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A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for 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 si ...
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 on roads consists of ''road users'' including pedestrians, ridden or herded animals, vehicle A vehicle (from la, vehiculum) is a machine that transport Transport (commonly used in the U.K.), or transportation (used in th ...

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 Film *Rails (film), ''Rails'' (film), a 1929 Italian film by Mario Camerini *Rail (1967 fil ...

rail
traffic, or for a
canal Canals are waterways Channel (geography), channels, or artificial waterways, for water conveyance, or to service water transport vehicles. They may also help with irrigation. It can be thought of as an artificial version of a river. Canals ...
. The central portions of a
rapid transit Rapid transit or mass rapid transit (MRT), also known as heavy rail, metro, subway, tube, U-Bahn, metropolitana or underground, is a type of high-capacity public transport generally found in urban areas. Unlike buses or trams, rapid transit s ...
network are usually in the tunnel. Some tunnels are used as sewers or
aqueducts Aqueduct may refer to: Bridges *Aqueduct (bridge) Aqueduct of Vanvitelli, Italy, built by Luigi Vanvitelli. It is a World Heritage Site and one of the finest examples of an aqueduct in Europe. Aqueducts or water bridges are bridges constructe ...
to supply water for consumption or for
hydroelectric Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to produce electricity or to power machin ...
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 ...

Utility tunnel
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 A prison (also known as a jail or gaol (dated, British, Australian, and to a lesser extent Canadian ...
of
weapon A weapon, arm or armament is any implement or device that can be used with the intent to inflict damage or harm. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, self-defense, and w ...
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 of ...
, or
people A people is a plurality of person A person (plural people or persons) 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 s ...

people
. Special tunnels, such as
wildlife crossing Wildlife crossings are structures that allow animals to cross human-made barriers safely. Wildlife crossings may include Tunnel, underpass tunnels or wildlife tunnels, viaducts, and overpasses or green bridges (mainly for large or herd-type animals) ...

wildlife crossing
s, are built to allow wildlife to cross human-made barriers safely. Tunnels can be connected together in
tunnel network In transport, tunnel A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used imme ...
s.


Terminology

A tunnel is relatively long and narrow; the length is often much greater than twice the
diameter In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...
, 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,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shortha ...

United Kingdom
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 Commercial and cultural venues * The Underground (Boston), a music club in the Allston neighborhood ...

Underground
" or the "
Tube Tube or tubes may refer to: *Tube (2003 film), ''Tube'' (2003 film), a 2003 Korean film *The Tube (TV series), ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom *"Tubes" (Peter Dale), performer on the Soccer AM ...

Tube
" in
London London is the capital city, capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom. The city stands on the River Thames in the south-east of England, at the head of its estuary leading to the Nor ...

London
, the "
Subway
Subway
" in
Glasgow Glasgow ( ; sco, Glesga; gd, Glaschu) is the most populous city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science ...
, and the "
Metro Metro, short for metropolitan, may refer to: Geography * Metro (city), a city in Indonesia * A metropolitan area A metropolitan area or metro is a region consisting of a densely populated core city, urban core and its less-populated surro ...
" in
NewcastleNewcastle usually refers to either: *Newcastle upon Tyne Newcastle upon Tyne (, ), often simply Newcastle, is the most populous City status in the United Kingdom, city and metropolitan borough in North East England. It forms the Tyneside conurbati ...

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 A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to ...

bridge
or, if passing under a canal, an
aqueduct Aqueduct may refer to: Bridges *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, railways or r ...
. 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. 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 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 A bridge is a Nonbuilding structure, structure built to Span (engineering), span a physical obstacle, such as a body of water, valley, or road, ...

footbridge
s.


History

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. These deposits form a mineralized commodity that is of economic interest to t ...

mining
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 ...
. 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 words. By extension, th ...
of the terms "mining" (for mineral extraction or for siege attacks), "military engineering", and "
civil engineering Civil engineering is a Regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, ...
" reveals these deep historic connections.


Antiquity and early middle ages

Predecessors of modern tunnels were
adit Gated entrance of an abandoned adit near Medford, Oregon, United States 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, ...
s to transport water for
irrigation Irrigation is the artificial process of applying controlled amounts of water to land to assist in production of crops. Irrigation helps to grow agricultural crops, maintain landscapes, and revegetate disturbed soils in dry areas and during p ...

irrigation
or drinking, and
sewerage Sewerage is the infrastructure Infrastructure is the set of fundamental facilities and systems that support the sustainable functionality of households and firms. Serving a country, city, or other area, including the services and facilities nece ...
. The first
Qanat A qanat or kariz, is a system for transporting water from an aquifer An aquifer is an underground layer of water-bearing permeability (Earth sciences), permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt). Groun ...

Qanat
s are known from before 2000 B.C. The
Tunnel of Eupalinos
Tunnel of Eupalinos
is a tunnel
aqueduct Aqueduct may refer to: Bridges *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, railways or r ...
long running through Mount Kastro in
Samos Samos (, also ; el, Σάμος ) is a Greek island in the eastern Aegean Sea The Aegean Sea ; tr, Ege Denizi is an elongated Bay, embayment of the Mediterranean Sea located between Europe's Geography of Europe, Balkan peninsula and Asia' ...
,
Greece Greece ( el, Ελλάδα, Elláda, ), officially the Hellenic Republic, is a country located in Southeastern Europe Southeast Europe or Southeastern Europe () is a geographical region of Europe Europe is a continent A contin ...

Greece
, built in the 6th century BC to serve as an
aqueduct Aqueduct may refer to: Bridges *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, railways or r ...
. It is the second known tunnel to have been excavated from both ends, after the
Siloam tunnel The newer Siloam Tunnel ( he, נִקְבַּת הַשִּׁלֹחַ, ''Nikbat HaShiloah''), also known as Hezekiah's Tunnel, is a water channel that was carved beneath the City of David The City of David ( he, עיר דוד, ''Ir David''), calle ...
in the neighbourhood of
Silwan Silwan or Siloam ( ar, سلوان, translit=Siloan, he, כְּפַר הַשִּׁילוֹחַ, translit=''Kfar ha-Shiloaḥ'', gr, Σιλωὰμ, translit=Siloam) is a predominantly Palestinians, Palestinian neighborhood in East Jerusalem, o ...

Silwan
in eastern
Jerusalem Jerusalem (; he, יְרוּשָׁלַיִם ; ar, القُدس, ', , (combining the Biblical and common usage Arabic names); grc, Ἱερουσαλήμ/Ἰεροσόλυμα, Hierousalḗm/Hierosóluma; hy, Երուսաղեմ, Erusałē ...

Jerusalem
. In
Ethiopia Ethiopia, officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea and Djibouti to the north, Somaliland to the northeast, Somalia to the east, Kenya to the south ...

Ethiopia
, the Siqurto foot tunnel, 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 Water is an Inorganic compound, inorganic, Transparency a ...
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 Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usabl ...

Groundwater
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 for ...
, 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 at the corners.


Choice of tunnels versus bridges

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 in East Sussex East Sussex is a county A county is a geographical region of a country used for administrative or other purposesChamber ...
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 and the urban core of the New York metropolitan area, is the most densely populated of the five boroughs of New York City New York City (NYC), often simply called New York, is the List of Unit ...

Manhattan
and urban
Hong Kong Hong Kong (, ), officially the Hong Kong Special Administrative Region of the People's Republic of China (HKSAR) (), is a metropolitan area and Special administrative regions of China, special administrative region of the China, People's Repu ...

Hong Kong
, this is a strong factor in favor of a tunnel. Boston's
Big Dig The Central Artery/Tunnel Project (CA/T), 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 km) t ...
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 The Queensway tunnel is a road tunnel under the River Mersey, in the north west of England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotla ...
under the
River Mersey The River Mersey () is a river in the North West England, North West of England. Its name is derived from the Anglo-Saxon language and translates as "boundary river". The river may have been the border between the ancient kingdoms of Mercia and ...
at
Liverpool Liverpool is a City status in the United Kingdom, city and metropolitan borough in Merseyside, England. Its population in 2019 was approximately , making it the List of English districts by population, tenth-largest English district by popu ...

Liverpool
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 road, A59. It was built because the Queensway Tunnel – which was built in the 1930s to carry vehi ...
under the Mersey. In
Hampton Roads, Virginia Hampton Roads is the name of both a body of water that serves as a wide channel for the James, Nansemond and Elizabeth rivers between Old Point Comfort and Sewell's Point Sewells Point is a peninsula A peninsula ( la, paeninsula from ...
, tunnels were chosen over bridges for strategic considerations; in the event of damage, bridges might prevent
US Navy ), (unofficial)."''Non sibi sed patriae''" ( en, "Not for self but for country") (unofficial). , colors = Blue and gold  , colors_label = Colors , march = " Anchors Aweigh" ...
vessels from leaving
Naval Station Norfolk Naval Station Norfolk is a United States Navy ), (unofficial)."''Non sibi sed patriae''" ( en, "Not for self but for country") (unofficial). , colors = Blue and gold  , colors_label = Colors , mar ...

Naval Station Norfolk
. Water-crossing tunnels built instead of bridges include the
Holland Tunnel The Holland Tunnel is a vehicular tunnel A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent ...

Holland Tunnel
and
Lincoln Tunnel The Lincoln Tunnel is an approximately tunnel A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline is not a tunnel, though some ...

Lincoln Tunnel
between
New Jersey New Jersey is a U.S. state, state in the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. It is bordered on the north and east by the state of New York (state), New York; on the ...
and Manhattan in
New York City New York City (NYC), often simply called New York, is the List of United States cities by population, most populous city in the United States. With an estimated 2019 population of 8,336,817 distributed over about , New York City is also the L ...

New York City
; the Queens-Midtown Tunnel between Manhattan and the
borough A borough is an administrative division Administrative division, administrative unit,Article 3(1). country subdivision, administrative region, subnational entity, first-level subdivision, as well as many similar terms, are generic names for g ...
of
Queens Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. It is the largest borough of New York City New York City (NYC), often simply called New York, is the List of United States cities by po ...

Queens
on
Long Island Long Island is a densely populated island in the southeast part of the U.S. state of New York (state), New York, part of the New York metropolitan area. At New York Harbor, it begins approximately east of Manhattan, Manhattan Island and exten ...
; the Detroit-Windsor Tunnel between
Michigan Michigan () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

Michigan
and
Ontario , Label_map = yes , image_map = Ontario in Canada 2.svg , map_alt = Map showing Ontario's location east/central of Canada. , coordinates = , capital = Toronto , larges ...

Ontario
; and the Elizabeth River tunnels between
Norfolk Norfolk () is a Counties of England, county in East Anglia in England. It borders Lincolnshire to the northwest, Cambridgeshire to the west and southwest, and Suffolk to the south. Its northern and eastern boundaries are the North Sea and to t ...
and
Portsmouth, Virginia Portsmouth is an Independent city (United States), independent city in Virginia southwest and across the Elizabeth River (Virginia), Elizabeth River from Norfolk, Virginia, Norfolk. As of the 2010 United States Census, 2010 census, the population ...
; the 1934
River Mersey The River Mersey () is a river in the North West England, North West of England. Its name is derived from the Anglo-Saxon language and translates as "boundary river". The river may have been the border between the ancient kingdoms of Mercia and ...
road
Queensway Tunnel The Queensway tunnel is a road tunnel under the River Mersey, in the north west of England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotla ...
; the
Western Scheldt Tunnel Western Scheldt Tunnel ( nl, Westerscheldetunnel, Westerscheldetunnel) is a tunnel in the Netherlands The Netherlands ( nl, Nederland ), informally referred to as Holland, is a country primarily located in Western Europe and partly in the Dutc ...
, Zeeland, Netherlands; and the tunnel in
Pittsburgh, Pennsylvania Pittsburgh ( ) is a city in the Commonwealth (U.S. state), Commonwealth of Pennsylvania in the United States and the county seat of Allegheny County, Pennsylvania, Allegheny County. A population of 302,971 residents lives within the city limits ...

Pittsburgh, Pennsylvania
. 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: link=no, Le tunnel sous la Manche), also referred to as the Eurotunnel or Chunnel, is a railway tunnel that connects Folkestone (Kent Kent is a Counties of England, county in South East England and one of the h ...
), 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 and the
Chesapeake Bay Bridge-TunnelChesapeake often refers to: * Chesapeake people, a Native American tribe also known as the Chesepian * The Chesapeake, a.k.a. Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic ...
in
Virginia Virginia (), officially the Commonwealth of Virginia, is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic and Southeastern United States, Southeastern regions of the United States, between the East Coast of the United St ...

Virginia
. 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 Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodi ...
te users, as happened at the
Gotthard Road Tunnel The Gotthard Road Tunnel in Switzerland ,german: Schweizer(in),french: Suisse(sse), it, svizzero/svizzera or , rm, Svizzer/Svizra , government_type = Federalism, Federal semi-direct democracy under a multi-party assembly-independent Directo ...
in
Switzerland ,german: Schweizer(in),french: Suisse(sse), it, svizzero/svizzera or , rm, Svizzer/Svizra , government_type = Federalism, Federal semi-direct democracy under a multi-party assembly-independent Directorial system, directorial republic , leader_t ...

Switzerland
in 2001. One of the worst railway disasters ever, the Balvano train disaster, was caused by a train stalling in the Armi tunnel in
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a Northern Italy, continental part, delimited by the Alps, a Italian Peninsula, peninsula and List of islands of Italy, se ...

Italy
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 Project team, 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 pr ...
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 Working on a project WBS A work-breakdown structure (WBS) in project management Project management is the process of leading the work of a team to achieve goals and meet success criteria at a specified time. The primary challenge of project mana ...
(WBS) and
critical path method The critical path method (CPM), or critical path analysis (CPA), is an algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorit ...
(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 Research is "creativity, creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization, and analysis of information to increase understanding of a topic or is ...
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 New Jersey is a U.S. state, state in the Mid-Atlanti ...
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

Cut-and-cover is a simple method of construction for shallow tunnels where a
trench A gas main being laid in a trench A trench is a type of excavation or depression 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). ...
is excavated and
roof A roof is the top covering of a building A building, or edifice, is a structure with a roof and walls standing more or less permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, ...

roof
ed over with an overhead support system strong enough to carry the load of what is to be built above the tunnel. Two basic forms of cut-and-cover tunneling are available: * ''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 walling 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 The tunnelling shield used for the construction of the Xinyi Line on the Taipei Metro system in Taiwan. A tunnelling shield is a protective structure used during the excavation of large, man-made tunnels. When excavating through ground that is so ...
. 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 A metropolitan area or metro is a region consisting of a densely populated core city, urban core and its less-populated surro ...
stations, such as
Canary Wharf tube station Canary Wharf is a 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, ...
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 ...

London Underground
, where bored tunnels were used for stations and passenger access. Nevertheless, the original parts of the London Underground network, the Metropolitan and District Railways, were constructed using cut-and-cover. These lines pre-dated electric traction and the proximity to the surface was useful to ventilate the inevitable smoke and steam. A major disadvantage of cut-and-cover is the widespread disruption generated at the surface level during construction. 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 Boring (eart ...
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 ...
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 Phreatic zone, 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 s ...

water table
. 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, Glarus, Linthal in the canton of Glarus, Switzerland. The system uses five reservoirs and four power stations at steep variations in altitude. ...
located south of
LinthalLinthal may refer to: * Linthal, Glarus, a settlement in the upper valley of the Linth river, in the canton of Glarus in Switzerland * Linthal, Haut-Rhin, a commune in the Haut-Rhin department in Alsace in north-eastern France * The valley of the L ...
in the
canton of Glarus The canton of Glarus or canton of Glaris (german: Kanton Glarus ) is a cantons of Switzerland, canton in east central Switzerland. The capital is Glarus. The population speaks a variety of Alemannic German. The majority of the population (81%) iden ...
. The borehole has a diameter of . The four TBMs used for excavating the
Gotthard Base Tunnel it, Galleria di base del San Gottardo rm, Tunnel da basa dal Son Gottardfrench: Tunnel de base du Saint-Gothard , image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg , image_size = 250 , caption = Turnout at Faido multifunction st ...

Gotthard Base Tunnel
, in
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Switzerland
, 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 Belgium–Netherlands border, Belgian border, w ...
in the Netherlands, with a diameter of . This in turn was superseded by the Madrid M30 ringroad,
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Spain
, and the tunnels in
Shanghai Shanghai (, , Standard Chinese, Standard Mandarin pronunciation: ) is one of the four Direct-administered municipalities of China, direct-administered municipalities of the China, People's Republic of China. The city is located on the sout ...

Shanghai
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the List of countries and dependencies by population, world's most populous country, with a population of around 1.4 billion. Covering approximately 9.6& ...
. All of these machines were built at least partly by
Herrenknecht Herrenknecht AG is a German construction equipment manufacturer. The company manufactures 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 ...
. , the world's largest TBM was "
Big BerthaBig Bertha is a Phonaesthetics, euphonious term for an unusually large example of a class of object; notable examples include: Military guns * Big Bertha (howitzer), a heavy mortar-like howitzer built and used by Germany during World War I ** Paris ...
", 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, Heavy equipment (construction), construct ...
, 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 Seattle ( ) is a port, seaport city on the West Coast of the United States. It is the county seat, seat ...
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 bot ...

Seattle, Washington
(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,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shortha ...

United Kingdom
of digging tunnels in strong clay-based soil structures. Unlike previous manual methods of using
mattock A mattock is a hand tool A hand tool is any tool that is powered manual labour, by hand rather than a motor. Categories of hand tools include wrenches, pliers, cutter (disambiguation), cutters, File (tool), files, hammer, striking tools, chise ...

mattock
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 Victorian or Victorians may refer to: 19th century * Victorian era, British history during Queen Victoria's 19th-century reign ** Victorian architecture ** Victorian house ** Victorian decorative arts ** Victorian fashion ** Victorian literature ...
civil engineering, the method found favor in the renewal of Britain's ancient
sewerage Sewerage is the infrastructure Infrastructure is the set of fundamental facilities and systems that support the sustainable functionality of households and firms. Serving a country, city, or other area, including the services and facilities nece ...
systems, by not having to remove all property or infrastructure to create a small tunnel system. During the
First World War World War I, often abbreviated as WWI or WW1, also known as the First World War or the Great War, was a global war that began on 28 July 1914 and ended on 11 November 1918. It involved much of Europe, as well as Russia, the Unite ...
, the system was used by
Royal Engineer tunnelling companies Royal Engineer tunnelling companies were specialist units of the Corps of Royal Engineers The Corps of Royal Engineers, usually just called the Royal Engineers (RE), and commonly known as the '' Sappers'', is a corps Corps (; plural ''corps ...
to put mines beneath the
German Empire The German Empire or the Imperial State of Germany,, officially '.Herbert Tuttle Herbert Tuttle (1846–1894) was an American historian. Biography Herbert Tuttle was born in Bennington, Vermont Bennington is a New England town, town ...
lines. The method was virtually silent and so not susceptible to listening methods of detection.


Shafts

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 whic ...
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 ventilation shaft Image:Velsertunnel ventilatiegebouw noord.png, Ventilation shafts of the Velsen, Velser tunnel, the Netherlands In subterranean civil engineering, ventilation shafts, also known as airshafts or vent shafts, are vertical pass ...
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 A tunnel is an underground passageway, dug through the surrounding soil/e ...
(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 of the surrounding
rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition and the way in w ...
mass Mass is the physical quantity, quantity of ''matter'' in a physical body. It is also a measure (mathematics), measure of the body's ''inertia'', the resistance to acceleration (change of velocity) when a net force is applied. An object's mass ...
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#REDIRECT geotechnical engineering#REDIRECT geotechnical engineering {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...

geotechnical
measurements, an optimal
cross section Cross section may refer to: * Cross section (geometry), the intersection of a 3-dimensional body with a plane * Cross section (electronics), a common sample preparation technique in electronics * Cross section (geology), the intersection of a 3-dim ...
is computed. The excavation is protected by a layer of sprayed concrete, commonly referred to as
shotcrete Shotcrete nozzle with 75  mm concrete hose from line pump and 20 mm compressed air line. Image:Shotcrete Covered Cliff Auckland.jpg, Shotcrete-stabilized cliff above a motorway in New Zealand Shotcrete, gunite (), or sprayed concre ...
. 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 (mechanics), 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) 250px, Display device of a medical monitor as used in anesthesia. In medicine, monitoring is the observation of a disease, condition or one or several m ...
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 tools for tunnel Strength of materials, strengthening.


Pipe jacking

In pipe jacking, hydraulic jacks 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. Submerged floating tunnels 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 spoil tip, excavated spoil, often narrow gauge so that it can be double track to allow the operation of empty and loaded trains at the same time. The temporary way is replaced by the permanent way 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 status in the United Kingdom, city and metropolitan borough in Merseyside, England. Its population in 2019 was approximately , making it the List of English districts by population, tenth-largest English district by popu ...

Liverpool
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 Chinese, Standard Mandarin pronunciation: ) is one of the four Direct-administered municipalities of China, direct-administered municipalities of the China, People's Republic of China. The city is located on the sout ...

Shanghai
, 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 Seattle ( ) is a port, seaport city on the West Coast of the United States. It is the county seat, seat ...
, 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 City (NYC), often simply called New York, is the List of United States cities by population, most populous city in the United States. With an estimated 2019 population of 8,336,817 distributed over about , New York City is also the L ...

New York City
's 63rd Street Tunnel under the East River, between the boroughs of
Manhattan Manhattan (), known regionally as the City and the urban core of the New York metropolitan area, is the most densely populated of the five boroughs of New York City New York City (NYC), often simply called New York, is the List of Unit ...

Manhattan
and
Queens Queens is a borough of New York City, coextensive with Queens County, in the U.S. state of New York. It is the largest borough of New York City New York City (NYC), often simply called New York, is the List of United States cities by po ...

Queens
, 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 The Queensway tunnel is a road tunnel under the River Mersey, in the north west of England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotla ...
under the
River Mersey The River Mersey () is a river in the North West England, North West of England. Its name is derived from the Anglo-Saxon language and translates as "boundary river". The river may have been the border between the ancient kingdoms of Mercia and ...
between
Liverpool Liverpool is a City status in the United Kingdom, city and metropolitan borough in Merseyside, England. Its population in 2019 was approximately , making it the List of English districts by population, tenth-largest English district by popu ...

Liverpool
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 Aqueduct may refer to: Bridges *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, railways or r ...
, 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

The term underpass refers to a road or railway 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 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. Motor vehicle tunnels usually require
ventilation shaft ventilation shaft Image:Velsertunnel ventilatiegebouw noord.png, Ventilation shafts of the Velsen, Velser tunnel, the Netherlands In subterranean civil engineering, ventilation shafts, also known as airshafts or vent shafts, are vertical pass ...
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), 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 km) t ...
tunnel in Boston, Massachusetts, may have a dedicated 24-hour manned 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

's watercolour of the Edge Hill tunnel portals . This and a short section of the original tunnel nearer to Lime Street, are the oldest rail tunnels in the world still in active use. and used to drill the first large tunnels through the Alps. 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 The Aegean Sea ; tr, Ege Denizi is an elongated Bay, embayment of the Mediterranean Sea located between Europe's Geography of Europe, Balkan peninsula and Asia' ...
(North Aegean,
Greece Greece ( el, Ελλάδα, Elláda, ), officially the Hellenic Republic, is a country located in Southeastern Europe Southeast Europe or Southeastern Europe () is a geographical region of Europe Europe is a continent A contin ...

Greece
) 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 The Aegean Sea ; tr, Ege Denizi is an elongated Bay, embayment of the Mediterranean Sea located between Europe's Geography of Europe, Balkan peninsula and Asia' ...
. 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 status in the United Kingdom, city and metropolitan borough in Merseyside, England. Its population in 2019 was approximately , making it the List of English districts by population, tenth-largest English district by popu ...

Liverpool
, 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 status in the United Kingdom, city and metropolitan borough in Merseyside, England. Its population in 2019 was approximately , making it the List of English districts by population, tenth-largest English district by popu ...

Liverpool
, 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 The tunnelling shield used for the construction of the Xinyi Line on the Taipei Metro system in Taiwan. A tunnelling shield is a protective structure used during the excavation of large, man-made tunnels. When excavating through ground that is so ...
. 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 ...

London Underground
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 status in the United Kingdom, city and metropolitan borough in Merseyside, England. Its population in 2019 was approximately , making it the List of English districts by population, tenth-largest English district by popu ...

Liverpool
, 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 ...

London Underground
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 A tunnel is an underground passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent ...

Holland Tunnel
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 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,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shortha ...

United Kingdom
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 List of countries and dependencies by population, world's most populous country, with a population of around 1.4 billion. Covering approximately 9.6& ...
, opened in 2009, is the third longest water tunnel in the world at length. * The
Gotthard Base Tunnel it, Galleria di base del San Gottardo rm, Tunnel da basa dal Son Gottardfrench: Tunnel de base du Saint-Gothard , image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg , image_size = 250 , caption = Turnout at Faido multifunction st ...

Gotthard Base Tunnel
in
Switzerland ,german: Schweizer(in),french: Suisse(sse), it, svizzero/svizzera or , rm, Svizzer/Svizra , government_type = Federalism, Federal semi-direct democracy under a multi-party assembly-independent Directorial system, directorial republic , leader_t ...

Switzerland
, 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: link=no, Le tunnel sous la Manche), also referred to as the Eurotunnel or Chunnel, is a railway tunnel that connects Folkestone (Kent Kent is a Counties of England, county in South East England and one of the h ...
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,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shortha ...

United Kingdom
. It has a total length of , of which are the world's longest undersea tunnel section. * The Lötschberg Base Tunnel in
Switzerland ,german: Schweizer(in),french: Suisse(sse), it, svizzero/svizzera or , rm, Svizzer/Svizra , government_type = Federalism, Federal semi-direct democracy under a multi-party assembly-independent Directorial system, directorial republic , leader_t ...

Switzerland
was the longest land rail tunnel, with a length of , from its inauguration in 2007 until the completion of the
Gotthard Base Tunnel it, Galleria di base del San Gottardo rm, Tunnel da basa dal Son Gottardfrench: Tunnel de base du Saint-Gothard , image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg , image_size = 250 , caption = Turnout at Faido multifunction st ...

Gotthard Base Tunnel
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

File:Sideling Hill Tunnel 2009.jpg, The eastern portal of the abandoned Sideling Hill Tunnel, Pennsylvania, USA in 2009 * 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 status in the United Kingdom, city and metropolitan borough in Merseyside, England. Its population in 2019 was approximately , making it the List of English districts by population, tenth-largest English district by popu ...

Liverpool
, 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 date of 2020, 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 of ...
, such as illegal drugs and
weapon A weapon, arm or armament is any implement or device that can be used with the intent to inflict damage or harm. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, self-defense, and w ...
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 * Welwyn Tunnel rail crash (1866) – train failed in tunnel, guard did not protect train. * Balvano train disaster (1944) * 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)