Evaluation of geotextiles as separators in roadways

This study was performed to experimentally assess for separation geotextiles (1) their survivability, (2) their ability to retard fines migration, (3) their influence on subgrade pore pressure dissipation, and (4) their performance overlying stiff subgrades. This experimental study consisted of a full scale road test and laboratory model tests. A new design method was also developed.;The results of the full scale road test indicated that the presence of a geotextile resulted in more uniform rut depths. The geotextiles did not, however, appear to reduce rut depths in test sections where the subgrades had a modest shear strength. Observations indicated that subgrade drainage during construction was enhanced by the thicker needlepunched nonwoven geotextiles.;Based on the results from the laboratory model tests, Task Force 25 survivability recommendations can be applied to most geotextiles, but it is conservative for the two lightweight geotextiles tested. The presence of a geotextile increases the bearing capacity of the subgrade, if the geotextile can survive the construction process. Rut depth was significantly affected by the presence of a geotextile, but not geotextile type and weight. In terms of their filtration function, geotextiles performed as well as a granular filter. However, the use of a granular filter could result in large stress increases on the subgrade surface and deeper ruts. Under dynamic loading, peak pore pressures within the subgrades were not significantly influenced by geotextile type and weight. A test with an impervious separator had the highest long-persisting pore pressure. All separators performed well in retarding fines migration, if they survived the dynamic loading. Clogging in geotextiles was observed but it did not cause any significant increase in pore pressure.;The results also showed that geotextiles may not be needed for good subgrades (CBR ;Based on the results from the laboratory model tests and Task Force 25 recommendations, a new design method for pavements with geotextiles as separators is proposed. Two examples are selected to illustrate the use of the new design method.