A number of submarine landslides have traveled large distances (100 kilometers or more) once the slide movement was initiated. A growing amount of evidence suggests that one of the reasons for the relatively large travel distances is that the slide mass hydroplanes on a layer of water as the slide movement progresses. Several theoretical models have been developed to simulate this process of hydroplaning and confirm hydroplaning as a viable mechanism for slide movements. However, the theoretical models have generally made simplifying assumptions regarding how the fluid surrounding a slide mass interacts with the moving soil. The study described in this report was undertaken to understand better the fluid-slide mass interaction and develop a better representation of the hydrodynamic forces acting on a moving slide mass.
Numerical modeling, using commercially available fluid modeling software (FLUENT), was carried out to study the fluid forces on a slide mass. The analyses showed that there is a significant “lift” effect that the surrounding fluid exerts on the slide mass. This lift effect has not been considered in any of the previous models for slide hydroplaning.
Once the hydrodynamic forces on a moving slide mass were understood better, simplified representations of these forces were developed. These representations were then incorporated into a “block” model of the moving slide (soil) mass to simulate the movement of a slide through water, including the formation of a fluid layer between the slide mass and underlying parent material. Once the numerical model for the moving slide mass was developed it was used to simulate soil movements measured in a previous investigation with a series of laboratory-scale model tests. Results of the numerical model developed in the present study were found to agree well with the experimental
observations. This good agreement seems to confirm the likelihood that some submarine slides may hydroplane and travel relatively large distances.
The model has not yet been exercised to examine how predicted slide movements might compare with actual field observations. Although all the data necessary to conduct simulations of actual slides is often not available, some comparisons should be feasible and would provide a valuable confirmation of the model development to date and help guide further developments. These comparisons are recommended as the next step for future studies.
Lastly, the model that has been developed considers the slide mass as a rigid block because of the complexity of the fluid-slide mass interaction. This approach was convenient for developing a computer program to model the progression of slide movements, including the motion of the block, the interaction with the surrounding fluid, and the eventual onset of hydroplaning. For the slide motion prior to the onset of hydroplaning, the interaction with the slide mass and underlying soil foundation was also included. However, the current model developed does not consider deformation of the moving slide mass itself, including the possible separation of portions of the slide mass from each other as they move. There is some evidence from actual slides that this aspect of the movement may also be important and can have an effect on when slide movement stops. Also, the existing model uncouples the soil and water motions, while in actuality the motions are fully coupled. Further studies are still needed to develop a model that includes these additional aspects of slide movement and hydroplaning.
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