A novel and unified solution to multi-phase mass flows
Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
Physical Geography
Theoretical Chemistry: Molecules, Materials, Surfaces
Final Report Abstract
We constructed a small-scale physical model test consisting of an inclined outflow channel which transits into a three-dimensional water reservoir. We conducted several mass flow experiments for flows initiating from a subaerial region. Our experimental results reveal strong effects of debris-flow volume and composition (water, clay, sand and gravel contents) on tsunami generation and evolution, wave celerity and amplitude. Once the debris flow impacts the water body, it pushes the water forward until wave celerity exceeds subaqueous debris-flow velocity. Afterwards the wave detaches from the debris flow and travels into the far-field. The wave celerity is strongly related to the debris-flow velocity. We observed similarity and contrasts between subaerial and subaqueous debris-flow. Subaqueous deposits appear to be shorter and wider than those in subaerial flows. Importantly, the levees are able to laterally confine the subaerial flows, however, the subaqueous deposits widen with distance offshore with the frontal snout often very dispersed which resulted due to the fluidization of subaqueous flows and the momentum exchange between the debris-flow and reservoir water. These findings largely agree with observations of subaqueous pyroclastic flow deposits. The similarity in subaerial and subaqueous deposits area suggest that we can apply empirical relations based on subaerial flows to estimate the inundation area and flow volume of subaqueous flows. For the purpose of simulating complex cascading mass flows interacting with the environment, we have presented a first-ever multi-phase, multi-mechanical mass flow model. This basic model is being extended to include the dispersion effects, multi-phase erosion and phase separation. This allows us to model very complex process chains often observed in natural events. The model has been applied to simulate the mixture mass flows impacting water body, producing tsunami and submarine mass transport. The model has been validated with different field events. The three-phase model has been applied for the predictive simulations of the catastrophic events, including the 2002 Kolka-Karmadon event (Russian Caucasus), and Huascaran 1962 and 1970 events (Chile). This was made possible with the upgraded version of our innovative, user-friendly, efficient and high-resolution GIS GRASS based open source computational software, r.avaflow v2. r.avaflow is physically constrained, robust and advanced multi-phase computational tool. In contrast to most existing tools, it employs our own fully mechanics-based, complete and real multi-phase mixture model allowing interactions between solid, fine-solid and fluid components in the flow with fundamentally different material and rheological properties. It is suitable for modelling complex process chains and interactions. It explicitly considers entrainment and stopping, and allows multiple release masses and/or hydrographs with parallel processing and high-performance computation. This is the reason it has been utilized to simulate several real flows by different universities, research institutes and public services in different countries for teaching and research with applications in hazard mitigation, early warning, and planning. The three-phase mechanical model and r.avaflow is being applied to several real events from Peru, Switzerland, Iceland, France, Russia and Indonesia to name a few. The r.avaflow is being widely and actively used internationally by more than twenty Universities and Research Institutes, and the number is growing. We are extending r.avaflow to include dispersion mechanism, slow to rapid deformation and also earth flows. These novel models are capable of solving some long-standing problems of multi-phase mass flows and the associated dispersion, e.g., as the landslide impacts the water body. All in all, our results demonstrate the general ability of r.avaflow to reproduce the evolution of flow heights, velocities, travel times and volumes reasonably well, but also highlight the challenges and uncertainties in simulations with parameter sets obtained from back-calculations. So, the further scrutiny of the physical-mathematical model and r.avaflow is required. We have also presented another novel, mechanically coupled, general three-phase model for simulating subaerial and submarine landsliding and associated tsunami in a single framework. The model incorporates different interfacial momentum transfers: between the solid particles and the viscous fluid in the landslide, and between the impacting landslide and the water body, and includes intrusion of water from water body to landslide. Our modelling frame allows to accurately track the interface between the submarine two-phase landslide and the water body. Incorporation of the new full and analytical generalized drag and virtual mass force models have further strengthened the physical aspects of our three-phase mass flow models. All together, we have now presented a more general, more complete, multi-phase and multi-mechanical mass flow model that can be applied to solve much complex and wider spectrum of mass flows than ever before, ranging from dry avalanche to viscous flood. This constitutes a novel and unified solution to multi-phase mass flows. The erosion and phase separation have been simulated around the flow transition to the lake environment. Our simulations indicate that the presence of obstacles and lake fundamentally influence the erosion and phase separation patterns in particle-fluid mixture flows. The three-phase models should further be complemented by incorporating multi-phase erosion and phase separation mechanisms. The data produced at Univ. Utrecht are being applied to validate the model for flow transformation from subaerial to submarine flows, tsunami generation, and submarine mass transport, separation between phases, and particle sorting.
Publications
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(2019): A multi-phase mass flow model. Journal of Geophysical Research: Earth Surface, 124, 2920-2942
Pudasaini, S.P., Mergili, M.
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(2019): Dynamic response of submarine obstacles to two-phase landslide and tsunami impact on reservoirs. Acta Mechanica 230 (9), 3143-3169
Kafle, J., Kattel, P., Mergili, M., Fischer, J.-T., Pudasaini, S.P.
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(2020): A full description of generalized drag in mixture mass flows. Engineering Geology 265, 105429
Pudasaini, S.P.
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(2020): A general analytical model for superelevation in landslide. Landslides
Pudasaini, S.P., Jaboyedoff, M.
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(2020): A mechanical erosion model for two-phase mass flows. International Journal of Multiphase Flow
Pudasaini, S.P., Fischer, J.-T.
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(2020): A mechanical model for phase separation in debris flow. International Journal of Multiphase Flow, 129
Pudasaini, S.P., Fischer, J.-T.
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(2020): Back calculation of the 2017 Piz Cengalo- Bondo landslide cascade with r. avaflow: what we can do and what we can learn. Nat. Hazards Earth Syst. Sci. 20, 505-520
Mergili, M., Jaboyedoff, M., Pullarello, J., Pudasaini, S.P.
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(2020): Debris-flow generated tsunamis and their dependence on debris-flow dynamics. Coastal Engineering 157, 103623
de Lange, S.I., Santa, N., Pudasaini, S.P., Kleinhans, M.G., de Haas, T.
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(2020): Reconstruction of the 1941 GLOF process chain at Lake Palcacocha (Cordillera Blanca, Peru). Hydrology and Earth System Sciences 24 (1), 93-114
Mergili, M., Pudasaini, S.P., Emmer, A., Fischer, J.T., Cochachin, A., Frey, H.
