Soil-nonwoven geotextile filtration behavior under contact with drainage materials

Abstract

The seepage rate and clogging potential for a soil–geotextile–drainage system were assessed using experimental tests. An ASTM gradient ratio test apparatus was used to perform the tests by adding a drainage layer downstream of a geotextile specimen. The gradient ratio is defined as the ratio of the hydraulic gradient through a soil–geotextile system to the hydraulic gradient through the soil alone. Two types of drainage layers including a uniform-sized steel bead layer and a steel plate punctured with uniform-diameter holes were used to simulate conditions downstream from a field-inserted geotextile. The direct contact between the granular particles or concrete block and the geotextile reduced the open area for water flow. Tests performed on different bead sizes and different plate perforated areas showed: (1) For the bead sizes used in the experiments, the smaller the open area the lower the flow discharge rate. However, the flow discharge rate was not linearly proportional to the open area at the geotextile and steel bead interface. (2) For a drainage layer formed by steel beads, the clogging potential increased with the reduction in open area between the geotextile and drainage material. These results indicate that filtration tests on a drainage system without blocking materials downstream of a geotextile may underestimate the clogging potential for the filtration system. (3) Beads of different sizes can be formed into drainage layers with the same percentage of open area. However, the GR values exhibit minor changes when the open area remains the same.