Geotextile Turbidity Curtain Failure

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Case history of a geotextile turbidity curtain failure. Presented at the North American Geosynthetics Society 2005 conference.

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Geotextile Turbidity Curtain Failure

  1. 1. Case History: Failure of a Geotextile Turbidity Curtain Michael D. Harney Robert D. Holtz University of Washington
  2. 2. Presentation Overview Project Background Containment System Failure Laboratory Testing Program Conclusions & Lessons Learned
  3. 3. Project Background Wood treating facility Contaminants (incl NAPLs) migrated into offshore sediments Remediation involved dredging and disposal of 31,000 m3 of contaminated sediments Initiated in July 2001; completed in early 2002
  4. 4. Project Background N Land-based Marine-based excavation excavation zone zone Sediment containment boom Floating breakwater dock Shoreline NAPL area Groundwate r treatment facility Upland containment cell Marina
  5. 5. Project BackgroundProject challenges NAPL in the sediments Limited sediment disposal options Large tidal fluctuations Sediment characteristics Protection of local wildlife and surface water quality
  6. 6. Project Objectives Remove contaminated sediments from marine environment (dredging operation) Dispose and contain contaminants on-site Restore site’s aquatic habitat Suspended sediments contained by sediment containment boom (turbidity curtain)
  7. 7. Containment SystemComponents Boom flotation Geotextile curtain from Water level (varies) seafloor to water Curtain panel surface Rope connection Concrete block anchors Curtain skirt Anchor chain sewn to Concrete block Anchor chain anchor (0.6-m x 0.6-m curtain x 1-m) Existing mudline (elevation varies) Floats
  8. 8. Containment SystemCurtain 540 g/m2 NW NP PP selected by boom supplier
  9. 9. Containment SystemCurtain Water exchange forces computed by consulting engineer Calculations used manufacturer’s published values of mat’l properties (Ψ = 0.7 sec-1) Assumed tidal fluctuation of 6.4-m, and half the geotextile openings were clogged (FS = 2) Design accepted by owner’s engineer
  10. 10. Failure Curtain failure occurred within several hours of completing deployment
  11. 11. Failure Curtain billowed out with outgoing tide Flow diverted over boom Divers noted large tears
  12. 12. FailureBoom modifications Float weighted down (temporary) Large “windows” cut into curtain (permanent)Curtain not retrieved, but sample provided for analysis
  13. 13. Laboratory Testing ProgramSamples obtained All samples: Undeployed 2001  Black 540 g/m2 curtain (2001 Virgin) nonwoven needlepunched staple Undeployed 1998 pilot filament polypropylene study (1998 Virgin) Deployed 2001 curtain Noticeably infused with (2001 Deployed) red-brown biological material
  14. 14. Laboratory Testing ProgramTests Mechanical characterization: Wide width tensile (ASTM D 4595) Hydraulic characterization: Permittivity testing (ASTM D 4491)
  15. 15. Laboratory Testing ProgramMechanical Test Results Mean Yield Tensile Strength Mean Elongation at Rupture (%) Number of (kN/m) Sample tests (MD/XD) Machine Cross Machine Cross Direction Direction Direction Direction (MD) (XD) (MD) (XD) 2001 Virgin (6/6) 30.6 52.5 80 68 2001 Deployed (5/5) 28.9 49.9 81 70 1998 Virgin (2/2) 30.6 51.7 80 70 1994 through 2004 Virgin N/A 31.0 51.5 62 59 (commercial laboratory)
  16. 16. Laboratory Testing ProgramHydraulic Test Results Permittivity (1/sec) Material Tests Coefficient of Mean Range Variation Five specimens @ two heads 2001 virgin 0.26 17% 0.16-0.30 (five runs of each) Two specimens @ two heads 1998 virgin 0.27 5.3% 0.25-0.30 (five runs of each) Five specimens @ two heads 2001 deployed 0.03 59% 0.01-0.07 (five runs of each)
  17. 17. Conclusions 1.00 0.75 Manufacturer’s published value = 0.70Permittivity (sec-1) 0.50 Engineer’s allowable (FS=2) value = 0.35 2001 Virgin sample tested value = 0.26 0.25 2001 Deployed sample tested value = 0.03
  18. 18. Conclusions Poor flow-through of the curtain ⇒ large tidal forces applied to geotextile Geotextile’s strength eventually exceeded, causing failure
  19. 19. Conclusions A critical application? – Approx $0.5-million containment system – Environmental ramifications Severe hydraulic conditions? – Tidal fluctuation > 6-m Typical critical app / severe condition recommendations: – Test! – Safety factor = 10
  20. 20. ConclusionsIf recommendations for critical / severe followed: Ψ = 0.26 sec-1 FS = 10 ⇒ Ψdesign = 0.026 sec-1 Failure?
  21. 21. Lessons Learned Necessity of quality laboratory characterization for geosynthetics in critical / severe applications Appropriate safety factors must be used
  22. 22. Acknowledgements Bob Holtz, University of Washington Reid Carscadden, Integral Consulting, Inc.
  23. 23. Questions
  24. 24. 1998 Virgin Permittivity Tests 0.3 0.25 0.2 Permittivity (sec-1) 0.15 0.1 0.05 2" Head, Spec 1 2" Head, Spec 2 1" Head, Spec 1 1" Head, Spec 2 0 1 2 3 4 5 Trial
  25. 25. 2001 Virgin Permittivity Tests 0.3 0.25 0.2 Permittivity (sec ) -1 0.15 2" Head, Spec 1 0.1 2" Head, Spec 2 2" Head, Spec 3 2" Head, Spec 4 2" Head, Spec 5 1" Head, Spec 1 0.05 1" Head, Spec 2 1" Head, Spec 3 1" Head, Spec 4 1" Head, Spec 5 0 1 2 3 4 5 Trial
  26. 26. 2001 Deployed Permittivity Tests 0.3 2" Head, Spec 1 2" Head, Spec 2 2" Head, Spec 3 0.25 2" Head, Spec 4 2" Head, Spec 5 1" Head, Spec 1 1" Head, Spec 2 0.2 1" Head, Spec 3 1" Head, Spec 4 Permittivity (sec-1) 1" Head, Spec 5 0.15 0.1 0.05 0 1 2 3 4 5 Trial

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