Geotextile tubes for dewatering and decontamination of fine-grained soils

Abstract The use of fabrics in the form of large geotextile bags, containers, and tubes is well advanced, as indicated in the previous chapter of this book. The focus in that case was the use of granular soil (sand, gravel, shells, etc.) infills to form permanent erosion control structures in marine environments. The focus in this chapter shifts in that geotextile tubes are now filled using dredged slurries consisting of fine-grained soils (silts, clays, sludges, etc.) with immediate dewatering as the objective. Upon reaching the desired low moisture content of the contained sediment, the fabric enclosure is cut open and the now stabilized soil is taken to a proper disposal area. Because the typical scenario is the dredging of rivers and harbors, the fine-grained sediments are often contaminated. Therefore, both dewatering and decontamination are often the objective and are addressed accordingly in this chapter. Two large-scale performance tests (hanging bag and pillow) are presented, both of which are being used on a regular basis. They serve to challenge the type of fabric being used and to quantify the amount of flocculants necessary to promote flow through the tube by mitigating the effects of a low-permeability filter cake forming on the inside surface of the geotextile enclosure. Test results presented here indicate the effectiveness of using such flocculants. Even further, the addition of decontaminants to the infilling slurry is presented with the choices of activated carbon, charcoal, or phosphoric rock. In this regard, several numeric examples of pollution removal efficiency are presented along with estimated costs. Research is ongoing in this regard.