Assessment of Environmental, Seasonal, and Regional Variations in Pavement Base and Subgrade Properties
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2020-01-01
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Edition:[Final Report] [December 2015 to December 2018]
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Abstract:LTRC has conducted an extensive research project to determine the seasonal variation in the subgrade MR from 14 sites throughout Louisiana. The study (1) conducted FWD testing on the 14 sites seasonal for a period of at least 3 years; (2) developed an online web application to determine the soil types throughout Louisiana based upon NCHRP soil units; (3) obtained Shelby tube samples from seven of the 14 sites and conducted soil classifications on the samples; and (4) conducted an assessment of the 14 sites with PavementME using soil data from both Shelby tube samples and NCHRP soil units. FWD tests were grouped together based upon the predominate soil type at each site: A-4, A-6, and A-7. The corresponding equations for the A-4, A-6, and A-7 soil types had r2 values of 0.2067, 0.1243, and 0.0709, respectively Software was developed to interface with NCHRP soil units for Louisiana with DOTD databases, allowing the user to determine the soil type for any DOTD roadway. Comparisons were made between samples taken from Shelby tubes and the NCHRP soil unit database. In the first and second soil strata, 43 percent of sites had similar soil types while the third strata 67 percent similar soil types. The overall average of the similar soil types in the strata were 50 percent. Considering the high variability in soil types that can be found in anyone location, the soil types from the NCHRP soil unit samples may be considered to provide a reasonable estimate of the soils present for the purpose of pavement design. PavementME was used to conduct an analysis of the seasonal changes in the subgrade MR from the 14 sites using soils data from both the NCHRP soil units, Shelby tube samples and FWD tests. Based upon the results, 43 percent of the PavementME results where the soil types and depths were taken from the NCHRP soil units and Shelby tube data were similar to the results from FWD testing. Comparisons of the subgrade MR values produced by PavementME for the Shelby tube and NCHRP soil unit data indicated that they were similar 86 percent of the time. Therefore, based upon the comparisons in this research, it is reasonable to use NCHRP soil unit data as a substitute for Shelby tube samples when Shelby tube samples are not available.
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