Bunker
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A bunker is a defensive warfare fortification to protect oneself.
- A bunker is also:
- a hazard, usually filled with sand, on a golf course.
- a storage bin or tank for a bulk product, such as coal, fuel oil or wood
Albania_bunkers.jpg
Bunkers are mostly below ground, while a blockhouse is mostly above ground level. They were used extensively in World War I and World War II. In the 1950s, the bunker became part of Americana culture. A famous bunker is the North American Aerospace Defense Command (NORAD). Some installations are giant underground complexes. The Soviet Union maintained huge bunkers during the Cold War. In Albania, Enver Hoxha littered the small country with 500,000 - 700,000 bunkers.
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Bunkers as part of a trench system
Another type of bunker or blockhouse is a little concrete post, partly dug into the ground, which is usually a part of a trench system. Such bunkers give the defending soldiers better protection than the open trench and also include top protection against aerial attack (grenades, mortar shells). The front bunker of a trench system usually includes machine guns or mortars and form a domainant shooting post. The Rear bunkers are usually used as command posts, for storage and as field hospitals to attend to wounded soldiers.
Pillbox
Dug-in guard posts (with shooting slights) made from concrete are also known as "pillboxes". Some of the pillboxes have camouflage in order to provide the guards better protection and the element of surprise. They may be part of a trench system, or with other pillboxes form an interlocking line of defence by providing covering fire to each other, or they may be placed to guard strategic structures such as bridges and jetties.
Industrial bunker
Typical industrial bunkers include mining sites, food storage areas, dumps for materials, and sometimes living quarters.
Design of Blast-resisting Bunkers
Bunkers deflect the blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. While frame buildings collapse from as little as 3 psia of overpressure, bunkers are regularly constructed to survive several hundred psia. Since a shockwave's overpressure falls as the square of the distance from a bomb, this substantially decreases the likelihood that a bomb can harm the structure.
The basic plan is to provide a structure that is very strong in compression. The most common purpose-built structure is a buried, steel-reinforced concrete vault or arch. Most expedient blast shelters are civil engineering structures that contain large buried tubes or pipes such as sewage or rapid transit tunnels. Improvised purpose-built blast shelters normally use earthen arches or vaults. To form these, a narrow (1-2 metre) flexible tent of thin wood is placed in a deep trench (usually the apex is below grade), and then covered with cloth or plastic, and then covered with 1-2 meters of tamped earth.
Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shockwave passes, and prompt radiation. Usually these features are easy to provide. The overburden and structure provide substantial radiation shielding, and the negative pressure is usually only 1/3 of the overpressure.
The doors must be at least as strong as the walls. The usual design is a trap-door, to minimize the size and expense. To reduce the weight, the door is normally constructed of steel, with a fitted steel lintel and frame. Very thick wood also serves, and is more resistant to fire because it chars rather than melts. If the door is on the surface and will be exposed to the blast wave, the edge of the door is normally counter-sunk in the frame so that the blast wave or a reflection cannot lift the edge. A bunker must have two doors. Normally one door is convenient, and the other is strong. Door shafts may double as ventilation shafts to reduce the digging.
A large ground shock can move the walls of a bunker several centimeters in a few milliseconds. Bunkers designed for large ground shocks must have sprung internal buildings, hammocks, or bean-bag chairs to protect inhabitants from the walls and floors.
Earth is an excellent insulator. In bunkers inhabited for prolonged periods, large amounts of ventilation or air-conditioning must be provided in order to prevent heat prostration. In bunkers designed for war-time use, manually-operated ventilators must be provided because supplies of electricity or gas are unreliable. One of the most efficient manual ventilator designs is the "Kearny air pump".
Ventilation openings in a bunker must be protected by blast valves. A blast valve is closed by a shock wave, but otherwise remains open. One form of expedient blast valve are tire-treads nailed or bolted to frames strong-enough to resist the maximum overpressure.
If a bunker is in a built-up area, it may include water-cooling or an immersion tub and breathing tubes to protect inhabitants from fire storms.
Bunkers must also protect the inhabitants from normal weather, including rain, summer heat and winter cold. A normal form of rainproofing is to place plastic film on the bunker's main structure before burying it. Thick (5-mil), inexpensive polyethylene film serves quite well, because the overburden protects it from degradation by wind and sunlight.
Experts in preparedness (Such as Cresson Kearny, see below) for war recommend purchasing and stockpiling the materials for an expedient blast or fallout shelter, and then constructing it only if war appears very likely. In real wars, such materials have almost immediately become unavailable as emergency construction depleted stocks. The storage needed is modest, and the materials are inexpensive in peacetime, and easy to inspect and maintain.
When a house is purpose-built with a bunker, the normal location is a reinforced below-grade bathroom with large cabinets.
Some vendors provide true bunkers engineered to provide good protection to individual families at modest cost. One common design approach uses fiber-reinforced plastic shells. Compressive protection may be provided by inexpensive earth arching. The overburden is designed to shield from radiation. To prevent the shelter from floating to the surface in high groundwater, some designs have a skirt held-down with the overburden. A properly designed, properly installed home shelter does not become a sinkhole in the lawn.
See also
- Flak Tower
- Führerbunker
- bunker buster, nuclear bunker buster
- fallout shelter
- air raid shelter
- World War II concrete bunker fortifications Maginot Line, Siegfried Line, Atlantic Wall GHQ Line,
References
Kearny, Cresson, "Nuclear War Survival Skills""
External links
- British World War 2 Pillboxes (http://www.pillboxesuk.co.uk)
- UK Heritage: Pillboxes - "miniature modern castles" (http://www.heritage.me.uk/misc/pillboxes.htm)
- Subterranea Britannica (http://www.subbrit.org.uk/rsg/index.shtml) Information on Cold War-era underground structures in Britain
- British World War 2 Pillboxes in Malta (http://www.educ.um.edu.mt/militarymalta/html/pillboxes.html)
- German Fortifications Observed in Italy (WWII intelligence report) (http://www.lonesentry.com/articles/fortifications/index.html)
- Image of one of the hochbunker of Vienna
- Image of the hochbunker of Trier
- Information on Australian World War 2 Fortifications (http://www.tunnelrats.org.au)de:Bunker (Militär)