In the Tunnel and Rock Parameters dialog, you must enter the following tunnel parameters:
Tunnel Radius
In-Situ Stress
Estimate In-Situ Stress
If an in-situ stress is not known, it
can be estimated as a product of tunnel depth and unit weight of rock.
Click on the Estimate 
button next to the In-Situ Stress
edit field, and another dialog will appear that lets you enter those values.
Clicking on OK will close that dialog and automatically enter the estimated
In-Situ Stress value into the Tunnel
and Rock Parameters dialog.