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Federal Highway Administration Research and Technology
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Publication Number: FHWA-HRT-08-057
Date: November 2008
During Phase I of the project, the research team assessed the availability of the LTPP data needed to support the enhanced algorithm for evaluation of frost penetration. This assessment included data utilized by the existing FROST procedure and the LTPP data that will be utilized by the enhanced FROST procedure. The results of the assessment are summarized in this section.
The following LTPP database tables containing subsurface temperature, electrical resistivity, and moisture data were used to determine frost penetration under bound pavement layers:
Data from 1993 to 2001 were used to reinterpret previous frost estimates, and data from 2001 to 2004 were used to develop new frost estimates.
In applying the EICM, the project team used section-specific data where they were available and pertinent to subsurface temperature prediction. The actual climatic measurements, layer, and material information collected at the site were used as inputs to the EICM. These measurements are included in the following tables:
Default or assumed values were used for some of the required data elements that were not included in the LTPP database. The climatic data from the National Climatic Data Center for a specified longitude and latitude were used where section-specific weather data were not available. These climatic data are integrated in the EICM program. EICM inputs are provided in appendix B.
The data from the LTPP tables discussed above were assembled in the analysis database. All records were organized by LTPP site, date, and measurement depth. For each analysis site and date, up to 35 records containing ER, temperature, and moisture data were prepared—one for each analysis depth.
One of the issues in processing electrical resistivity, moisture, and soil temperature data was that these data elements are measured at different depths. Therefore, data manipulation was required to correlate various electrical resistivity, soil temperature, and moisture values. To preserve the same interpretation depths as were used in the previous LTPP frost studies,(3) linear interpolation was used to obtain soil temperature and moisture values at the ER interpretation depth. In the previous LTPP frost studies, ER interpretation depth was defined as a middepth between two neighboring electrodes, resulting in 35 analysis depths for 36 electrodes included in the resistivity probe.
Only dates that had either ER or temperature data were included in the analysis database. Records for the months with the minimum monthly temperature above +1 °C and with no ER data were not included in the analysis database because no freeze conditions are possible when temperatures are above +1 °C.
EICM-predicted temperatures were added to the database to fill in the gaps in measured temperature data. EICM predictions were provided only for the sites that had sufficient site-specific EICM inputs. Only gaps of less than one month were filled with EICM predicted temperature values. Source of temperature data was specified in the analysis database to differentiate between measured and predicted temperature data.
Table 5 summarizes the number of records that were assembled in the analysis database for each of the 41 LTPP SMP sites included in the frost study. As can be seen, measured temperature data were the most complete data element, corresponding to the largest number of records in the analysis database.
|State code||SHRP ID||Years with data||Days with data||Minimum date||Maximum date||Number of ER data records||Number of measured temperature records||Number of EICM- modeled temperature records||Number of volumetric moisture records|
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