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Browsing by Author "Birgisson, Bjorn"

Now showing 1 - 2 of 2
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    Characterizing Seasonal Variations in Pavement Material Properties for use in a Mechanistic-Empirical Design Procedure
    (2000-09-01) Ovik, Jill M; Birgisson, Bjorn; Newcomb, Dave
    Recent advances in flexible pavement design have prompted agencies to move toward the development and use of mechanistic-empirical (M-E) design procedures. This report analyzed seasonal trends in flexible pavement layer moduli to calibrate a M-E design procedure specific to Minnesota. Seasonal trends in pavement layer moduli were quantified using data from the Minnesota Road Research Project (Mn/ROAD) and Long Term Pavement Performance Seasonal Monitoring Program (LTPP SMP) sites located in Minnesota. The relationships investigated were between climate factors, subsurface environmental conditions, and pavement material mechanical properties. The results show that pavement layer stiffness is highly respondent to changes in the average daily temperature and available moisture. Five seasons were used to characterize the seasonal variations in pavement layer moduli for design purposes. Seasonal factors were used to quantify the cyclic variations in the pavement layer stiffness for a typical year. The maximum stiffness of the pavement layers is reached when temperatures are cooler. The hot mix asphalt layer moduli is at a minimum in the summer when temperatures are high. The granular base layer moduli is at a minimum during the early spring-thaw period when excess moisture is unable to drain. Finally, the fine-grained subgrade layer moduli is at a minimum late spring and summer due to the low permeability and slow recovery of the material. The Integrated Climate Model (ICM) was used in this study to compared predicted data to actual data from Mn/ROAD. It was found that the ICM data compared favorably, however, it was not able to predict the spring-thaw period.
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    Evaluation of a Field Permeameter to Measure Saturated Hydraulic Conductivity of Base/Subgrade Materials
    (2001-06-01) Clyne, Timothy R; Voller, Vaughan; Birgisson, Bjorn
    This report presents the results of a cooperative study on the field use of a permeameter, built by researchers at the Minnesota Department of Transportation (Mn/DOT) and the University of Minnesota, to estimate the saturated hydraulic conductivity of pavement base materials. Field measurements using the permeameter were taken on various highway construction projects, and researchers measured the saturated hydraulic conductivity of samples in the laboratory. Researchers also reviewed theories for converting a field-measured flow rate into a saturated hydraulic conductivity estimate. By numerical simulation and analysis of the field data, researchers determined an appropriate method for converting the Mn/DOT permeameter flow measurements into estimates of hydraulic conductivity. Variations between the field estimated and laboratory measured hydraulic conductivity are within one order of magnitude. Variations between the field estimate and numerical simulation, however, are much closer. The study found the Mn/DOT permeameter can be used to obtain a reliable estimate of the base hydraulic conductivity provided that the base layer is at least 15 cm (six inches) deep. When the base is to thin, permeameter readings are restricted to early infiltration times.