Logistics and Overall Strategy

For this example, CalBack files were provided, which contained the pavement structure and the layer stiffnesses and variabilities. The first step is to upload the CalBack file into CalME. CalME generates a series of trials, one for each section as determined in CalBack. The project screen after importing the CalBack file is shown below:

Trials from CalBack in CalME do not allow the user to change the layer stiffnesses. These trials contain the information about the existing structure as determined in CalBack. The user can change the structure within the rules set in CalME, by adding additional layers, reducing the existing layer thickness, or removing existing layers.

CalBack files do not contain any project location, climate, or design traffic information so these inputs need to be entered for each of the trial separately.

Calback does not have material type of the subgrade. It is necessary to select the correct material type for the subgrade (SC in this example). 

Once all the missing information has been updated in the existing trials. Make a copy of this trial for the first alternative design. This allows one to evaluate multiple alternatives with the same starting point.

Overall Strategy

In this example, the CalBack file contains six sections for the 7.43-mile long project. One should review the sections and find the weakest section and the strongest section. In case there is no clear way to determine the relative strength of different sections, one would have to design for all sections.

Whether to use a single design for all sections should depend on whether the difference in design thicknesses between the weakest section and the strongest section is large enough to justify the additional cost associated with multiple cross sections.

For this example, Section 3 has the weakest subgrade with a subgrade stiffness of 3.6 ksi. Accordingly, Section 3 will be used here to illustrate how the various design alternatives are determined. Note that one should also review the strongest section before deciding whether to use a single design throughout the project.

The existing structure for Section 3 is shown in the following figure.

After entering the project location and design traffic, the project input screen for Section 3 is shown below:

Save a copy of this trial under a new name "Section 3: Baseline".