Solar Effects on Frost-Thaw Patterns at Two Adjacent Roadway Test Sections: Case Study

摘要

Many roads in seasonal frost areas experience costly damage as a result of freeze-thaw processes. In order to reduce damage, road management agencies apply Spring Load Restrictions (SLRs), which restrict the allowable load on a road during the critical time interval when the pavement is most vulnerable to damage. Methods of determining SLRs include use of set dates and/or visual inspection procedures, conducting falling weight deflectometer (FWD) testing, monitoring subsurface temperatures and/or moisture, and use of predictive models (based upon atmospheric weather data) to predict subsurface frost-thaw profiles. Regardless of which approach is used, a challenge in SLR posting is that many miles of roadway must be posted based on a very limited set of observations and data. This paper presents data from two closely spaced field test sections: one located in a very sunny area and the other located in a shaded area. Other than solar exposure, conditions at the two sites were considered the same. During the two-year study period, subsurface temperature monitoring showed substantial variation in frost-thaw patterns, particularly with regard to the end of thaw dates, which occurred 30 and 38 days later at the shaded site compared to the sunny site. FWD testing conducted at the sites also showed similar differences in thaw weakening and recovery patterns. Results of this study suggest that variability in solar radiation can have a significant impact upon appropriate SLR posting dates, particularly with regard to removing the SLR. Additionally, the project suggests a need for more cost-efficient monitoring systems, so that variability might be better quantified and accounted for by agencies charged with making SLR posting decisions.