Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Risk Assessment for Submarine Slope Stability: Numerical Modeling of Flow around a Sliding Soil Mass

Prinicipal Investigators:

Stephen G. Wright

Sponsor:

Minerals Management Service

Completion Date:

December, 2005

Final Report ID#

B159(Click to view final report abstract)

OBJECTIVE:

This project seeks to develop the tools needed to assess the risk of submarine slope failures. One of the greatest sources of uncertainty, and thus risk, is the distance that submarine landslides can travel once they are initiated. Accordingly, this project is focusing on the mechanisms that lead to large movements of seafloor slides caused by hydroplaning.

APPROACH:

Existing analytical and numerical models of slope failure and post-initiation slide movements have been reviewed. Hydroplaning has been identified as the most probable mechanism explaining large post-initiation slide movements.

A simple analytical model for hydroplaning has been evaluated and limitations of the model have been identified. Several important assumptions have been identified including: (1) all resistance to post-hydroplaning slide movement is produced by viscous shear at the slide mass-parent material interface; (2) movement is steady state and does not describe either the initiation or cessation processes for hydroplaning; (3) movements and flow are one-dimensional (4) the moving slide mass is a rigid rectangular block, and does not allow the slide to spread out laterally or change in thickness; and (5) the flow is laminar. Preliminary studies showed that the fluid resistance at the leading and trailing edges of a moving slide mass during hydroplaning could be appreciable and greatly affect the movement.

Numerical models are being used to examine more closely the interaction between a slide mass that is hydroplaning and the surrounding water with particular emphasis on the leading and trailing edges of the slide mass. The goal of the numerical modeling is to provide a basis for better characterizing the soil-fluid interaction at the boundaries of the slide mass. Once a better understanding of the slide mass-fluid interaction has been established attention will be given to the processes whereby hydroplaning is initiated and eventually terminated.

DEPLOYMENT OF RESULTS:

Results of the research will be a model for predicting when hydroplaning may occur and how far a slide mass may move once hydroplaning is initiated. Ultimately it is expected that the model will serve as a basis for prediction of slide movements as part of an overall assessment of risk of submarine slope failures. Much of the risk associated with a seafloor slope failure is based on the distance a slide may travel once it is initiated. Slides which occur far from an area of interest and do not travel far pose far less risk than slides that can travel large distances.

PROJECT PLAN:

Scope of Work: During this year work will be focused on numerical analyses to:

(1) Better understand the mechanism of hydroplaning and the interaction between a moving slide mass and the surrounding water.
(2) Verify the assumptions currently made in analytical models and in particular the use of boundary layer theory to characterize the fluid behavior at the slide mass-parent soil interface during hydroplaning.
(3) Develop suitable representations for the fluid pressures at the leading and trailing edge of a slide mass during hydroplaning with the objective of improving the existing analytical models.

Anticipated Results: We anticipate developing a suitable model for predication slide movements where hydroplaning occurs.

 

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