Influence of Nonhomogeneous Viscosity on the Dynamics of Debris Flow: A Numerical Study

Debris flow is a geological phenomenon occurring in nature under the action of gravitational forces over a sloping surface and exists in different forms, e.g. landslides, rockfalls, debris avalanches or mudslides. The significance of studying debris flow lies in the effective estimation of flow-height, front velocities, impact pressures and amount of material deposition at the runout zone, which are essential for designing barriers, rock fence or rock sheds as protective measures against such mass movements. A numerical framework can be adopted to solve the field equations associated with the debris flow phenomenon in conjunction with a suitable material model mimicking the constitutive behaviour of the flowing mass. The front velocity and debris runout length are better predicted when the momentum balance equation takes into account the flow resistance due to turbulence, which inherently results in a nonhomogeneous distribution of the flow viscosity. Moreover, due to the heterogeneous nature of the debris mixture there appears to be no plausible reason for the mechanical model to assume a homogeneous rheological parameter. The influence of nonhomogeneous viscosity on the dynamics of debris flow has been explored in this work, through Newtonian, single-phase, multi-material, laminar-flow simulations. An efficient adaptive-mesh hybrid finite-element/control volume (FE/CV) framework—Fluidity, which enables full Eulerian-based large deformation analysis has been utilised for this purpose. Based on the results obtained, it is noticed that the viscous nature of the lower layer primarily dictates the final flow pattern of the debris.