http://postimg.org/image/44q2m49q9
Here's what happened when I tried to dig my first tunnel. Floor leveled out, but roof kept going down. Couldn't dig any further due to this.
Tried to correct it by extending the ramp.
http://postimg.org/image/680hts9j5
That just made things worse.
Sorry to the server... I really messed up a nice part of your map.