A Bunker Underground an Existing Home

All good considerations to factor in.

How about installing a large capacity septic system? And then repurposing it....as far as anyone knows...it is full of sh!t, rather than a temporary bug in place bolt hole / cache stash.

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Any municipal approvals can be obtained and registered as a septic sh!t pit before repurposing...

It may not be a suitable strategy in some urban / suburban locations.

 

Some areas of the world cannot support the concept of a basement, due to the water table depth. Most of the southern USA doesn't bother, oftentimes because of that reason. And because, unlike up north, where you almost NEED a basement (for running water service, if nothing else), it simply doesn't get cold enough. So instead of going down, I'd go OVER.
My house, in Texas, I considered putting a decent sized shelter underground (I'm on top of a hill, so the water table shouldn't be a worry), right outside the master bedroom (on the back of the house). That would, of course, be considered a storm shelter, down there. Then build a deck, on top of it (helps to disguise it), and an opening out in the yard (where the yard slopes down). Inside the bedroom, I planned on replacing one of the windows with a French door, and if possible, have a hole cut in the slab, to allow an inside doorway into the shelter, with a lift-up hatch in the floor/slab. Easily concealable with a rug, and if you DO have to shelter from a tornadic storm, you're not forced to go outside, to get into the shelter.
How bad can the water table problem be? Up in Oklahoma, during a spring that gave them an extraordinary amount of rain, some of the storm shelters, which are either nothing more than a blow molded plastic bubble, or welded metal, buried in the ground, ended up being pushed back up above ground, by the rising water table! Yep! Floated them, just like a ship!!
So that's a definite consideration, before you go DOWN.....make sure you can divert any drained water, to prevent your hidey hole from becoming an oops, dammit!

 

I have given this some thought over the years. I have a 40x60 ft. metal barn that sits on a reinforced concrete slab that is over a foot thick. The barn was over-built so that it could accommodate semi-tractors and farm equipment. I have thought that I might "cut" a hole in the slab and tunnel underneath the concrete. Tunneling by hand would be hard, as the gravel and chert sub-foundation is gonna be as hard as the concrete slab itself. However, if I could use a "little" black powder for blasting, or better still, a pressure washer to cut through the material and a pump to remove the wastewater it would be easier. Just a narrow straight tunnel with nooks along the walls for people, supplies, sleeping, etc., and LOTS of supports! I've got the tools and I have the knowledge (I have watched the movie "The Great Escape" about a dozen times). The barn does have a VERY large set of doors in one end and is a little drafty, but I'm sure that we could tighten things up a bit. It will never be air-tight, but then I don't want it to be. We have electricity (utility hook-up, generators, solar and maybe wind), heat (electric, propane and woodstove), water (utility hook-up and well), and a simple septic system for sanitation. Give me 24 hours to prepare and I'm good, give me 48 hours and I'm great, any more than that and I'm unbeatable!

 

I've thought of putting about a 3 ft pipe , leading away from and under my home ,, and I could have it dump out at the creek bank a hundred foot or so from the house ,, but I'd have to get a water tight door to stop the water whe the creek rises .

 

unless you have a labor saving dirt removal system - like a motorized conveyor into a trailer or dump truck >>> the actual digging is the easiest part of the excavation ....

I extended my existing basement into the crawlspace - 3 foot deep on average - dig out a 4' X 4' section - carry out the sightly bigger "yard" of clay mix in 5 gallon buckets - load it up and take it out to the landfill - pour a 4-5" thick concrete bag mix floor - move onto the next 4' X 4' .....

with my soil mix it was eaziest to expose a wall area - let it dry for a few days - 6">>10" of the now drier mix would just peel away from the wall face -

 

@Wildbilly
"However, if I could use a "little" black powder for blasting, or better still, a pressure washer to cut through the material and a pump to remove the wastewater it would be easier."

Last summer here in Arizona I dug some trenches for conduit. The ground in AZ, if you're unfamiliar with it, is nearly as hard as concrete in most places. Impossible to dig by hand, and I didn't want to rent or buy a backhoe (yet), so I purchased an electric jackhammer.

There are a number of attachments you can get. One is a small spade about 6" across that I used to break up the hard stuff. If I ran into rocks, the jackhammer simply sheared them off even with the side of the trench, so that removing the whole rock wasn't necessary.

The Jackhammer itself weighs 35 pounds, and the attachments another 6 or 7. So by the end of the day you know you've worked. I'm coming up on 70 here pretty fast and could only manage 4 or 5 hours a day.

 

Hard to go under a existing structure Doable but not easy and you have to reinforce the slab assuming it has a slab or it will be crack city. The Rat Tunnel as Mrs Krap calls it was easy but it went in before the slab was poured. If I was going to do it with a existing slab I would follow Altoids advice sort of Cut the slab, bust it up and cart it out, Dig the dirt out and cart it out, put the tunnel structure in and repour the removed slab. Very few places here that I can do underground structures so my existing underground structure is the 150 feet away from the house, no springs or ground water on that top until about 20 feet down. Water under the house at 6 feet down. 1' of 6" rip rap, 2' of 3" compressed rock and 4" of CA6 under the slab to compensate for that ground water and make a solid foundation. I would suggest off setting the bunker at least 10'away from the house with a short tunnel or a above ground entrance right out of the back door. 10' because you don't want to disturb the virgin soil around the slab anymore than you have to. Friend did theirs as a full basement with a staircase down from the back of the house to a hallway to the offset basement. Did a concrete and steel ceiling and used the dirt from the basement to raise the backyard up and put a couple of feet of dirt on top of the basement roof. Would never guess you were standing on top of a 1000sqft underground structure. That was expensive though and if I am remembering right cost in the neighborhood of $60,000 in 2020. They are a couple of miles off of the Aquifer I sit right on top of so they don't have the ground water issues to deal with that I do.

Zoning/Permits/Codes are a consideration for most. We have none of that nonsense where I am at other than if you drill a well or put in a septic system you are supposed to get permitted and inspected by the health department and follow the State Codes. Pretty much no one complies and only a handful of people care. But if you are in a zoning/permit/code local Government up your back side area............

Very first step if you DO NOT KNOW, I would suggest coring the ground down about 15-20 feet and learning what you have to work with down there because it can ruin your plans real quick if you are sitting on a shallow pocket of water. Neighbor up the road rented a track hoe and dug a real nice hole for his foundation and basement for his new dream home and it became a half filled mud swimming pool overnight. I liked his mud hole and bought his 20 acres at a fair price when he decided that if he couldn't build the house he wanted anywhere on the 20 then he had no use for it. Good hay field and pasture! and that is about all it is good for. Knowing what is under your land is as important as knowing what is on your land.

See that a lot around here with septic tanks. The installer does not fill them with water and the next heavy rain they float to the surface....... Even the concrete boxes if not water filled work their way up and out. Always a bad idea to have Billy and Bubba's Septic service or excavating install your storm shelter or septic tank! Or install it your self and not know to fill the tanks and put a good amount of dirt or other weight ontop of the shelter.

 

But if you cut the slab and repour it, there will always be a visible sign that the work has been done and the first question will be WHY?  Part of the reason for building an underground bunker is that it would be hidden and therefore secret!  Also, there is more protection underground.
My back-up plan is to design and have a prefab bunker stored in the barn, and that way I could quickly construct a bunker ON the concrete slab rather than under it. Wooden forms that bolt together that can be filled with soil, sand or gravel would make up the walls, but the roof is giving me fits...and that is when I go back to the tunnel idea!

 

We put stress cuts in every slab around here ...........

 

But inside the building and only in that one area?

 

I'm happy that water table concerns came up early. I hit ground water at 18" at the beach. It's the reason family cemeteries are located inland.

I have trouble getting past the first step for any underground bunker. Locate it on elevated, well drained land. I've scouted some, but it's three hours drive from here.

 

There's a procedure inground swimming pool builders use to divert the ground water around and below the pool to keep it in ground and not floating out, You may want to look into this?

 

My home sits on sand. Easy to dig, but tends to collapse.

 

Carpet, Tile, laminate, hardwood floor coverings. Or a partition wall built on top of the seam......... We might be primitives but we do use floor coverings and walls Concrete slabs are kind of on the ugly side of the spectrum!

 

I would recommend against putting all of the bunker under your house.

 

There may or may not be a 'Root Cellar' under the front porch of the house I own. Seems my grandparents back in the late 60s thought that a 'Root Cellar' should have a hookup for toilet and small sink along with room for bunk beds i mean 'storage shelves' would be a good idea. Walls, ceiling are reinforced concrete and the door is strangely heavy for it's size almost like someone thought lead sheeting was a good idea.