Above Ground Culverted Concrete Fallout Shelters

In seeking to develop a low cost fallout shelter suitable for areas well removed from projected blast zones (as all shelters should be anyway!), and additionally suited for installation in a garden setting or in undeveloped farmland, woodland, etc., we have devised a concept based on using precast concrete culverts to form modular sections of a bunker that can be fitted out and obscured on-site.

But before explaining the concept further, consider:

1. To safely absorb gamma radiation from settling fallout by a factor of 32 (this is enough for most areas, except directly downwind of targets - see question 14 in our FAQs for required thicknesses for higher factors), traditional fallout shelters require a ceiling thickness of one foot of concrete (reinforced for steel to maintain structural integrity, not for additional shielding) plus strong supporting side walls of similar thickness (if located aboveground, or around eight inches if buried underground) along with appropriate foundations capable of bearing the considerable weight. Naturally this is expensive, has to be constructed on-site with specialist help, and requires the extensive and costly input of a structural engineer.
2. The very popular Atlas survival shelters (which we deem unsuitable to many parts of the UK and Ireland where high water tables are common and where transporting them along narrow rural roads would be impractical) rely on three foot of soil above their steel-fabricated structures to achieve the factor-32 gamma reduction; remember, gamma rays pass through steel much as they do through paper, so the steelwork is purely load-bearing beneath the soil with the Atlas shelters.

Returning to our concept, the thickness of the walls (and thereby the roofs and ceilings) of the concrete culverts is around eight inches, which represents 2/3 of the gamma radiation shielding that one foot thickness of concrete would provide.

If we then top that off with one foot of soil (i.e. 1/3 of the soil thickness Atlas shelters avail of for their gamma radiation protection), we attain the same gamma radiation protection as either one foot of steel-reinforced concrete or three foot of soil, that is, a factor-32 gamma reduction, and we achieve this without the expense of a steel-reinforced concrete structure or an Atlas shelter, thanks to the low cost of precast concrete culverts (obviously, thicker culvert walls will enable us to use even less soil).

So much for the shielding principle, what of the implementation?

The off-the-shelf precast concrete culverts we prefer for this concept are square or rectangular in cross-section (although circular ones are also available and have been successfully converted into glamping pods).

The culverts are tall enough and wide enough to create room-sized structures (some of the larger examples being typically used to form rural road bridges over narrow rivers, for instance) and can be joined end-to-end through the watertight spigot-and-socket design of their open ends.

This enables us to design an internal layout bespoke to the client's requirements, sealing off the open ends through concrete formwork undertaken on-site or through custom-made end sections.

They do require a flat concrete slab foundation for stability, which (assuming no high water table issues) should ideally be created several feet below the ground, with the excavated soil reused for landscaping the sides of the structure and for topping it off (although additional soil may need to be delivered to the site, depending on the extent of the excavation).

When all the landscaping work is performed, the redistributed soil can be seeded with grass and the entire structure takes on the appearance of a raised garden feature, atop which one could plant a flower garden or other innocuous elements designed to obscure its true purpose, while the shelter's access is likewise obscured through expedients we prefer not to reveal online.