Geotextiles in Embankment Dams - Association of State Dam Safety ...

Geotextiles in Embankment DamsTable 7.1.—Summary of concerns regarding geotextile use.CONCERN SUSCEPTIBILITY DESIGN PROVISIONS CONSTRUCTIONPRACTICEMITIGATIONClogging thatinterferes withthe drainagefunctionFunction of geotextiletype, AOS, thicknessand stress state, &abutting upstream soiltypeSelect geotextile on filtering capabilityto pass appropriate small particles whileretaining particles above the sizenecessary to retain the upgradient zone,exclude from consideration wherebearing directly against problematic soilsand environments fostering biologicalproducts and chemical precipitatesProtect geotextilefrom contaminationin handlingProvide strategicallylocated drains;select dam sectionthat is safe underworst casegradients, providepiezometers tomonitor porewaterpressures in thecore near thegeotextileInability tosatisfy filtercriteria allowingpiping of theupstream soilzoneFunction of soil (mostdifficult for fine graineddispersive soils &broadly graded soilswith large coefficientsof uniformity),geotextile type, AOS,thickness and stressstateExclude certain soils from direct bearingagainst the geotextile, configuregeotextile interface so that it is incompression to maintain intimatecontact, use current filter criteria &conduct tests based on DesignClassification, e.g., in Class A applicationtest design under anticipated stress statewith representative samples.Protect geotextilefrom contaminationand damage inhandlingProvide strategicallylocated underdrainsumps withsediment traps tomonitor fines lossPost installationstrains thatadversely affectfiltering abilityand/orpermeabilityLarge tensile andcompressive stressescan change the voiddistribution affectingpermeability & filteringModel stress-strain response of thegeotextile to dam section geometry tounderstand sense of strain behavior andrun tests on the geotextiles that simulatethose conditions.Installationconditions whichresult in cuts,folds, wrinkles,punctures orgaps in whatwas to be acontinuouselement, canlocally shortcircuit it’sfilteringfunctionService conditionswhere the geotextilewould bear againstangular particles orlarge particles thatwould act to distort thestrain pattern locallyand stress thegeotextile in a mannernot anticipated in thedesignSelect a geotextile product that includesprotective layers to cushion loads andreduce incidences where the geotextilemust resist stress concentrations.Installation procedures must eliminateflods and wrinkles, since they canprovide unfiltered piping paths.Require oversizedand angularparticles beremoved that areimmediatelyadjacent to thegeotextile, protectgeotextile fromabrasion and cuts inhandling, sewsheets together soas to develop thefull sheet strengthacross seamsBased on DesignClass - a select zonemay be provided asa cushion, providestrategically locatedunderdrain sumpswith sediment trapsto monitor fines losspresumably from adamaged geotextilePlant intrusionthat clogs voidspace andreducespermeabilityVulnerability is afunction of the depth ofburial, (the shallowerthe burial the morelikely that roots wouldfind conditionsconducive to growth.Deeper burial would beassociated with coolertemperatures, lack oflight, minimal nutrients;the only plus would be aready source of water) ,Shallow burial increases exposure to thistype of damage but at the same time it ispractical to repair damage, deeper buriallikely results in cold, wet, low nutrientenvironments that are not conducive toroot penetration; to further discouragevegetation, if deemed necessary, thegeotextile could be held back from anassumed root penetration zone andwhere it would be replaced with aconventional granular drain,appropriately armor pipe outfall area tominimize surfaces for plant growth toStrip geotextilesubgrade and drainoutfall area oforganic rich soils toremove conditionsthat foster plantgrowthStress vegetationcontrol in theoperation andmaintenanceprogram140