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

Chapter 5—Current Status of Design Procedures5.5.1 Environmental degradation considerationsMicrobial growth associated with geotextiles raises two concerns: consumption ofthe carbon fraction of the polymers and clogging of the fabric as the microbes fill theopenings in the geotextile. Studies (Kossendey, Gartung, & Schmidt, 1996) of theinteraction of microbes with geotextiles permeated with landfill leachates have notfound that the polymers were consumed by either aerobic or anaerobic bacteria. Thepolymers did provide a site for microbial growth to occur and there was acommensurate reduction in permeability. Sands exposed to leachates suffered thesame fate. Relatively speaking, the overall decrease in permeability was greater in thesands than in the geotextile. The principal controlling factor in the process was theavailability of nutrients in the permeating fluid, in this case the leachate. In thetypical dam application one would expect that the seepage reaching the chimneydrain at depth would be largely devoid of nutrients and thus, a poor feed for bacterialgrowth. Given that sands are likewise susceptible and microbial clogging has notbeen a problem, the lack of nutrients in the seepage minimizes the microbial threatto geotextiles deeply embedded within dams.Exposure to ultraviolet light and oxidation will also degrade these materials. On apositive note a number of mechanisms that degrade the performance of geotextiles,i.e. exposure to sunlight and oxidation, are eliminated and greatly reducedrespectively by deeper burial. The threat of vandalism is eliminated. Burrowinganimal concerns are lessened as the deeper buried segments of the geotextile arefurther removed from the habitat an animal operates in normally.Burial minimizes this risk.The expected service life of a geotextile is dependant upon its resistance todegradation. For buried applications, a service life of over 100 years is anticipated.Most research has been conducted upon geomembranes where service lifepredictions in the range of 90 to 500 years have been forecast (Koerner, 2005c).Table 5.5 presents the susceptibility of geotextiles to environmental conditions:111