Development of a Database and Assessment of Seafloor Slope Stability based on Published Literatureby James Johnathan Hance, M.S.E. The University of Texas at Austin, 2003
SUPERVISOR: Stephen G. Wright
A database of seafloor slope failures has been created from the published literature. The database contains information on the geographic location, date and type of failure, potential triggering mechanisms, soil types, soil properties, dimensions, slope angle, and water depths for the slope failures. Data in the database have been examined to identify important characteristics of seafloor slope failures. However, while there is substantial information in the database, significant geotechnical information was lacking for many of the slope failures. Fourteen different triggering mechanisms have been identified and are included in the database. Each of these triggers is discussed. The most common trigger reported is earthquake loading. Seafloor slope failures (slides) can affect large areas and volumes of soil, and they tend to be larger than subaerial landslides. Also, in comparison to subaerial landslides, seafloor slides tend to travel larger distances and occur on flatter slopes. Slope stability analyses were performed and results are presented to assess the likelihood of slides being triggered by gravity, rapid sedimentation (underconsolidation) and earthquakes. The analyses reveal that it is unlikely that most seafloor slope failures are triggered by gravity loads alone; earthquake loading and rapid sedimentation (underconsolidation) are likely triggers of many slope failures. Many seafloor slides are accompanied by very large runout distances. Hydroplaning is one mechanism that may explain such large runout distances. The mechanism of hydroplaning is summarized, and a simple sliding block model is presented to illustrate how conditions for hydroplaning can be developed. Rheological models have also been developed to explain slide runout, and several models are described. However, the rheological models do not seem to explain some of the very large runout distances observed in both experiments and for actual seafloor slides. For many slides, hydroplaning appears to be the mechanism that best accounts for large runout distances.