The Geometry and Layer Properties panel allows specification of the basic geometry of the flexible pavement system. From this panel, the user defines the overall geometry of the model: Finite Plan Dimensions, Layer Properties, and boundary conditions (Boundaries).
The first step in creating a finite element (FE) model of a flexible pavement section is to choose the dimensions for the model's finite domain (Length, x and Length, y). This does not preclude the user from modeling an infinite domain. All models must include a finite domain which will bound the applied loads. The user can then choose whether to use fixed boundary conditions or infinite elements along the outer boundaries of the finite domain. Generally, it may be necessary to perform a convergence study to study the effect of the finite domain and other parameters in order to determine reasonable values with respect to solution accuracy (and efficiency if multiple analyses will be performed).
The next step is to choose the Number of Layers to be modeled through the depth of the pavement system. A typical flexible pavement section often consists of at least three material layers: asphalt (Layer 1), base (Layer 2), and subgrade (Layer 3). The layers do not necessarily need to represent unique materials. In fact, the user may wish to divide a single material layer into sub-layers with different constitutive properties (E and n) or mesh densities. The next step is to select the thickness and constitutive properties (E and n) for each layer.
Finally, the user must choose boundary conditions at the finite modeling extents for the horizontal plane at the "bottom" of the model and the vertical planes away from the wheel load. The Model Infinite Domain option may be appropriate for modeling roadways, whereas the Model Finite Domain option may be appropriate for modeling laboratory test sections. Both are idealizations of the actual complex boundary conditions that may exist. If the user chooses Model Infinite Domain, the Y-Boundary of Layer 1 Away From Wheel boundary condition can also be selected as Free or Infinite, which allows the user to simulate various realistic pavement boundary conditions. An example screenshot of the Geometry and Layer Properties tab is shown in Figure 1 below.