A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide (as opposed to a wider gully or ditch), and by being narrow compared to their length (as opposed to a simple hole).[1]
Trench shoring is often used in trenchworks to protect workers and stabilize embankments.
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Some trenches are created as a result of erosion by rivers (which may have long since fallen dry), others are created by geological movement of tectonic plates, such as rift valleys or more commonly oceanic trenches. Some oceanic trenches include the Mariana Trench and the Challenger Deep. The latter form is relatively deep (ca. 10 km), linear and narrow, and is formed by plate subduction when plates converge.[2]
In the civil engineering field of construction or maintenance of infrastructure, trenches play a major role. They may be created to search for pipes and other infrastructure that is known to be underground in the general area, but whose exact location has been lost ('search trench' or 'search slit'). They are also used to underground easily damaged and obstructive infrastructure or utilities (such as gas mains, water mains or telephone lines). A similar use for higher bulk would be in pipeline transport. Finally, trenches may be created as the first step of creating a foundation wall.
Trenches have often been dug for defense. In the pre-firearm eras, they were mainly a type of hindrance for 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.
With the advent of accurate firearms, trenches were used to shelter troops. The Māori of New Zealand used elaborate trench systems to defeat attacking British forces in several battles from 1840. Trench warfare and tactics evolved further in World War I and the Crimean War, 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 'trench method' is used for searching and excavating ancient ruins or to dig into strata of 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 employ combination methods.[3]