If you're digging out a room underground, how often and by what means should you place supports to prevent a cave in?

A lot depends on your situation’s variables. I might recommend this book which talks about the different shoring methods. I realize you want to dig right away, and not necessarily go buy a book, wait for shipping, and do too much figuring, but it might be safer than the other Wile E. Coyote methods of proceeding.

@laureth I don’t disagree by any means. In all honesty, it’s going to take a long time either way, so I don’t really mind waiting and figuring out the right way to go about things. I’ll check out the book; it looks like exactly what I’m in need of! Thank you! In the meantime I guess I’ll just work on moving away all the dirt I’ve displaced up till now. That’s gunna be a tiresome undertaking in and of itself.

Out of curiosity, why do you want a tunnel in the first place?

I believe OSHA/CSA require the use of a caisson.

@SmashTheState I think caissons are only required for below water structures.

@gorillapaws Ultimately I wouldn’t be trying to make a tunnel, but rather a house underground. It’s just one of the many, admittedly crazy (possibly insane), ideas I’ve come up with in my life.
My curiosity often drives me to exploring avenues I probably shouldn’t. For example, my last project was an attempt at making a ferrofluid sculpture with a plasma coating… I was basically trying to mix this with this. In the end I got the ferrofluid sculpture working, but put out the electricity to my apartment building once I tried adding plasma to the mix. =} Whooops~! haha

Anyways, this underground house idea is just another form of my crazy at work.

This is how it came about:
One night I woke up from a weird dream where I was living in an underground mansion. It got me thinking; if one were willing, given time and effort, you could actually make a giant house underground. Furthermore, this entire structure could be right under anything (i.e. a tennis court) and no one would ever know it. No property taxes, immense possibility for expansion, tap an electric line here, tap a water line there and BLAMO! You got yourself the most free, interesting, and private house for miles.

Granted that’s all VERY far fetched and probably entirely outside the realm or realistic possibilities; but hey… you never know unless you try, right? This specific attempt is more just to explore the feasibility of such an undertaking single-handedly. I don’t know how deep under the courts I can actually make it. And honestly, I don’t really care if I never get any further along than I am today. Right now I’m just having fun. I like making things, I like digging, it’s something new and interesting to me, and it beats the hell out of the gym. =] I’d rather not die, or be arrested in the process though, so I’m taking precautions where I can. Hence, currently, you absolutely can not tell there’s a giant hole right where it is. I built a door and covered it with dirt. HA-ha! =J

When my Dad built a bomb shelter in our yard, he dug a giant hole, like for a swimming pool, then built the shelter, then put the dirt back in the hole and covered it all up, except the entrance, which was like a manhole, connected to a short tunnel.

By the way, did you happen to call your local authorities to make sure there are no underground wires or such things where you’re digging? It could be dangerous.

As far as the whole “no property taxes, tap a line here and there,” etc. , I think you may be unwarrantedly optimistic. If you own the land, there are property taxes either way. The book I referenced is suddenly quite valid, though. My husband and I have considered this very thing… but it is complex. What is the water table like where you live, first?

Interesting project, stay safe. Living tax free underground isn’t much fun if you get buried alive. You should also think about earthquakes and flooding in a big rainstorm.

A concrete perimeter, floor and walls. Where I live the local zoning laws tell you what you can do and not do. Check with a pro.