Trench

For other uses of the word, seeTrench (disambiguation).

Atrenchis a type ofexcavationor depression in the ground that is generally deeper than it is wide (as opposed to aswaleor abar ditch), and narrow compared with its length (as opposed to a simpleholeorpit).

Agas mainbeing laid in a trench

Ingeology,trenches result fromerosionby rivers or by geological movement oftectonic plates.Incivil engineering,trenches are often created to install undergroundutilitiessuch asgas,water,powerandcommunicationlines. Inconstruction,trenches are dug for foundations of buildings, retaining walls and dams, and forcut-and-coverconstruction of tunnels. Inarchaeology,the "trench method" is used for searching andexcavatingancientruinsor to dig intostrataof sedimented material. Ingeotechnical engineering,trench investigations locate faults and investigate deep soil properties. Intrench warfare,soldiers occupy trenches to protect them against weapons fire and artillery.

Trenches are dug using manual tools such asshovelandpickaxeor heavy equipment such asbackhoe,trencher,andexcavator.

For deep trenches, the instability of steep earthen walls requires engineering and safety techniques such asshoring.Trenches are usually considered temporary structures that are backfilled withsoilafter construction or abandoned after use. Some trenches are stabilized using durable materials such asconcreteto create open passages such ascanaland sunken roadways.

Geology

Depiction of thetopographyof thePuerto Rico Trench,the deepest part of the Atlantic Ocean

Some trenches are created as a result oferosionby running water or byglaciers(which may have long since disappeared). Others, such asrift valleysoroceanic trenches,are created by geological movement oftectonic plates.Some oceanic trenches include theMariana Trenchand theAleutian Trench.The former geoform is relatively deep (approximately 10 kilometres (6.2 mi)), linear and narrow, and is formed byplate subductionwhen plates converge.

Civil engineering

See also:Utility tunnel

Automated trench digging on a street in Baku

In thecivil engineeringfields of construction and maintenance of infrastructure, trenches play a major role. They are used for installation of underground infrastructure or utilities (such asgas mains,water mains,communicationlines andpipelines) that would be obstructive or easily damaged if placed above ground. Trenches are needed later for access to these installations for service. They may be created to search for pipes and other infrastructure whose exact location is no longer known ( "search trench" or "search slit" ). Finally, trenches may be created as the first step of creating afoundation wall.Trench shoringis often used in trenchworks to protect workers and stabilise the steep walls.

An alternative to digging trenches is to create autility tunnel.Such a tunnel may be dug byboringor by using a trench forcut-and-coverconstruction. The advantages of utility tunnels are the reduction of maintenance manholes, one-time relocation, and less excavation and repair, compared with separate cable ducts for each service. When they are well mapped, they also allow rapid access to all utilities without having to dig access trenches or resort to confused and often inaccurate utility maps.

An important advantage to placing utilities underground is public safety. Underground power lines, whether in common or separate channels, prevent downed utility cables from blocking roads, thus speeding emergency access after natural disasters such asearthquakes,hurricanes, and tsunamis.

In some cases, a large trench is dug and deliberately preserved (not filled in), often for transport purposes. This is typically done to install depressedmotorways,openrailway cuttings,orcanals.However, these large, permanent trenches are significant barriers to other forms of travel, and often becomede factoboundaries between neighborhoods or other spaces.

Military engineering

Main article:Trench warfare

Trenches have often been dug for military purposes. In the pre-firearmera, they were mainly a type of hindrance to an attacker of a fortified location, such as themoataround acastle(this is technically called aditch). An early example of this can be seen in theBattle of the Trench,areligious war,one of the earlybattlesfought byMuhammad.

With the advent of accurate firearms, trenches were used to shelter troops. Trench warfare and tactics evolved further in theCrimean War,theAmerican Civil WarandWorld War I,until systems of extensive main trenches, backup trenches (in case the first lines were overrun) and communication trenches often stretched dozens of kilometres along a front without interruption, and some kilometres further back from the front line. The area of land between trenches in trench warfare is known as "No Man's Land"because it often offers no protection from enemy fire. AfterWW1had concluded, the trench became a symbol ofWW1and its horrors.

Gallery

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  Allied troops entrenched in theBattle of Tuyutí.
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  Soldiers in a trench during theGallipoli Campaignof World War I.
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  TheBoertrench at theBattle of Magersfonteincontributed to the surprise defeat of the Highland Brigade on 11 December 1899 during theSecond Boer War.
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  Soldiers in a trench on the Western Front inWorld War Iin winter.
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  A Ukrainian soldier, equipped with ananti-drone gun,in a trench during the2022 Russian invasion of Ukraine.

Archaeology

Archaeological trench on an English farm site

Trenches are used for searching andexcavatingancientruinsor to dig intostrataof sedimented material to get a sideways (layered) view of the deposits – with a hope of being able to place found objects or materials in a chronological order. The advantage of this method is that it destroys only a small part of the site (those areas where the trenches, often arranged in a grid pattern, are located). However, this method also has the disadvantage of only revealing small slices of the whole volume, and modern archeological digs usually employcombination methods.

Safety

Trenches that are deeper than about 1.5mpresent safety risks arising from their steep walls and confined space. These risks are similar those from pits or any steep-walled excavations. The risks include falling, injury fromcave-in(wall collapse), inability to escape the trench, drowning andasphyxiation.

• Fallinginto the trench. Mitigation methods include barriers such as railings or fencing.
• Injury from cave-in,meaning collapse of a steep wall. Mitigation includes construction of sloped walls (sloped trench) or stepped walls (benched trench). For vertical walls,trench shoringstabilizes the walls, andtrench shieldingprovides a barrier against collapsed material. The risk of cave-in increases fromsurcharge load,which is any weight placed outside the trench near its edge. These loads include thespoil pile(soil excavated from the trench) or heavy equipment. These add extra stress to the walls of the trench.
• Inability to escapethe trench because of steep and unstable walls, which may be difficult to climb. Ladders, stairs, or ramps allow exit.Cranesmay assist rescue.
• Drowningin water or mud that has accumulated in the trench from rain, seepage, or leaking water pipes.
• Asphyxiation, poisoning, fire and explosionfrom gasses that are denser than air that have settled in a trench. These may come from nearby industrial processing of these gasses, intentional use within the trench, or leakage from nearby plumbing. These present anasphyxiationhazard and may also be toxic. Burnable gasses such asnatural gaspresent a fire and explosion risk. Oxidizers such as pure oxygen increase the risk of fire from other fuels present in the trench. Gasses such as purenitrogenandnatural gashave densities similar to pure air but are denser when cold, for example when they have evaporated from liquid form, and may creep along the ground and fill the trench. Ventilation fans andductsreduce the risk.Oxygensensors and other gas sensors detect the danger; alarms from the sensors can warn the occupants.

See also

• Abyssal plain
• Cut (earthmoving)
• Cut and fill
• Ditch
• Gully
• Sunken lane#Erosion
• Trench(album)
• Trench coat
• Trench fever
• Trench foot
• Trench mouth
• Trench warfare
• Tunnel
• Tunnel warfare
• Underground city
• Underground living
• Utility tunnel

External links

• Trenching and Excavation(aNIOSHSafety and Health Topic,Centers for Disease Control and Prevention)
• Trench Safety Awareness(aNIOSHPublication,Centers for Disease Control and Prevention)