Prior research on submarine slides performed by OTRC has consisted of numerical and physical modeling and the development of both empirical and numerical models to predict the initiation and movement of slides. Research shows that under certain conditions a moving slide mass can hydroplane on a layer of water that becomes trapped between the moving slide mass and the underlying soil. One of the most important aspects of hydroplaning is the interaction between the moving slide mass and surrounding fluid. Project 556 builds on research conducted under Project Number 491, Phases I & II which focus on modeling the interaction between a moving slide mass and surrounding fluid. That modeling led to an improved understanding of the characteristics of the fluid-slide mass interaction.
In project 556, OTRC incorporated the understanding of the fluid-mass interaction into a numerical model that includes the moving and deforming soil slide mass. This model is intended to aid in predicting the movement of submarine slides, with emphasis on slides that travel large distances once they are initiated. In particular the research seeks to develop a numerical model for predicting the initiation of hydroplaning of a slide mass and the subsequent motion of the mass once hydroplaning is initiated. The numerical model developed in this project is applicable to subaqueous slides of any scale, and is expected to determine if hydroplaning is likely to be initiated as well as the magnitude of movements once hydroplaning is initiated. The sliding process was simulated based on the initial geometry of a slope failure, the geology of the nearby seafloor, and the mechanical properties of the slide material (including shear strength, stress-deformation properties and unit weight). The model describes (1) the variation of the velocity of the slide mass in time and space, and (2) the eventual run out distance and geometry of the slide mass. This information is beneficial in judging the potential risk associated with submarine slides.
Hydroplaning is believed to be one of the major reasons why some submarine slides travel large distances. To study this, a 'block' model was developed to simulate the process of sliding. Research focused on the verification and calibration of the block model using data from laboratory experiments conducted by Mohrig, et al. (1998, 1999). Once validated the block model was applied to simulate the movement of actual slides reported in the literature.
After preliminary studies with the model it was modified to allow the actual conditions of Mohrig's experiments to be simulated correctly. In the experiments, the soil mass was dumped from a soil tank at the head of a sloping channel. The soil mass remaining in the soil tank pushed the dumped mass down the channel. The original block model only represented the soil mass that is already in motion down a slope or channel. Thus, to simulate the experiments, an additional force was added to the end of the block in the block model to simulate the thrust applied by the soil behind the block. Mohrig et. al. (1998, 1999) also reported that the soil mass in their experiments could be highly viscous. Accordingly, a strain rate effect on soil resistance was added in the block model.
Research study completed in March 2007.