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Avoiding a Dam Midlife Crisis

Avoiding a Dam Midlife Crisis. By: Jeff Coffin, P.E. Sr. Civil Engineer/Hydrologist Kleinschmidt Associates. www.KleinschmidtUSA.com. Midlife Crisis. What causes a midlife crisis for a dam... ...and what can happen as a result?. www.KleinschmidtUSA.com. Midlife Crisis!. Symptoms:

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Avoiding a Dam Midlife Crisis

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  1. Avoiding a Dam Midlife Crisis By: Jeff Coffin, P.E. Sr. Civil Engineer/Hydrologist Kleinschmidt Associates www.KleinschmidtUSA.com

  2. Midlife Crisis What causes a midlife crisis for a dam... ...and what can happen as a result? www.KleinschmidtUSA.com

  3. Midlife Crisis! Symptoms: old, tired feeling in a rut may seek new partner www.KleinschmidtUSA.com

  4. Tools... Can’t monitor dam’s mental/emotional health, so need to focus on physical health. www.KleinschmidtUSA.com

  5. Congestive Dam Failure www.KleinschmidtUSA.com Want to avoid this type of midlife (or young-age) crisis.

  6. Why be Concerned? Consequence: • Owner: Lose ability to generate power • Others: Lose water supply, navigation, recreation benefits www.KleinschmidtUSA.com

  7. Consequence (cont.): • Downstream: Can be heavily impacted www.KleinschmidtUSA.com

  8. Dam-Safety Checkup – Basic Approach • Hazard Potential • Regular Inspections/Evaluations • PFMA / DSSMP www.KleinschmidtUSA.com

  9. 1. Hazard Potential Determination Based on Consequence of Failure: • High: Loss of life possible due to breach • Significant: No loss of life, but major property damage • Low: No significant impacts www.KleinschmidtUSA.com

  10. 2. Regular Inspection/Engineering Evaluation • Yearly by FERC engr. • Every 5 years by IC • Protocol: • Visual inspection to assess condition • Analysis (or review) of: • Spillway adequacy • Structural stability • Review of S&M data • Single most important inspection tool? www.KleinschmidtUSA.com

  11. The Most Important Dam Inspection Tool: The Eyes! www.KleinschmidtUSA.com (thanks to Kim de Rubertis)

  12. 3. Potential Failure Mode Analysis • Multi-disciplinary team • Review background info. • Identify PFMs • Classify PFMs (priority) • Focus DSSMP on PFMs www.KleinschmidtUSA.com

  13. Two Recent Dam Midlife “Incidents” 1. Embankment Dam with boils at toe after 9+ year drought 2. Gravity Dam hit by piece of rock from abutment www.KleinschmidtUSA.com

  14. 1. Embankment Dam – Nebraska • Constructed 1937-41 (age 70) / 163 ft high, 3.1 mi long • Earth foundation, sheetpile cutoff wall • Drought in CO-WY-NE: reservoir failed to fill 2002-2009 • High 2010 precip., raised res. 25 ft higher than prior 7 years • Boils at toe – raised concern, prompted investigation www.KleinschmidtUSA.com

  15. 1. Embankment Dam (cont.) • Boils noted in toe drains – lateral and longitudinal drainage ditches at toe of dam • Investigation: • Review of current and historical data (seepage flows, piezometer levels) • Site visit • Preliminary seepage analysis www.KleinschmidtUSA.com

  16. 1. Embankment Dam (cont.) • Findings: • Boils present historically (e.g. 1987) • 2010 boils similar to 1987 but smaller • No evidence of transport of soil • Current seepage flows and piezometer levels were within historical ranges (data since 1953) • Vert. hydraulic gradient estimated to be approximately 0.5-1.0 ft/ft (boils gen. result from 0.5-0.8) www.KleinschmidtUSA.com

  17. 1. Embankment Dam (cont.) • Recommendations: • Continue monitoring: • Visual monitoring of boils • Toe drain flows • Piezometer levels • Install 2 nested piezometers to verify vert. gradients • Evaluate in detail during next Part 12D inspection (2011-12) www.KleinschmidtUSA.com

  18. 2. Gravity Dam – Montana • Rock-filled timber crib construction • Constructed 1905-07 (age 104) • 38.5 ft high, 257 ft long • 3-ft thick reinforced concrete overlay with post-tensioned anchors added in 1989 www.KleinschmidtUSA.com

  19. 2. Gravity Dam (cont.) • Rock bolts added in 1974 to stabilize left abutment cliff www.KleinschmidtUSA.com

  20. 2. Gravity Dam (cont.) • POOP HAPPENS: August 2010 – piece of rock cliff fell from left abutment onto dam • Piece estimated at 205 tons: 32’ L x 11’ H x 2-17’ W • Damage to steel superstructure and gates, relatively minor apparent damage to dam crest www.KleinschmidtUSA.com

  21. 2. Gravity Dam (cont.) • Findings and follow-up: • PFM ID’d in 2005 PFMA (PFM No. 1, Cat. II) – est. up to 285-ton rock could fall • Rock fall came from formation to left of that stabilized in 1974 • Reservoir lowered to aid damage inspection/repair • Detailed inspection of rock face and rock bolts by geotech. engr. • Repairs to gates and superstructure planned • Further stabilization of rock cliff planned www.KleinschmidtUSA.com

  22. Re-Cap: To Avoid Dam Midlife Crisis • Know Dam’s Hazard Potential • Regular Inspections/Evaluations (Eyes!) • PFMA – to ID & Prioritize PFMs • DSSMP – focused on PFMs www.KleinschmidtUSA.com

  23. Let’s Keep Our Dams Healthy & Happy, With Long Lives www.KleinschmidtUSA.com

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