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TECHBRIEF
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Publication Number:  FHWA-HRT-15-037    Date:  August 2015
Publication Number: FHWA-HRT-15-037
Date: August 2015

 

Determination of In-Place Elastic Layer Modulus: LTPP Backcalculation Methodology and Procedures

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Figure Description

Figure 1. Flowchart. Simplified flowchart for the Back Calculator program using EVERCALC as the backcalculation software package. This flowchart shows the steps needed to generate the input files (i.e., the “.def” and the .gen” files) to execute the EVERCALC backcalculation process and then extract the output from EVERCALC and generate the summary reports. The flowchart begins with launching the Back Calculator software program and executing the Bulk Runner program, which allows users to process data from multiple files in a batch mode. The flowchart shows where the different supplementary data elements (sensor spacing configuration, temperature readings and depth, layer structure and thickness, layer types, and seed modulus values) are used within the process. The supplementary database contains multiple tables with the following information that provide the necessary data for creating the input files for EVERCALC analysis:

The generation of the EVERCALC input files is completed using the following steps:

  1. Read the delection data from the Long-Term Pavement Performance database.
  2. Generate identification descriptors.
  3. Merge the sensor spacing data from the supplementary table.
  4. Sort the deflection data by sensor offsets.
  5. Create an ordered array of the sorted deflection basin from step 4.
  6. Perform basin characterization.
  7. Merge temperature measurements and depth values.
  8. Add flags as issues are identified.
  9. Create an index table to track each created group.
  10. Read layer types, thicknesses, ranges, and seed values to create the EVERCALC input files for creating the “.gen” and “.def” files for the EVERECALC analysis.
  11. Run the EVERCALC analysis.

Results from the EVERCALC output are then extracted and imported into the Bulk Mover program. The Bulk Mover program or tab selects States from which EVERCALC output
results can be merged into the master database or dataset. A summary report is created from these results.

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