The Focus Line option allows you to define a line segment within the soil region, as a slip surface Focus Object. To create a Focus Line:
Select Add Focus Line from the toolbar (or select Add Line from the Focus Search sub-menu in the Surfaces menu).
You will be prompted to enter two points defining the line. Enter the points graphically with the mouse, or enter x,y coordinates in the prompt line.
After the second point is entered, the focus line will be added to the model, and you will automatically exit from the Focus Line option.
NOTE: the Focus Line option does NOT generate slip surfaces tangential to the line. If you wish to generate slip circles which are tangential to a line, then use the Focus Tangent option.
An example of a Focus Line, and the resulting analysis, showing all generated slip circles, is illustrated in the figures below.
Example of Focus Line used with Grid Search
How is the Focus Line used to generate the slip circle radii?
For a given slip center in a slip center grid, the Focus Line is used to generate the slip circle radii as follows:
The shortest distance from the slip center to the Focus Line is determined.
The longest distance from the slip center to the Focus Line 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.