Fourteen geotextile separators, with different in-service ages, were exhumed in western Washington and their short (survivability) and long-term (filtration/drainage) performances were evaluated. The geotextile samples, which included six woven slit- films, six needle-punched nonwovens, and two heat-bonded nonwovens, were taken back to the laboratory in order to evaluate their overall condition and to perform permittivity and strength tests on specimens of each fabric. Samples of the subgrade and base materials were also evaluated in the laboratory.
The results indicated that all of the geotextile separators adequately performed their intended separation function, although they experienced very different levels of damage during construction. There was evidence of in-service mechanical damage at one of the sites. The damage to the geotextiles was influenced more by the base aggregate type, rather than the initial lift thickness, although both must be considered in design. All of the recovered geotextiles which were installed under an angular base aggregate sustained damage to some degree. Even two heavier weight fabrics, a 231 g/sq m woven slit-film and a 204 g/sq m needle-punched nonwoven, sustained damage under angular base material. All of the fabrics which were installed under subrounded to rounded base aggregate experienced minor to no damage. The woven slit-films and the needle- punched nonwovens experienced similar reductions in strength and both survived the installation conditions reasonably well (except for one lightweight needle-punched nonwoven fabric which was overstressed during installation and also may have been installed under too thin of a pavement section). The heat-bonded nonwovens were heavily damaged during installation; however, they were installed under some of the higher site survivability conditions.
The results of the permittivity tests indicated that the woven slit-films and the needled- punched nonwovens both had similar percent increases after being washed. The heat- bonded nonwovens had the highest percent increases in permittivity after being washed, which suggests that they clog more than the other fabrics. There is evidence that the woven slit-films experienced much more blinding than the other fabrics, and that iron staining and caking could also have a detrimental effect on their drainage performance. In all but one case, the woven slit-film fabrics did not meet the Task Force 25 (1989) and Christopher and Holtz (1989) filtration requirements needed for the subgrade soils with which they were in contact. The unwashed (i.e., undisturbed) permittivity results also indicate that most of the permeabilities of the woven slit-film fabrics fell below WSDOTs required value. The presence of caked fines on the upper surface of three woven slit-films could have indicated that their pore openings were too large for the intended filtration function and they might be subject to fines migration, although this was inconclusive. There was no other evidence of fines migration at any of the sites.
All of the pavements were in good condition, and the damage of the geotextile separators appeared to have no negative impact on the pavements long-term performance. There was one pavement surface which showed signs of premature failure; however, this was not attributed to the performance of the geotextile separator.