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In some cases, debris flow consists of low-permeability soils in which run-out distances, velocities and lateral spreading are highly influenced by pore-water pressures. Basal screens are energy dissipation structures designed to reduce these velocities and run-out distances. These structures consist of grids built on horizontal decks where basal pore pressures of debris flows are made equal to the atmospheric pressure, which increases basal friction. Once the debris flows exit the structure, basal pore pressure increases as the basal surface is impermeable again, but the values have been reduced. In order to model these phenomena, it is necessary to use debris flow simulation models considering two phases and pore-water pressures. Here, a depth-integrated two-phase smooth particle hydrodynamics (SPH) model, previously developed by the authors, is improved by including the vertical structure of pore-water pressure. This is done by incorporating finite-differences meshes associated to each SPH node that represents a solid particle. In this way, a higher precision is obtained in describing excess pore pressure along depth, including the influence of vertical consolidation, height variation and changes in basal permeability. The proposed model is applied to describe debris flows with two different ranges of soil permeability propagating over grid structures. The authors have used laboratory tests run at the Norwegian University of Science and Technology and studied the efficiency of the basal grids by comparing cases equipped by them and cases without any obstacle. The results obtained from the proposed numerical experiments suggest that the proposed two-phase coupled model is able to properly reproduce the behaviour of debris flows, describing more accurately the time–space evolution of pore-water pressures during the whole propagation stage, considering both propagation impermeable beds and pore pressure dissipation structures such as grids.

Rapid flow-like landslides, particularly debris flows and debris avalanches, cause significant economic damage and many victims worldwide every year. They are usually extremely fast with the capability of travelling long distances in short times, sweeping away everything in their path. The principal objective of this paper is to test the ability of the ‘GeoFlow-SPH’ two-phase model developed by the authors, to reproduce the complex behaviour of natural debris avalanches where pore-water pressure evolution plays a key role. To reach this goal, the model is applied to reproduce the complex dynamic behaviour observed in Johnsons Landing debris avalanche including the observed bifurcation caused by the flowing out of part of the moving mass from the mid-channel. Initial thickness deposit trim-line, distribution of deposit volume, and the average velocities were provided for this real case, making it an appropriate case to validate the developed model. The paper also contributes to evaluate the SPH-FD model’s potentialities to simulate the structural countermeasure, like bottom drainage screens, used to reduce the impact of debris flows. The analysis of the results shows the adequacy of the proposed model to solve this complicated geophysical problem.

Debris flows are a type of fast landslides where a mixture of soil and water propagates along narrow channels. The main characteristics are (1) important relative displacements between the solid and fluid phases, and (2) development of pore-water pressures in excess to hydrostatic. The ratios between vertical and horizontal displacements of the flow, from the triggering point to the deposition, indicate that friction angles are much smaller than those measured in laboratories. Debris flows are modeled as two phases flow, but implementing pore-water pressure is an important issue. The purpose of this paper is to improve the existing two phases debris flow models by implementing pore-water pressures in excess to hydrostatic. It is found that pore pressure evolution depends on consolidation, changes in the flow depth, and changes and gradients of porosity. The proposed depth integrated mathematical model is discretized using two sets of SPH nodes (solid and fluid), with a set of finite difference meshes associated with each solid material SPH point. The paper presents two examples from where it is possible to gain insight into the differences between the models (with and without excess pore water pressure).

This paper presents a depth integrated, two-layer SPH new model for debris flows with finite differences meshes associated to nodes to describe pore pressure evolution. The proposed model is applied to describe how the flow evolves when arriving at a grid where pore pressure is made zero.

A debris flow is one of the most dangerous types of geophysical mass flows moving downward mountain slopes and consist of a mixture of soil and rocks with a significant quantity of interstitial fluid. They can travel at extremely rapid velocities affecting long distances due to the significant influence of pore-water pressures on the propagation stage. In this paper, a novel two-phase depth-integrated SPH numerical model is applied to simulate a debris flow in which the effects of bed entrainment and pore-water pressure evolution, essential components to performed debris flows risk assessment, are included. The model was applied to simulate the dynamics of Yu Tung debris flow which is an appropriate benchmark case to examine the applicability of the developed model, as bed entrainment and pore-water pressure evolution were key aspects that affected the moving mass dynamics. The developed two-phase depth-integrated SPH-FD model is applied to assess the structural countermeasure of the bottom drainage screen, used to reduce the impact of debris flows. The reasonable results obtained from the analysis indicate that the model is capable to properly reproduce the propagation of the debris flow and more importantly to correctly perform the time-space evolution of pore water pressures during the whole deformation process from initiation through propagation, over an impermeable and permeable bottom boundary, up to deposition.

In this work an approach to representing debris floods and flows is proposed, based on a depth-integrated mathematical model and smooth particle hydrodynamics numerical technique. The main contributions of the present work are twofold: (a) an improved rheological Bingham model where solid fraction concentration can change as solids are entrained by the current and (b) implementation of boundary conditions describing the injection process of water from channel weirs into the domain. The model has been applied to the case of Lo Wai debris flood (Hong Kong, August 2005). Numerical results obtained with the proposed model are in reasonable agreement with field observation. Fil: Lin, Chuan. Hohai University; China Fil: Pastor, Manuel. Universidad Politécnica de Madrid; España Fil: Yague, Angel. Universidad Politécnica de Madrid; España Fil: Tayyebi, Saeid Moussavi. Universidad Politécnica de Madrid; España Fil: Stickle, Miguel Martin. Universidad Politécnica de Madrid; España Fil: Manzanal, Diego. Universidad Politécnica de Madrid; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Tongchun Li. National Engineering Research Center Of Water Resource; China Fil: Liu, Xiaoqing. National Engineering Research Center Of Water Resource; China