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

1. Case History: Failure of a Geotextile
Turbidity Curtain
Michael D. Harney
Robert D. Holtz
University of Washington

2. Presentation Overview
 Project Background
 Containment System
 Failure
 Laboratory Testing
Program
 Conclusions & Lessons
Learned

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. 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. Project Background
Project challenges
 NAPL in the sediments
 Limited sediment disposal options
 Large tidal fluctuations
 Sediment characteristics
 Protection of local wildlife and surface water
quality

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. Containment System
Components
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. Containment System
Curtain
 540 g/m2 NW NP
PP selected by
boom supplier

9. Containment System
Curtain
 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. Failure
 Curtain failure
occurred within
several hours of
completing
deployment

11. Failure
 Curtain billowed
out with outgoing
tide
 Flow diverted over
boom
 Divers noted large
tears

12. Failure
Boom modifications
 Float weighted down
(temporary)
 Large “windows” cut
into curtain
(permanent)
Curtain not retrieved,
but sample provided
for analysis

13. Laboratory Testing Program
Samples 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. Laboratory Testing Program
Tests
 Mechanical characterization: Wide width
tensile (ASTM D 4595)
 Hydraulic characterization: Permittivity testing
(ASTM D 4491)

15. Laboratory Testing Program
Mechanical 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. Laboratory Testing Program
Hydraulic 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. Conclusions
1.00
0.75
Manufacturer’s published value = 0.70
Permittivity (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. Conclusions
 Poor flow-through of
the curtain ⇒ large
tidal forces applied
to geotextile
 Geotextile’s strength
eventually
exceeded, causing
failure

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. Conclusions
If recommendations for critical / severe followed:
 Ψ = 0.26 sec-1
 FS = 10 ⇒ Ψdesign = 0.026 sec-1
 Failure?

21. Lessons Learned
 Necessity of quality laboratory
characterization for geosynthetics in critical /
severe applications
 Appropriate safety factors must be used

22. Acknowledgements
 Bob Holtz, University of
Washington
 Reid Carscadden,
Integral Consulting, Inc.

23. Questions

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. 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. 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