Permeability of Soil-Geotextile Systems

Abstract

A specially designed laboratory-type permeameter was used to characterize liquid flow behavior through various combinations of soils and geotextile fabrics subject to different flow rates and hydrostatic pressures of water. Spunbonded geotextiles made from two different fiber types ( e.g., polyester and polypropylene) were selected for the study. Volume flow rates were varied up to 21 cm/second by adjusting hydrostatic pressure differences from 2.5 to 76.2 cm. The results suggest single layer barriers of the geotextiles alone have small effects on flow rates of water, but sand-geotextile combinations exhibited strikingly different behavior. In prewashed soil-geotextile combinations, the permeability decreased non linearly with increasing depth of soil above the fabrics, independent of the supporting fabric. For soils that were not prewashed, however, fine particles in suspension settled at the soil-water interface to produce an almost impervious layer or cake structure. This caking was a function of time and became the controlling factor of flow throughout the composite. High clogging in even thin fabrics was observed when sand was replaced by fine material such as Kaolite. The behavior was different than that of the fine material in unwashed sand. In addition, geotextile fabrics showed low resiliency to recovery from cyclic compression. The practical interpretation of this is that the porosity of the fabric may decrease significantly with time if incorporated into structures that are subject to compressive forces.