HEAVY VEHICLE EVALUATION FOR OVERLOAD PERMITS

Abstract

Highway agencies often receive requests for permits to allow the movement of overloaded machinery, structures, and other commodities. Many highway departments issue permits up to a standard axle loading of approximately 27,000 lb; however, they do not have sufficient data to respond to requests for other loads and axle configurations. A study for the Pennsylvania Department of Transportation analyzed the expected pavement damage resulting from overloaded axle configurations, in particular, four- and five-axle configurations with loads up to 34,000 lb. A computer simulation approach was used to model both flexible and rigid pavements. Flexible pavements were analyzed with structural numbers of 2.92 and 4.82 representing a low and high structural capacity, respectively. Rigid pavement was analyzed as a 10-inch slab on 6 inches of crushed aggregate base. Calculated strains and deflections were compared to limiting tensile and vertical strains (flexible pavements) and stress ratios (rigid pavements). The remaining life of each pavement was evaluated. It was found that four- and five-axle configurations developed the same tensile stresses as the single- and tandem-axle configurations for a thin flexible pavement, but the strains were lower for the thick pavement cross section. The stress ratios for the rigid pavement for all axle loads and configurations were below 50%, which implies that an unlimited number of repetitions can be applied.