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Minnesota Department of Transportation
The pavement design package created by Itasca extends the capabilities of PFC3D to support triaxial testing of a synthetic unsaturated aggregate base containing geogrid. The geogrid provides lateral restraint to the aggregate base as a result of interlocking and friction between the geogrid and the aggregate particles. The macroscopic system properties are affected by the microstructural system properties. Therefore, the modeled system was used to study and quantify the effect of microstructural properties on the macroscopic properties, which include the stress-strain curves produced during triaxial tests at different confinements. The microstructural properties of the aggregate base include: particle size, particle type (density, Youngs modulus, and Poissons ratio of each particle; and friction between particles), aggregate base moisture content (suction and gap), and initial aggregate base porosity. The microstructural properties of the geogrid include: geometry (aperture and rib dimensions), Youngs modulus, bond stiffness, and grid-grain interface behavior. The pavement design package provides a mechanistically defensible model for aggregate-geogrid interaction, which was used to improve pavement design by estimating geogrid gain factors for typical geogrid-reinforced aggregate roadways. It is anticipated that a simplified geogrid gain factor adjustment will be trialed during pavement design for projects where geogrid is being considered. As expected, this study concludes that geogrid provides benefit and that this benefit varies during the year. Therefore, it is recommended that the seasonal effects be included during implementation. This would allow the fatigue and rutting to be more accurately estimated over the expected pavement design life.
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