Study of the mechanical properties of geotextile exhumed 30 yrs after installation from the world\'s first geotextile-reinforced column-supported embankment. Presented at TRB in 2006.

1. Mechanical Properties of
Geotextile Reinforcement, 30
Years After Installation
Michael D. Harney
Robert D. Holtz
University of Washington

2. Presentation Overview
• Geosynthetic durability
• Brief project
background
• Laboratory testing
program
• Test results and
discussion
• Conclusions
• Q & (hopefully) A

3. 12
10
8
Load (kN)
6
4
2
Virgin Sample
Exhumed Sample
0
0 5 10 15 20 25 30
Elongation (%)

4. Geosynthetic Durability
• Changes in mechanical behavior over service life
(“How long will my geosynthetic last?”) ⇒ a key
question
• Causes?
– Installation damage
– Time-dependant mechanisms (biological, UV, hydrolysis or
other chemical)
• Investigation?
– Standardized tests for effects of damage or degradation
– Studies of exhumed geosynthetics

5. Project Background
• 1972, near Nol, Sweden

6. Project Background
• First pile-supported bridge approach embankment to
use geotextile reinforcement

7. Project Background
• Research project on driven piles at same site ⇒ Well-
documented, well-instrumented

8. Project Background
• Displacement and stability problems anticipated

9. Project Background
• Highly irregular bedrock
dipping towards creek
⇒ end-bearing battered
piles may not seat
• ∴ Drive piles vertically,
use geotextile to carry
horizontal loads

10. Project Background
• Three layers of geotextile, 15-cm of compacted sand
between

11. Project Background
• Industrial grade 100 g/m2 multifilament
woven polyester

12. Project Background
• Embankment cross-section

13. Project Background
• 2001: highway rebuilt, geotextile sample recovered

14. Laboratory Testing Program
• Main goal: characterize combined effects of
installation damage and degradation on
strength and stress-strain behavior
• Wide width tensile tests (ASTM D 4595)
• Compare exhumed (~30 yr in-service) to virgin

15. Laboratory Testing Program
• Exhumed geotextile
sample: 1.5-m by 1.0-m
• Free of surficial soil;
some embedded
particles
• Selvage present
• Relatively intact;
several large tears Exhumed sample, 2001 (installed 1972)

16. Laboratory Testing Program
• No WWT in 1972
• Virgin geotextile sample
• Same multifilament
woven polyester,
obtained and stored
since 1974
Virgin sample, 1974
• Selvage present

17. Laboratory Testing Program
• 60x magnification inspection
Exhumed sample

18. Laboratory Testing Program
• Specimen selection: FHWA-RD-00-157
(2001)

19. Laboratory Testing Program
• Tests performed in
machine direction
• Curtis “Sure-Grip”
hydraulic clamps
• Jaws padded (tongue-
depressors and 0.3-mm
latex)
• Strain rate: 10% / minute
• Strains measured globally
(LVDTs on clamps)

20. Laboratory Test Results
• 18 total virgin tests
• 9 exhumed tests (limited
material)
• No evidence of slippage in
the jaws
• No exhumed specimens
ruptured at the jaws
• One virgin specimen
ruptured at jaws (omitted)

21. Laboratory Test Results
Wide width tensile test results: virgin specimens
3000
2500
2000
Load (lbs)
1500
1000
500
0
0 5 10 15 20 25 30
Elongation (%)

22. Laboratory Test Results
Wide width tensile test results: exhumed specimens
3000
2500
2000
Load (lbs)
1500
1000
500
0
0 5 10 15 20 25 30
Elongation (%)

23. Laboratory Test Results
Wide width tensile test results
3000
2500
2000
Load (lbs)
1500 Virgin
1000
Exhumed
500
0
0 5 10 15 20 25 30
Elongation (%)

24. Laboratory Test Results
Wide width tensile test results
Mean 10%
Mean yield Mean Mean offset
secant
tensile elongation at tensile
tensile
strength rupture modulus
Sample modulus
(lb/in.) (%) (lb/in.)
(lb/in.)
[C.V.] [C.V.] [C.V.]
[C.V.]
(%) (%) (%)
(%)
1972
334 21.9 2060 1230
Virgin
[3.7] [3.8] [13.0] [3.8]
(17 tests)
2001
149 15.4 1390 1010
Exhumed
[17.9] [13.7] [16.9] [7.1]
(9 tests)
>50% reduction ~33% reduction

25. Laboratory Test Results
Wide width tensile test results
Mean 10%
Mean yield Mean Mean offset
secant
tensile elongation at tensile
tensile
strength rupture modulus
Sample modulus
(lb/in.) (%) (lb/in.)
(lb/in.)
[C.V.] [C.V.] [C.V.]
[C.V.]
(%) (%) (%)
(%)
1972
334 21.9 2060 1230
Virgin
[3.7] [3.8] [13.0] [3.8]
(17 tests)
2001
149 15.4 1390 1010
Exhumed
[17.9] [13.7] [16.9] [7.1]
(9 tests)

26. Conclusions: Tensile Strength
• Mean yield tensile strength reduced by >50%
over the service life
• No sample retrieved after installation ⇒ effects
of installation damage and degradation cannot
be separated. (View as a cumulative effect)

27. Conclusions: Tensile Strength
• Long-term geotextile tensile strength typically
reduced in practice (Elias et al. 2001):
Tult
Tal =
RFCR ⋅ RFD ⋅ RFID
where : Tal = allowable long - term tensile strength
Tult = yield tensile strength
RFCR = creep reduction (1.6 ~ 2.5 for PET)
RFD = durability reduction (1.1 ~ 2.0)
RFID = installation reduction (1.05 ~ 3.0)
• Durability and installation damage reductions
warranted in this case

28. Conclusions: Stress-Strain
• Reduction of almost 33% in offset tensile
modulus (represents initial elastic modulus)
• Installation damage and degradation cannot
be separated, must view as a cumulative effect
• Significant softening of the reinforcement

29. Conclusions: Variability
• Behavior of exhumed sample much more
variable than the uninstalled sample
• Evidenced by the computed coefficients of
variation
• Likely due to inherent spatial variability in the
damage and/or degradation processes

30. Acknowledgements
• Bob Holtz
• Per Riise, geotechnical engineer with Jacobsson &
Widmark for retrieving the sample
• Rainier Massarch, geotechnical consultant, for
transporting the sample
• Gunnar Löngårdh of AB Fodervävnader,
manufacturer of the geotextile; supplied the virgin
sample in 1974

31. References and Related Mat’l
Nol Embankment Case History
• Harney, M.D., 2006, “Mechanical properties of geotextile
reinforcement, 30 years after installation,” Proceedings of the 8th
International Conference on Geosynthetics, Yokohama, 18-22
September 2006.
• Holtz, R.D., and Massarch, K.R., 1976, “Improvement of the Stability
of an Embankment by Piling and Reinforced Earth,” Proceedings of
the Sixth European Conference on Soil Mechanics and Foundation
Engineering, Vienna, Vol. 1.2, pp. 473-478.
• Holtz, R.D., and Massarch, K.R., 1993, “Geotextile and Relief Piles for
Deep Foundation Improvement Embankment Near Göteborg,
Sweden,” Geosynthetics Case Histories, International Society for Soil
Mechanics and Foundation Engineering, pp. 168-169.

32. References and Related Mat’l
Reports, etc
• Elias, V., 2001, “Long-term Durability of Geosynthetics Based on
Exhumed Samples from Construction Projects,” Report No. FHWA-
RD-00-157, U.S. Department of Transportation, Federal Highway
Administration.
• Elias, V., Christopher, B.R., and Berg, R.R., 2001, “Mechanically-
Stabilized Earth Walls and Reinforced Soil Slopes Design and
Construction Guidelines,” Report No. FHWA-NHI-00-043, U.S.
Department of Transportation, Federal Highway Administration.

33. Questions?
The Godfather?
• Michael Harney, University of Washington, harney@u.washington.edu
• Ditto, Shannon & Wilson, mdh@shanwil.com