Filtration of Fly Ash Using Nonwoven Geotextiles: Effect of Sample Preparation Technique and Testing Method

Abstract

Abstract The long-term filtration behavior of nonwoven geotextiles with fly ash is investigated using gradient ratio tests [ASTM Test Method for Measuring the Soil-Geotextile Clogging Potential by the Gradient Ratio (D 5101-90)] for the duration of approximately ≈4000 h under an applied hydraulic gradient of 3. In parallel, rigid wall permeability tests under the relatively high hydraulic gradient of 25 are conducted to investigate the potential of expediently simulating the long-term filtration behavior of the geotextile-fly ash system. Four nonwoven geotextiles ranging in apparent opening size from No. 70 to 170 are used with specimens prepared using a dry method and a slurry method of preparation and then back-saturated with deaired water. Results indicated that the fly ash-geotextile systems are stabilized after approximately 2000 h with less piping observed for the slurry specimens. Permeability across the slurry specimens is measured to be 1/2 to 1/3 that of the dry specimens. Testing under a hydraulic gradient of 25 and for the duration of 25 h has yielded a steady state k value similar to those obtained from the GR tests after a testing duration of 4000 h. All the geotextile-fly ash systems are categorized as stable based on the stability limit set for the granular filters with the measured rate of fly ash passing through the geotextiles found to be less than or equal to 0.04 g/cm2.