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Geotextiles in Coastal Revetments Geotechnical Considerations Lex Nielsen September 2009

Geotextiles in Coastal Revetments Geotechnical Considerations Lex Nielsen September 2009. Stockton Surf Club sandbag revetment Stockton Beach rock revetment. Section Header Sub-heading. STORM 9 TH March 2001. IEAust Maritime Panel - Geotextiles in Coastal Revetments.

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Geotextiles in Coastal Revetments Geotechnical Considerations Lex Nielsen September 2009

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  1. Geotextiles in Coastal RevetmentsGeotechnical Considerations Lex NielsenSeptember 2009

  2. Stockton Surf Club sandbag revetment Stockton Beach rock revetment Section HeaderSub-heading STORM 9TH March 2001

  3. IEAust Maritime Panel - Geotextiles in Coastal Revetments Stockton Surf Club Sandbag Seawall Soil Filters

  4. IEAust Maritime Panel - Geotextiles in Coastal Revetments Stockton Seawall- PWD Design

  5. IEAust Maritime Panel - Geotextiles in Coastal Revetments Soil Mechanics 101Slope Stability Rock @ 35° Sand @ 28°

  6. IEAust Maritime Panel - Geotextiles in Coastal Revetments Soil Mechanics 101 Internal Friction (Φ)

  7. IEAust Maritime Panel - Geotextiles in Coastal Revetments Soil Mechanics 101Shear strength

  8. IEAust Maritime Panel - Geotextiles in Coastal Revetments Soil Mechanics 101Typical shear strengths / stable infinite slopes

  9. IEAust Maritime Panel - Geotextiles in Coastal Revetments Revetment Structure The revetment structures comprise several layers • Armour layer • Rock, Concrete units, sandbags • Underlayer • Rock • Sandbag • Separation layer • Rock filters • Geotextile • Base layer • Rock core • Dune sand • Soil embankment The slope stability of each layer’s interface needs to be examined in respect of inter-facial frictional strength

  10. IEAust Maritime Panel - Geotextiles in Coastal Revetments Geotextile Interface Frictional PropertiesSand/GTX (Φsg) GTX/GTX (Φgg) Manufacturers Recommendations Soil Filters testing (Terrafax 1200R) Literature review

  11. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/GTX (Φsg) Manufacturers Recommendations • Exxon: • tan Φsg = CI × tanΦs • CI = 0.7 – 0.8 • tan Φsg = 0.7 to 0.8 × tanΦs • For Φs = 32° – 35° • Φsg = 24° – 29°

  12. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/GTX (Φsg) Geofabrics-Elco

  13. Geofabrics-ElcoSand/Terrafix 1200R Φsg = 31°

  14. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/GTX (Φsg) Literature review Dixon, N., DRV Jones & GJ Fowmes (2006). “Interface shear strength variability and its use in reliability-based landfill stability analysis”, Geosynthetics International, vol. 13, no. 1, pp 1-14.  Koerner, GR & D Narejo (2005). Direct Shear Database of Geosynthetic-to-Geosynthetic and Geosynthetic-to-Soil Interfaces, Geosynthetic Research Institute, GRI Report No. 30, June.  Martin JP, RM Koerner & JE Whitty (1984). “Experimental friction Evaluation of Slippage between Geomembranes, Geotextiles and Soils”, Proc. Int. Conf. Geomembranes, Denver, USA pp 191-196.  Williams, ND & MF Houlihan (1987). “Evaluation of Interface Friction Properties between Geosynthetics and Soils”, Proc. of Geosynthetics ’87 Conference, New Orleans, USA, February, pp 616-627. Tan, SA, SH Chew & WK Wong (1998). “Sand-geotextile interface shear strength by torsional ring shear tests”, Geotextiles and Geomembranes 16 pp161-174.

  15. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/NWNPGTX Friction AngleDixon, Jones & Fowmes (2006)

  16. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/NWNPGTX Friction AngleDixon, Jones & Fowmes (2006) Low Confining Stress Data For low confining stress data (10kPa-30kPa), adopting a characteristic value being the mean minus 1.0  SD, ensuring about 90% of the data lie above the value, results in (for σn=10kPa): sg = 27 = 34.5 = 27.1

  17. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/NWNPGTX Friction Angle Koerner, GR & D Narejo (2005)

  18. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/NWNPGTX Friction Angle Martin Koerner & Whitty (1984) • Present two test results: • 30 for Ottawa sand • 26 for concrete sand

  19. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/NWNPGTX Friction Angle Williams & Houlihan (1987) • Advocate the use of a large shear box (305 mm  305 mm). • The CI was around 0.9 for needle-punched geotextile with clean sands. • For Φs = 32° – 35° • Φsg = 29° – 32°

  20. IEAust Maritime Panel - Geotextiles in Coastal Revetments Sand/NWNPGTX Friction Angle Tan, SA, SH Chew & WK Wong (1998) Peak = 33° Residual = 26°

  21. IEAust Maritime Panel - Geotextiles in Coastal Revetments Summary Φsg 1/ tan 27.5° = 1.9; 1.5/tan 27.5° = 2.9

  22. IEAust Maritime Panel - Geotextiles in Coastal Revetments NWNPGTX/NWNPGTX Friction Angle Geofabrics-Elco Peak: 1.0/tan26° = 2.0 1.5/tan26° = 3.1 Residual: 1.0/tan20° = 2.7 1.5/tan20° = 4.1

  23. NWNPGTX/NWNPGTX Friction Angle From Coghlan, Carley, Cox Blacka, Mariani, Restall, Hornsey & Sheldrick, Coasts & Ports 2009

  24. NWNPGTX/NWNPGTX Friction Angle From Coghlan, Carley, Cox, Blacka, Mariani, Restall, Hornsey & Sheldrick, Coasts & Ports 2009

  25. IEAust Maritime Panel - Geotextiles in Coastal Revetments Section HeaderSub-heading Sandbag/Geotextile Friction?

  26. IEAust Maritime Panel - Geotextiles in Coastal Revetments Infinite slopes - For Factor of Safety = 1.0 i.e. slope = 1/tanΦ For sand, Φ = 33° 1/tanΦ = 1.5 Sand slope 1:1.5 NWNPGTX on sand 1:2.0 NWNPGTX on NWNPGTX 1:2.7 33° 27°

  27. IEAust Maritime Panel - Geotextiles in Coastal Revetments Coastal Revetments • Coastal revetments will have factors of safety higher than those for infinite slopes because of: • Finite height • Toe

  28. IEAust Maritime Panel - Geotextiles in Coastal Revetments

  29. IEAust Maritime Panel - Geotextiles in Coastal Revetments On an Infinite 2:1 slope for Φsg = 29°, FoS = 2 × tan29° = 1.1 Rock toe improves FoS from 1.1 to 1.5 Toe is critical for stability

  30. IEAust Maritime Panel - Geotextiles in Coastal Revetments Small Rock Revetment on Sand 4m High with toeSensitivity of FoS to Slope and adopted Φsg Slope 1:2.5 Slope 1:2.0

  31. IEAust Maritime Panel - Geotextiles in Coastal Revetments Small Rock Revetment on Sand 4.0m High with toeAlternate (preferred) design

  32. IEAust Maritime Panel - Geotextiles in Coastal Revetments Conclusions • For preliminary text-book design of revetments using non-woven needle-punched geotextiles, recommend adopting: • Φsg = 27°Φgg = 20° • For the use of geotextile underneath a rock armoured revetment, GTX/sand interface slope must be flatter than 1:2.5 for an adequate factor of safety for overall geotechnical stability • For overall geotechnical stability of sandbag armoured revetment slopes in sand, slopes must be flatter than 1:3.0

  33. IEAust Maritime Panel - Geotextiles in Coastal Revetments Section HeaderSub-heading

  34. IEAust Maritime Panel - Geotextiles in Coastal Revetments Section HeaderSub-heading

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