tunnels

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:

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.
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

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

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

Tunnels in Planning or Under Construction

Hindhead Tunnel
   A3, Hindhead, Hampshire
   1800m, twin bored, due to open 2011
   built under a conservation area

Mottram Tunnel
   A57, Mottram-in-Longendale, Greater Manchester
   170m, cut-and-cover, due to open ????
   built under woodland

New Tyne Crossing
   A19, Jarrow, Tyne and Wear
   2600m, immersed tube, due to open 2011
   crosses the River Tyne

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

with thanks to Charles Amis, Ray Pettit and Paul for providing additional tunnel information.