Retention performance of geotextile containers confining geomaterials

The design of geotextile containers for dewatering applications typically requires hydraulic compatibility between the geotextile and the confined fill material. Ideally, a geotextile container must successfully retain the solid phase of the fill material and must not be clogged during the dewatering process. This becomes difficult to achieve when the fill material is fine grained and the pore openings are large, such as with traditional geotextile containers. Fly ash and bottom-sea dredged sediments are some of the fine-grained geomaterials that exhibit behaviour that is different from that of regular soils because of differences in their particle structure and chemical composition. In most cases, existing geotextile filter selection criteria are not directly applicable to these unusual geomaterials: therefore an evaluation of the filtration performance of such materials is necessary. A laboratory testing programme was conducted to evaluate the retention performance of geotextiles with fly ash and bottom-sea dredged sediments. The results indicated that both fly ash and dredged sediments could be successfully retained by a variety of woven geotextiles and nonwoven/woven combinations. Results also showed that use of a double-layer geotextile system, rather than a single woven geotextile, significantly increased the retention capacity. Geotextile hydraulic properties such as permittivity and the apparent opening size had little effect on dewatering efficiency; however, the same properties directly influence the retention performance. Additionally, a relatively low initial water content of slurry and the filter cake formed at the soil/geotextile interface promote the retention performance. Geotextile apparent opening size-to-soil particle size ratios in the existing retention criteria did not always accurately predict the observed performance. Therefore a parametric study is needed to evaluate various ratios and to find the most discriminating ratio for retention performance.