Editing Tunnel (section)

=== Cut-and-cover ===
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[[File:Paris Metro construction 03300288-3.jpg|thumb|Cut-and-cover construction at [[Saint-Michel (Paris Métro)|Saint-Michel]] on [[Paris Métro]] [[Paris Métro Line 4|Line 4]] (c. 1910)]]

'''Cut-and-cover''' is a simple method of construction for shallow tunnels where a [[trench]] is excavated and [[roof]]ed over with an overhead support system strong enough to carry the load of what is to be built above the tunnel.{{sfn|Ellis|2015|p=118}}

There are two basic forms of cut-and-cover tunnelling:
* ''Bottom-up method'': A trench is excavated, with ground support as necessary, and the tunnel is constructed in it. The tunnel may be of in situ concrete, precast concrete, precast arches, or corrugated steel arches; in early days brickwork was used. The trench is then carefully back-filled and the surface is reinstated.
* ''Top-down method'': Side support walls and capping beams are constructed from ground level by such methods as [[slurry wall]]ing or contiguous bored piling. Only a shallow excavation is needed to construct the tunnel roof using precast beams or in situ concrete sitting on the walls. The surface is then reinstated except for access openings. This allows early reinstatement of roadways, services, and other surface features. Excavation then takes place under the permanent tunnel roof, and the base slab is constructed.

Shallow tunnels are often of the cut-and-cover type (if under water, of the immersed-tube type), while deep tunnels are excavated, often using a [[tunnelling shield]]. For intermediate levels, both methods are possible.

Large cut-and-cover boxes are often used for underground [[Rapid transit|metro]] stations, such as [[Canary Wharf tube station]] in London. This construction form generally has two levels, which allows economical arrangements for ticket hall, station platforms, passenger access and emergency egress, ventilation and smoke control, staff rooms, and equipment rooms. The interior of Canary Wharf station has been likened to an underground cathedral, owing to the sheer size of the excavation. This contrasts with many traditional stations on [[London Underground]], where bored tunnels were used for stations and passenger access. Nevertheless, the original parts of the London Underground network, the Metropolitan and District Railways, were constructed using cut-and-cover. These lines pre-dated electric traction and the proximity to the surface was useful to ventilate the inevitable smoke and steam.

A major disadvantage of cut-and-cover is the widespread disruption generated at the surface level during construction.<ref>{{Cite journal |last=Konyukhov |first=D. S. |date=12 April 2022 |title=Analysis of mechanized tunneling parameters to determine the overcutting characteristics |url=https://mst.misis.ru/jour/article/view/330 |journal=Gornye Nauki I Tekhnologii = Mining Science and Technology (Russia) |volume=7 |issue=1 |pages=49–56 |doi=10.17073/2500-0632-2022-1-49-56 |s2cid=248136002 |issn=2500-0632|doi-access=free }}</ref> This, and the availability of electric traction, brought about London Underground's switch to bored tunnels at a deeper level towards the end of the 19th century.

Prior to the replacement of manual excavation by the use of boring machines, [[Victorian era|Victorian]] tunnel excavators developed a specialized method called clay-kicking for digging tunnels in clay-based soils. The clay-kicker lies on a plank at a 45-degree angle away from the working face and rather than a [[mattock]] with his hands, inserts with his feet a tool with a cup-like rounded end, then turns the tool with his hands to extract a section of soil, which is then placed on the waste extract.
Clay-kicking is a specialized method developed in the [[United Kingdom]] of digging tunnels in strong clay-based soil structures. This method of cut and cover construction required relatively little disturbance of property during the renewal of the United Kingdom's then ancient [[sewerage]] systems. It was also used during the [[First World War]] by [[Royal Engineer tunnelling companies]] placing mines beneath [[German Empire|German]] lines, because it was almost silent and so not susceptible to listening methods of detection.<ref>{{cite web |date=2009 |title=Tunnelling |url=http://tunnellersmemorial.com/Tunnelling.htm |url-status=dead |archive-url=https://web.archive.org/web/20100823081917/http://tunnellersmemorial.com/Tunnelling.htm |archive-date=23 August 2010 |access-date=20 June 2010 |website=The Tunneller's Memorial, Givenchy |publisher=}}</ref>