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

Chapter 5—Current Status of Design Procedures5.2 Filter DesignA large variety of geotextiles including nonwoven needle-punched, nonwoven heatbonded,woven (usually monofilament) and knitted geotextiles have beensuccessfully used for filtration in embankment dams. Each type of geotextile has itsplace in filtration applications. Although nonwoven geotextiles are most commonlyemployed as filters, they are not automatically the best choice for a given application.The key filtration properties of geotextiles with respect to their commercialavailability are presented in Table 5.2:Table 5.2.—Range of material properties for geotextiles commonly used for filtration.GeotextileTypeApparentOpening Size(O 95 ) ASTM D4751 (mm)PermittivityASTM D 4491sec -1CommentsWovencommon range:0.212 to 0.85can be as lowas 0.05(Ramesy andNarejo, 2005)commonrange:0.05 to 1.5can rangefrom 0.01 to4.0 (Ramesyand Narejo,2005)They do not transmit flow in theplane of the geotextile, they arestiffer than nonwovens making directsoil contact more difficult to achieveand have lower interface frictionstrength than nonwovens. If heatbonded(calendared) the fibers arefused together at the weaveintersections providing excellentdimensional stability (maintains AOS).Percent open area (POA), is animportant design property regardingpermeability.NonwovenNeedlepunchedcommon range:0.15 to 0.5can be as lowas 0.074(Hwang andOthers, 1998)commonrange: 0.7 to2.5can be as lowas 0.5 (Ramesyand Narejo,2005) and ashigh as 4.5(Hwang andOthers, 1998)Flexible, conforms well to soilsurfaces and has higher interfacefriction than woven or heat-bondedgeotextiles. Provides higher flowrates than heat bonded geotextilesand can transmit flow in the plane ofthe geotextile. The AOS andpermeability decrease due toincreasing depth of burial which canlead to clogging if not evaluatedduring design. Thicker fabrics havegreater strength but may be moreprone to clogging.Nonwoven HeatBonded0.1 to 0.3 0.2 to 0.8 These geotextiles are thin and stifferthan needlepunched nonwovens, maybe hydrophobic and require a drivinghead for significant flow to occur.97