Offshore Technology Research Center

 

OTRC Project Summary

Project Title:

Seafloor Slope Stability Under Static and Seismic Loading Conditions

Prinicipal Investigators:

Stephen Wright

Sponsor:

Minerals Management Service

Completion Date:

August, 2003

Final Report ID#

B121(Click to view final report abstract)

OBJECTIVE:

At the outset of this project the intent was to calibrate one or more of the existing models for sea-floor slope stability using either results from centrifuge model tests performed by C-CORE or data from actual sea-floor slope failures documented in the literature. Particular attention was to be devoted to applicability of the work performed by C-CORE and the Phase I Project Offshore Deep Slopes (PODS) project to U. S. waters, including the Gulf of Mexico. After initiation, the project scope was expanded by the addition of a "Forum" on "Risk Assessment of Slope Stability", which has now been successfully completed. Since completion of the Forum the work plan has been modified for several reasons. Principal among the reasons for modification was the lack of data from centrifuge model tests and the limited availability of case history data for actual slope failures that could be used to verify and calibrate very sophisticated numerical models. Work currently is focused on identifying a more complete set of data and establishing a database of these documented submarine slope failures along with any pertinent information related to the failures. One of the objectives of this effort is to provide preliminary guidance for the development of Recommended Practices for investigation of sea-floor slopes and assessment of risk of submarine slope instability.

PROGRESS:

The Forum on Risk Assessment of Submarine Slope Stability has been organized and successfully conducted. A draft report was prepared and submitted to all attendees for comment. The report is now being finalized for final printing and distribution. A technical paper on the workshop finding has been offered and accepted for the Deep Offshore Technology conference in New Orleans, in November 2002. This paper is now being prepared for that conference.

Because of the lack of information on well-documented case histories suitable for analyses and calibration of existing numerical models of sea-floor stability, a substantial portion of the recent project effort has been directed to compiling a comprehensive collection of data from the published literature on sea-floor stability. Although C-CORE had identified several case histories as part of the Phase I PODS project, these case histories lacked important geotechnical data that would be needed to provide verification of most of the more sophisticated numerical models. Thus, it was felt that a more thorough investigation was needed to determine if case histories could be found with more complete geotechnical data. To date in excess of over 100 case histories have been identified and data from them have been summarized in a database.

The over 100 case histories that have been identified to date all seem to lack much of the geotechnical information needed to provide a reliable assessment of the validity of numerical models. This finding is consistent with what we concluded from the several case histories that C-CORE had investigated and also with what was generally indicated by participants in the recent Forum that was held as part of this project. Unfortunately most case histories that are well documented are the proprietary property of oil companies and not in the public domain. However, the collection of case histories that has been developed as part of the current project is still useful. One of the conclusions that was reached from the Forum was that there was a need for either "standards" or "guidelines" for assessment of slope stability similar to the API RP2A recommended practices for pile foundations. The case history data that has been compiled provides a useful framework for developing recommended practices for assessment for slope stability. Clearly any guidelines must enable potential causes of slope failure to be identified and provide steps for assessment of the associated risks.

PLANNED WORK THROUGH PROJECT COMPLETION:

Work will continue to complete and submit the paper to the D.O.T. conference and present the paper at their meeting in New Orleans in November. We will also work to complete the compilation of case history data, including the case history database. Finally, we plan to use the information from the case histories to develop preliminary requirements for a "Recommended Practice" on submarine slope stability assessment. The emphasis of these recommendations will be on deep water. We are hopeful that this will provide a basis for developing a complete Recommended Practice or guideline for assessment of slope stability in deep water.

Related Publications: Wright, Stephen G., "Forum On Risk Assessment For Submarine Slope Stability - Report Of A Forum Held In Houston, Texas - May 10 And 11, 2002", June, 2002 (Report In Final Preparation By Offshore Technology Research Center).

Wright, Stephen G., Gilbert, Robert B., and Smith, Charles E., "Risk Assessment of Submarine Slope Stability in Deepwater - Issues and Priorities", Proceedings, 14th Deep Offshore Technology Conference, New Orleans, Louisiana, November 13-15, 2003.

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