties of the flowing debris mass, along with the aspect ratio of the dislodged debris mass, influence the runout of the debris flow considerably. In order to understand the large-scale debris flow phenomena, horizontal flume tests are often used at the lab scale, wherein a soil-fluid mixture is allowed to flow under gravity loading condition and is commonly referred to as the dam break problem. In this regard, the use of scaling laws becomes necessary with due account to the rheology and aspect ratio of the debris mass. In the present study, a dam break problem has been simulated employing the 3D finite volume method in ANSYS with a focus on the effects of debris rheology and aspect ratio. The Herschel-Bulkley model has been used to mimic the non-Newtonian rheology of the flowing soil-fluid debris mixture. A systematic mesh convergence study has been performed by considering the interface thickness and flow runout profile. The dam break simulation results from the converged mesh have been further validated against the experimental data reported in the literature. The effect of aspect ratio and rheological parameter on the depositional characteristics of debris flow has been investigated in light of the scaling laws. For higher aspect ratios, a shift has been observed in the trend of the scaling law, i.e., from linear to a nonlinear one, with an increase in the viscosity of the debris flow.