The first step in creating a Slide model (after setting the Project Settings) is to create the External Boundary.
To add the External Boundary to your model:
Select Add External Boundary from the toolbar or the Boundaries menu.
Enter the vertices of the External Boundary, as described in Entering Coordinates.
The External Boundary must always be closed. To close the External Boundary, after all vertices are entered, right-click and select Close Boundary, or you can type c and Enter in the prompt line. This automatically and correctly closes the External Boundary, and saves the user the trouble of having to re-enter the first vertex to complete the boundary.
As soon as the External Boundary has been created, you will notice two things:
The area enclosed by the boundary will be filled with the default material colour. This represents the default material property assignment.
Two green triangular markers will be displayed, at the left and right limits of the upper segments of the External Boundary. These are the Slope Limits, which are used for slip surface filtering and generation purposes. See the Slope Limits topic for details.
NOTE: since only one External Boundary is permitted in a Slide model, the Add External Boundary option is disabled as soon the External Boundary is created. Furthermore, all other Slide modeling options are enabled when the External Boundary is created, since the External Boundary must exist in order to proceed with the modeling.
What is the External Boundary?
The External Boundary, as defined in Slide, must encompass the entire soil region you wish to analyze. The External Boundary can also encompass the extents of any PONDED WATER in your model, if you are using a "No Strength" material to model ponded water.
Size and Extents of the External Boundary
The shape, size and extents of the External Boundary are arbitrary, and up to the user to define. Slide is designed to accommodate the analysis of any arbitrary External Boundary shape. However, note the following general guidelines:
The upper segments of the External Boundary will of course model the slope surface you are analyzing.
The left, right and lower extents of the External Boundary are arbitrary, and can be extended as far out as the user deems necessary for a complete analysis of the problem.
Expand / Shrink External Boundary
After the External Boundary has been defined for a Slide model, there may be times when the user finds it necessary to extend the boundary to make it larger, or to make it smaller.
Because of the way in which boundaries are defined and edited in Slide, it can be difficult to modify the External Boundary, after it has been created, using the regular boundary editing options (e.g. Add Vertices, Move Vertices etc).
For this purpose, the Expand / Shrink External Boundary option is provided. It allows the user to easily make the External Boundary larger or smaller, after it has been created with the Add External Boundary option. See the Expand / Shrink External Boundary topic for more information.