Reexamination of the 2004 Failure of Big Bay Dam, Mississippi- ON-DEMAND

This webinar will review the 2004 failure of Big Bay Dam.  A potential failure modes framework was used to make the forensic root-cause assessment based on data and information provided by the State of Mississippi.  A detailed timeline of the failure obtained through review of court proceedings will be presented including the appearance of a number of distress indicators, the seriousness of which were not recognized and acted upon by the Owner and the owner Engineer.  Of particular interest is the influence of piping and erosion of highly erodible fine sandy silt and silty fine sand through open defects in the outlet works conduit.   The full failure mode likely developed through a series of backward erosion initiation/continuation cycles that began under the upstream slope of the dam and moved toward the downstream end of the conduit over a period of about thirteen years.  The rapidity of the final steps in the failure mode development leading to breach of the dam are quite stunning and serve to reinforce the importance of detecting and mitigating seepage distress in embankments as early as possible in the development process and prior to later stages of continuation/progression when adequate time or intervention methods are not available to stop the failure process.  A generalized risk analysis event tree of the failure mode will be presented and described.

Keith A. Ferguson, P.E.,DWRE

HDR Engineering, Inc./Dam and Hydraulic Structures Practice Leader

Keith Ferguson has over 40 years of planning, design, and construction experience for over 160 dams, levee, spillways, outlet works, canals and tunnels projects across the US and internationally.  He holds Bachelor and Master of Science degrees from the University of Colorado in Civil and Geotechnical Engineering and is a registered professional engineer in 18 states.  He is a recognized leader in dam safety, risk analysis, seepage and stability analyses, seismic response evaluations for embankment and concrete dams, in rock mechanics, and in design of embankment, roller compacted concrete, and rockfill dams.  He recently completed a 7 year term as Director including a 2 year term as President of USSD.  He was chair of the ASDSO Dam Safety Journal Editorial Committee from 2008 through 2013. He is currently serving a chair of the USSD Advocacy initiative and the joint USSD Advocacy, Communication, and Public Awareness Committee.  He is Vice-chair of the USSD History Committee. 

  1. Introduction
    1. Summarize overall Incident and Timeline
  2. Key Learning Objectives
    1. Expanded understanding of Potential Failure Modes (PFM’s), and how to identify and assess them
    2. Expanded understanding of key factors that contribute to seepage failure mode development
  3. Some Seepage Basics;
    1. Internal Erosion (IE)Mechanisms
    2. The IE/Piping Failure Mode Continuum: Initiation, Continuation, Progression, and Breach Formation
    3. Factors Influencing IE and Piping Processes
    4. Key Factors in Assessing Dam Safety Risks of IE/Piping
  4. Design and Construction of Big Bay Dam
    1. Examination of cross-section
    2. Lack of critical design features that reduce risk of PFM development
    3. Lack of monitoring
  5. Distress Indicators;
    1. Conduit cracks and leakage
    2. Sinkhole(s)
    3. Sediment filled outlet discharge basin
    4. Changes in seepage outflow from toe drain system
  6. Detailed failure development timeline
  7. PFM description (building from the IE/Piping failure mode continuum)
  8. Lessons learned
  9. Summary and Conclusions

 

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Completion Quiz
# of Questions: 10 | Total Points: 10 | Passing Score:  6
# of Questions: 10 | Total Points: 10 | Passing Score:  6
Completion Certificate
2.00 PDH credits  |  Certificate available
2.00 PDH credits  |  Certificate available