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ABSTRACT: Submarine debris flows are an extremely complex phenomenon that involves phase transition of the material from solid to semi-fluid. This is caused by large deformation and possible occurrence of entraining ambient fluid. In the conventional 'equivalent fluid method' based on Non-Newtonian fluid models, constant rheological parameters are assumed and calibrated using the evidence of previous debris flows. Such parameters, however, do not accurately represent the material behavior and the real physics involved in submarine debris flows. The aim of this study is to develop a new modeling framework for submarine debris flows based on the critical state soil mechanics. The effect of phase transition is incorporated in a modified Cam clay based constitutive model. The diagnostic analyses indicate that the proposed model is capable of reproducing the previous flow event by using the material parameters derived from the conventional soil tests.
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1INTRODUCTION
Submarine debris flows can cause significant damage to offshore structures. Their mechanism is not well understood due to the difficulty of directly observing the phenomenon. For example, submarine debris flows typically travel longer than subaerial flows despite the resistance due to the ambient water. Better understanding of the physics of submarine debris flows is necessary for further development in offshore regions. In particular, estimating the extent and impact of potential submarine flows is important when designing subsea facilities.
In this study, our focus is on numerical modeling of submarine clay-rich debris flows (or strongly coherent debris flows), in which the main component is finegrained seabed sediment. Submarine clay-rich debris flows typically originate from collapse of seabed sediment. The flow process involves a phase transition of the material from solid to semi-fluid by shearing, mixing, and entraining ambient water underneath the slide front. The mechanical properties of the material change dramatically during the event, especially at the sliding plane where deformation is most significant.
In the conventional 'equivalent fluid method' based on Non-Newtonian fluid models (e.g. Mazzanti & Bozzano 2009), the change in material properties during flow is neglected by assuming constant rheological parameters throughout the flow event. Often the rheological parameters are calibrated using the evidence of previous flow events. Such parameters may not represent the real physics involved in submarine debris flows. The aim of...