Geotextiles in Coastal Revetments
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Geotextiles in Coastal Revetments Geotechnical Considerations Lex Nielsen September 2009 PowerPoint PPT Presentation


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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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Geotextiles in Coastal RevetmentsGeotechnical Considerations Lex NielsenSeptember 2009


Stockton Surf Club sandbag revetment

Stockton Beach rock revetment

Section HeaderSub-heading

STORM 9TH March 2001


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Stockton Surf Club Sandbag Seawall

Soil Filters


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Stockton Seawall- PWD Design


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101Slope Stability

Rock @ 35°

Sand @ 28°


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101

Internal Friction (Φ)


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101Shear strength


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101Typical shear strengths / stable infinite slopes


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


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


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°


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Sand/GTX (Φsg)

Geofabrics-Elco


Geofabrics-ElcoSand/Terrafix 1200R

Φsg = 31°


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.


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Sand/NWNPGTX Friction AngleDixon, Jones & Fowmes (2006)


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


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Sand/NWNPGTX Friction Angle Koerner, GR & D Narejo (2005)


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


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°


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Sand/NWNPGTX Friction Angle

Tan, SA, SH Chew & WK Wong (1998)

Peak = 33°

Residual = 26°


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Summary Φsg

1/ tan 27.5° = 1.9; 1.5/tan 27.5° = 2.9


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


NWNPGTX/NWNPGTX Friction Angle

From Coghlan, Carley, Cox Blacka, Mariani, Restall, Hornsey & Sheldrick, Coasts & Ports 2009


NWNPGTX/NWNPGTX Friction Angle

From Coghlan, Carley, Cox, Blacka, Mariani, Restall, Hornsey & Sheldrick, Coasts & Ports 2009


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Section HeaderSub-heading

Sandbag/Geotextile Friction?


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°


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


IEAust Maritime Panel - Geotextiles in Coastal Revetments


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


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


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Small Rock Revetment on Sand 4.0m High with toeAlternate (preferred) design


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


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Section HeaderSub-heading


IEAust Maritime Panel - Geotextiles in Coastal Revetments

Section HeaderSub-heading


Section HeaderSub-heading


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