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

Geotextiles in Embankment Damsreductions (perhaps installation-related) being 30%” (Koerner, 2005c). A thirtypercent reduction in material properties in the matter of a decade of any feature of adam’s design would likely be a “show stopper” for its continued use, let alone theexpanded use of such a material.To clarify the questions arising from the 30 percent reduction in physical properties,the authors contacted Dr. Giroud, one of the principal designers of Valcros Dam.Dr. Giroud (Giroud, 2005) stated that “the reduction in properties was observed the first timetests were made, i.e. 6 years after construction. Reduction in tensile strength was 10 to 20%. Testswere done for the second time 22 years after construction. No reduction was observed between year 6and year 22. This is why mechanical damage during construction was assumed.”In response to the question whether ultra-violet exposure was a significant factor inthe degradation of the geotextile, Dr. Giroud responded as follows: “We were aware ofthe potential for UV degradation, but the geotextile was made of polyester and had a high resistanceto UV light. Furthermore, construction was quick. Therefore, I do not think that UV degradationplayed a role.” Dr. Giroud felt the degradation typified the “ordinary type of constructiondamage. We could perhaps have taken more precautions, but I do not think there was poorconstruction practice. I think that the amount of construction damage that took place at Valcrosdam probably occurs in many projects.” The foregoing comment is sobering. Itemphasizes the need for a rigorous quality control/quality assurance program tominimize such damage. Even with such a program, liberal factors of safety in thedesign phase are a must for those geotextile properties germane to the satisfactoryperformance of the material in the application at hand.Given the uncertainty associated with the aging of geotextiles, the practitioner shouldidentify an anticipated design life for the geotextile at which point some furtheraction will be required to assess the condition of the material. One should havedetails, plans and a cost estimate for removal and replacement of the geotextile in thedesign documentation. The owner can then make a decision whether the costsavings and a more timely reduction in risk posture warrant the use of geotextilesgiven their finite but unknown service life. At present, when the engineer dismissesthe use of geotextiles outright for durability concerns, that individual is making thatdecision for the owner.5.1.2 Consequences of poor geotextile performanceIf an internal feature of a dam does not perform as expected, it is not automaticallyrepaired. Installations that are deeper than 20 feet are generally not easily accessiblefor removal and replacement. Instead, it may become a risk that may be accepted.Options to remedy the situation are balanced with cost, and are prioritized withother O&M work. Installation of geotextile products should be evaluated withrespect to potential consequences should they fail to perform as expected.92