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Mechanisms of Reinforcement Benefit from Geosynthetics Used as Subgrade Stabilization

Geogrids and geotextiles are routinely used to stabilize weak subgrade soils during road construction. Typical subgrade stabilization applications are temporary haul roads or unpaved low-volume roads, but can also include paved roads built on poorer foundation materials. Full-scale tests were constructed, trafficked and monitored (in two distinct phases) to compare the relative operational performance of geosynthetics used as subgrade stabilization, as well as determine which material properties are most related to performance. During the separate phases of this project, test sections were constructed using ten different geosynthetics (Phase I) and twelve different geosynthetics (Phase II), both consisting of geogrids and geotextiles. Multiple control test sections were also built to evaluate the effect that subgrade strength, base course thickness, and/or presence of the geosynthetic had on performance. Using longitudinal rut as the primary indicator of performance, it was determined through a linear regression analysis that the strength and stiffness of the junctions and tensile strength properties in the cross-machine direction correlated well with performance in this application, depending on the level of surface distress. Furthermore, instrumentation installed during the field experiment helped describe the behavior of the geosynthetics as rut developed under trafficking loads. Instrumentation consisted of displacement measurements using linear variable differential transformers (LVDTs) and strain measurements using bonded strain gages. Data from these instruments helped describe the method of reinforcement the geosynthetic provided as it transitioned from lateral confinement of the base layer to tensioned-membrane support, and how this transition related to rutting at the road surface.