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ASSESSING SPRING LOAD RESTRICTIONS USING CLIMATE CHANGE AND MECHANISTICEMPIRICAL DISTRESS MODELS

Abstract

During the spring, as the average daily air temperature and declination of the sun increases, so does the temperature of the asphalt surface layer. As the increase in temperature travels through the surface layer and reaches the unbound aggregate base layer, the saturated base layer begins to thaw. For a flexible pavement with a fine-grained subgrade, the moisture in the base becomes trapped between the impermeable asphalt concrete layer and the frozen, finegrained subgrade. The excess water requires a long period of time to properly drain. During this period, the subgrade becomes considerably softer and decreases in stiffness, and the roadway experiences an increase in damage and reduction in service life. The duration of thaw for a typical pavement structure depends on soil type, moisture and thermal properties, air temperature, solar radiation, drainage and the location of the site. Spring load restrictions are applied to protect weak pavement structures that would otherwise experience excessive deflections. Nearly 58% of the Manitoba Provincial pavement network is subjected to spring load restrictions, and most of these roads consist of a thin flexible pavement or an asphalt surface treatment. This paper relates pavement deflection data from FWD testing to environmental indices such as the thaw index. Deflection data collected since 1990 on pavement sections and the LTPP site in Manitoba are used to establish network-level and statistically representative values for pavement properties during the thaw weakening and recovery period. The base and subgrade moduli during spring thaw are computed using a back-calculation algorithm and categorized in terms of ranges of the thaw index. The data is used with the prediction models of the AASHTO Mechanistic Empirical Design Guide to assess the impact of spring load restrictions on pavement service life. Five scenarios are considered and these accounted for base conditions on an unrestricted road and for the cases of reducing axle loads, with and without an increase in the number of trips, required to transport a certain payload. An economic analysis on a typical pavement structure reveals that the cost of removing the restrictions can be assessed using the service life predicted by the models. The results indicate that, in some cases, spring load restrictions may in fact adversely impact pavement life. An understanding of the relationship between axle loads and generated traffic volumes is necessary in order to optimize the utilization of the network and protect investment in infrastructure. 

Conference Paper Details

Session title:
IMPACT OF CLIMATE CHANGE ON INFRASTRUCTURE CONSTRUCTION, MAINTENANCE AND OPERATIONS
Author(s):
Jesse Crowder
Ahmed Shalaby
Ray Van Cauwenberghe
Alan Clayton
Topics:
Construction, Maintenance and operations
Year:
2008