Trench

A trench is a type of excavation or depression in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole or pit).^[1]

In

Trenches are dug by use of manual tools such as shovels and pickaxes, or by heavy equipment such as backhoes, trenchers and excavators.

For deep trenches, the instability of steep earthen walls requires engineering and safety techniques such as shoring. Trenches are usually considered temporary structures to be backfilled with soil after construction, or abandoned after use. Some trenches are stabilized using durable materials such as concrete to create open passages such as canals and sunken roadways.

Geology

Some trenches are created as a result of erosion by running water or by glaciers (which may have long since disappeared). Others, such as rift valleys or oceanic trenches, are created by geological movement of tectonic plates. Some oceanic trenches include the Mariana Trench and the Aleutian Trench.^[2][3] The former geoform is relatively deep (approximately 10 kilometres (6.2 mi)), linear and narrow, and is formed by plate subduction when plates converge.^[4]

Civil engineering

In the

An alternative to digging trenches is to create a utility tunnel. Such a tunnel may be dug by boring or by using a trench for cut-and-cover construction. 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 as earthquakes, hurricanes, and tsunamis.^[5]

In some cases, a large trench is dug and deliberately preserved (not filled in), often for transport purposes. This is typically done to install depressed

Trenches have often been dug for military purposes. In the pre-firearm era, they were mainly a type of hindrance to an attacker of a fortified location, such as the moat around a castle (this is technically called a ditch). An early example of this can be seen in the Battle of the Trench, a religious war, one of the early battles fought by Muhammad.^[6]

With the advent of accurate firearms, trenches were used to shelter troops. Trench warfare and tactics evolved further in the Crimean War, the American Civil War and World 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. After WW1 had concluded, the trench became a symbol of WW1 and its horrors.

Gallery

• 
  Allied troops entrenched in the Battle of Tuyutí.
• 
  Soldiers in a trench during the

  Gallipoli Campaign

  of World War I.
• 
  The

  Boer trench at the Battle of Magersfontein contributed to the surprise defeat of the Highland Brigade on 11 December 1899 during the Second Boer War

  .
• 
  Soldiers in a trench on the Western Front in World War I in winter.
• 
  A Ukrainian soldier, equipped with an

  2022 Russian invasion of Ukraine

  .

Archaeology

Trenches are used for searching and

• Falling into 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 shoring stabilizes the walls, and trench shielding provides a barrier against collapsed material. The risk of cave-in increases from surcharge load, which is any weight placed outside the trench near its edge. These loads include the spoil pile (soil excavated from the trench) or heavy equipment. These add extra stress to the walls of the trench.
• Inability to escape the trench because of steep and unstable walls, which may be difficult to climb. Ladders, stairs, or ramps allow exit. Cranes may assist rescue.
• Drowning in water or mud that has accumulated in the trench from rain, seepage, or leaking water pipes.
• Asphyxiation, poisoning, fire and explosion from 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 an
  asphyxiation hazard and may also be toxic. Burnable gasses such as natural gas present 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 pure nitrogen and natural gas have 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 and ducts reduce the risk. Oxygen
  sensors and other gas sensors detect the danger; alarms from the sensors can warn the occupants.

References

External links

Wikimedia Commons has media related to Trenches.

Look up trench in Wiktionary, the free dictionary.

• Trenching and Excavation (a
  NIOSH Safety and Health Topic, Centers for Disease Control and Prevention
  )
• Trench Safety Awareness (a
  NIOSH Publication, Centers for Disease Control and Prevention
  )