The efficacy and use of small centrifuge for evaluating geotextile tube dewatering performance

Geotextile tube dewatering technology has been widely used over the past two decades for dewatering high water content slurries. The dewatering process in geotextile tubes aims to decrease the volume of the dewatered slurry, which helps in the transportation, disposal, and reuse of the dewatered material. Several researchers have emphasized the effect of the retained sediment (filter cake) properties, in particular final solids content and volume (height) change, on the feasibility of geotextile tube dewatering projects. Retained sediment properties are often evaluated using small scale tests such as rapid dewatering test, falling head test, pressure filtration test (PFT), and field scale tests such as hanging bag test (HBT) and geotextile tube demonstrations test (GDT). In this study, centrifuge test is introduced as an alternative for the widely used pressure filtration and falling head tests to evaluate retained sediments properties. Centrifuge test provides a mechanism for understanding the response of slurries to externally applied pressure in geotextile tube environment. Centrifuge test was used to evaluate maximal solids content of the retained sediments and change in slurry volume of four soils that represent typical dredged soils. Tully sand, Tully fines, Elliott silt loam, and kaolin slurries were used at varying solids concentrations. Slurries were subjected to external stresses between 0.1 and 40 kPa by applying centrifugal speeds between 300 rotation per minute (rpm) and 1800 rpm. Both centrifuge test and PFT were conducted with unconditioned and cationic polyacrylamide conditioned slurries. Centrifuge tests results were compared with PFT results with respect to retained sediments final solids content and volume change. Tests results indicated that the maximal solids concentration of the retained sediments in saturated conditions is unique for each soil and is independent of the initial slurry solids concentration. Tests results also indicated that there is linear relationship between the initial concentration of the slurry and the final volume change at any externally applied stress. Finally, a relationship between the total pumped slurry volume and the final height of the dewatered sediments in a geotextile tube is presented.