>>592911>Anyone have any advice on increasing the tunnel size?And that was the last anyone ever heard of OP.
No, seriously, don't go caving willy nilly. It can be very dangerous. You're not far from civilization, but you might as well be on the moon because no one can hear you or see that you passed by. You ALWAYS want a team with you and someone else at home who knows exactly where you went and when you intend to be back. Now this is just about twisting your ankle and not being able to climb out unassisted.
Messing with the structure is a whole new risk. The only reason you have to believe the cave is stable is that it has been there a while and doesn't show signs of collapsing. If you start taking material out of walls or ceiling that shaky certainty goes away. The only right answer is DON'T! To affect construction under ground you need massive braces to support the weight of the ceiling = the mass of material on top which could well equal a mountain. But half a ton would already be enough to bury you instantly, never to be seen again. People have died in sand piles on construction sites.
