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.