Effects of pore-fluid pressure on the motion of debris flows

Pore-fluid pressure mediates the shear strength between soil particles and significantly controls the movement of debris flows. This study analyzes the effects by proposing a numerical model to solve the pore-fluid diffusion equation coupled to changes in surge motion of debris flows. The model was established by combining a Lagrangian method solving the depth-averaged one-dimensional equations for the debris-flow motion and a Fourier-series solution for the pore-fluid diffusion equation. Owing to the source term related to the change in surge depth, the Fourier-series solution shows that the excess pore-fluid pressure near the bed dissipates faster and exhibits a non-monotonic profile. The results of numerical calculations reveal that the diffusivity of excess pore-fluid pressure and the liquefaction condition have significant impacts on the depth profiles and velocities of debris-flow surges.