Geotextiles in Coastal Revetments
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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 revetments geotechnical considerations lex nielsen september 2009

Geotextiles in Coastal RevetmentsGeotechnical Considerations Lex NielsenSeptember 2009


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

Stockton Surf Club sandbag revetment

Stockton Beach rock revetment

Section HeaderSub-heading

STORM 9TH March 2001


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Stockton Surf Club Sandbag Seawall

Soil Filters


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Stockton Seawall- PWD Design


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101Slope Stability

Rock @ 35°

Sand @ 28°


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101

Internal Friction (Φ)


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101Shear strength


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Soil Mechanics 101Typical shear strengths / stable infinite slopes


Revetment structure

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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°


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Sand/GTX (Φsg)

Geofabrics-Elco


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

Geofabrics-ElcoSand/Terrafix 1200R

Φsg = 31°


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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.


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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°


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Sand/NWNPGTX Friction Angle

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

Peak = 33°

Residual = 26°


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Summary Φsg

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

NWNPGTX/NWNPGTX Friction Angle

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

NWNPGTX/NWNPGTX Friction Angle

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

Section HeaderSub-heading

Sandbag/Geotextile Friction?


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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°


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

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


Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

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Geotextiles in coastal revetments geotechnical considerations lex nielsen september 2009

IEAust Maritime Panel - Geotextiles in Coastal Revetments

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