Evaluation of Bearing Capacity of Low-Volume Roads in Minnesota

Deflection testing and analysis are routinely used to evaluate the spring load capacity of pavements and to design structural overlays. The current falling-weight deflectometer (FWD) deflection analysis process used by the Minnesota Department of Transportation was found to be unreliable. Traditionally, the process used to interpret FWD deflection measurements converted the measured maximum FWD deflection to an equivalent Benkelman beam deflection and compared it with the allowable deflection for a pavement with given asphalt surface thickness and anticipated traffic. Because the maximum FWD deflection is greatly affected by the subgrade stiffness, the computer program TONN may underestimate the allowable axle load for subgrades depending on the subgrade material. As a result, the researchers determined that the allowable axle load rating procedure should be revised. Those revisions and the development of a new rating procedure for low-volume roads are detailed.