A coupled two-phase model for numerical simulation of a real debris avalanche

Abstract

Debris flows are characterized as mixtures of solid particles and pore fluids, in which coupling between phases plays a paramount role in the dynamic behaviour. Due to the strong coupling between phases, pore pressures can be generated if the fluidized mass contains solid particles with low permeability. As such, a two-phase propagationconsolidation model should be applied to take into account the motion of each constituent and the time-space evolution of pore-water pressure. In this regard, the capability of a depth-integrated two-phase model, recently developed by the authors, to study the coupled behaviour of solid and fluid in a fluidized geomaterial is evaluated. The developed model is based on the mixture theory in which balance of mass and linear momentum are established for each phase. The computational framework is based on the mesh-free smoothed particle hydrodynamics (SPH), incorporating a 1D finite-difference mesh describing pore pressure's evolution along the vertical distribution of flowing mass. The model is applied to simulate the Johnsons Landing debris avalanche in order to reproduce its complex behaviours, including bifurcation occurred at the mid-channel. The developed two-phase depth-integrated SPH-FD model is also applied to assess the structural countermeasure of the bottom drainage screen, used to reduce the impact of debris flows. The analysis of the results indicates the adequacy of the method to model large deformation of the two-phase materials over an impermeable and permeable bottom boundary. This suggests that the proposed particle-based method is a promising approach for future studies of coupled geophysical problems.

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