Evaluation of transverse behavior of geosynthetics when used for subgrade stabilization
Morris, Zachary Lee
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State departments of transportation (DOTs) routinely use geogrids and geotextiles for subgrade stabilization. There is a general consensus between state DOTs concerning the effectiveness of these geosynthetics for this application; however, there is a lack of understanding and agreement with respect to the material properties of the geosynthetics that most directly relate to performance. A full-scale field study using geosynthetics as subgrade stabilization was conducted to analyze the performance and transverse behavior of 14 reinforced test sections under vehicular loads. Insight into the mechanisms of support that geosynthetics provide was determined based on strain gage and LVDT measurements, and transverse rut profiles. Mechanical properties of geosynthetics were compared to truck passes at the transition from lateral confinement to membrane support as well as at failure to evaluate which properties best predicted field performance. The properties evaluated included wide-width tensile strength, cyclic tensile modulus, resilient interface shear stiffness, junction strength, and aperture stability modulus. The behavior of geosynthetics was primarily characterized by when they started to transition from lateral confinement to membrane support. The results indicate that in general, the geosynthetics transitioned between truck pass 80 to 300 at a corresponding average elevation rut of about 1.7 inches, or between 1.7 to 3.1 inches of apparent rut. Failure was defined as 3 inches of elevation rut, and in general, the geosynthetics that transitioned to membrane support before truck pass 80 to 300 failed early. The results from the field study indicate that junction strength and stiffness, and wide-width tensile strength at 2% and 5% strain may be the most pertinent mechanical properties of geogrids, and surface friction may be the most pertinent property of geotextiles, for estimating field performance when used for subgrade stabilization applications with 10 to 12 inches of base aggregate, CBR strength values between 1.5 to 2.2, and elevation ruts less than 3.0 inches (or less than 5.4 inches of apparent rut).