Before I find a real life person to ask , I had a question of how much work it would take...

I have a rancher where half the house is full basement, and the other half slab on grade.  I want to tunnel under the slab and connect it to the full basement which has cinder block.  I would like to do a roughly 6' wide by 30' tunnel to possibly use but not really use for things like suppressed shooting.  Or perhaps a bowling alley would be nice.  Or an archery range.  The use is not relevant.

The slab is 10" thick with rebar.  I have drilled down and cut in to multiple spots for plumbing issues.  The slab is on grade, but it is also resting on top of the cinder wall towards the basement side.  A plumbing issue from the previous owner essentially left a 2' gap under the slab closest to the concrete wall (the main drain runs along the cinder wall, UNDER the slab and the pipe broke at some point).  Something needs to be done eventually anyway to fill that void (probably just pump the mud in there at some point), thus my brilliant idea of an archery range/something like that.  

Feasible?  Not feasible do to cost restrictions?  Not feasible at all?

Digging under the house, eh?

You should ask VBC. He's a pro at such matters.

I'd be REALLY shocked if your slab is actually uniformly 10" thick and doubly reinforced.  I've designed industrial one way slabs for very high floor live loads that were not that thick.

Eta: after thinking about it for a minute, I wonder if you have really crappy/unstable soils, and your slab is actually a waffle slab on grade beam system?

Think he'll get a building permit?

Nah, you don't need that. Or soils information. Or calculations.  Or a working knowledge of structural mechanics. Just get a shovel and git 'er done.

I wonder whether he has a PTSOG.

That would be even more rare than a 2 way slab/grade beam scenario, especially in a residence.

It is definitely 10" thick in multiple spots far away from other spots. It could be less in certain spots though. There are no beams.  I thought it was odd when I did the plumbing stuff.  I was pretty pissed off when I was expecting 4-8".

And yes, honestly this would be with a building permit.  I got a permit for cutting down two trees for crying out loud.  

I was thinking 1 or 2 30' beams with cross sections on lollys/posts every 6' with concrete on the ground tied to the existing basement floor would make it plausible and not all that expensive.  Dang, that's a run on.

I'll let you Jr. engineers handle it for a while and if there is no progress, I'll give it a shot.

Go hire an engineer.

Hmm
I think you missed my first post, or maybe someone pissed in your Cheerios.

This was meant to be is it possible.  Is it possible without major expenses incurred.  Is it not possible.

I figured if it were option c, it would be pointless to hire a structural engineer and I would strike it as just another dumb idea.  If you don't want to help, just say so or don't reply?  Heck, I'm not even asking for details on how to do it, just thinking that it would be possible and not that expensive.  If it is not easily doable or not doable at all, I'd like to not think about it.

Got any "Basement's and Crawlspaces 'R Us" type business in your area?  I've seen some that advertise being able to turn a crawlspace into  basement and I assume that they have an engineer of staff to handle such issues before they take a job and start digging.

I would be surprised if there is really rebar in the slab...

What do you consider a major expense?

Over $20k I wouldn't even consider it.  I think $10k would probably be the realistic line drawn.

Just in the spots the plumber moved the fixtures in both bathrooms  

Then again, I guess it's possible the bath area was reinforced do to the giant holes they used originally for drains?

Can I assume that may be true?  And if so, does that make the idea way less likely of even being possible?

Yes, I'm an electrician and have done electric for projects like that.  They basically dig around the existing supports for the beams then just relocate, so it's really not the same thing.  I wish I just had a full basement.  

I think it is possible, and if your slab is as described, you're better off.  That said, $10k won't touch that project.  

I'd charge you between $1500 and $2000 just to evaluate it, and give you a design.

See, that is all I needed to know.  Just good old bringing me back to reality.  Thank you!

It would be cool to have, but I think anyhing over $10k, I'm better off just going to the indoor shooting/archery range 5 minutes away and continuing to pay the $200/year membership.  

If you have a budget, it is. An indoor shooting range is more than just a concrete box with targets at one end. If you're going to be shooting down there, you need to keep in mind there will be significant costs for proper air handling and filtration.  Lead poisoning isn't something you want to subject yourself or your family to (especially if you have kids).

I was thinking more so archery, and maybe a round or two to sight in 22's, certainly not heavy or even medium use.  I know if a lot of shooting were tj be done, serious expenses would happen with ventilation.  Thst was never an intention though.

The thought has been washed away anyway and I'm back on earth,

With the liability, I'd charge at least 8k for plans and specs.  And then even more for observation.

CA, where even the janitors make bank!