Laboratory and Field Investigations of Separation Geotextiles

The paper describes research on separation geotextiles performed at the University of Washington and supported largely by the Washington State Department of Transportation. The studies involved forensic investigations of separation geotextile installations throughout Washington State, repeated plate load tests on laboratory model soil-geosynthetic-aggregate test sections, and a full scale road test with end-of-construction and two subsequent forensic investigations. The results of all these studies are summarized and an extensive reference list is provided. We found that geotextile separators, if they survive construction and installation stresses, perform exactly as intended. All geotextiles worked well, although some performed better than others, depending on site specific conditions. On very soft subgrades, bearing capacity increased, rut depths decreased, and induced pore pressures in saturated subgrades dissipated faster with a geotextile; thus subgrades consolidated and gained strength, mostly in the first few months after construction. Short-term benefits of separator geotextiles appear to be more important than long-term for pavement performance.