I have been researching the Lower-Cost alternatives.....None are really low cost.
There are two methods that could be done a lot less expensively than what has been list here.
1. Concrete or galvanized pipe, the BIG kind. This is not cheap, but you could bury it 100 feet down. Build out is a bit more complex, requiring no real errors. Also really requires big iron to install. Shipping cost is going to hurt. All heavy / out-sized loads.
2. Shipping containers, but with a few twists..... I will explain.
Shipping containers are designed to have all of the load sitting on the floor of the container, and properly distributed. That load is then spanned to the four corners, and longitudinal bottom side rails. The corners use steel vertical posts, and corner shoes. This is how the stacking works. In theory, and in practice, you can stack a lot of dead weight in this way.
When you look at using these shipping containers for a buried shelter, all of the load ends up on the ceiling. Which is not at all reinforced. The result is that the walls buckle, the roof collapses, and you now have a pile of rusting scrap.
There are two ways around this problem.
1. Use one of the flatbed style platforms (Plats) that are designed to stack in the same way as the containers. The Plat is stacked on top of the container, and welded in place. Now you can pile up to 80,000 Lbs of dirt on top. By tying the Plat into a supplementary support system, you could reasonably double that load. I also believe that by using 20 foot containers instead of 40 foot containers, you effectively double your load carry capability. NOTE: You could also try to just cut down a standard shipping container and use the floor, The only real problem with this idea is that the containers come with a variety of floors. Since this is going to be buried, you would want to ensure that it is going to last. Wood will not cut it. I am still researching this for feasibility.
2. The Army had a FM (do not remember the number or exact title) where standard 8x10 COMEX containers would be inverted, floor side up. Then half buried, and sandbagged with up to four layers of sandbags covering. Worked for Comm set-ups, and other non-permanent installations.... We used to build pallet bunks in these along one wall. The same method could be applied to commercial shipping containers I believe. Still not sure of feasibility.
The steps for a really inexpensive shelter would be something like this:
- Pick a hill or other natural rise to build into as your site.
- Scoop out lots of dirt, creating a very level pad, with a very slight grade for incidental drainage. A front-loader / Backhoe would work well for this. You want to try to remain as close to grade level so as to avoid water issues.
- Then dig trenches for your foundations. I think that the ends do not need to be connected. So two 20 or 40 foot long trenches, 3-4 foot deep. Fill with concrete or rubble, then top with concrete. This is what needs to be level. Too much tilt will cause the entire container to warp under load.
- Place the container on the foundation, attach if you feel the need.
- Run any utilities to the container. Water, septic, power, comm. Whatever.
- Spray the ENTIRE surface of the container with insulating foam. Like GreatStuff. A 2-3 inch thick layer will provide good water repellence, and insulation of R13-R18. Not too bad.
- Install whatever supporting systems that you need. Cistern, Septic, etc.
- Create whatever type of entrance you want. Take care to ensure that the entrance is water tight and goon proof. Camo counts here.
- Bury. You may want to consider using a big, nasty, plastic sheet to cover the container with first, then bury. The Plastic sheet is just a small insurance policy. Not required.
If I am correct in all of my assumptions, math, chemistry, and other engineering, this should last a good 50-75 years with little maintenance. Temperature should be between 55-67 F. year round depending on how much dirt is surrounding the container.
Obviously, multiple containers could be married together to form a larger space, or additional storage. When taken in concert with adequate food, a good water source, and properly designed septic system, a family of 5 could survive in a 40 foot container for almost 16 months. Assuming that daily calorie intake is less than 2200, and most of the space is used for food.
BTW: I left out ventilation on purpose. In order to ensure a safe existence in some bad scenarios, a 10-25 PSI overpressure must be maintained. This is where a lot of care and time must be taken to ensure that it works, and continues to work. Also, air filtration becomes a real issue. This is the really hard issue to overcome. Designing and maintaining the air system.