select the Deform
Boundaries 
button in the toolbar, OR
select the Deform
Boundaries checkbox under the General tab of the Display Options
dialog.
The Deform Boundaries option will draw the deformed shape of the excavation and ground surface boundaries, magnified by a scale factor. To display Deformed Boundaries:
select the Deform
Boundaries button in the toolbar, OR
select the Deform
Boundaries checkbox under the General tab of the Display Options
dialog.
Deformed boundary shape magnified by scale factor
Deformation Scale Factor
When you select Deform Boundaries, the deformations are automatically magnified by a default scale factor, in order to make the deformation visible. The apparent deformation of the boundaries can be customized with the Scale Factor option for Deformations, under the General tab of Display Options. A default scale factor is automatically in effect, but you can enter any number to magnify the deformation as desired.
NOTE: the same Scale Factor is also used for the display of Deformation Vectors.