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UBC Theses and Dissertations

Filtration behaviour of non-woven geotextiles in the gradient ration test Shi, Yucheng


A series of tests was performed on four uniform soils, which have a D85 from 70 Am, with four nonwoven geotextiles, which have a filtration opening size (FOS) from 60 Am to150 Am. No observations of impending clogging were made, however piping occurred in some tests. A ratio of FOS/D85 < 1.5 has been found to be appropriate effective retention of soils without significant piping. A series of tests was also performed on broadly graded soils, which have a D85 from 57 m to 1400 m and a silt content from 3% to 90%, with one geotextile. Gradient ratio values grater than one were observed, which imply the soil-geotextile composite permeability was less than that of the soil alone. This is attributed to some minor clogging of the geotextile. Soil retention criteria are performed, based on geotextile. Soil retention criteria are proposed based on the experimental results, in termsD15 and D50 of the soil and the D5of which is that of the fraction less than the FOS of the geotextile. Tests performed for more than 100 hours show both the gradient ratio and soil permeability are constant at each imposed hydraulic gradient, and it is concluded that a test duration of 24 hours at each gradient is adequate to characterize soil-geotextile performance. Finally, a comprehensive relationship is established that unifies observations of water head distribution, gradient ratio, permeability of the soil and permeability of the soil-geotextile composite. The unified relationship leads to the identification of three zones that describe the distribution of water head in a gradient ratio test.

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