Geotextiles in EmbankmentDamsBy: Michael J. Gobla, P.E.
Purpose of this PresentationDiscuss controversial aspects regardinggeotextile use in filtration and drainagePresent both sides of the issueReview a few case historiesStimulate a discussion of the subject
Original study for FEMA publishedas a Compact Disc in 2009:Geotextiles in Embankment DamsStatus Report on the Use of Geotextiles inEmbankment Dam Construciton and RehabilitationFEMA P-730 CD/ January 2009
• Funding by FEMA and Bureau of Reclamation– Team Member Organizations contributed labor.• Team Members:Michael Gobla, P.E. – Bureau of ReclamationDave Paul, P.E. – Bureau of ReclamationJay Swihart, P.E. – Bureau of ReclamationDouglas Crum, P.E. – Corps of EngineersSteve Reinsch, P.E. – Natural Resources Conservation ServiceRon Frobel, P.E. – Private Sector ConsultantJohn Falk, P.E. – State of OregonJerald LaVassar, P.E. – State of Washington
Policy:It is the policy of the National Dam SafetyReview Board that geotextiles should not beused in locations that are critical to the safetyof the dam.
Types ofGeotextiles• Woven• Non-woven Needle Punched• Non-woven Heat Set• Knitted• 95% of new geotextiles aremade from polypropylene
Woven Geotextiles• Monofilament• Slit film• Multifilament• Used in dams for filtration,reinforcement, separationand erosion control.
Nonwoven Needlepunched Geotextiles• Staple fiber• Continuous filament• Used in dams for protection,filtration, drainage, separation,reinforcement, erosion control
NonWoven Heat Set Geotextiles• Fibers are fused together by heat• Produces thin fabrics used to filterfine-grained soils• Wick drains are a typical application
Knitted GeotextileUsed as a filter wrappingaround drainage pipe
Geocomposites• Geotextile bonded to ageomembrane• Geotextile bonded to geonet• Geotextile wrapping adrainage core• Two or more geotextilesbonded together
An October 2000 FEMA Research NeedsWorkshop Concluded:“ The current practice for the use of geotextiles in seepagecollection systems varies widely among organizations andpractitioners involved in dam engineering.”• Geotextiles should not be used in locations that are bothcritical to safety and inaccessible for replacement.• Geotextiles can be used in locations that are critical for safetybut accessible for replacement. However, the engineer mustassess the potential hazard posed by failure of the geotextileand the time available to respond and repair or replace thegeotextile.• This position may change in the future based on developmentof data on long-term, in-place performance of geotextiles indam applications.”
Geotextile Functions in Embankment Dams• Internal filter (not accepted practice)• Internal drain (not accepted practice)• Toe drain filter (acceptability depends on design)• Separation between embankment zones.• Slope reinforcement• Protective cushion and drainage layer for a membrane• Erosion control / filter underneath riprap
Geotextile Functions inEmbankment Dams
Controversial Embankment Applications• Filter• Drain• Crack Stopper• Deeply buried• Non-redundant feature• Critical to dam safety
Toe Drain EconomyShielded trenchingmachine andgeotextile filterreduced excavationand granular filterneeds by 90 %.
Major IssueShould geotextiles be usedin embankment filtration asthe sole means of defenseagainst internal erosion?
Where Has it Been Done?1970 – 17 meter high Valcross Dam, FranceDr. J. P. Giroud designed a 9 oz geotextile filterwrapped around a gravel drain. Dam is ahomogeneous silty sand embankment.
Valcros Dam, France – 1970 17 m Still FunctioningBrugnens Dam, France – 1973Formitz Dam, Germany – 1975 (86 meters high)Frauenau Dam, Germany – 1980Schonstadt Dam, Germany – 1982Chateauvieux Dam, France – 1983La Parade Dam, France – 1987Reeves Lake Dam, USA – 1990 (10.7 meters high)Mafeteng Dam, South Africa – 1993Teppe Rosse Dam, Corsica - 1995Lavaud-Gelade Dam, France – 1996Dzoumogne Dam, Mayotte – 2000 (24.5 meters high)Samira Dam, Niger – 2001Olmito-Garcias No. 2 Dam, USA – 2002 (6.4 meters high)Red Willow Dam, USA – 2012 (49 meters high)
2001 – 18 meter highSamira Dam, NigerA composite geotextileAOS 0.1 wrapped asand drain andhorizontal blanket tofilter a fine lateriticsoil
How Is It Accomplished?• Many use a 2-layer geotextile• Meet permeability criteria• Meet clogging criteria, 1” gravel• Filtration testing with site soils• Design for loading• Strict QC/QA during construction
Advocates View:• Geotextiles filters cost less than processed granularfilters• Geotextile filters are lightweight, easy to transport tothe work site.• Installation is simple.• Inspection of subgrade, deployment, seaming, andcovering can be performed visually.• Geotextile filters will act as crack stoppers becausethey have tensile strength and will span across anopen crack• Multi-layer products provide required survivability.
Traditional View:• Geotextiles are prone to installation damage• There is no way to detect construction damage• Geotextiles are prone to clogging• Geotextiles will not act as a crack stopper• Geotextiles have an unknown service life• Granular filters have an excellent track record• Stay with what worksReality is somewhere inbetween these opposingviews
Recent Geotextile Trends in the US:Use as a separator between downstream side of agravel drain and the downstream shell of a dam isan accepted application.NRCS with special approval is using geotextiles torepair cracked embankments. Although it serves asa primary filter/crack stopper these are normally dryflood detention embankments where there is littlerisk of clogging the filter.
Red Willow Dam Repair BOR 2012• Geocomposite drain as primary filter and drain, finesand and coarse sand downstream of this. It is a 16oz geotextile on a triaxial geogrid with a 6 ozgeotextile on top. Design required special permissionand much debate over clogging.
Next Steps To Acceptance As Filters• Geotextiles as filters can provide savings and allowfor more timely dam repairs. They must be usedwisely.• A vetting process and strict standards are needed forthis type of application.• ICOLD is trying to revive the committee to prepare anupdate of their Bulletin 55 “ Geotextiles as filters andtransitions in fill dams.