Doc has some good stuff there, but there is a lot more to it then what he is mentioning above. You need to check the water tables, or your bunker will
unbury itself, leak, or deteriorate. Water is the biggest problem with building anything in the ground. If there is too much water around the
structure, it can actually enhance the shockwave of an explosion, and be a death trap rather than a safe haven. Underground structures that are not
correctly insulated will have problems with condensation constantly forming inside them, and will become a flooding, mildew ridden, mess of a fungus
farm. You need to have proper drainage and a footer, just like the basement in your house. It’s been awhile since I took basic architecture, but a
footer looks something like this:
If you do not know how to pour a footer or a slab, you will need to hire a professional to do it for you. It can be somewhat complex, and even I would
not attempt it.
Then you have the issue of just digging. You cannot simply dig a hole in the dirt then start building. The first good rain you have it will be a muddy
hole in the ground, and if you have not protected it right, it will collapse into itself (hopefully not while you’re in it). There are underground
lines, gas, electric, water, sewage, possibly even a drainage field for a septic tank or a sprinkler system. You hit a gas line, or knock out half
your neighborhoods power/water, you’re gon’na have some splaining to do to the authorities. You need to make sure that you are not building on an
easement. You need to ensure that you have the rights to dig past a certain depth, I.E. you have the mineral rights to the property. Believe it or
not, you do not own the ground beneath your feet all the way to the core of the earth any more then you own the sky above your house.
Then you need the permits to build, and you have to build it according to code. If you start building, and you do not have the right permits, they can
make you remove it. Nothing would suck more then to have the authorities show up, condemn the structure, and make you dig it back up, after you have
invested tens of thousands of dollars into building it. Professionals will not touch such a project with a 10 foot pole unless you have gotten the
proper permits. Again if you hire a professional, they should take care of all this for you.
BTW, building a fallout shelter is a whole different ball of wax then building an emergency/storm shelter. With fallout shelters you have to worry
about a lot of additional stuff that you can skip on a storm shelter. You need to worry about the shockwave, over pressurization, radiation shielding,
EMP shielding, and fallout filtration in the ventilation system. Really good shelters have multiple escape tunnels or “dig-outs”,
decontamination/lockout room(s), pressure release valves, multiple filtered ventilation systems, climate control (it’s going to get really hot and
stinky in there after a few weeks), generators with underground fuel storage tanks, underground water tanks and/or an electric/hand pumpable well,
septic tank with drainage field, hydraulic door clearance rams (to clear debris off the upper hatch), a seriously heavy duty door locking mechanism,
EMP shielding, and packed layers of different shielding material (so many feet of gravel, so many feet of packed sand, so many feet of clay, so many
feet of packed dirt, so many inches of lead plating, etc). It can be QUITE expensive to build such a place.
You can get some prefab ones that will allow you to skip on much of the self construction, but again they are not cheap:
Utah Sheltering Systems
Hardened Structures LLC