The Focus Window option allows you to define an arbitrary quadrilateral window within the soil region, as a slip surface focus object. To create a Focus Window:
Select Add Focus Window from the toolbar (or select Add Window from the Focus Search sub-menu in the Surfaces menu).
You will be prompted to enter four points defining the window. Enter the points graphically with the mouse, or enter x,y coordinates in the prompt line.
As soon as the fourth point is entered, the focus window will be added to the model, and you will automatically exit from the Focus Window option.
An example of a Focus Window, and the resulting analysis, showing all generated slip circles, is illustrated in the figures below.
Example of Focus Window used with Grid Search
How is the Focus Window used to generate the slip circle radii?
For a given slip center in a slip center grid, the Focus Window is used to generate the slip circle radii as follows:
The shortest distance from the slip center to the focus window is determined.
The longest distance from the slip center to the focus window is determined.
These distances determine the MINIMUM and MAXIMUM slip circle radii, for the slip center.
The Radius Increment then determines the number of circles generated between the MINIMUM and MAXIMUM radii slip circles. See the Grid Search topic for illustration of the Radius Increment.
It is important to realize that, due to the nature of the slip circle generation for a Focus Window, the Focus Window simply guarantees that all slip circles will pass through the Focus Window. The Focus Window is NOT a tangent or "Radius Line" method, as used in some other slope stability programs. If you wish to generate slip circles which are tangential to a line, then use the Focus Tangent option.