Sandbag

A sandbag or dirtbag is a bag or sack made of hessian (burlap), polypropylene or other sturdy materials that is filled with sand or soil and used for such purposes as flood control, military fortification in trenches and bunkers, shielding glass windows in war zones, ballast, counterweight, and in other applications requiring mobile fortification, such as adding improvised additional protection to armored vehicles or tanks.

Without proper training, sandbag walls can be constructed improperly causing them to fail at a lower height than expected, when used in flood-control purposes.

[1] In a military context, improvised up-armouring of tanks or armored personnel carriers with sandbags is not effective against cannons (though it may offer protection against some small arms).

Each bag must be set consecutively with the tightly packed bottom slightly overlapping the previously placed sandbag.

Subsequent layers of bags should be offset by 1/2 the length of a sandbag to eliminate voids and improve the wall seal.

The friction created by moving soil or sand grains and tiny air gaps makes sandbags an efficient dissipator of explosive blast.

[5][6] These dimensions, and the weight of sand a bag this size can hold, allow for the construction of an interlocking wall like brickwork.

However, the vast majority of sandbags used by modern military and for flood prevention are made of circular woven polypropylene.

During World War II in Great Britain, some aircraft revetments and pillboxes were made from concrete filled sandbags, again these have lasted well.

For example, the rebellious Mughal governor Mirza Jani Beg used improvised sandbags made out of boat sails to construct a makeshift fort at Unarpur, Sindh, in 1592.

Nathanael Greene was familiar enough with the fortification technique to equip his troops with hooks to pull down the sandbag and log walls when they stormed the Star Redoubt in Ninety Six, South Carolina.

Large bags of sand are often used in flood control and making temporary patches to water barriers.

If ever stuck, sand can be removed and placed directly onto the slippery surface thereby providing greatly improved traction.

Sandbags are often used to temporarily stabilize soil from erosion, such as oceanfront structures whose foundations have been undermined by heavy waves.