![Southern portal of Chirk canal tunnel - geograph](https://upload.wikimedia.org/wikipedia/commons/d/d3/Southern_portal_of_Chirk_canal_tunnel_-_geograph.org.uk_-_1293092.jpg)
A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A
pipeline
Pipeline may refer to:
Electronics, computers and computing
* Pipeline (computing), a chain of data-processing stages or a CPU optimization found on
** Instruction pipelining, a technique for implementing instruction-level parallelism within a s ...
is not a tunnel, though some recent tunnels have used
immersed tube
An immersed tube (or immersed tunnel) is a kind of undersea tunnel composed of segments, constructed elsewhere and floated to the tunnel site to be sunk into place and then linked together. They are commonly used for road and rail crossings of r ...
construction techniques rather than traditional tunnel boring methods.
A tunnel may be for foot or vehicular road
traffic
Traffic comprises pedestrians, vehicles, ridden or herded animals, trains, and other conveyances that use public ways (roads) for travel and transportation.
Traffic laws govern and regulate traffic, while rules of the road include traffic ...
, for
rail
Rail or rails may refer to:
Rail transport
*Rail transport and related matters
*Rail (rail transport) or railway lines, the running surface of a railway
Arts and media Film
* ''Rails'' (film), a 1929 Italian film by Mario Camerini
* ''Rail'' ( ...
traffic, or for a
canal
Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flow un ...
. The central portions of a
rapid transit
Rapid transit or mass rapid transit (MRT), also known as heavy rail or metro, is a type of high-capacity public transport generally found in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be c ...
network are usually in the tunnel. Some tunnels are used as
sewers or
aqueducts
Aqueduct may refer to:
Structures
*Aqueduct (bridge), a bridge to convey water over an obstacle, such as a ravine or valley
*Navigable aqueduct, or water bridge, a structure to carry navigable waterway canals over other rivers, valleys, railw ...
to supply water for consumption or for
hydroelectric
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...
stations.
Utility tunnel
A utility tunnel, utility corridor, or utilidor is a passage built underground or above ground to carry utility lines such as electricity, steam, water supply pipes, and sewer pipes. Communications utilities like fiber optics, cable television ...
s are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment.
Secret tunnels are built for military purposes, or by civilians for
smuggling
Smuggling is the illegal transportation of objects, substances, information or people, such as out of a house or buildings, into a prison, or across an international border, in violation of applicable laws or other regulations.
There are various ...
of
weapon
A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, s ...
s,
contraband
Contraband (from Medieval French ''contrebande'' "smuggling") refers to any item that, relating to its nature, is illegal to be possessed or sold. It is used for goods that by their nature are considered too dangerous or offensive in the eyes o ...
, or
people
A person (plural, : people) is a being that has certain capacities or attributes such as reason, morality, consciousness or self-consciousness, and being a part of a culturally established form of social relations such as kinship, ownership of pr ...
. Special tunnels, such as
wildlife crossing
Wildlife crossings are structures that allow animals to cross human-made barriers safely. Wildlife crossings may include underpass tunnels or wildlife tunnels, viaducts, and overpasses or green bridges (mainly for large or herd-type animals); ...
s, are built to allow wildlife to cross human-made barriers safely. Tunnels can be connected together in
tunnel network
In transport, tunnels can be connected together to form a tunnel network. These can be used in mining to reach ore below ground, in cities for underground rapid transit systems, in sewer systems, in warfare to avoid enemy detection or attacks, as ...
s.
Terminology
![Tampereen rantatunneli](https://upload.wikimedia.org/wikipedia/commons/4/46/Tampereen_rantatunneli.jpg)
A tunnel is relatively long and narrow; the length is often much greater than twice the
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
, although similar shorter excavations can be constructed, such as cross passages between tunnels.
The definition of what constitutes a tunnel can vary widely from source to source. For example, the definition of a road tunnel in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
is defined as "a subsurface highway structure enclosed for a length of or more." In the United States, the
NFPA definition of a tunnel is "An underground structure with a design length greater than and a diameter greater than ."
In the UK, a pedestrian, cycle or animal tunnel beneath a road or railway is called a
subway, while an underground railway system is differently named in different cities, the "
Underground
Underground most commonly refers to:
* Subterranea (geography), the regions beneath the surface of the Earth
Underground may also refer to:
Places
* The Underground (Boston), a music club in the Allston neighborhood of Boston
* The Underground (S ...
" or the "
Tube
Tube or tubes may refer to:
* ''Tube'' (2003 film), a 2003 Korean film
* ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom
* "Tubes" (Peter Dale), performer on the Soccer AM television show
* Tube (band), a ...
" in
London
London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...
, the "
Subway" in
Glasgow
Glasgow ( ; sco, Glesca or ; gd, Glaschu ) is the most populous city in Scotland and the fourth-most populous city in the United Kingdom, as well as being the 27th largest city by population in Europe. In 2020, it had an estimated popul ...
, and the "
Metro
Metro, short for metropolitan, may refer to:
Geography
* Metro (city), a city in Indonesia
* A metropolitan area, the populated region including and surrounding an urban center
Public transport
* Rapid transit, a passenger railway in an urba ...
" in
Newcastle Newcastle usually refers to:
*Newcastle upon Tyne, a city and metropolitan borough in Tyne and Wear, England
*Newcastle-under-Lyme, a town in Staffordshire, England
*Newcastle, New South Wales, a metropolitan area in Australia, named after Newcastle ...
. The place where a road, railway, canal or watercourse passes under a footpath, cycleway, or another road or railway is most commonly called a
bridge
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
or, if passing under a canal, an
aqueduct. Where it is important to stress that it is passing underneath, it may be called an underpass, though the official term when passing under a railway is an
underbridge
Rail terminology is a form of technical terminology. The difference between the American term ''railroad'' and the international term ''railway'' (used by the International Union of Railways and English-speaking countries outside the United St ...
. A longer underpass containing a road, canal or railway is normally called a "tunnel", whether or not it passes under another item of infrastructure. An underpass of any length under a river is also usually called a "tunnel", whatever mode of transport it is for.
In the US, the term "subway" means an underground rapid transit system, and the term
pedestrian underpass
A subway, also known as an underpass, is a grade-separated pedestrian crossing which crosses underneath a road or railway in order to entirely separate pedestrians and cyclists from motor traffic or trains respectively.
Terminology
In the Un ...
is used for a passage beneath a barrier. Rail station platforms may be connected by pedestrian tunnels or
footbridge
A footbridge (also a pedestrian bridge, pedestrian overpass, or pedestrian overcrossing) is a bridge designed solely for pedestrians.''Oxford English Dictionary'' While the primary meaning for a bridge is a structure which links "two points at a ...
s.
History
![Joralemon Street Tunnel postcard, 1913](https://upload.wikimedia.org/wikipedia/commons/c/cd/Joralemon_Street_Tunnel_postcard%2C_1913.jpg)
Much of the early technology of tunneling evolved from
mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
and
military engineering
Military engineering is loosely defined as the art, science, and practice of designing and building military works and maintaining lines of military transport and military communications. Military engineers are also responsible for logistics be ...
. The
etymology
Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...
of the terms "mining" (for mineral extraction or for
siege attacks), "military engineering", and "
civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewage ...
" reveals these deep historic connections.
Antiquity and early middle ages
Predecessors of modern tunnels were
adit
An adit (from Latin ''aditus'', entrance) is an entrance to an underground mine which is horizontal or nearly horizontal, by which the mine can be entered, drained of water, ventilated, and minerals extracted at the lowest convenient level. Adits ...
s to transport water for
irrigation
Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...
or drinking, and
sewerage
Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff (stormwater, meltwater, rainwater) using sewers. It encompasses components such as receiving drainage, drains, manholes, pumping stations, storm overflows, a ...
. The first
Qanat
A qanat or kārīz is a system for transporting water from an aquifer or water well to the surface, through an underground aqueduct; the system originated approximately 3,000 BC in what is now Iran. The function is essentially the same across ...
s are known from before 2000 B.C.
The
Tunnel of Eupalinos
The Tunnel of Eupalinos or Eupalinian aqueduct ( el, Ευπαλίνιον όρυγμα, translit=Efpalinion orygma) is a tunnel of length running through Mount Kastro in Samos, Greece, built in the 6th century BC to serve as an aqueduct. The tunn ...
is a tunnel
aqueduct long running through Mount Kastro in
Samos
Samos (, also ; el, Σάμος ) is a Greek island in the eastern Aegean Sea, south of Chios, north of Patmos and the Dodecanese, and off the coast of western Turkey, from which it is separated by the -wide Mycale Strait. It is also a separate ...
,
Greece
Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...
, built in the 6th century BC to serve as an
aqueduct. It is the second known tunnel to have been excavated from both ends, after the
Siloam tunnel in the neighbourhood of
Silwan
Silwan or Siloam ( ar, سلوان, translit=Silwan; gr, Σιλωὰμ, translit=Siloam; he, כְּפַר הַשִּׁילוֹחַ, translit=''Kfar ha-Shiloaḥ'') is a predominantly Palestinian neighborhood in East Jerusalem, on the outski ...
in eastern
Jerusalem
Jerusalem (; he, יְרוּשָׁלַיִם ; ar, القُدس ) (combining the Biblical and common usage Arabic names); grc, Ἱερουσαλήμ/Ἰεροσόλυμα, Hierousalḗm/Hierosóluma; hy, Երուսաղեմ, Erusałēm. i ...
.
In
Ethiopia
Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...
, the
Siqurto foot tunnel
The Siqurto foot tunnel crosses beneath the Imba Tsiyon ridge, which forms the water divide between the Giba and Weri'i basins. The ridge is part of the Mugulat Mountains, Tigray, Ethiopia,
Design and construction
The tunnel was hewn in th ...
, hand-hewn in the Middle Ages, crosses a mountain ridge.
Geotechnical investigation and design
A major tunnel project must start with a comprehensive investigation of ground conditions by collecting samples from
borehole
A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petro ...
s and by other geophysical techniques. An informed choice can then be made of machinery and methods for excavation and ground support, which will reduce the risk of encountering unforeseen ground conditions. In planning the route, the horizontal and vertical alignments can be selected to make use of the best ground and water conditions. It is common practice to locate a tunnel deeper than otherwise would be required, in order to excavate through solid rock or other material that is easier to support during construction.
Conventional desk and preliminary site studies may yield insufficient information to assess such factors as the blocky nature of rocks, the exact location of fault zones, or the stand-up times of softer ground. This may be a particular concern in large-diameter tunnels. To give more information, a pilot tunnel (or "drift tunnel") may be driven ahead of the main excavation. This smaller tunnel is less likely to collapse catastrophically should unexpected conditions be met, and it can be incorporated into the final tunnel or used as a backup or emergency escape passage. Alternatively, horizontal boreholes may sometimes be drilled ahead of the advancing tunnel face.
Other key geotechnical factors:
* Stand-up time is the amount of time a newly excavated cavity can support itself without any added structures. Knowing this parameter allows the engineers to determine how far an excavation can proceed before support is needed, which in turn affects the speed, efficiency, and cost of construction. Generally, certain configurations of rock and clay will have the greatest stand-up time, while sand and fine soils will have a much lower stand-up time.
*
Groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
control is very important in tunnel construction. Water leaking into a tunnel or vertical shaft will greatly decrease stand-up time, causing the excavation to become unstable and risking collapse. The most common way to control groundwater is to install dewatering pipes into the ground and to simply pump the water out. A very effective but expensive technology is
ground freezing
Ground freezing is a construction technique used in circumstances where soil needs to be stabilized so it will not collapse next to excavations, or to prevent contaminants spilled into soil from being leached away.
Ground freezing has been used f ...
, using pipes which are inserted into the ground surrounding the excavation, which are then cooled with special refrigerant fluids. This freezes the ground around each pipe until the whole space is surrounded with frozen soil, keeping water out until a permanent structure can be built.
* Tunnel
cross-sectional shape is also very important in determining stand-up time. If a tunnel excavation is wider than it is high, it will have a harder time supporting itself, decreasing its stand-up time. A square or rectangular excavation is more difficult to make self-supporting, because of a concentration of
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
at the corners.
Choice of tunnels versus bridges
![2007 09 19 - 895tunnel - WB 3](https://upload.wikimedia.org/wikipedia/commons/3/37/2007_09_19_-_895tunnel_-_WB_3.JPG)
For water crossings, a tunnel is generally more costly to construct than a bridge. However, navigational considerations may limit the use of high bridges or
drawbridge
A drawbridge or draw-bridge is a type of moveable bridge typically at the entrance to a castle or tower surrounded by a moat. In some forms of English, including American English, the word ''drawbridge'' commonly refers to all types of moveable ...
spans intersecting with shipping channels, necessitating a tunnel.
Bridges usually require a larger footprint on each shore than tunnels. In areas with expensive real estate, such as
Manhattan
Manhattan (), known regionally as the City, is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state ...
and urban
Hong Kong
Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China ( abbr. Hong Kong SAR or HKSAR), is a city and special administrative region of China on the eastern Pearl River Delt ...
, this is a strong factor in favor of a tunnel. Boston's
Big Dig
The Central Artery/Tunnel Project (CA/T Project), commonly known as the Big Dig, was a megaproject in Boston that rerouted the Central Artery of Interstate 93 (I-93), the chief highway through the heart of the city, into the 1.5-mile (2.4& ...
project replaced elevated roadways with a tunnel system to increase traffic capacity, hide traffic, reclaim land, redecorate, and reunite the city with the waterfront.
The 1934
Queensway Tunnel under the
River Mersey
The River Mersey () is in North West England. Its name derives from Old English and means "boundary river", possibly referring to its having been a border between the ancient kingdoms of Mercia and Northumbria. For centuries it has formed part ...
at
Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
was chosen over a massively high bridge for defense reasons; it was feared that aircraft could destroy a bridge in times of war. Maintenance costs of a massive bridge to allow the world's largest ships to navigate under were considered higher than for a tunnel. Similar conclusions were reached for the 1971
Kingsway Tunnel
The Kingsway Tunnel (or Wallasey Tunnel) is a toll road tunnel under the River Mersey between Liverpool and Wallasey. The tunnel carries the A59. It was built because the Queensway Tunnel – which was built in the 1930s to carry vehicles b ...
under the Mersey. In
Hampton Roads, Virginia
Hampton Roads is the name of both a body of water in the United States that serves as a wide channel for the James, Nansemond and Elizabeth rivers between Old Point Comfort and Sewell's Point where the Chesapeake Bay flows into the Atlantic O ...
, tunnels were chosen over bridges for strategic considerations; in the event of damage, bridges might prevent
US Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage of ...
vessels from leaving
Naval Station Norfolk
Naval Station Norfolk is a United States Navy base in Norfolk, Virginia, that is the headquarters and home port of the U.S. Navy's Fleet Forces Command. The installation occupies about of waterfront space and of pier and wharf space of the Hamp ...
.
Water-crossing tunnels built instead of bridges include the
Holland Tunnel
The Holland Tunnel is a vehicular tunnel under the Hudson River that connects the New York City neighborhood of Hudson Square in Lower Manhattan to the east with Jersey City in New Jersey to the west. The tunnel is operated by the Port Author ...
and
Lincoln Tunnel
The Lincoln Tunnel is an approximately tunnel under the Hudson River, connecting Weehawken, New Jersey, to the west with Midtown Manhattan in New York City to the east. It carries New Jersey Route 495 on the New Jersey side and unsigned New Y ...
between
New Jersey
New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
and Manhattan in
New York City
New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
; the
Queens-Midtown Tunnel between Manhattan and the
borough
A borough is an administrative division in various English-speaking countries. In principle, the term ''borough'' designates a self-governing walled town, although in practice, official use of the term varies widely.
History
In the Middle Ag ...
of
Queens
Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. Located on Long Island, it is the largest New York City borough by area. It is bordered by the borough of Brooklyn at the western tip of Long ...
on
Long Island
Long Island is a densely populated island in the southeastern region of the U.S. state of New York (state), New York, part of the New York metropolitan area. With over 8 million people, Long Island is the most populous island in the United Sta ...
; the
Detroit-Windsor Tunnel between
Michigan
Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...
and
Ontario
Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
; and the
Elizabeth River tunnels between
Norfolk
Norfolk () is a ceremonial and non-metropolitan county in East Anglia in England. It borders Lincolnshire to the north-west, Cambridgeshire to the west and south-west, and Suffolk to the south. Its northern and eastern boundaries are the No ...
and
Portsmouth, Virginia
Portsmouth is an independent city in southeast Virginia and across the Elizabeth River from Norfolk. As of the 2020 census, the population was 97,915. It is part of the Hampton Roads metropolitan area.
The Norfolk Naval Shipyard and Naval M ...
; the 1934
River Mersey
The River Mersey () is in North West England. Its name derives from Old English and means "boundary river", possibly referring to its having been a border between the ancient kingdoms of Mercia and Northumbria. For centuries it has formed part ...
road
Queensway Tunnel; the
Western Scheldt Tunnel
Western Scheldt Tunnel ( nl, Westerscheldetunnel, Westerscheldetunnel) is a tunnel in the Netherlands that carries highway N62 under the Western Scheldt estuary between Ellewoutsdijk and Terneuzen. It is the longest tunnel for highway traffic in ...
, Zeeland, Netherlands; and the
North Shore Connector
The North Shore Connector is a light-rail extension opened in 2012 in Pittsburgh, Pennsylvania. The connector extends the Pittsburgh Light Rail system from its previous terminus at Gateway Center Station in the Central Business District to the n ...
tunnel in
Pittsburgh, Pennsylvania
Pittsburgh ( ) is a city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania, United States, and the county seat of Allegheny County, Pennsylvania, Allegheny County. It is the most populous city in both Allegheny County and Wester ...
.
Other reasons for choosing a tunnel instead of a bridge include avoiding difficulties with tides, weather, and shipping during construction (as in the
Channel Tunnel
The Channel Tunnel (french: Tunnel sous la Manche), also known as the Chunnel, is a railway tunnel that connects Folkestone (Kent, England, UK) with Coquelles ( Hauts-de-France, France) beneath the English Channel at the Strait of Dover. ...
), aesthetic reasons (preserving the above-ground view, landscape, and scenery), and also for weight capacity reasons (it may be more feasible to build a tunnel than a sufficiently strong bridge).
Some water crossings are a mixture of bridges and tunnels, such as the
Denmark to Sweden link and the
Chesapeake Bay Bridge-Tunnel Chesapeake often refers to:
*Chesapeake people, a Native American tribe also known as the Chesepian
* The Chesapeake, a.k.a. Chesapeake Bay
*Delmarva Peninsula, also known as the Chesapeake Peninsula
Chesapeake may also refer to:
Populated plac ...
in
Virginia
Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...
.
There are particular hazards with tunnels, especially from vehicle fires when combustion gases can
asphyxia
Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
te users, as happened at the
Gotthard Road Tunnel in
Switzerland
). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
in 2001. One of the worst railway disasters ever, the
Balvano train disaster
The Balvano train disaster was the deadliest railway accident in Italian history and one of the worst railway disasters ever. It occurred on the night between 2–3 March 1944 in Balvano, Basilicata. Over 500 people in a steam-hauled, coal-burning ...
, was caused by a train stalling in the Armi tunnel in
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
in 1944, killing 426 passengers. Designers try to reduce these risks by installing emergency ventilation systems or isolated emergency escape tunnels parallel to the main passage.
Project planning and cost estimates
Government funds are often required for the creation of tunnels. When a tunnel is being planned or constructed, economics and politics play a large factor in the decision making process. Civil engineers usually use
project management
Project management is the process of leading the work of a team to achieve all project goals within the given constraints. This information is usually described in project documentation, created at the beginning of the development process. Th ...
techniques for developing a major structure. Understanding the amount of time the project requires, and the amount of labor and materials needed is a crucial part of project planning. The project duration must be identified using a
work breakdown structure
A work-breakdown structure (WBS) in project management and systems engineering is a deliverable-oriented breakdown of a project into smaller components. A work breakdown structure is a key project deliverable that organizes the team's work into ...
(WBS) and
critical path method (CPM). Also, the land needed for excavation and construction staging, and the proper machinery must be selected. Large infrastructure projects require millions or even billions of dollars, involving long-term financing, usually through issuance of
bonds.
The
costs and benefits
In production, research, retail, and accounting, a cost is the value of money that has been used up to produce something or deliver a service, and hence is not available for use anymore. In business, the cost may be one of acquisition, in which ...
for an infrastructure such as a tunnel must be identified. Political disputes can occur, as in 2005 when the US House of Representatives approved a $100 million federal grant to build a tunnel under New York Harbor. However, the
Port Authority of New York and New Jersey
The Port Authority of New York and New Jersey, PANYNJ; stylized, in logo since 2020, as Port Authority NY NJ, is a joint venture between the U.S. states of New York and New Jersey, established in 1921 through an interstate compact authorized ...
was not aware of this bill and had not asked for a grant for such a project. Increased taxes to finance a large project may cause opposition.
Construction
Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the groundwater conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and the shape of the tunnel and appropriate risk management.
There are three basic types of tunnel construction in common use. Cut-and-cover tunnels are constructed in a shallow trench and then covered over. Bored tunnels are constructed in situ, without removing the ground above. Finally, a tube can be sunk into a body of water, which is called an immersed tunnel.
Cut-and-cover
![Paris Metro construction 03300288-3](https://upload.wikimedia.org/wikipedia/commons/f/f7/Paris_Metro_construction_03300288-3.jpg)
Cut-and-cover is a simple method of construction for shallow tunnels where a
trench
A trench is a type of excavation or in the ground that is generally deeper than it is wide (as opposed to a wider gully, or ditch), and narrow compared with its length (as opposed to a simple hole or pit).
In geology, trenches result from eros ...
is excavated and
roof
A roof ( : roofs or rooves) is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of temper ...
ed over with an overhead support system strong enough to carry the load of what is to be built above the tunnel.
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
A slurry wall is a civil engineering technique used to build reinforced concrete walls in areas of soft earth close to open water, or with a high groundwater table.
This technique is typically used to build diaphragm (water-blocking) walls surro ...
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
A tunnelling shield is a protective structure used during the excavation of large, man-made tunnels. When excavating through ground that is soft, liquid, or otherwise unstable, there is a potential health and safety hazard to workers and the proj ...
. For intermediate levels, both methods are possible.
Large cut-and-cover boxes are often used for underground
metro
Metro, short for metropolitan, may refer to:
Geography
* Metro (city), a city in Indonesia
* A metropolitan area, the populated region including and surrounding an urban center
Public transport
* Rapid transit, a passenger railway in an urba ...
stations, such as
Canary Wharf tube station
Canary Wharf is a London Underground station at Canary Wharf and is on the Jubilee line, between and stations. The station is located in Travelcard Zone 2 and was opened on 17 September 1999 as part of the Jubilee Line Extension. Over 40&nbs ...
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
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
, 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. 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.
Boring machines
Tunnel boring machine
A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore throu ...
s (TBMs) and associated back-up systems are used to highly automate the entire tunnelling process, reducing tunnelling costs. In certain predominantly urban applications, tunnel boring is viewed as a quick and cost-effective alternative to laying surface rails and roads. Expensive
compulsory purchase
Compulsion may refer to:
* Compulsive behavior, a psychological condition in which a person does a behavior compulsively, having an overwhelming feeling that they must do so.
* Obsessive–compulsive disorder, a mental disorder characterized by i ...
of buildings and land, with potentially lengthy planning inquiries, is eliminated. Disadvantages of TBMs arise from their usually large size – the difficulty of transporting the large TBM to the site of tunnel construction, or (alternatively) the high cost of assembling the TBM on-site, often within the confines of the tunnel being constructed.
There are a variety of TBM designs that can operate in a variety of conditions, from hard rock to soft water-bearing ground. Some types of TBMs, the bentonite slurry, and earth-pressure balance machines have pressurized compartments at the front end, allowing them to be used in difficult conditions below the
water table
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
T ...
. This pressurizes the ground ahead of the TBM cutter head to balance the water pressure. The operators work in normal air pressure behind the pressurized compartment, but may occasionally have to enter that compartment to renew or repair the cutters. This requires special precautions, such as local ground treatment or halting the TBM at a position free from water. Despite these difficulties, TBMs are now preferred over the older method of tunnelling in compressed air, with an airlock/decompression chamber some way back from the TBM, which required operators to work in high pressure and go through decompression procedures at the end of their shifts, much like
deep-sea divers.
In February 2010, Aker Wirth delivered a TBM to Switzerland, for the expansion of the
Linth–Limmern Power Stations
The Linth–Limmern Power Stations are a system of hydroelectric power stations located south of Linthal in the canton of Glarus, Switzerland. The system uses five reservoirs and four power stations at steep variations in altitude.
Works on the c ...
located south of
Linthal in the
canton of Glarus
The canton of Glarus (german: Kanton Glarus rm, Chantun Glaruna; french: Canton de Glaris; it, Canton Glarona) is a canton in east central Switzerland. The capital is Glarus.
The population speaks a variety of Alemannic German.
The majority of ...
. The borehole has a diameter of . The four TBMs used for excavating the
Gotthard Base Tunnel
, rm, Tunnel da basa dal Sogn Gottard
, image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg
, image_size = 250
, caption = Turnout at Faido multifunction station
, line = Gotthard Line
, location = Switzerland (Uri, Grisons and ...
, in
Switzerland
). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
, had a diameter of about . A larger TBM was built to bore the Green Heart Tunnel (Dutch: Tunnel Groene Hart) as part of the
HSL-Zuid
The HSL-Zuid ( nl, Hogesnelheidslijn Zuid, en, High-speed Line South), is a 125 kilometre-long (78 miles) Dutch high-speed railway line running between the Amsterdam metropolitan area and the Belgian border, with a branch to Breda, North ...
in the Netherlands, with a diameter of . This in turn was superseded by the
Madrid M30 ringroad,
Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, i ...
, and the
Chong Ming tunnels in
Shanghai
Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flow ...
,
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
. All of these machines were built at least partly by
Herrenknecht
Herrenknecht AG is a German company that manufactures tunnel boring machines, headquartered in Allmannsweier, Schwanau, Baden-Württemberg. It is the worldwide market leader for heavy tunnel boring machines. Roughly two-thirds of its 5,000 employ ...
. , the world's largest TBM was "
Big Bertha", a diameter machine built by
Hitachi Zosen Corporation
is a major Japanese industrial and engineering corporation. It produces waste treatment plants, industrial plants, precision machinery, industrial machinery, steel mill process equipment, steel structures, construction machinery, tunnel boring ma ...
, which dug the
Alaskan Way Viaduct replacement tunnel
The State Route 99 tunnel, also known as the Alaskan Way Viaduct replacement tunnel, is a bored highway tunnel in the city of Seattle, Washington, United States. The , double-decker tunnel carries a section of State Route 99 (SR 99) under ...
in
Seattle, Washington
Seattle ( ) is a port, seaport city on the West Coast of the United States. It is the county seat, seat of King County, Washington, King County, Washington (state), Washington. With a 2020 population of 737,015, it is the largest city in bo ...
(US).
Clay-kicking
Clay-kicking is a specialized method developed in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
of digging tunnels in strong clay-based soil structures. Unlike previous manual methods of using
mattock
A mattock is a hand tool used for digging, prying, and chopping. Similar to the pickaxe, it has a long handle and a stout head which combines either a vertical axe blade with a horizontal adze (cutter mattock), or a pick and an adze (pick matt ...
s which relied on the soil structure to be hard, clay-kicking was relatively silent and hence did not harm soft clay-based structures. The clay-kicker lies on a plank at a 45-degree angle away from the working face and inserts a tool with a cup-like rounded end with the feet. Turning the tool manually, the kicker extracts a section of soil, which is then placed on the waste extract.
Used in
Victorian civil engineering, the method found favor in the renewal of Britain's ancient
sewerage
Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff (stormwater, meltwater, rainwater) using sewers. It encompasses components such as receiving drainage, drains, manholes, pumping stations, storm overflows, a ...
systems, by not having to remove all property or infrastructure to create a small tunnel system. During the
First World War
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, the system was used by
Royal Engineer tunnelling companies
Royal Engineer tunnelling companies were specialist units of the Corps of Royal Engineers within the British Army, formed to dig attacking tunnels under enemy lines during the First World War.
The stalemate situation in the early part of the war ...
to put mines beneath the
German Empire
The German Empire (),Herbert Tuttle wrote in September 1881 that the term "Reich" does not literally connote an empire as has been commonly assumed by English-speaking people. The term literally denotes an empire – particularly a hereditary ...
lines. The method was virtually silent and so not susceptible to listening methods of detection.
Shafts
![Mersey Railway Tunnel - ventilation and drainage machinery](https://upload.wikimedia.org/wikipedia/commons/2/23/Mersey_Railway_Tunnel_-_ventilation_and_drainage_machinery.png)
A temporary access
shaft
Shaft may refer to:
Rotating machine elements
* Shaft (mechanical engineering), a rotating machine element used to transmit power
* Line shaft, a power transmission system
* Drive shaft, a shaft for transferring torque
* Axle, a shaft around whi ...
is sometimes necessary during the excavation of a tunnel. They are usually circular and go straight down until they reach the level at which the tunnel is going to be built. A shaft normally has concrete walls and is usually built to be permanent. Once the access shafts are complete, TBMs are lowered to the bottom and excavation can start. Shafts are the main entrance in and out of the tunnel until the project is completed. If a tunnel is going to be long, multiple shafts at various locations may be bored so that entrance to the tunnel is closer to the unexcavated area.
[United States Army Corps of Engineers. (1978). Tunnels and shafts in rock. Washington, DC: Department of the Army.]
Once construction is complete, construction access shafts are often used as
ventilation shaft
In subterranean civil engineering, ventilation shafts, also known as airshafts or vent shafts, are vertical passages used in mines and tunnels to move fresh air underground, and to remove stale air.
In architecture, an airshaft is a small, ...
s, and may also be used as emergency exits.
Sprayed concrete techniques
The
New Austrian Tunnelling method
The New Austrian tunneling method (NATM), also known as the sequential excavation method (SEM) or sprayed concrete lining method (SCL), is a method of modern tunnel design and construction employing sophisticated monitoring to optimize various wa ...
(NATM)—also referred to as the Sequential Excavation Method (SEM)
[—was developed in the 1960s.
The main idea of this method is to use the geological ]stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
of the surrounding rock
Rock most often refers to:
* Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids
* Rock music, a genre of popular music
Rock or Rocks may also refer to:
Places United Kingdom
* Rock, Caerphilly, a location in Wales ...
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
to stabilize the tunnel, by allowing a measured relaxation and stress reassignment into the surrounding rock to prevent full loads becoming imposed on the supports. Based on geotechnical
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It als ...
measurements, an optimal cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
is computed. The excavation is protected by a layer of sprayed concrete, commonly referred to as shotcrete
Shotcrete, gunite (), or sprayed concrete is concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique, first used in 1907 invented by Carl Akeley. It is typically r ...
. Other support measures can include steel arches, rock bolts, and mesh. Technological developments in sprayed concrete technology have resulted in steel and polypropylene fibers being added to the concrete mix to improve lining strength. This creates a natural load-bearing ring, which minimizes the rock's deformation
Deformation can refer to:
* Deformation (engineering), changes in an object's shape or form due to the application of a force or forces.
** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies.
* Defo ...
.[
]
By special monitoring
Monitoring may refer to:
Science and technology Biology and healthcare
* Monitoring (medicine), the observation of a disease, condition or one or several medical parameters over time
* Baby monitoring
* Biomonitoring, of toxic chemical compounds, ...
the NATM method is flexible, even at surprising changes of the geomechanical rock consistency during the tunneling work. The measured rock properties lead to appropriate tool
A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task. Although many animals use simple tools, only human beings, whose use of stone tools dates ba ...
s for tunnel strengthening
Chinese food therapy (, also called nutrition therapy and dietary therapy) is a mode of dieting rooted in Chinese beliefs concerning the effects of food on the human organism, and centered on concepts such as eating in moderation. Its basic pr ...
.[
]
Pipe jacking
In pipe jacking Pipe ramming (sometimes also called pipe jacking) is a trenchless method for installation of steel pipes and casings. Distances of 30 m (150 feet) or more and over 500 mm (20 inches) in diameter are common, although the method can be used for m ...
, hydraulic jack
A jack is a mechanical lifting device used to apply great forces or lift heavy loads. A mechanical jack employs a screw thread for lifting heavy equipment. A hydraulic jack uses hydraulic power. The most common form is a car jack, floor jack o ...
s are used to push specially made pipes through the ground behind a TBM or shield. This method is commonly used to create tunnels under existing structures, such as roads or railways. Tunnels constructed by pipe jacking are normally small diameter bores with a maximum size of around .
Box jacking
Box jacking is similar to pipe jacking, but instead of jacking tubes, a box-shaped tunnel is used. Jacked boxes can be a much larger span than a pipe jack, with the span of some box jacks in excess of . A cutting head is normally used at the front of the box being jacked, and spoil removal is normally by excavator from within the box. Recent developments of the Jacked Arch and Jacked deck have enabled longer and larger structures to be installed to close accuracy. The 126m long 20m clear span underpass below the high-speed rail lines at Cliffsend in Kent, UK is an example of this technique.
Underwater tunnels
There are also several approaches to underwater tunnels, the two most common being bored tunnels or immersed tube
An immersed tube (or immersed tunnel) is a kind of undersea tunnel composed of segments, constructed elsewhere and floated to the tunnel site to be sunk into place and then linked together. They are commonly used for road and rail crossings of r ...
s, examples are Bjørvika Tunnel and Marmaray
The Marmaray () is a intercontinental commuter rail line in Istanbul, Turkey. A rail tunnel running under the Bosphorus strait was connected to an upgraded version of the old suburban train service (known as the banliyö), allowing trains ...
. Submerged floating tunnel
A submerged floating tunnel (SFT), also known as submerged floating tube bridge (SFTB), suspended tunnel, or Archimedes bridge, is a proposed design for a tunnel that floats in water, supported by its buoyancy (specifically, by employing the hydro ...
s are a novel approach under consideration; however, no such tunnels have been constructed to date.
Temporary way
During construction of a tunnel it is often convenient to install a temporary railway, particularly to remove excavated spoil, often narrow gauge
A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge narrower than standard . Most narrow-gauge railways are between and .
Since narrow-gauge railways are usually built with tighter curves, smaller structu ...
so that it can be double track
A double-track railway usually involves running one track in each direction, compared to a single-track railway where trains in both directions share the same track.
Overview
In the earliest days of railways in the United Kingdom, most lin ...
to allow the operation of empty and loaded trains at the same time. The temporary way is replaced by the permanent way
A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleepers, ...
at completion, thus explaining the term "Perway".
Enlargement
The vehicles or traffic using a tunnel can outgrow it, requiring replacement or enlargement:
* The original single line Mount Gibraltar, Gib Tunnel near Mittagong was replaced with a double-track tunnel, with the original tunnel used for growing mushrooms.
* The 1832 double-track -long tunnel from Edge Hill railway sta ion, Edge Hill to Liverpool Lime Street railway station, Lime Street in Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
was near totally removed, apart from a section at Edge Hill and a section nearer to Lime Street, as four tracks were required. The tunnel was dug out into a very deep four-track cutting, with short tunnels in places along the cutting. Train services were not interrupted as the work progressed. There are other occurrences of tunnels being replaced by open cuts, for example, the Auburn Tunnel.
* The Farnworth Tunnel in England was enlarged using a tunnel boring machine (TBM) in 2015. The Rhyndaston Tunnel was enlarged using a borrowed TBM so as to be able to take ISO containers.
* Tunnels can also be enlarged by lowering the floor.
Open building pit
An open building pit consists of a horizontal and a vertical boundary that keeps groundwater and soil out of the pit. There are several potential alternatives and combinations for (horizontal and vertical) building pit boundaries. The most important difference with cut-and-cover is that the open building pit is muted after tunnel construction; no roof is placed.
Other construction methods
* Drilling and blasting
* Hydraulic splitter
* Slurry-shield machine
* Wall-cover construction method.
Variant tunnel types
Double-deck and multipurpose tunnels
Some tunnels are double-deck, for example, the two major segments of the San Francisco–Oakland Bay Bridge (completed in 1936) are linked by a Yerba Buena Tunnel, double-deck tunnel section through Yerba Buena Island, the largest-diameter bored tunnel in the world. At construction this was a combination bidirectional rail and truck pathway on the lower deck with automobiles above, now converted to one-way road vehicle traffic on each deck.
In Turkey, the Eurasia Tunnel under the Bosphorus, opened in 2016, has at its core a two-deck road tunnel with two lanes on each deck.
Additionally, in 2015 the Turkish government announced that it will build the world's first ''three''-level tunnel, also under the Bosporus. The tunnel is intended to carry both the Istanbul metro and a two-level highway, over a length of .
The French A86 Duplex Tunnel in west Paris consists of two bored tunnel tubes, the eastern one of which has two levels for light motorized vehicles, over a length of . Although each level offers a physical height of , only traffic up to tall is allowed in this tunnel tube, and motorcyclists are directed to the other tube. Each level was built with a three-lane roadway, but only two lanes per level are used – the third serves as a hard shoulder within the tunnel. The A86 Duplex is Europe's longest double-deck tunnel.
In Shanghai
Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flow ...
, China, a two-tube double-deck tunnel was built starting in 2002. In each tube of the Fuxing Road Tunnel both decks are for motor vehicles. In each direction, only cars and taxis travel on the high two-lane upper deck, and heavier vehicles, like trucks and buses, as well as cars, may use the high single-lane lower level.
In the Netherlands, a two-storey, eight-lane, cut-and-cover road tunnel under the city of Maastricht was opened in 2016. Each level accommodates a full height, two by two-lane highway. The two lower tubes of the tunnel carry the A2 motorway (Netherlands), A2 motorway, which originates in Amsterdam, through the city; and the two upper tubes take the N2 regional highway for local traffic.
The Alaskan Way Viaduct replacement tunnel
The State Route 99 tunnel, also known as the Alaskan Way Viaduct replacement tunnel, is a bored highway tunnel in the city of Seattle, Washington, United States. The , double-decker tunnel carries a section of State Route 99 (SR 99) under ...
, is a $3.3 billion , double-decker bored highway tunnel under Downtown Seattle. Construction began in July 2013 using "Bertha (tunnel boring machine), Bertha", at the time the world's largest earth pressure balance tunnel boring machine, with a cutterhead diameter. After several delays, tunnel boring was completed in April 2017, and the tunnel opened to traffic on February 4, 2019.
New York City
New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
's 63rd Street Tunnel under the East River, between the boroughs of Manhattan
Manhattan (), known regionally as the City, is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state ...
and Queens
Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. Located on Long Island, it is the largest New York City borough by area. It is bordered by the borough of Brooklyn at the western tip of Long ...
, was intended to carry New York City Subway, subway trains on the upper level and Long Island Rail Road commuter trains on the lower level. Construction started in 1969, and the two sides of the tunnel were bored through in 1972. The upper level, used by the 63rd Street lines, IND 63rd Street Line () of the New York City Subway, was not opened for passenger service until 1989. The lower level, intended for commuter rail, will not see passenger service until completion of the East Side Access project, expected in late 2022.
In the UK, the 1934 Queensway Tunnel under the River Mersey
The River Mersey () is in North West England. Its name derives from Old English and means "boundary river", possibly referring to its having been a border between the ancient kingdoms of Mercia and Northumbria. For centuries it has formed part ...
between Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
and Birkenhead was originally to have road vehicles running on the upper deck and trams on the lower. During construction the tram usage was cancelled. The lower section is only used for cables, pipes and emergency accident refuge enclosures.
Hong Kong's Lion Rock Tunnel, built in the mid 1960s, connecting New Kowloon and Sha Tin New Town, Sha Tin, carries a motorway but also serves as an aqueduct, featuring a gallery containing five water mains lines with diameters between 1.2m and 1.5m below the road section of the tunnel.
Wuhan's Yangtze River Highway and Railway Tunnel is a 2.59 km two-tube double-deck tunnel under the Yangtze, Yangtze River completed in 2018. Each tube carries 3 lanes of local traffic on the top deck with one track Wuhan Metro Line 7 (Wuhan Metro), Line 7 on the lower deck.
Some tunnels have more than one purpose. The SMART Tunnel in Malaysia is the first multipurpose "''Stormwater Management And Road Tunnel''" in the world, created to convey both traffic and occasional flood waters in Kuala Lumpur. When necessary, floodwater is first diverted into a separate bypass tunnel located ''underneath'' the double-deck roadway tunnel. In this scenario, traffic continues normally. Only during heavy, prolonged rains when the threat of extreme flooding is high, the upper tunnel tube is closed off to vehicles and automated flood control gates are opened so that water can be diverted through both tunnels.
Common utility ducts or utility tunnels carry two or more utility lines. Through co-location of different utilities in one tunnel, organizations are able to reduce the costs of building and maintaining utilities.
Covered passageways
Over-bridges can sometimes be built by covering a road or river or railway with brick or steel arches, and then leveling the surface with earth. In railway parlance, a surface-level track which has been built or covered over is normally called a "covered way".
Snow sheds are a kind of artificial tunnel built to protect a railway from avalanches of snow. Similarly the Stanwell Park, New South Wales "steel tunnel", on the Illawarra railway line, protects the line from rockfalls.
Underpass
An underpass is a road or railway or other passageway passing ''under'' another road or railway, under an overpass. This is not strictly a tunnel.
Safety and security
Owing to the enclosed space of a tunnel, fires can have very serious effects on users. The main dangers are gas and smoke production, with even low concentrations of carbon monoxide being highly toxic. Fires killed 11 people in the Gotthard Road Tunnel#History, Gotthard tunnel fire of 2001 for example, all of the victims succumbing to smoke and gas inhalation. Over 400 passengers died in the Balvano train disaster
The Balvano train disaster was the deadliest railway accident in Italian history and one of the worst railway disasters ever. It occurred on the night between 2–3 March 1944 in Balvano, Basilicata. Over 500 people in a steam-hauled, coal-burning ...
in Italy in 1944, when the locomotive halted in a long tunnel. Carbon monoxide poisoning was the main cause of death. In the Caldecott Tunnel fire of 1982, the majority of fatalities were caused by toxic smoke, rather than by the initial crash. Likewise 84 people were killed in the Paris Métro train fire of 1904.
Motor vehicle tunnels usually require ventilation shaft
In subterranean civil engineering, ventilation shafts, also known as airshafts or vent shafts, are vertical passages used in mines and tunnels to move fresh air underground, and to remove stale air.
In architecture, an airshaft is a small, ...
s and powered fans to remove toxic exhaust gases during routine operation.
Rail tunnels usually require fewer air changes per hour, but still may require Ventilation (architecture), forced-air ventilation. Both types of tunnels often have provisions to increase ventilation under emergency conditions, such as a fire. Although there is a risk of increasing the rate of combustion through increased airflow, the primary focus is on providing breathable air to persons trapped in the tunnel, as well as firefighters.
Aerodynamics, Aerodynamic Longitudinal wave, pressure wave produced by High-speed rail, high speed trains entering a tunnel reflects at its open ends and changes sign (Compression (physics), compression wave-front changes to rarefaction wave-front and vice versa); When two wave-front of the same sign meets the train, significant and rapid air pressure may cause aural discomfort to passengers and crew. When high-speed trains exit tunnels, a loud "Piston effect#Tunnel boom, Tunnel boom" may occur, which can disturb residents near the mouth of the tunnel, and it is exacerbated in mountain valleys where the sound can echo.
When there is a parallel, separate tunnel available, airtight but unlocked emergency doors are usually provided which allow trapped personnel to escape from a smoke-filled tunnel to the parallel tube.
Larger, heavily used tunnels, such as the Big Dig
The Central Artery/Tunnel Project (CA/T Project), commonly known as the Big Dig, was a megaproject in Boston that rerouted the Central Artery of Interstate 93 (I-93), the chief highway through the heart of the city, into the 1.5-mile (2.4& ...
tunnel in Boston, Massachusetts, may have a dedicated 24-hour staffed operations center which monitors and reports on traffic conditions, and responds to emergencies. Video surveillance equipment is often used, and real-time pictures of traffic conditions for some highways may be viewable by the general public via the Internet.
A database of seismic damage to underground structures using 217 case histories shows the following general observations can be made regarding the seismic performance of underground structures:
* Underground structures suffer appreciably less damage than surface structures.
* Reported damage decreases with increasing over burden depth. Deep tunnels seem to be safer and less vulnerable to earthquake shaking than are shallow tunnels.
* Underground facilities constructed in soils can be expected to suffer more damage compared to openings constructed in competent rock.
* Lined and grouted tunnels are safer than unlined tunnels in rock. Shaking damage can be reduced by stabilizing the ground around the tunnel and by improving the contact between the lining and the surrounding ground through grouting.
* Tunnels are more stable under a symmetric load, which improves ground-lining interaction. Improving the tunnel lining by placing thicker and stiffer sections without stabilizing surrounding poor ground may result in excess seismic forces in the lining. Backfilling with non-cyclically mobile material and rock-stabilizing measures may improve the safety and stability of shallow tunnels.
* Damage may be related to peak ground acceleration and velocity based on the magnitude and epicentral distance of the affected earthquake.
* Duration of strong-motion shaking during earthquakes is of utmost importance because it may cause fatigue failure and therefore, large deformations.
* High frequency motions may explain the local spalling of rock or concrete along planes of weakness. These frequencies, which rapidly attenuate with distance, may be expected mainly at small distances from the causative fault.
* Ground motion may be amplified upon incidence with a tunnel if wavelengths are between one and four times the tunnel diameter.
* Damage at and near tunnel portals may be significant due to slope instability.
Earthquakes are one of nature's most formidable threats. A magnitude 6.7 earthquake shook the San Fernando valley in Los Angeles in 1994. The earthquake caused extensive damage to various structures, including buildings, freeway overpasses and road systems throughout the area. The National Center for Environmental Information estimates total damages to be 40 billion dollars. According to an article issued by Steve Hymon of TheSource – Transportation News and Views, there was no serious damage sustained by the LA subway system. Metro, the owner of the LA subway system, issued a statement through their engineering staff about the design and consideration that goes into a tunnel system. Engineers and architects perform extensive analysis as to how hard they expect earthquakes to hit that area. All of this goes into the overall design and flexibility of the tunnel.
This same trend of limited subway damage following an earthquake can be seen in many other places. In 1985 a magnitude 8.1 earthquake shook Mexico City; there was no damage to the subway system, and in fact the subway systems served as a lifeline for emergency personnel and evacuations. A magnitude 7.2 ripped through Kobe Japan in 1995, leaving no damage to the tunnels themselves. Entry portals sustained minor damages, however these damages were attributed to inadequate earthquake design that originated from the original construction date of 1965. In 2010 a magnitude 8.8, massive by any scale, afflicted Chile. Entrance stations to subway systems suffered minor damages, and the subway system was down for the rest of the day. By the next afternoon, the subway system was operational again.
Examples
In history
The history of ancient tunnels and tunneling in the world is reviewed in various sources which include many examples of these structures that were built for different purposes. Some well known ancient and modern tunnels are briefly introduced below:
* The qanat or kareez of Persia are water management systems used to provide a reliable supply of water to human settlements or for irrigation in hot, arid and semi-arid climates. The deepest known qanat is in the Iranian city of Gonabad, which after 2700 years, still provides drinking and agricultural water to nearly 40,000 people. Its main well depth is more than , and its length is .
* The Siloam Tunnel was built before 701 Common Era, BCE for a reliable supply of water, to withstand siege attacks.
* The Eupalinian aqueduct on the island of Samos
Samos (, also ; el, Σάμος ) is a Greek island in the eastern Aegean Sea, south of Chios, north of Patmos and the Dodecanese, and off the coast of western Turkey, from which it is separated by the -wide Mycale Strait. It is also a separate ...
(North Aegean, Greece
Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...
) was built in 520 BCE by the ancient Greek engineer Eupalinos of Megara under a contract with the local community. Eupalinos organised the work so that the tunnel was begun from both sides of Mount Kastro. The two teams advanced simultaneously and met in the middle with excellent accuracy, something that was extremely difficult in that time. The aqueduct was of utmost defensive importance, since it ran underground, and it was not easily found by an enemy who could otherwise cut off the water supply to Pythagoreion, the ancient capital of Samos
Samos (, also ; el, Σάμος ) is a Greek island in the eastern Aegean Sea, south of Chios, north of Patmos and the Dodecanese, and off the coast of western Turkey, from which it is separated by the -wide Mycale Strait. It is also a separate ...
. The tunnel's existence was recorded by Herodotus (as was the mole and harbour, and the third wonder of the island, the great temple to Hera, thought by many to be the largest in the Greek world). The precise location of the tunnel was only re-established in the 19th century by German archaeologists. The tunnel proper is and visitors can still enter it.
* One of the first known drainage and sewage networks in form of Drainage tunnel, tunnels was constructed at Persepolis in Iran at the same time as the construction of its foundation in 518 BCE. In most places the network was dug in the sound rock of the mountain and then covered by large pieces of rock and stone followed by earth and piles of rubble to level the ground. During investigations and surveys, long sections of similar rock tunnels extending beneath the palace area were traced by Herzfeld and later by Schmidt and their archeological teams.
* The Via Flaminia, an important Roman road, penetrated the Furlo pass in the Apennines through a tunnel which emperor Vespasian had ordered built in 76–77 CE. A modern road, the SS 3 Flaminia, still uses this tunnel, which had a precursor dating back to the 3rd century BCE; remnants of this earlier tunnel (one of the first road tunnels) are also still visible.
* The world's oldest tunnel traversing under a water body is claimed to be the ''Terelek kaya tüneli'' under Kızıl River, a little south of the towns of Boyabat and Durağan in Turkey, just downstream from where Kizil River joins its tributary Gökırmak. The tunnel is presently under a narrow part of a lake formed by a dam some kilometers further downstream. Estimated to have been built more than 2000 years ago, possibly by the same civilization that also built the royal tombs in a rock face nearby, it is assumed to have had a defensive purpose.
* Sapperton Canal Tunnel on the Thames and Severn Canal in England, dug through hills, which opened in 1789, was long and allowed Barge, boat transport of coal and other goods. Above it the Sapperton railway tunnel, Sapperton Long Tunnel was constructed which carries the "Golden Valley" railway line between Swindon and Gloucester.
* The 1791 Dudley Tunnel, Dudley canal tunnel is on the Dudley Canal, in Dudley, England. The tunnel is long. Closed in 1962 the tunnel was reopened in 1973. The series of tunnels was extended in 1984 and 1989.
* Fritchley Tunnel, constructed in 1793 in Derbyshire by the Butterley Company to transport limestone to its ironworks factory. The Butterley company engineered and built its own railway. A victim of the depression the company closed after 219 years in 2009. The tunnel is the world's oldest railway tunnel traversed by rail wagons. Gravity and horse haulage was utilised. The railway was converted to steam locomotion in 1813 using a Steam Horse locomotive engineered and built by the Butterley company, however reverted to horses. Steam trains used the tunnel continuously from the 1840s when the railway was converted to a narrow gauge. The line closed in 1933. In the Second World War, the tunnel was used as an air raid shelter. Sealed up in 1977 it was rediscovered in 2013 and inspected. The tunnel was resealed to preserved the construction as it was designated an ancient monument.
* The 1794 Butterley Tunnel, Butterley canal tunnel canal tunnel is 3,083 yards (2,819m) in length on the Cromford Canal in Ripley, Derbyshire, England. The tunnel was built simultaneously with the 1773 Fritchley Tunnel, Fritchley railway tunnel. The tunnel partially collapsed in 1900 splitting the Cromford Canal, and has not been used since. The Friends of Cromford Canal, a group of volunteers, are working at fully restoring the Cromford Canal and the Butterley Tunnel.
* The 1796 Stoddart Tunnel in Chapel-en-le-Frith in Derbyshire is reputed to be the oldest rail tunnel in the world. The rail wagons were originally horse-drawn.
* Smuggling tunnel#Derby Tunnels, Derby Tunnels in Salem, Massachusetts, were built in 1801 to smuggle imports affected by President Thomas Jefferson's new customs duties. Jefferson had ordered local militias to help the Custom House in each port collect these dues, but the smugglers, led by Elias Derby, hired the Salem militia to dig the tunnels and hide the spoil. The tunnels ran 3 miles connecting the wharfs in town to an underground train station. Along the way they connected prominent businessmen and politicians homes to their stores, bank, and museums. Members of the Salem Commons Fund hid the tunnels behind a project to fill in the ponds and grade the local common. Tunnel dirt was hidden in those ponds and was used to fill in rivers to create new wharfs to connect the tunnels to. Many politicians were involved including a Superior Court justice, a Secretary of the Navy, and many senators in the Federalist Party.
* A tunnel was created for the first true steam locomotive, from Penydarren to Abercynon. The Penydarren locomotive was built by Richard Trevithick. The locomotive made the historic journey from Penydarren to Abercynon in 1804. Part of this tunnel can still be seen at Pentrebach, Merthyr Tydfil, Wales. This is arguably the oldest railway tunnel in the world, dedicated only to self-propelled steam engines on rails.
* The Montgomery Bell Tunnel in Tennessee, an water diversion tunnel, , to power a water wheel, was built by slave labour in 1819, being the first full-scale tunnel in North America.
* Bourne's Tunnel, Rainhill, near Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
, England. long. Built in the late 1820s, the exact date is unknown, however probably built in 1828 or 1829. This is the first tunnel in the world constructed under a railway line. The construction of the Liverpool to Manchester Railway ran over a horse-drawn tramway that ran from the Sutton collieries to the Liverpool-Warrington turnpike road. A tunnel was bored under the railway for the tramway. As the railway was being constructed the tunnel was made operational, opening prior to the Liverpool tunnels on the Liverpool to Manchester line. The tunnel was made redundant in 1844 when the tramway was dismantled.
* Crown Street railway station, Crown Street station, Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
, England, 1829. Built by George Stephenson, a single track railway tunnel , was bored from Edge Hill to Crown Street to serve the world's first intercity passenger railway terminus station. The station was abandoned in 1836 being too far from Liverpool city centre, with the area converted for freight use. Closed down in 1972, the tunnel is disused. However it is the oldest passenger rail tunnel running under streets in the world.
* The 1829 Wapping Tunnel in Liverpool, England, at long on a twin track railway, was the first rail tunnel bored under a metropolis. The tunnel's path is from Edge Hill in the east of the city to Wapping Dock in the south end Liverpool docks. The tunnel was used only for freight terminating at the Park Lane railway goods station, Park Lane goods terminal. Currently disused since 1972, the tunnel was to be a part of the Merseyrail metro network, with work started and abandoned because of costs. The tunnel is in excellent condition and is still being considered for reuse by Merseyrail, maybe with an underground station cut into the tunnel for Liverpool university. The river portal is opposite the new Echo Arena Liverpool, King's Dock Liverpool Arena being an ideal location for a serving station. If reused the tunnel will be the oldest used underground rail tunnel in the world and oldest section of any underground metro system.
* 1832, Liverpool Lime Street railway station, Lime Street railway station tunnel, Liverpool. A two track rail tunnel, long was bored under the metropolis from Edge Hill in the east of the city to Lime Street in Liverpool's city centre. The tunnel was in use from 1832 being used to transport building materials to the new Lime St station while under construction. The station and tunnel was opened to passengers in 1836. In the 1880s the tunnel was converted to a deep cutting, open to the atmosphere, being four tracks wide. This is the only occurrence of a major tunnel being removed. Two short sections of the original tunnel still exist at Edge Hill station and further towards Lime Street, giving the two tunnels the distinction of being the oldest rail tunnels in the world still in use, and the oldest in use under streets. Over time a section of the deep cutting has been converted back into tunnel due to sections having buildings built over.
* Box Tunnel in England, which opened in 1841, was the longest railway tunnel in the world at the time of construction. It was dug by hand, and has a length of .
* The 1842 Prince of Wales Tunnel, in Shildon near Darlington, England, is the oldest sizeable tunnel in the world still in use under a settlement.
* The Victoria Tunnel (Newcastle), Victoria Tunnel Newcastle opened in 1842, is a 2.4 mile subterranean wagonway with a maximum depth of that drops from entrance to exit. The tunnel runs under Newcastle upon Tyne, England, and originally exited at the River Tyne. It remains largely intact. Originally designed to carry coal from Spital Tongues to the river, in WW2 part of the tunnel was used as a shelter. Under the management of a charitable foundation called the Ouseburn Trust it is currently used for heritage tours.
* The Thames Tunnel, built by Marc Isambard Brunel and his son Isambard Kingdom Brunel opened in 1843, was the first tunnel (after Terelek) traversing under a water body, and the first to be built using a tunnelling shield
A tunnelling shield is a protective structure used during the excavation of large, man-made tunnels. When excavating through ground that is soft, liquid, or otherwise unstable, there is a potential health and safety hazard to workers and the proj ...
. Originally used as a foot-tunnel, the tunnel was converted to a railway tunnel in 1869 and was a part of the East London Line of the London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
until 2007. It was the oldest section of the network, although not the oldest purpose built rail section. From 2010 the tunnel became a part of the London Overground network.
* The Victoria Tunnel (Liverpool), Victoria Tunnel/Waterloo Tunnel in Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
, England, was bored under a metropolis opening in 1848. The tunnel was initially used only for rail freight serving the Waterloo Freight terminal, and later freight and passengers serving the Liverpool Riverside railway station, Liverpool ship liner terminal. The tunnel's path is from Edge Hill in the east of the city to the north end Liverpool docks at Waterloo Dock (Liverpool), Waterloo Dock. The tunnel is split into two tunnels with a short open air cutting linking the two. The cutting is where the cable hauled trains from Edge Hill were hitched and unhitched. The two tunnels are effectively one on the same centre line and are regarded as one. However, as initially the long Victoria section was originally cable hauled and the shorter Waterloo section was locomotive hauled, two separate names were given, the short section was named the Waterloo Tunnel. In 1895 the two tunnels were converted to locomotive haulage. Used until 1972, the tunnel is still in excellent condition. A short section of the Victoria tunnel at Edge Hill is still used for shunting trains. The tunnel is being considered for reuse by the Merseyrail network. Stations cut into the tunnel are being considered and also reuse by a monorail system from the proposed Liverpool Waters redevelopment of Liverpool's Central Docks has been proposed.
* The vertex tunnel of the Semmering railway, the first Alpine tunnel, was opened in 1848 and was long. It connected rail traffic between Vienna, the capital of Austro-Hungarian Empire, and Trieste, its port.
* The Giovi Rail Tunnel through the Appennini Mounts opened in 1854, linking the capital city of the Kingdom of Sardinia, Turin, to its port, Genoa. The tunnel was long.
* The oldest underground sections of the London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
were built using the cut-and-cover method in the 1860s, and opened in January 1863. What are now the Metropolitan line, Metropolitan, Hammersmith & City and Circle lines were the first to prove the success of a rapid transit, metro or subway system.
*On 18 June 1868, the Central Pacific Railroad, Central Pacific Railroad's 1,659-foot (506 m) Summit Tunnel (Tunnel #6) at Donner Pass in the California Sierra Nevada (U.S.), Sierra Nevada mountains was opened, permitting the establishment of the commercial mass transportation of passengers and freight over the Sierras for the first time. It remained in daily use until 1993, when the Southern Pacific Railroad closed it and transferred all rail traffic through the 10,322-foot (3,146 m) long Tunnel #41 (a.k.a. "The Big Hole") built a mile to the south in 1925.
* In 1870, after fourteen years of works, the Fréjus Rail Tunnel was completed between France and Italy, being the second-oldest Alpine tunnel, long. At that time it was the longest in the world.
* The third Alpine tunnel, the Gotthard Rail Tunnel, between northern and southern Switzerland, opened in 1882 and was the longest rail tunnel in the world, measuring .
* The 1882 Col de Tende Road Tunnel, at long, was one of the first long road tunnels under a pass, running between France and Italy.
* As the last bit is drilled, on 26 October 2017, Ryfast becomes the longest undersea road tunnel with its 14.3 km length surpassing that of the tunnel under Tokyo Bay, Japan (9,583 m.), and previously the Shanghai Yangtze River Tunnel (8,950 m.). The tunnel is projected to open for use in 2019.
* The Mersey Railway tunnel opened in 1886, running from Liverpool to Birkenhead under the River Mersey. The Mersey Railway was the world's first deep-level underground railway. By 1892 the extensions on land from Birkenhead Park station to Liverpool Central Low level station gave a tunnel in length. The under river section is in length, and was the longest underwater tunnel in world in January 1886.
* The rail Severn Tunnel was opened in late 1886, at long, although only of the tunnel is actually under the River Severn. The tunnel replaced the Mersey Railway tunnel's longest under water record, which was held for less than a year.
* James Greathead, in constructing the City & South London Railway tunnel beneath the Thames, opened in 1890, brought together three key elements of tunnel construction under water: 1) shield method of excavation; 2) permanent cast iron tunnel lining; 3) construction in a compressed air environment to inhibit water flowing through soft ground material into the tunnel heading.
* Built in sections between 1890 and 1939, the section of London Underground's Northern line from Morden to East Finchley via Bank was the longest railway tunnel in the world at in length.
* St. Clair Tunnel, also opened later in 1890, linked the elements of the Greathead tunnels on a larger scale.
* In 1906 the fourth Alpine tunnel opened, the Simplon Tunnel, between Switzerland and Italy. It is long, and was the longest tunnel in the world until 1982. It was also the deepest tunnel in the world, with a maximum rock overlay of approximately .
* The 1927 Holland Tunnel
The Holland Tunnel is a vehicular tunnel under the Hudson River that connects the New York City neighborhood of Hudson Square in Lower Manhattan to the east with Jersey City in New Jersey to the west. The tunnel is operated by the Port Author ...
was the first underwater tunnel designed for automobiles. The construction required a novel Holland Tunnel#Ventilation system, ventilation system.
* In 1945 the Delaware Aqueduct tunnel was completed, supplying water to New York City in the US. At it is the longest tunnel in the world.
* In 1988 the long Seikan Tunnel in Japan was completed under the Tsugaru Strait, linking the islands of Honshu and Hokkaido. It was the longest railway tunnel in the world at that time.
Longest
* The Thirlmere Aqueduct in North West England, United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
is sometimes considered the longest tunnel, of any type, in the world at , though the aqueduct's tunnel section is not continuous.
* The Dahuofang Water Tunnel in China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
, opened in 2009, is the third longest water tunnel in the world at length.
* The Gotthard Base Tunnel
, rm, Tunnel da basa dal Sogn Gottard
, image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg
, image_size = 250
, caption = Turnout at Faido multifunction station
, line = Gotthard Line
, location = Switzerland (Uri, Grisons and ...
in Switzerland
). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
, opened in 2016, is the longest and deepest railway tunnel in the world at length and maximum depth below the Saint-Gotthard Massif, Gotthard Massif. It provides a NRLA, flat transit route between the North and South of Europe under the Swiss Alps, at a maximum elevation of .
* The Seikan Tunnel in Japan connects the main island of Honshu with the northern island of Hokkaido by rail. It is long, of which are crossing the Tsugaru Strait undersea.
* The Channel Tunnel
The Channel Tunnel (french: Tunnel sous la Manche), also known as the Chunnel, is a railway tunnel that connects Folkestone (Kent, England, UK) with Coquelles ( Hauts-de-France, France) beneath the English Channel at the Strait of Dover. ...
crosses the English Channel between France and the United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
. It has a total length of , of which are the world's longest undersea tunnel section.
* The Lötschberg Base Tunnel in Switzerland
). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
was the longest land rail tunnel, with a length of , from its inauguration in 2007 until the completion of the Gotthard Base Tunnel
, rm, Tunnel da basa dal Sogn Gottard
, image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg
, image_size = 250
, caption = Turnout at Faido multifunction station
, line = Gotthard Line
, location = Switzerland (Uri, Grisons and ...
in 2016.
* The Lærdal Tunnel in Norway from Lærdal to Aurland is the world's longest road tunnel, intended for cars and similar vehicles, at .
* The Zhongnanshan Tunnel in People's Republic of China opened in January 2007 is the world's second longest highway tunnel and the longest mountain road tunnel in Asia, at .
* The longest canal tunnel is the Rove Tunnel in France, over long.
Notable
* The Moffat Tunnel, opened in 1928, passes under the Continental Divide of the Americas in Colorado. The tunnel is long and at an elevation of is the highest active railroad tunnel in the U.S. (The inactive Tennessee Pass Line and the historic Alpine Tunnel are higher.)
* Williamson's tunnels in Liverpool
Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a popul ...
, from 1804 and completed around 1840 by a wealthy eccentric, are probably the largest underground folly in the world. The tunnels were built with no functional purpose.
* The Chicago Tunnel Company, Chicago freight tunnel network is the largest urban street tunnel network, comprising of tunnels beneath the majority of downtown Chicago streets. It operated between 1906 and 1956 as a freight network, connecting building basements and railway stations. Following a Chicago flood, 1992 flood the network was sealed, although some parts still carry utility and communications infrastructure.
* The Pennsylvania Turnpike opened in 1940 with seven tunnels, most of which were bored as part of the stillborn South Pennsylvania Railroad and giving the highway the nickname "Tunnel Highway". Four of the tunnels (Allegheny Mountain Tunnel, Allegheny Mountain, Tuscarora Mountain Tunnel, Tuscarora Mountain, Kittatinny Mountain Tunnel, Kittatinny Mountain, and Blue Mountain Tunnel, Blue Mountain) remain in active use, while the other three (Laurel Hill Tunnel, Laurel Hill, Rays Hill Tunnel, Rays Hill, and Sideling Hill Tunnel, Sideling Hill) were bypassed in the 1960s; the latter two tunnels are on a bypassed section of the Turnpike now commonly known as the Abandoned Pennsylvania Turnpike.
* The Essingeleden, Fredhälls road tunnel was opened in 1966, in Stockholm, Sweden, and the Elbe Tunnel (1975), New Elbe road tunnel opened in 1975 in Hamburg, Germany. Both tunnels handle around 150,000 vehicles a day, making them two of the most trafficked tunnels in the world.
* The Honningsvåg Tunnel ( long) opened in 1999 on European route E69 in Norway as the world's northernmost road tunnel, except for mines (which exist on Svalbard).
* The Central Artery road tunnel in Boston, Massachusetts, is a part of the larger Big Dig (Boston, Massachusetts), Big Dig completed around 2007, and carries approximately 200,000 vehicles/day under the city along Interstate 93, U.S. Route 1 in Massachusetts, US Route 1, and Massachusetts Route 3, which share a Concurrency (road), concurrency through the tunnels. The Big Dig replaced Boston's old badly deteriorated I-93 elevated highway.
* The Stormwater Management And Road Tunnel or SMART Tunnel, is a combined storm drainage and road structure opened in 2007 in Kuala Lumpur, Malaysia. The tunnel is the longest stormwater drainage tunnel in South East Asia and second longest in Asia. The facility can be operated as a simultaneous traffic and stormwater passage, or dedicated exclusively to stormwater when necessary.
* The Eiksund Tunnel on national road Rv 653 in Norway is the world's deepest subsea road tunnel, measuring long, with deepest point at below the sea level, opened in February 2008.
* Gerrards Cross Tunnel, Gerrards Cross railway tunnel, in England, opened in 2010, is notable in that it converted an existing railway cutting into a tunnel to create ground to build a supermarket over the tunnel. The railway in the cutting was first opened around 1906, stretching over 104 years to complete a railway tunnel. The tunnel was built using the cover method with craned in prefabricated forms in order to keep the busy railway operating. A branch of the Tesco supermarket chain occupies the newly created ground above the railway tunnel, with an adjacent existing railway station at the end of the tunnel. During construction, a portion of the tunnel collapsed when soil cover was added. The prefabricated forms were covered with a layer of reinforced concrete after the collapse.
* The Fenghuoshan tunnel, completed in 2005 on the Qinghai-Tibet railway is the world's highest railway tunnel, about above sea level and long.
* The La Línea (Road Pass), La Linea Tunnel in Colombia, 2016, is the longest, , mountain tunnel in South America. It crosses beneath a mountain at above sea level with six traffic lanes, and it has a parallel emergency tunnel. The tunnel is subject to serious groundwater pressure. The tunnel will link Bogotá and its urban area with the coffee-growing region, and with the main port on the Colombian Pacific coast.
* The Tunnel and Reservoir Plan, Chicago Deep Tunnel Project is a network of of drainage tunnels designed to reduce flooding in the Chicago metropolitan area, Chicago area. Started in the mid-1970s, the project is due to be completed in 2029.
* New York City Water Tunnel No. 3, started in 1970, has an expected completion beyond 2026, and will measure more than .
Mining
The use of tunnels for mining is called drift mining.
Military use
Some tunnels are not for transport at all but rather, are fortifications, for example Mittelwerk and Cheyenne Mountain Complex. Excavation techniques, as well as the construction of underground bunkers and other habitable areas, are often associated with tunnel warfare, military use during armed conflict, or civilian responses to threat of attack. Another use for tunnels was for the storage of chemical weapon
Secret tunnels
secret passage, Secret tunnels have given entrance to or escape from an area, such as the Cu Chi Tunnels or the Gaza Strip smuggling tunnels, smuggling tunnels in the Gaza Strip which connect it to Egypt. Although the Underground Railroad network used to transport escaped slaves was "underground" mostly in the sense of secrecy, hidden tunnels were occasionally used. Secret tunnels were also used during the Cold War, under the Berlin Wall and elsewhere, to smuggle refugees, and for espionage.
Smugglers use secret tunnels to transport or store contraband
Contraband (from Medieval French ''contrebande'' "smuggling") refers to any item that, relating to its nature, is illegal to be possessed or sold. It is used for goods that by their nature are considered too dangerous or offensive in the eyes o ...
, such as illegal drugs and weapon
A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, s ...
s. Elaborately engineered tunnels built to smuggle drugs across the Mexico-US border were estimated to require up to 9 months to complete, and an expenditure of up to $1 million. Some of these tunnels were equipped with lighting, ventilation, telephones, drainage pumps, hydraulic elevators, and in at least one instance, an electrified rail transport system. Secret tunnels have also been used by thieves to break into bank vaults and retail stores after hours. Several tunnels have been discovered by the Border Security Forces across the Line of Control along the India-Pakistan border, mainly to allow terrorists access to the Indian territory of Jammu and Kashmir (union territory), Jammu and Kashmir.
The actual usage of erdstall tunnels is unknown but theories connect it to a rebirth ritual.
Natural tunnels
* Lava tubes are emptied lava conduits, formed during volcanic eruptions by flowing and cooling lava.
* Natural Tunnel State Park (Virginia, US) features an natural tunnel, really a limestone cave, that has been used as a railroad tunnel since 1890.
* Punarjani Guha in Kerala, India. Hindus believe that crawling through the tunnel (which they believe was created by a Hindu god) from one end to the other will wash away all of one's sins and thus allow one to attain rebirth. Only men are permitted to crawl through the tunnel.
* Torghatten, a Norwegian island with a hat-shaped silhouette, has a natural tunnel in the middle of the hat, letting light come through. The long, high, and wide tunnel is said to be the hole made by an arrow of the angry troll Hestmannen, the hill being the hat of the troll-king of Sømna trying to save the beautiful Lekamøya. The tunnel is thought actually to be the work of ice. The sun shines through the tunnel during two few minutes long periods every year.[The hobby photograph has waited three years for this rare shot of the sun shining through Torghatten mount]
* Small "snow tunnels", called burrows, are created by voles, chipmunks and other rodents for protection and access to food sources.
Major accidents
* Clayton Tunnel rail crash (1861) – confusion about block signals leading to collision, 23 killed.
* Welwyn Tunnel rail crash (1866) – train failed in tunnel, guard did not protect train.
* Paris Métro train fire (1904) - train fire in Couronnes underground station, 84 killed by smoke and gases.
* Balvano train disaster
The Balvano train disaster was the deadliest railway accident in Italian history and one of the worst railway disasters ever. It occurred on the night between 2–3 March 1944 in Balvano, Basilicata. Over 500 people in a steam-hauled, coal-burning ...
(1944) - asphyxiation of about 500 "unofficial" passengers on freight train.
* Caldecott Tunnel fire (1982) – major motor vehicle tunnel crash and fire.
* 1996 Channel Tunnel fire, Channel Tunnel fire (1996)
* Death of Diana, Princess of Wales, Princess Diana's death (1997) – Car crash in Pont de l'Alma tunnel, Paris, which killed Princess Diana.
* Mont Blanc tunnel fire, Mont Blanc Tunnel fire (1999)
See also
*Euphrates Tunnel
*Cattle creep
*Culvert
*Hobby tunneling
*Megaproject
* Rapid transit
*Sequential Excavation Method
*Structure gauge – measure of maximum physical clearance in a tunnel
*Tree tunnel – tunnel-like effect from tree canopies above a road
*Tunnel tree – tunnel bored through the trunk of a tree
*Tunnels in popular culture
* Underground living
*United States Army Corps of Engineers
References
Bibliography
*
* Railway Tunnels in Queensland by Brian Webber, 1997, .
* Sullivan, Walter
Progress In Technology Revives Interest In Great Tunnels
New York Times, 24 June 1986. Retrieved 15 August 2010.
External links
ITA-AITES International Tunnelling Association
Tunnels & Tunnelling International magazine
{{Authority control
Tunnels,
Crossings
Civil engineering
Transport buildings and structures
Earthworks (engineering)