Agencies faced with maintenance of secondary roads in frost areas often choose to restrict vehicle or axle loads during spring thawing to minimize the detrimental effects of heavy loads on severely weakened pavements. Thirty-two summer pavement structures were definedto represent "typical" restricted pavements. Layered elastic analyses were performed for these pavements for different levels of reduction in resilient moduli at three different times during spring thawing, including (a) base thawing, (b) 4 in. Of subgrade thawing, and (c) total thawing. Allowable loads for deflection, fatigue, and subgrade vertical strain were identified by comparing the spring thaw response to the summer response. It was found that many thin pavements (2 in. Asphalt concrete) reached critical conditions by the time of base thaw, and asphalt tensile strain was the critical response parameter for the majority of these pavements in spring. Four-inch asphalt concrete pavements did not experience strains or deflections in excess of those in summer until some subgrade thawing occurred; subgrade vertical strain was the critical parameter for these pavements. It was also found that deflections are not a reliable indicator of when critical conditions are realized in a thaw weakened pavement. Finally, a method of evaluating the relative benefits of applying various levels of spring load restrictions is presented. This paper appears in transportation research record no. 1252, Design, management, and operation of pavements.
Abstract