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Last edited 07 Oct 2020
A trench is an excavation the length of which greatly exceeds the depth. Shallow trenches are usually considered to be less than 6m deep and deep trenches greater than 6 m. Depending on the dimensions of a trench, excavation can be carried out by hand or by a mechanical digger.
Spades or digging shovels can be used for the first foot of trench depth, but for deeper trenches, special hand trenching tools and shovels are more appropriate. These allow the user to stand straighter and remain at ground level.
This type of shovel is usually employed after a powered trencher and is designed to clear loose material from the bottom of a narrow trench. The narrow width of trenching shovels means they are not suitable for digging.
Trenchers are pieces of mechanical equipment used to excavate and prepare trenches. Different kinds of trencher can be used depending on the width and depth required and the nature of the material to be cut.
Also known as rockwheels, wheel trenchers are fitted with a toothed metal wheel and can be used in hard or soft soils. They can also be used for cutting pavements and for creating access to utilities under roads. They can be mounted on tracks or rubber tyres.
Depending on diameter, there are 6-8 cutting elements placed around the wheel which bear high-strength steel teeth, arranged in a semi-spherical configuration to increase material removal. The design of the wheel enables cutting of varying depths, and a constant soil working angle with a relatively small wheel diameter.
This is a chainsaw-like trencher which uses a digging chain or belt to cut the ground. The belt is driven around a rounded metal frame or boom, the angle of which can be adjusted to control the cut depth. The boom is held at a fixed angle while the machine slowly moves.
Chain trenchers are used to cut hard ground, and are flexible enough to be able to cut narrow, deep and wider trenches for utilities. A conveyor belt on either side of the trencher removes the excavated materials.
Also known trenching machines, skimmers are used for excavating long trenches, such as those necessary for pipelines. They will normally dig trenches 0.25-1.5 m wide and up to 3 m deep, where a high degree of accuracy is required. The machine moves forwards, excavating with buckets either mounted on a wheel at the front, or on a chain which is carried by a jib.
The reduced trench size means that there is a reduction in the volume of excavated waste material, and disturbance can be minimised. They are sometimes radio-controlled and are used for road maintenance and to gain access to utilities under the road surface.
Portable trenchers are lightweight and easy to handle, and can used to instal landscape edging and irrigation lines. They use a chain or a blade, similar to a rotary lawnmower, rotating in a vertical plane.
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