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Building an Underground Bunker

Sep 29, 2017 0 comments
Building an Underground Bunker

The idea of owning a survival shelter is a popular one. I guess we all like the idea of being able to get out of Dodge to a place that's ready and waiting to us. In an emergency, such a place can mean the difference between life and death. Even if it doesn't, living in a place that's prepared and stocked is much easier than any other option you can think of.

While survival shelters can take on many styles, they basically break down into two groups: cabins and underground bunkers. I personally prefer the idea of having a cabin in the woods, but there are many people out there who like the idea of an underground bunker. There are things that a bunker can protect you from, which a cabin can't. Should a nuclear war ever take place, the bunker is going to win as being the place to be, hands down.

Of course, building an underground bunker is not an inexpensive undertaking. It's even worse trying to buy one from one of the companies that builds read-made ones. But if you're after security, they're hard to beat. The trick is in building one which is affordable, while still being effective.

Some people have succeeded in building their own. Other than excavating the hole in the ground, this really isn't all that unrealistic an option. While it may be difficult to do, building an underground bunker really isn't much harder than building any other sort of structure. You can save lots of money by doing it yourself, as well as end up with a design that's just like you want.

What You Don't Want to Do

Before talking about what to do, let me mention one common idea that you don't want to do. That's to buy a used shipping container and bury it underground. While a shipping container makes a fairly nice structure in the sense of being easy to work with, it's not designed for supporting the weight of the backfill. All the strength of a shipping container is in the corners. The roof and walls are only strong enough to hold in the merchandise being shipped.

The problem comes when you try to backfill the hole. For those that aren't familiar with construction terminology, that means filling the dirt back in, over and around the container. With the weak sides and roof, there's a chance that the weight of the soil alone will be enough to cause it to collapse. If the bulldozer that's doing the backfilling happens to drive over the container at all, it will surely collapse; and it's just about impossible to finish off the backfill without doing that.

About the only way that a shipping container can be used for an underground bunker is to add a protective shell around it. That raises the question of what the container is doing there. If you need a protective shell anyway, why not just build that and forego the container?

Picking a Location

It is theoretically possible to build an underground bunker anywhere. However, selecting a good location can make it easier to build and maintain. Both of these are important, especially when you consider some of the heavy equipment that might be needed, in order to build the bunker.

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Generally speaking, a hillside is better than flatlands, although the opposite seems to be the answer on the surface. The biggest advantage that a hillside gives you is that of drainage. If you build on flatlands, you're going to have to have a pump to get water out of the ground, so that it doesn't fill your bunker. Otherwise, a heavy rainfall could flood you out.

More than anything, you want to keep your bunker hidden. The idea is to be able to go in there and hide, waiting out any problems on the surface. If others know you are there, they could seek a means of attacking you. That's what you want to avoid.

The more remote your location, the less chance that someone will stumble on your bunker and wonder about it. So pick a location that nobody will expect. That way, you'll be less likely to have someone trying to find a way in or kill your family.

The other thing you want to consider is hiding your location. This is somewhat contradictory to the needs of getting heavy equipment in there to build with. The heavy equipment is easier to work with if you have an open field. But it will be easier to hide your bunker if it is in the woods. Obviously, you can't have solid woods all around, so you'll need to figure out some sort of compromise.

Possible Bunker Designs

If we leave out the shipping container, we are still left with a myriad of designs possible for making an effective underground bunker. Many people choose to use a metal culvert or tank for their bunker. The round shape makes it possible for the bunker's structure to support the weight of the overburden; and while it is not the easiest structure to turn into a living space, it is possible.

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The biggest complication in using a culvert or tank as an underground bunker, is that it provides a curved floor. While it is possible to walk on that curved floor, it's not easy. Your ankles will get tired after a while and there's always a chance of injury. The solution is to install a flat floor. The space under the floor can be used as storage.

One of the main things that make the idea of metal culvert or tanks attractive for underground bunkers is their relative availability. While not quite as available as shipping containers, you can find them. You can also find rectangular cement culverts, but they are not as common. Actually, it's easier to find the culvert material than the tanks; and any tank you find will have to be cleaned out from whatever chemicals it held before.

Another possibility is to build your bunker out of cement or a combination of cement and cinder blocks. Military and government bunkers are built in this way, mostly for the strength they provide. At the same time, you don't have to deal with the difficulties of arranging a circular living space.

Building a cement and cinder block bunker is much like building the same sort of building above ground. This is actually the most common building method in Mexico, as well as many other developing nations. It provides an inexpensive, flexible building method, which most people can accomplish on their own. That makes it a very attractive for building your own bunker. Instead of being stuck in a tube or stuck with the dimensions of a shipping container, you could build your bunker any size and shape you want. If I were to build an underground bunker, this is the method I'd choose.

Preparing the Site

The first step in building your bunker is, of course, designing it. You need to have a pretty good idea what you're going to do, before you start, especially when it comes to things like plumbing. Otherwise, you're going to find that you have to get underneath your bunker, after you've already built it. Just in case you weren't sure, that's more or less impossible to do.

So your design needs to take into consideration the overall configuration of the shelter, how you're going to divide up the area, entry and exit routes and plumbing. If you have that, as a minimum, the details can be worked out as you go, if necessary.

You'll need at least a backhoe to dig the hole for your bunker. Depending on the size, you might need more than a backhoe. Typically, this part is contracted out, so it's up to the contractor to know what they will need and bring the necessary equipment in. The dirt that comes out of the hole will either need to be carted off or piled somewhere. Some of it will be used as backfill and the rest can go over the shelter, making somewhat of a mound, be spread out or be carted off.

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The hole for your bunker will need to be deeper than the height of the bunker itself. You need to leave space for the overburden of dirt above, which will protect your bunker. You also need to have several inches of gravel below the shelter, to act as a drain bed. This is to keep water out of your bunker, by giving it a place to go, so that it can be removed from the ground. If the bunker is built into the side of a hill, the dirt under the gravel bed can be sloped slightly downhill and drain pipes put from the downhill side, allowing the water to flow out onto the side of the hill. If the ground is flat, a sump will need to be added, along with a sump pump to remove excess water.

The other thing that is usually added below the bunker is the septic tank. This can be problematic. Bunkers typically have small septic tanks, which are fine if you are going to only use them for a short period of time. But if you end up having to spend a year in them, the septic tank may not be big enough.

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A better option is to put the septic tank a little bit off to the side of the bunker itself, so that you can have an access pipe for pumping it out. If planned out correctly, this access pipe can run up the side of the bunker, which will support it during the backfill operation. At the surface, the access pipe can be capped, preventing it from fouling the air.

The septic system should also have a leech field, like a normal septic tank does. While the greater depth will make the leech field less efficient, it will still be able to help the fluids in the septic tank drain off and evaporate. If the bunker is being built into the side of a hill, the leech field can be downhill of the bunker and septic tank. This allows it to be at the standard depth of 18 to 30 inches deep, increasing its efficiency. Just make sure that it runs across the fall line of the hill, so that the water flows into the whole leech field.

The other thing you should consider burying is your water supply tank. While it is possible to leave this above ground, that makes it much easier to find the bunker. It is also much more susceptible to tampering, if it is left where it is easy to get to. On the other hand, since you are excavating a hole anyway, adding a little more space for your water tank isn't a big deal.

Most water tanks can withstand burying, without problem. But don't take that for granted. Before buying a water tank or even fitting it into your plans, make sure that it can hold up under the weight of the overburden, with a wide leeway. You can't have the tank collapsing just because someone walks over it.

Keep in mind that you'll need some sort of water pump for moving the water from your tank to your shelter. You need that pump to be accessible, whether it is from the surface or from your bunker. That way, you can replace or repair it if needed. You'll also need some sort of locking cap and pipe to use as a water inlet for filling your tank.

The one thing you're going to have to have above ground, besides the entry and access to the various fill and drain points, is electrical power, assuming that you're going to use electrical power. That means installing solar panels or a wind turbine on the surface and connecting them to your bunker. This is unfortunately going to be visible to anyone who comes by. Both are hard to hide and hiding them tends to reduce their power production capability.

Building a Tubular Bunker

A tubular bunker is probably the easiest to make, either using a used storage tank or a piece of round culvert. If it is used, it will need to be cleaned out thoroughly and the inside checked for rust; then the inside surface needs to be sealed to protect the occupants from any chemicals.

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But you can't just bury that tank or culvert and call it good. Considerable modifications need to be done. These are much easier to accomplish while it is above ground, perhaps working on it in your driveway, before transporting it to its ultimate destination. Of course, working on it in your driveway pretty much ends any idea of OPSEC. Your neighbors will know what you are doing.

If you are using a culvert, the ends will need to be capped. It's easier to cap just one end before finishing it out, leaving the other end to go on after the inside is finished. That way, you'll have a large opening to bring materials through.

Entry and exit points need to be added. These are typically installed on center in the ends. The main entry and exit will be at one end, by the main living quarters. The emergency exist, which is usually smaller, is at the other end, in the master bedroom. Building the outer part of the exit and entry out of corrugated pipe, should be the last thing you do.

The first thing is to install a floor, so that you have a level surface to walk on. Don't make the floor any wider than you have to, as the wider it is, the more vertical height you take up too. However, that vertical height converts into extra storage space below the floor.

Once the floor is in place, the interior can be partitioned into rooms or living areas and the furniture can be built in. This type of bunker requires built-in furniture, as there is not enough flat floor space for it to sit on. Basically, all the furniture has to be custom built, making this a rather involved project. However, that built-in furniture makes for very efficient use of your available space, just like in a camper.

You can make your bunker as fancy as you like, but doing things like adding paneling to the walls does mean that you are giving up a little bit of space. You'll have to decide whether it's worth losing that space for nice walls, or not.

All piercings of the shell should be done early on in the build process. These include:

  • Entry
  • Emergency exit
  • Water inlet from tank
  • Sewage
  • Electrical power inlet
  • Air circulation (inlet and outlet)
  • Chimney (for stove or heater)

To avoid damage, only put a short stub sticking out for all of these connection points. The longer pipe or connection can be added on site, either just before lowering the bunker into the ground or once it is there, but before backfilling.

Building a Cinder Block and Cement Bunker

If I were to build an underground bunker, this is the way that I would go. Start by putting in the septic tank and gravel bed, using large sized gravel or even crushed rock. Pieces 2 to 4 inches are ideal. Put in any plumbing necessary, burying it in the gravel.

With the gravel bed and plumbing in place, you can pour a cement slab. This is going to act as the floor and foundation. You really don't need a footer for the bunker, as the whole floor will be acting as a foundation. A four inch slap, made with rebar or remesh should be sufficient. The outer dimensions of the slab should exactly match those of your shelter. You don't need any extra hanging out.

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The walls are built out of cinder block, which is fairly easy to work with. If you've ever seen anyone build a brick wall, it's essentially the same, although usually not as neat. Keep a consistent thickness of 1/2 inch of mortar, so that your walls stay even. Build it up to the height you need.

To make support columns for the roof, all you need to do is fill one vertical row of cement blocks with concrete. Before doing this though, run your electrical wiring, if you want to hide it in the wall. Personally, I'd forego the hidden wiring, even though it looks better, just to have the capability of modifying it easily, if necessary. Electrical wiring in cinder block walls is typically run in flexible plastic conduit. With the wiring in place, you can pour your columns.

There are two ways to go about the roof of your bunker. One is to use corrugated steel over a wood structure and the other is to pour a cement slab over corrugated steel. Either way, you need the corrugated steel.

If you are going to use corrugated steel, without the cement slab, your best bet is to build an arched roof structure, down the length of the bunker. Be sure to anchor it well to the walls. The corrugated steel then goes over the structure, with the corrugation running lengthwise. This will give the roof the strength needed to carry the weight of the overburden. But it may not be strong enough to support a vehicle.

For a cement roof, you'll need to install the corrugated steel running crosswise to the bunker. This way, the corrugations themselves act like a small beam, giving it strength. The steel will need to be supported by 2"x 4" studs for the pour, putting them every 18" to 24". Remesh is used to strengthen the concrete and another four inch slab is poured. Once the concrete sets, the 2"x 4" supports can be removed, as the roof will be self-supporting, as well as being strong enough to support the overburden.

With this sort of construction, the entryway is usually a normal industrial metal door, set into one of the walls. A cement stairwell with cinder block walls has to be built down from the surface to this entryway. While not well hidden, this entry will be hard to breach.

Another option, if building on a hillside, is to actually allow the wall of the bunker to protrude from the hillside and put the doorway in that wall. This makes it easy to enter, while still offering protection. Building an additional cement wall in front of the doorway makes it hard for anyone to use a battering ram on the door, as well as providing a fighting position that can be used, before retreating inside the bunker.

I like this option of having a cement wall fighting position in front of the doorway, as it makes the overall security of the bunker better. When leaving the bunker, it is possible to stop a moment in this protected area and scan the countryside around, looking for danger. If any is encountered, you are in a protected place to fight from. About the only way anyone could get to you unseen would be from above. That problem could be mitigated with cameras or by building in such a way that approach from above is difficult.

Some Final Considerations

The idea of a bunker isn't so much to have a place to fight from, as to have a place to hide. By and large, bunkers are hard to fight from, unless they have been designed as military bunkers, such as those built by the Germans along the Normandy beach in France, during World War II. Those weren't comfortable, per se, as they were designed to be fighting positions. That's different than what you're doing.

When in a bunker, you are essentially blind to any enemies. This problem can be alleviated somewhat with cameras, but you will need electrical power for the cameras. Cameras can also be taken out by any enemy, eliminating your eyes topside.

The greatest weakness on any bunker is the air handling system. Bunkers, by their very nature, don't have any natural airflow. So, it's necessary to install some sort of air handling system to bring in fresh air from the outside and remove stale air from the inside. The problem is, everyone knows this and can find your air intake. When they do, all they have to do is attach a vehicle exhaust and they can smoke you out.

There are ways of handling this. The first is to make your air intake come from far enough away, that it's hard to find. This requires a larger diameter pipe for your air intake, but that's really not a problem. Then, place the outlet in an area which is hard to find and even harder to get a vehicle to. That will reduce the chances of using car exhaust against you. They could still try smoke, or plugging the inlet, but they couldn't poison you.

Filtering the incoming air helps some, but only in a limited way. Most air filters aren't designed to catch carbon monoxide. You would need a pretty sophisticated air filtration system to eliminate carbon monoxide or take care of excessive carbon dioxide.

However, another option exists. That is to fool anyone who would try to mess with your air handling system by having two or more air inlets, with the capability of closing them off or opening them up by remote control. That way, if they find one, you can switch to an alternate. Few people would expect this, but instead be waiting for you to pop out the entryway.

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One other recommendation for protecting your air inside the bunker is to keep an air tank inside, such as scuba divers would use. Fill it with pure oxygen, so that in an emergency, you have oxygen that you can use to keep yourself alive, while you wait out any attackers.

While the main idea behind a bunker is to be able to hide from any attackers and wait them out, there is always the possibility that you won't be able to do that. In that case, you need some means of fighting.

Your most vulnerable moment would be leaving the exit of the bunker. All any attacker would have to do is wait for that moment and shoot you. Building in some sort of automated defensive system, such as something like flamethrowers around the entry would be somewhat helpful for this, but not foolproof. There would always be the possibility that they could just wait outside the range of the flamethrowers.

Building a wall around the entryway, so that you could have some protection from fire while leaving the door would help. But that means that the entryway won't be well hidden. So, realize that whatever you do, it's not going to be a perfect solution. You're going to have to make some compromises, one way or another. Think through your defensive strategy as part of your design process; that's the only way you can handle it.

Dave Steen

About The Author: Dave is a 58 year old survivalist; father of three; with over 40 years of survival experience. He started young, learning survival the hard way, in the school of hard knocks. Now, after years of study, he's gray-haired and slightly overweight. That hasn't dimmed his interest in survival though. If anything, Dave has a greater commitment to survival than ever, so that he can protect his family. Click Here To Read More About Dave


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