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

Geotextiles in Embankment DamsTable 5.4.—Strength Requirements for geotextiles (AASHTO, 1996)Application Contact Stress GrabStrengthpoundsElongation%SewnSeamStrengthpoundsPunctureStrengthpoundsBurstStrengthpoundsTrapezoidTearpoundsSubsurfaceDrainageSubsurfaceDrainageHigh Stress -angulardrainagemedia, heavycompaction,high confiningstressLow Stress –roundeddrainagemedia, lightcompaction,low confiningstress180 - 160 80 290 5080 - 70 25 130 25ArmoredErosionControlDirect stoneplacement 200 15 180 80 320 50ArmoredErosionControlSand cushion,low dropheight90 15 80 40 140 30This realization led to the development of a two-layer geotextile for dam filtration(Giroud, Delmas, and Artieres, 1998), (Artieres and Tcherniavsky, 2003). One canselect the optimum nonwoven geotextile for a filtration application, but this is oftena light weight geotextile that may be at risk to installation damage. By bonding asecond geotextile to the filter fabric, the strength can be increased. The secondfabric is one that is selected for strength but has a very open and permeable structureso it has little effect upon the filter performance of the two-layer geotextilecombination.The initial French two-layer geotextile was made by needlepunching to bond a thinnonwoven filtering geotextile to a thick nonwoven geotextile. At present it is notonly possible to bond two or more nonwoven geotextiles together, it is also possibleto bond two woven geotextiles together, or a nonwoven can be bonded to a wovengeotextile. Such multi-layer systems provide an advancement in filtration capacity(Jeon and Mlynarek, 2004) and continue to be an important area of geotextilefiltration research (Kutay and Aydilek, 2005). Even three layer and multi-layerproducts are possible to manufacture. It is possible to manufacture a gradedgeotextile filter, also called “depth filtration,” with enhanced filtration andsurvivability characteristics.106