2011 MADCS Conference. FMA is a tool to help identify: Priorities for rehabilitation Improvements...
-
Upload
merryl-rodgers -
Category
Documents
-
view
213 -
download
0
Transcript of 2011 MADCS Conference. FMA is a tool to help identify: Priorities for rehabilitation Improvements...
FMA is a tool to help identify: Priorities for rehabilitation Improvements for operation, maintenance
and data collection
Uses a team of people to brainstorm possible modes of failure Facilitator, Dam owner, engineer and dam
safety person
Looks at all the potential ways a dam could fail and their likelihood of failure
Not just “another study”
Not a result of analysis by only one engineer or one company - all information is reviewed by a team with different perspectives
Not just a group of outside professionals – the owner is involved for the whole process
Many eyes looking at data may uncover unforeseen problems
Obvious concerns may be of less significance than previously thought
Enhancements in monitoring and inspections
Data gaps exposed Broader range of individuals become
educated and aware of potential problems
WHY DO A FAILURE MODE ANALYSIS?
Same concept as a FERC FMA, but requiring far less time and money
More applicable to typical Montana earthen dams
Reasonable cost and effort for private owners
Four basic components1) identify facilitator and assemble core team2) collect data for team review3) conduct FMA (morning dam inspection, afternoon brainstorming
session)4) summarize results in a report
Collect Data Construction drawings &
reports Monitoring data Inspection reports &
photographs Studies O&M plans
Core Team Review of Data Thorough review Ask, “How could the dam fail?” Have failure modes been identified and
is proper monitoring being done? Review should be accompanied by
Questionnaire sent by Facilitator to “think failure modes”
Things to Do Before FMA (Facilitator & Organizer)
Meeting time and location Visual aids Conference call before meeting
Morning Inspection Before FMA All participants involved Look over dam/appurtenances “Think and see” potential failure
modes Interview dam tender or operation
personnel
Afternoon Brainstorm FMA Session All participants involved Identify and discuss potential failure
modes Organize into failure conditions:
Normal operationSeismic loadingHydrologic loading
Categorize failure modes
Failure Categories
I – Highlighted Failure Modes (High repair priority; high failure risk; high failure consequences)
II – Failure Modes Considered but not Highlighted (A concern, but lower repair priority; lower failure consequences)
III – More Info Needed in Order to Classify (Information lacking; need more data)
IV – Failure Mode Unlikely but Not Ruled Out (Unlikely but not impossible; low priority)
V – Failure Mode Ruled Out (Not realistic; no concern)
Failure Mode Considerations Factors making it less
likely or more likely Consequences Risk Reduction Measures Future Data Needs
Major Findings and Understandings Probably the most important
component All participants state their own MFU’s Summation of FMA Recorded for the
results report
Documentation of Major Findings and Understandings
Summary of FMA Actions recommended Statement on adequacy of
documentation Appendices of data Core team should review before
finalizing
Get “free” participants toreduce cost but don’t sacrifice quality
Clearly organize data foreasier review
Make all visuals large and easy to read Clearly document everything Stay on task – facilitator needs to be
efficient Write up results immediately to maintain
correctness Get Dam Safety to help
Guidance for future operationsDetermine rehabilitation decisions Identify investigations neededPrioritize maintenance and repairs
Example – Eureka Dam
Eureka Dam located in Teton County, northwest of Choteau
FMA for Eureka Dam was conducted in 2008
Relatively informal – not organized in standard fashion
If Eureka Dam failed, Choteau and the highway would be flooded
Issues:
1. Old outlet pipe showing corrosion and settlement
2. Seepage exiting at toe and collected in toe drain trench
Example Category I ModeCategory I - Corrosion and failure where gate tower connects to outlet conduit, causing
piping along outlet, progressive erosion of embankment
Factors that make this more likely
• Settlement at connection, previous gap
sealed recently
• Age of pipe
• Similar failure mechanism in many
Montana dams
• Uncertainty with bituminous coating
in this area;
• Difficult to inspect
Factors that make this less likely
• Bituminous coating appears to
protect pipe well
Example Category I ModeCategory I - Corrosion and failure where gate tower connects to outlet conduit,
causing piping along outlet, progressive erosion of embankment
Consequences of Failure
• Failure of dam
• Loss of reservoir contents
Risk Reduction Measures
• Increase inspections to an annual basis
• Add diaphragm filter around outlet pipe
Data / Information Needs
• Can embankment soils withstand erosion?
• Need sample of embankment soils
Example Category III ModeCategory III - Piping of embankment materials into foundation
Factors that make this more likely
• Some unexplained depressions on
upstream face could be related to piping
of embankment materials into foundation
• No filters or drains in embankment
• No knowledge about foundation preparation
• Settlement of outlet pipe after construction
suggests foundation problems and possible
internal cracking of embankment
Example Category III ModeCategory III - Piping of embankment materials into foundation
Factors that make this less likely
• Embankment constructed under supervision of State Water Conservation Board; foundation prep likely
• Beck piezometers show slight upward gradient from foundation
• Dry embankment and wet foundation support idea that upward gradient is present (water is moving directly from reservoir through bedrock foundation)
• Low percentage of piping failures in dams are from this failure mode
Example Category III ModeCategory III - Piping of embankment materials into foundation
Consequences of Failure
• Failure of Dam
Data / Information Needs
• Is embankment made of material
that is subject to piping?
• Need sample of embankment soils
• What is phreatic gradient within dam
and foundation?
• Nested piezometers in embankment
and toe are needed
Example FMA Results
Recommendations from Simplified Failure Mode Analysis
1. Implement risk reduction measures for Category I failure modes
• Increase outlet inspection frequency
• Diaphragm filter around outlet pipe
2. Collect missing information on Category I and III issues
• Install nested piezometers in embankment and foundation
• Collect samples of embankment and foundation materials
3. Make plans to rehabilitate outlet works
Simplified FMA is cheap and not time consuming
Good for when repair $ are tightGood when unsure where to focus
investigationsHelps get more people involvedCan open eyes to things not thought
of
Gary Fischer, P.E.Hydrometrics, Inc./Carroll [email protected]