Effect of pore size distribution on sediment retention and passing

Geotextile tubes are widely used for the dewatering of high water content slurries. Several sediments types that vary in size (sand, silt, and clay), composition (fly ash and sludge), and water content (80%-1600%) are generally pumped in to the geotextile tubes. For sediments retention of such high water contents, the selected geotextiles must be compatible with the pumped slurry. The geotextile tube pore openings must be tight enough for the sediments to be retained inside the tube, and at the same time they should allow the drainage of water through the geotextile tube. Therefore, successful dewatering performance requires evaluation of the pore openings of geotextile and hydraulic properties on the retention of sediments. In this study, the complete Pore Size Distribution (PSD) of four woven nonwoven and composite geotextiles with similar bubble point O95 was determined using capillary flow test (ASTM-D6767). Additionally, Pressure Filtration Tests (PFT) were conducted over a wide a range of water contents (150% -1900%). The sediment retention performances of the geotextiles were evaluated with d85 of 90μm and 65μm respectively. The results of this study indicated that complete bubble point PSD of woven, nonwoven and composite geotextiles can be measured using a capillary flow test. It was also found that geotextiles having the same O95 but different PSD showed different level of sediment retention over a range of water contents of the slurry and this is a clear indication of the contribution of other pore sizes of the geotextiles on retention performance.