Filtration Performance Testing of Geotextiles for Vacuum Consolidation Drains

The effectiveness of a drainage system used for vacuum consolidation of dredged sludge is very important since it affects consolidation of the sludge and the removal of drained water. The performance of soil-geotextile systems in a filtration test under unidirectional flow is reported for five drains. A new apparatus was developed for filtration tests under a simulated vacuum pressure and tests were conducted with sludge and different nonwoven geotextiles in order to evaluate the clogging potential and retention capacity of these materials under rather severe combinations of geotextile and soil characteristics. Testing under hydraulic gradients of 40 to 60, and for a duration of 200 hours, yielded a steady state permeability value for four sludge-geotextile systems. Progressive increase of the permeability was observed for one geotextile. Results from the filtration tests are compared and discussed.