From Wikipedia, the free encyclopedia

Building a sandbag dike along the Skagit River in anticipation of a flood, October 2003.

A sandbag is a burlap or plastic mesh bag filled with sand or soil, in an amount that a person can carry from where it is filled, to where it will be used. They are used in a number of applications, including flood control, military fortifications, and ballast.

They are used for water control during emergencies when rivers are threatening to flood outside their normal channel, or if a levee or dike is damaged. However, sandbags often are used in non-emergency situations (or after the emergency has passed) as the foundation for new (or just higher) levees, or other water-control structures. Many people find sandbags ineffective at holding back water during floods, as neither sand nor dirt will actually stop water from flowing through it, and finer materials such as clay will often run out of the bag's wideley-spaced threads.

In military science, sandbags are also used for field fortifications, or as a temporary protective measure for civilian structures. Because burlap and soil are very inexpensive, quite thick protective structures can be erected cheaply. The friction generated between moving soil or sand grains, and the multiple tiny air gaps, also make sandbags quite efficient dissipators of explosive blast. Sandbags used in fortification generally have dimensions carefully calculated so that the finished bags can be interlocked like brickwork, and are of such a weight as to maximise the efficiency of manual labour in filling and laying them. They may be laid in excavated defences as revetment, or as free-standing walls above ground where excavations are impractical. Plain burlap sandbags deteriorate fairly quickly, so if it is anticipated that a sandbag structure will remain in place for a long time, it may be painted with a portland cement slurry to reduce the effects of rot and abrasion. Cotton Ducking sandbags last considerably longer than burlap and therefore are used for long-term placement of sandbags. However, the vast majority of sandbags used by the US Military and for the prevention of flooding are made of circular woven polypropylene.

Sandbags are also used for disposable ballast in hot air balloons, and as counterweights for theatre sets.

Historically, sandbags have typically been filled manually by people wielding shovels, although machines able to fill bags at a much greater rate have been in use since the 1990s.

"Sandbag" can also refer to a crude weapon consisting of a small bag filled with sand for use as a cudgel typically by criminals, or to the act of striking a person on the head with such a weapon. This usage is obsolescent in normal speech, appearing mainly in legal codes. However the verb form is extended metaphorically in several slang expressions.

See also sandbagging.

In games and adversarial settings, to "sandbag" is to intentionally understate one's strength, with the intention of deceiving one's opponents into overreaching. The sandbagger can then reveal a hidden strength to take the opponent by surprise. The usage has been noted in Demolition Derby, when drivers refuse to be aggressive and/or pretend to have mechanical problems until the last two or three cars are running then their car will start running just fine and/or they become more aggressive; poker, in which a player with a strong hand bets small amounts to convince opponents to stay in the game, and in golf, where a "sandbagger" is someone who misrepresents his handicap to gain an advantage over other players. Similarly, "sandbagging" is also regularly used in law to refer to the process of concealing winning arguments for as long as possible, to prevent the opposing attorney from preparing effectively to counter them. Rules of evidence and procedure often require early disclosure of certain kinds of arguments to prevent unfair sandbagging.

Sandbags are also used in weight training.

Hesco bastion