Filtration Performance of Two-Layer Geotextile Systems

Nonwoven geotextiles are commonly used in filtration applications. For some applications, however, a nonwoven geotextile filter may not have the required mechanical properties to withstand deformations, and an additional woven geotextile is usually employed in design. While reinforcement is an important function expected from these two-layer geotextile systems, filtration is another function that is critical for the long-term performance. Recent observations in geotextile filter design suggested that the filtration characteristics of these systems can be highly different than those of single-layer systems. A laboratory test program was undertaken to evaluate the filtration performance of four different woven/nonwoven geotextile combinations with fly ash and bottom-sea dredged sediments. For comparison, these geomaterials were also tested with two single-woven geotextiles. The results indicated that both fly ash and dredged sediments could be successfully filtered by a variety of woven geotextiles and nonwoven/woven combinations. Results also showed that use of a two-layer geotextile system, rather than a single-woven geotextile, significantly increased the filtration capacity. Higher amounts of fines accumulated at the sediment-geotextile interface than the fly ash-geotextile interfaces, indicating that geotextiles are more prone to clogging during filtering dredged sediments.