LumenRT Clipping Plane Questions

Questions on clipping planes in LumenRT:

1. What does the infinite/finite clipping plane option do?  It appears to just turn off the clipping plane when I uncheck infinite.

2. I have two objects in a scene, the existing terrain and a new object.  The new object is would remove some of the existing terrain, a cut in a hillside for a road, for example.  Can I use multiple clipping planes to cut out part of the existing terrain, while still have the new object shown?  It's not possible to model the two objects together, as they are coming from different software platforms.

Thanks for any help you can provide.

Steve