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UBC Theses and Dissertations

Geosynthetic stabilization of unpaved roads on soft ground : a field evaluation Sigurdsson, Oddur


A full scale field trial was carried out to investigate the performance of different geosynthetics in unpaved road construction over soft ground. The test site comprises five 16 m long, by 4.5 m wide test sections, built on a subgrade of undrained shear strength approximately 40 kPa. One is unreinforced and serves as a control section in the study, three sections include a geotextile, and one includes a geogrid. Each test section incorporated a variable thickness of sandy gravel base course material, between 25 and 50 cm thick. They were trafficked in sequence by a vehicle of standard axle load. An important governing parameter for interpretation of behavior is the influence of base course thickness on the relationship between number of passes and rut depth. Performance of the test sections was evaluated from measurements of rut depth, base course thickness, base course deformations, geosynthetic strain, and deformed profile of the geosynthetic, with increasing number of vehicle passes. Vehicle trafficking was continued to a rut depth of about 20 cm, which constitutes a serviceability failure. Results from the full scale field trial show a better performance in the reinforced sections than the unreinforced section. The performance of the unreinforced section shows good agreement with other well-documented field data at large rut depths, between 10 and 15 cm, but not at small ruts. Although the four geosynthetics exhibited a broad range of stiffness and material properties, the general performance of the four reinforced sections was similar on the thicker base course layers. This is attributed to a reinforced mechanism governed by stiffness and separation, and all materials appear adequately stiff for the site condition and vehicle loading. On the thinner subgrades, a tensioned-membrane effect is mobilized, and a significant difference is observed between the geosynthetics.

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