Pavement Structure

The following controls, located on the Input -> Project Information Page, are used to specify the structure for the pavement project.

The pavement structure is defined using a grid in which each row is one layer of the structure. You need to define at least two layers, but you may have as many layers as necessary.

You can add layers to the bottom of the current structure, insert before a layer and delete layers. You will be asked to confirm layer deletion.

There are four buttons at the bottom of the structure grid that allow you to add multiple layers at once and with layers of a specific type based on the number of layers. For example, selecting the "Add 3 Layers" button results in the following three-layer system: HMA, AB and SG. These buttons are only active if the current structure grid is empty.

CalME has many "rules" to assist in constructing a valid structure, such as the topmost layer must be either HMA or RHMA, and the last layer must be SG (Subgrade).

Rows (layers) are put into Edit mode by selecting the "Edit" button at the right of a row. Once in Edit mode, the list of buttons changes to "Save" and "Cancel". In edit mode, you can make changes to all fields that allow editing. You select the "Save" button to save your edits for the layer.

Shown below is how the Pavement Structure grid looks after selecting the Add 3 Layers button and selecting the Edit Button for the first layer (row) and entering a value of 1.0 ft for the layer thickness. All layers generated using one of the four layer generation buttons need to have a specific material selected since just the type of material (e.g., HMA) for each layer is generated by the layer generation buttons. The thickness for each layer is also required.

As shown below, CalME also checks the specified layer thickness against minimum and maximum values, as specified in Caltrans' Highway Design Manual (HDM), e.g., for HMA, the minimum thickness is 0.15 ft; there isn't a maximum value for HMA in the HDM.

After saving the changes made to the first layer (row) using the Save Button in the Actions column, CalME will indicate that Layer 2 (and subsequently Layer 3) needs to have a specific material selected.

Shown below is how the grid looks after selecting a specific material for all three layers, along with specifying an acceptable layer thickness. At this point, CalME shows an informational message indicating the minimum thickness for the AB layer; this minimum is a function of the type (USC) of subgrade. In the example shown below, the subgrade is a type "CL", which has a minimum AB thickness of 0.50 ft.

Each layer has the following data items:

•Layer number - this is a link item that navigates to the Edit Pavement Layer Material page

•Type: this is the HDM type code for the layer material: HMA, RHMA-G, FDR-FA, FDR-NS, CIR, PCC, LCB, CTB-Class A, CTB-Class B, AB ATPB, CTPB, AS, LTS and SG (Subgrade)

•Old - a flag (checkbox) to indicate if a layer should be considered an existing layer, i.e., a layer that exists before any rehabilitation is done. When importing a CalBack file, all layers that are generated during the import process are flagged as Old, and they cannot be changed from that state. Any layers added to the imported pavement structure can be selected as Old or New (unchecked); typically, added layers to a CalBack imported structure are not selected as Old since they are new layers added for a rehabilitation project.

•Age - the age at loading, in days

•Material - a specific material associated with the HDM type code

•Thickness - layer thickness (recall that CalME will check the specified thickness value against minimum and maximum limits). When a project is created from a CalBack import, thickness is set to the value contained in the import file.

•Modulus - this field gives the reference modulus for the material from the Material Library. You may change this value as necessary. When you change the modulus for a subgrade layer, the R-value is also changed using the equation: E (psi) = R-value * 551 + 1117. When a project is created from a CalBack import, the layer modulus is set to the average of the modulus points for a section defined in the import file.

•R-value - this field gives the Caltrans "R" value from the Material Library. You may change this value as necessary for subgrade layers. When you change the R-value for a subgrade layer, the modulus is also changed using the equation: E (psi) = R-value * 551 + 1117.

•GF (Gravel Factor) - this is a read-only field that gives the equivalent gravel factor for the material

•Cost ($) - This field gives the cost per volume from the Material Library. You may change this value as necessary.

The last column of the structure grid either contains three buttons (Edit, Delete, Insert) or two buttons (Save, Cancel), depending in the row is in viewing mode or edit mode:

•Edit - puts the row (layer) into Edit mode allowing you to make changes to the layer's properties

•Delete - deletes the row (layer); you will be asked to confirm this operation

•Insert - inserts a row above the row in which you selected the Insert

•Save - saves the changes to the row (layer)

•Cancel - puts the row back into viewing mode, basically canceling any changes

At the top of the structure grid are three controls:

•Unconfined Compressive Strength (UCS) for an LTS (or CSS) layer, if it has been used in the structure. Changing this value will also change the modulus for the LTS layer, using the following equation: Mr (ksi) = 0.124 * UCS (psi) + 9.98. Conversely, changing the modulus for an LTS layer will change the UCS using the same equation. See Table 666.1A in the HDM.

•Delete All - this button will delete all layers currently defined in the structure grid. You will be asked to confirm this operation.

The question mark in the blue circle in the upper-right of the control group allows you to get help on the controls (this topic).