SPH-FDM propagation and pore water pressure modelling for debris flows in flume tests

Debris flows are dangerous phenomena due to their large run-out distances and high velocities. The time-space evolution of the interstitial pore water pressures much affects the propagation stage of debris flows. Thus, a quantitative physically-based combined modelling of both flow propagation and pore water pressure changes is a fundamental issue for landslide risk analysis and to design effective control works. The paper provides a contribution to this topic through the use of an enhanced numerical model, which combines a 3D depth-integrated hydro-mechanical coupled SPH (Smooth Particles Hydrodynamics) model for the propagation analysis and a 1D vertical FDM (Finite Difference Method) model for the evaluation of the pore water pressure along the height of the flowing mass. In this paper, the SPH-FDM model is used to simulate, in 2D and 3D analyses, well-documented flume tests performed in USA through a 90 m long channel exiting at a sub-horizontal pad. The model is later used to simulate other flume tests, performed in Japan in a 3.4 m long channel, equipped without or with a (permeable) rack at the end of the channel, which allows the pore water pressures reducing until the mass eventually stops. Doing so, the paper shows that the SPH-FDM model is capable to properly reproduce the time-space evolution of the pore water pressures during the propagation stage with different geometries of experimental flumes and different hydraulic boundary conditions, such as an impervious or permeable bottom. (C) 2016 Elsevier B.V. All rights reserved.