After the External Boundary has been defined for a Slide model, there may be times when it is necessary to extend the boundary to make it larger, or to make it smaller. For example, if the extents of the External Boundary need to be expanded, in order to expand the search for critical slip surfaces; or made smaller, in order to generate Composite circular / non-circular slip surfaces.
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). This can be especially difficult for complicated models with complex slope geometry, many different material boundaries, 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.
Expand External Boundary
The External Boundary is expanded by simply drawing a polyline "outside" of the existing external boundary. The polyline must be attached at both ends to the existing External Boundary. When the polyline is entered, a new External Boundary will automatically be created, by creating a union of the area encompassed by the original External Boundary, and the new polyline.
To expand the External Boundary:
Select Expand / Shrink External from the Boundaries menu, or the drop down list beside the Add Material Boundary toolbar button.
As you move the mouse, you will see that a small green cross is visible, which follows the movement of the mouse, but is restrained to move along the existing External Boundary.
The green cross allows you to enter the first point of the new polyline graphically with the mouse. When the cross is at a desired location on the existing External Boundary, click the mouse, and this will be the first point of the polyline you are creating.
NOTE: the green cross will automatically "snap" to existing vertices on the External Boundary, as you move the mouse near a vertex. In most cases, it will probably be convenient to begin the new polyline on an existing vertex of the External Boundary.
Now enter all of the intermediate vertices of the polyline, which will become the new vertices of the new External Boundary. These vertices are entered just like any other boundary in Slide (i.e. you may enter them graphically with the mouse, or in the prompt line with the keyboard).
NOTE: when you are EXPANDING the external boundary, all of the intermediate vertices which you enter in Step 4, must be OUTSIDE of the existing External Boundary.
When you have entered all intermediate vertices of the polyline, the LAST vertex you enter, must be ON the existing External Boundary, so that the polyline is connected to the existing External Boundary at both the first and last points.
Like the first point, the LAST point must be entered graphically with the mouse (it cannot be entered through the keyboard). The Snap option is automatically in effect, which means that if you move the cursor near any line segment of the existing External Boundary, the cursor will change to an X icon, indicating that you can snap to that exact location on the boundary, by clicking the mouse. Or, if you move the cursor near a VERTEX of the existing External Boundary, the cursor will change to a circle, indicating that you can snap exactly to that vertex, by clicking the mouse. Enter the last point of the polyline graphically.
Finally, you will see a dialog, which will ask you if you want to convert the deleted segments of the ORIGINAL External Boundary, into Material Boundaries. Select Yes or No, and the new, expanded External Boundary will automatically be created.
Remember, if the results are not what you intended, you can always select Undo and start over again.
Shrink External Boundary
To Shrink the External Boundary (i.e. make it smaller), follow the same steps as described above (to expand the External Boundary), but draw the polyline INSIDE of the existing external boundary. The model will be cropped along this polyline. NOTE:
When you are SHRINKING the external boundary, any intermediate vertices which you enter in Step 4, must be INSIDE of the existing External Boundary.
After Step 6, you will be asked to pick which side of the model you wish to keep. Place the mouse cursor inside the portion of the model you wish to keep. The region will automatically be highlighted. Click the mouse in the highlighted region, and the region that you did NOT select will be deleted.
If you make a mistake and delete the wrong portion of the model, you can always select Undo and start again.