A tunnel, by definition, is an underground passage that is (generally) that has a length at least twice as long as its width. It must also be completely enclosed, except for the entrances at either end.
The UK has a comprehensive network of tunnels, built for roads, railways, pedestrians and even canals. They pass through hills, under rivers and even pass beneath car parks and airport runways!
Yet, in fact, there are a number of different tunnel types, relating to the way that the tunnel has been constructed. This section briefly explains these tunnel types, alongside a list of the locations of road tunnels in the UK.
Types of tunnel construction
Cut-and-Cover
This is the simplest, and possibly most common, method of tunnel construction in
the UK. The method is designed for shallow tunnels, where a trench is excavated
then the roof built over the top of it. In many cases, supporting beams will be
required to support the roof and prevent it from falling into the tunnel itself.
There are two ways in which the construction of cut-and-cover tunnels are carried out:
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Bottom-up: simply, the trench is excavated using any necessary ground support, with the tunnel constructed within it. The floor is lined with concrete, then the walls are lined or built with pre-cast arches, then the roof is put in place to reinstate the surface.
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Top-down: narrow trenches are initially built where the sides of the tunnel will be, then the walls are put in place within then. Next, a shallow trench is built and the roof put in place, allowing a for quicker reinstatement of the surface (and any roads etc on top). Beneath the surface, the rest of tunnel is excavated using lowered machinery.
Bored
This is an automated method of tunnel construction that involves the use of a
Tunnel Boring Machine, which cuts into the rock using a number of circular
blades built into a shield that chip away at the rock.
Loose rock is then conveyed to the back of the machine on a belt or mixed with
water, turned into slurry and pumped backwards. The machine itself is constructed
to work in either hard rock, soft rock or beneath the water table, pressurising
the rock ahead of it. This allows contractors to continue working behind the
machine.
Pipe Jacking
Similar to boring, except that the machine used utilises hydraulic jacks to push
pipes into the tunnel behind the machine to strengthen the rock around it.
Immersed Tube
This method is usually used where a tunnel travels under water. It involves the
construction of a trench along the river bed, then a series of concrete tubes -
built off site - are floated onto the river and lowered into place. The
remaining space in the trench is filled in and the river bed reinstated.
New Austrian Tunnelling
Developed in the 1960s, this method is used in areas of geological stress of the
surrounding rock. The stress is calculated and used to stabilize the tunnel
itself; when the tunnel is excavated, sprayed concrete is used to keep the rock
in place and prevent it from deforming.
Archimedes Tunnelling
A relatively new concept, but not used in the UK, this method involves concrete
tubes being sunk beneath the water, but rather than laid on the river bed, they
are held above it using a weighting device or held up by reinforced concrete
legs.
Tunnel locations
Beaminster Tunnel
A3066, Beaminster
110m, bored, opened 1832
built through a steep hill
Bell Common Tunnel
M25, Epping Forest, Essex
450m, cut-and-cover, opened 1984
built under woodland
Blackfriars Underpass
A3211, Central London
320m, cut-and-cover, opened c.1965
built under a railway station and commerical properties
Blackwall (no. 1) Tunnel
A102, East London
1362m, bored, opened 1897
crosses the River Thames
Blackwall (no. 2) Tunnel
A102, East London
1201m, bored, opened 1967
crosses the River Thames
Brynglas Tunnel
M4, Newport, Gwent
365m long, twin bored, opened 1965
goes through a steep hill
Burghmuir Road Tunnel
A9, Stirling
100m, cut-and-cover, opened n/a
built under road junction and entrance to railway station
Caernarfon Tunnel
Glan mor Ucha, Caernarfon
20m, cut-and-cover, opened 1998
passes under buildings, originally a railway tunnel (from 1852 to 1970)
Canon Street Station Underpass
A3211, City of London
67m, cut-and-cover, opened 1965
built under a railway station
Central Library Underpass
A38, Birmingham
500m, cut-and-cover, built n/a
passes under Central Library
Charing Cross Tunnel
M8, Glasgow
150m, cut-and-cover, built 1972
passes under a road junction
Chestfield Tunnel
A299, Chestfield, Kent
320m, cut-and-cover, opened 1998
built under a golf course
Clyde Tunnel
A739, Glasgow
760m, twin bored, opened 1963
crosses the River Clyde
Conwy Tunnel
A55, Conwy, North Wales
1060m, immersed tube, opened 1991
crosses beneath the River Conwy
Cuilfail Tunnel
A26, Lewes, East Sussex
365m, bored, opened 1980
built under residential properties
Dartford (no. 1) Tunnel
A282, Dartford, Kent
1436m, bored, opened 1963
crosses the River Thames
Dartford (no. 2) Tunnel
A282, Dartford, Kent
1436m, bored, opened 1980
crosses the River Thames
East India Dock Link
A1261, East London
110m, bored, opened 1993
built under a residential area
Fore Street Underpass
A406, Edmonton, London
310m, cut-and-cover, opened n/a
passes under a railway and road junction
Gibraltar Hill Tunnels
A40, Monmouth
185m, twin bored, opened 1960s
built through an escarpment
George Green Tunnel
A12, Wanstead, London
300m, cut-and-cover, opened c. 2002
built under a park
Green Man Tunnel
A12, Wanstead, London
174m, cut-and-cover, opened c. 2002
passes under a road junction
Hanger Lane Underpass
A40, West London
241m, cut-and-cover, opened n/a
passes under a road junction
Hatfield Tunnel
A1(M), Hatfield, Hertfordshire
1400m, cut-and-cover, opened 1984
built beneath the Galleria Shopping Centre
Heathrow Vehicle Tunnel
unclass., Heathrow Airport, London
628m, cut-and-cover, opened n/a
built under an airport runway
Hindhead Tunnel
A3, Hindhead, Hampshire
1800m, twin bored, opened 2011
built under a conservation area
Holbeck Tunnel
A643, Holbeck, West Yorkshire
160m, cut-and-cover, opened n/a
built under recreational land
Holmesdale Tunnel
M25, Waltham Abbey, Essex
600m, cut-and-cover, opened 1984
built under residential properties
Hyde Park Corner Underpass
A4, Central London
310m, cut-and-cover, opened 17 October 1962
passes under a road junction
Kingsway Mersey Tunnel
(Tunnel), Liverpool
2483m, bored, opened 1971
crosses the River Mersey
Lancaster Circus Tunnel
A4400, Birmingham
197m, cut-and-cover, opened n/a
passes under a road junction
Limehouse Link Tunnel
A1203, East London
1800m, cut-and-cover, opened 1993
built under Limehouse Basin
Marketgait Tunnel
A991, Dundee
100m, cut-and-cover, opened n/a
built under a road junction
Manchester Airport Tunnels
A538, Ringway, Greater Manchester
225 + 175m (two tunnels), cut-and-cover, opened n/a and 2000
built under airport runways
Medway Tunnel
A289, Chatham, Kent
720m, immersed tube, opened 1996
crosses the River Medway
Meir Tunnel
A50, Meir, Stoke-on-Trent
280m, cut-and-cover, opened n/a
passes under a road junction
Pen-y-ClipTunnel
A55, Penmaenmawr, North Wales
930m, bored, opened 1993
goes through a steep cliff
Penmaenmawr Tunnel
A55 (westbound), Penmaenmawr, North Wales
660m, bored, opened 1983
goes through a steep cliff
Penmaenmawr Headland Tunnel
A55 (eastbound), Penmaenmawr, North Wales
172m, bored, opened 1932
goes through a steep cliff
Queens Gate
(Butetown) Tunnel
A4232, Cardiff Bay
715m, bored, opened c.1998
built under the Cardiff Bay development
Queensway Mersey Tunnel
(Tunnel), Liverpool
3237m, bored, opened 1934
crosses the River Mersey
Queensway Underpass
A38, Birmingham
548m, cut-and-cover, opened c. 1970
passes under a road junction
Ramsgate Harbour Tunnel
A299, Ramsgate, Kent
800m, bored, opened 2000
built under a residential area
Rotherhithe Tunnel
A101, East London
1705m, bored, opened 1908
crosses the River Thames
Round Hill Tunnel
A20, Folkestone, Kent
365m, twin bored, opened 2001
goes through a steep hill
St Chad's Circus Underpass
A38, Birmingham
192m, cut-and-cover, opened c. 1970
passes under a road junction
Saltash Tunnel
A38, Saltash, Devon
370m, bored, opened 1981
built under residential properties
Southwick Tunnel
A27, Mile Oak, West Sussex
390m, twin bored, opened 1994
goes through a steep hill
St. Helier Tunnel
A17, St Helier, Jersey
320m, bored, opened n/a
built under a hill
Strand Underpass
A301, London
365m, cut-and-cover, opened 1964
built under the Aldwych Gyratory, originally a tram tunnel (1906 to 1957)
Swainsley Tunnel
unclass., Swainsley, Derbyshire
100m, bored, opened n/a
goes through a steep hill
Tyne Tunnel
A19, Jarrow, Tyne and Wear
1645m, bored, opened 1967
crosses the River Tyne
Tyne Tunnel (New)
A19, Jarrow, Tyne and Wear
2600m, immersed tube, opened 2011
crosses the River Tyne
Upper Thames Street Tunnel
A3211, City of London
67m, cut-and-cover, opened 1965
built under a railway station
Victoria Avenue Tunnel
A658, Leeds-Bradford Airport
237m, cut-and-cover, opened n/a
built under an airport runway
West Hall Underpass
A2, Eltham, London
160m, cut-and-cover, opened 1989
passes under a railway station
Westgate Tunnel
A58(M), Leeds
367m, cut-and-cover, opened 1964
built under Leeds General Infirmary
Weston Hills Tunnel
A505, Baldock, Hertfordshire
230m, cut-and-cover, opened 2006
built through steep hills
Woodpecker Tunnel
A58(M), Leeds
298m, cut-and-cover, opened 1964
built under a car park
Closed tunnels
Charmouth Tunnel
Charmouth, former A35
1800m, twin bored, opened 1835, closed 1991
built under a hill, now converted into a sports centre
Reigate Tunnel
Reigate, former A217
50m, bored, opened 1823, closed c.1972
built under castle mound