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

Chapter 5—Current Status of Design Procedures5.2.7 Performance testingIn overseas practice, laboratory performance testing procedures have become thenorm for embankment dam filter design. Performance testing has the advantage ofbeing able to integrate many complex issues regarding geotextile-soil interactionduring filtration thus overcoming many of the uncertainties in the design procedure.Uncertainties in filtration performance include:• The actual size distribution of the openings in the geotextile are different thanthe single AOS value reported by the manufacturer (Aydilek, et al., 2005).• Soil particles embedded in the geotextile reduce porosity and permeability.• Compression caused by burial reduces opening size, porosity, and permeability(Legge, 2004).• Variations in seepage gradients and flow rates in the base soil affect filterbehavior.• Variations in soil gradation, compaction, and particle shape affect filterbehavior.5.3 Design for drainageDrainage implies that water will be transported in the plane of the geotextile orgeocomposite material. In contrast, filtration considers flow perpendicular to theplane of the geotextile. Normally, the geotextile must be designed to performproperly as a filter if it is also intended to function as a drain. Calculation proceduresare presented in (Koerner, 2005a) and other standard geotextile design references.5.3.1 PermeabilityIn order to function as an effective drain the geotextile or geocomposite mustremain permeable and not clog. The design requirements for retention andpermeability also apply to drains.5.3.2 TransmissivityThe added dimension of drainage design is that it must have adequate flow capacity.Flow in the plane of the geotextile is governed by the following formula:107