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Sonia Stamatelos Administrator Posts: 25
12/8/2020
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The Manual Backcalculation Deflection Tool allows for the backcalculation of layer stiffnesses, for individual deflection bowls, from Falling Weight Deflectometer (FWD) or Dual Wheel load (i.e. Benkelman Beam) data. Manual Backcalculation is often done for deflection bowls that are recorded at known positions, and on test pits, where the layer thicknesses and materials are known in some detail.
Getting Started
The Manual Backcalculation Deflection Tool is accessed through the Deflection Analysis icon on the Rubicon Toolbox Online Tools.
If this is the first time you are using the Online Tools, you will need to set up a project by clicking on the Manage Projects link and create a new project. Alternatively, you can use an existing project if one has already been created.
Once you have created a new project or selected an existing project, click on the Deflection Analysis icon and select Manual Backcalc from the list. A Manual Backcalculation page will open.
To start, download the example template, enter the relevant data and save the template. Alternatively, import data from a saved Auto Backcalculation analysis.
The Excel Template contains three sheets, namely Data, Thickness and Notes. The template needs to be completed exactly as indicated, detailed notes are provided within the template as guidance.
The extract from the Data Template shows the sensor positions, D0, D200 etc. These offset positions are the positions of the actual sensors, and can be changed to suit your sensor positions. If you have more than 9 sensors, you can add more columns and the software will stop reading when an empty column is read. The software reads these headings to obtain the sensor positions. It is therefore imperative to check that the number of sensors and offsets represent the actual configuration used during testing.
The Thickness sheet is optional, thicknesses can also be controlled from within the Tool. The thickness of 3 to 5 Substratum layers can be input, the Semi-finite Subgrade is automatically added. The last layer in the template is assumed to be the Upper Subgrade, and must be between 300 and 3000 mm thick. See Subgrade Characterization for help in adding the Upper Subgrade.
Note, if you choose to import data, you will bypass the data selection step and proceed to measure the the deflection bowl.
Running the Analysis
Once you have completed the template, proceed to the Tool.
If you selected Not Applicable for your Thicknesses, the thickness settings options will become active and you will be able to manually add or delete layers and populate the thickness column.
 
Note, for a new analysis, the Save option is initially inactive. Once an analysis is saved for the first time, the save option becomes active. For overwriting an existing saved analysis, click on Save. To save as an alternative analysis, click on Save As. Alternatively you can clone your analysis, from the Online Tools page, and rename it as needed.
To import results from the Auto Backcalculation Tool, Export the Auto Backcalc results to Excel, then import in the Manual Backcalculation Tool using the Import Auto BC link.
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