A full-scale field study was conducted to investigate the influence of five different geotextile separators on the performance of a pavement system. Five years after the geotextiles had been installed, the site was excavated to evaluate the soil and geotextile conditions, collect representative samples for laboratory testing, and perform a series of in-situ tests.
The fine-grained subgrade soils appeared to have consolidated since the geotextiles were installed. Density tests suggested that the subgrade in sections containing geotextiles consolidated more than in the test sections without geotextiles. Evidence of subgrade fines migration into the base course aggregates was found at some of the explorations where geotextiles were installed. However, the fines migration did not appear to adversely affect the performance of the pavement system.
Permittivity testing suggested that heat-bonded geotextiles are more susceptible to clogging than needle-punched or slit-film geotextiles. Initial base course layer thickness was found to significantly affect the strength and elongation at failure of the geotexties. The lighter-weight geotextiles contained more construction damage; however, the damage was not reflected in results of the strength tests.
Evaluation of current filtration and survivability criteria indicated that the FHWA filtration design criteria produce reasonable predictions of filtration performance, whereas the maximum AOS values specified by Task Force 25 and WSDOT may not always be effective in preventing fines migration. The Task Force 25 survivability criteria for geotextile separators appear reasonable, whereas the WSDOT survivability criteria may be too restrictive for some conditions.