Globally, there is a growing need for technologies that efficiently dewater high-water containing sediments that are dredged from canals, harbors, and lakes. Geotextile tube dewatering of dredged sediments is steadily increasing in practice, as they enable the controlled dewatering of sediments resulting in substantial volume reduction, rendering the retained sediments manageable for disposal. Despite successful applications reported around the world, there is little guidance on the design and selection of geotextiles for dewatering applications. Several empirical tests are available to evaluate the suitability of geotextile materials for dewatering, but there is no information on the utility of such tests in predicting actual geotextile tube dewatering performance. Technological advances in the use and application of chemical conditioners has facilitated the use of geotextile tubes to dewater fine-grained dredged sediments; however, methodologies to evaluate processes of chemical conditioning are not available. This study is the first of its kind to look systematically at sediment characteristics (sedimentation test) and the bench-scale (jar test, falling head test, and pressure filtration test) and large-scale (hanging bag test) dewatering performance of natural non-cohesive sediments. Three natural sediment slurries were dewatered using five different geotextiles. One commercially available polymer was evaluated to enhance dewatering performance of fine-grained sediments. The major conclusions are: (1) Sedimentation characteristics were found to govern the dewatering rate of sediments. (2) A new criteria of (AOS/d 85 ) < 1.5 was found to limit piping to less than 1900 g/m 2 . (3) Optimal dewatering conditions were determined using the proposed innovative bench-scale test methodology (a combination of jar test and pressure filtration test) to simulate anticipated field conditions. For dewatering fine sediment slurry at 33% solids concentration, optimal conditions were observed corresponding to polymer dosage of 50 ppm mixed at a velocity gradient of 50s -1 for 300 s. (4) Experimental investigations of dewatering polymer-conditioned fine sediments using five different geotextiles indicated piping values less than 750 g/m 2 which suggest a need to review existing piping criteria which limits piping to 1900 g/m 2 . (5) Jar sedimentation, jar test, pressure filtration test and pilot scale tests are recommended to select geotextile materials and polymers for practical dewatering applications.
|Industrial Fabrics Association International
|Published - 2006