Tunnel

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Tunnel
From Wikipedia, the free encyclopedia

This article is about underground passages. For other uses, see Tunnel (disambiguation).
"Underpass" redirects here. For the John Foxx song, see Underpass (song).

Entrance to a road tunnel inGuanajuato, Mexico.

Utility tunnel for heating pipes between Rigshospitalet and Amagerværket in Copenhagen,Denmark

Tunnel on the Taipei Metro inTaiwan

Southern portal of the 421 m long (1,381 ft) Chirk canal tunnel

A tunnel is an underground or underwater 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 immersed tube construction techniques rather than traditional tunnel
boring methods.
A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of
a rapid transit network are usually in tunnel. Some tunnels are aqueducts to supply water for
consumption or for hydroelectric stations or are sewers. Utility tunnels 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 of weapons, contraband,
or people. Special tunnels, such aswildlife crossings, are built to allow wildlife to cross human-made
barriers safely.
Contents
[hide]


1 Terminology



2 History
o



2.1 Clay-kicking
3 Geotechnical investigation and design

o

3.1 Choice of tunnels vs. bridges

o

3.2 Cost estimates and overruns



4 Construction
o

4.1 Cut-and-cover

o

4.2 Boring machines

o

4.3 Shafts

o

4.4 Sprayed concrete techniques

o

4.5 Pipe jacking

o

4.6 Box jacking

o

4.7 Underwater tunnels

o

4.8 Temporary way

o

4.9 Enlargement

o

4.10 Open building pit

o

4.11 Other construction methods



5 Variant tunnel types
o

5.1 Double-deck and multipurpose tunnels

o

5.2 Covered passageways



6 Safety and security



7 Examples of tunnels
o

7.1 In history

o

7.2 Longest

o

7.3 Notable



8 Mining



9 Military use



10 Secret tunnels



11 Natural tunnels



12 Accidents



13 See also



14 Notes and references



15 Bibliography



16 External links

Terminology[edit]
A tunnel is relatively long and narrow; the length is often much greater than twice the diameter,
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 is defined as "a subsurface highway structure
enclosed for a length of 150 metres (490 ft) or more."[1] In the United States, the NFPA definition of a
tunnel is "An underground structure with a design length greater than 23 m (75 ft) and a diameter
greater than 1,800 millimetres (5.9 ft)."[2]
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, theUnderground or
the Tube in London, the Subway in Glasgow, and the Metro in 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 or, if passing under a canal, an aqueduct. Where it is important to stress
that it is passing underneath, it may be called an underpass, though the official term when passing
under a railway is an underbridge. 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 instead. Rail station platforms may be connected by pedestrian tunnels
or footbridges.

History[edit]
This section requires expansion.
(March 2013)

Joralemon Street Tunnel in 1913, part of the New York City Subwaysystem

Much of the early technology of tunneling evolved from mining and military engineering.
The etymology of the terms "mining" (for mineral extraction or for siege attacks), "military
engineering", and "civil engineering" reveals these deep historic connections.

Clay-kicking[edit]
Clay-kicking is a specialised method developed in the United Kingdom of manually digging tunnels in
strong clay-based soil structures. Unlike previous manual methods of using mattocks 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, he or she extracts a section of
soil, which is then placed on the waste extract.
Regularly used in Victorian civil engineering, the methods found favour in the renewal of the United
Kingdom's then ancient seweragesystems, by not having to remove all property or infrastructure to
create an effective small tunnel system. During the First World War, the system was successfully
deployed by theRoyal Engineer tunnelling companies to deploy large military mines beneath
enemy German Empire lines. The method was virtually silent, and so not susceptible to listening
methods of detection.[3]

Geotechnical investigation and design[edit]
Main article: Geotechnical investigation
A tunnel project must start with a comprehensive investigation of ground conditions by collecting
samples from boreholes 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 will make use of the best ground and water conditions.
Conventional desk and 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, may be driven ahead of the main drive. This tunnel will be easier to support should unexpected
conditions be met, and will be incorporated in the final tunnel. Alternatively, horizontal boreholes may
sometimes be drilled ahead of the advancing tunnel face.
Other key geotechnical factors include:


Stand-up time is the amount of time a tunnel will support itself without any added structures.
Knowing this time allows the engineers to determine how much can be excavated before
support is needed. The longer the stand-up time is the faster the excavating will go. Generally
certain configurations of rock and clay will have the greatest stand-up time, and sand and fine
soils will have a much lower stand-up time.[4]



Groundwater control is very important in tunnel construction. If there is water leaking into the
tunnel stand-up time will be greatly decreased. If there is water leaking into the shaft it will
become unstable and will not be safe to work in. To stop this from happening there are a few
common methods. One of the most effective is ground freezing. To do this pipes are inserted

into the ground surrounding the shaft and are cooled until they freeze. This freezes the ground
around each pipe until the whole shaft is surrounded frozen soil, keeping water out. The most
common method is to install pipes into the ground and to simply pump the water out. This works
for tunnels and shafts.[5]


Tunnel shape is very important in determining stand-up time. The force from gravity is
straight down on a tunnel, so if the tunnel is wider than it is high it will have a harder time
supporting itself, decreasing its stand-up time. If a tunnel is higher than it is wide the stand up
time will increase making the project easier. The hardest shape to support itself is a square or
rectangular tunnel. The forces have a harder time being redirected around the tunnel making it
extremely hard to support itself. This of course all depends what the material of the ground is. [6]

Choice of tunnels vs. bridges[edit]

The Harbor Tunnel in Baltimore, which carries I-95, serves as an example of a water-crossing tunnel built instead of a
bridge.

For water crossings, a tunnel is generally more costly to construct than a bridge. Navigational
considerations may limit the use of high bridges or drawbridge 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 and urbanHong Kong, this is a strong factor in tunnels' favor.
Boston's Big Dig project replaced elevated roadways with a tunnel system to increase traffic
capacity, hide traffic, reclaim land, redecorate, and reunite the city with the waterfront. In Hampton
Roads, Virginia, tunnels were chosen over bridges for strategic considerations; in the event of
damage, bridges would prevent U.S. Navy vessels from leaving Naval Station Norfolk.
The 1934 Queensway Road Tunnel under the River Mersey at Liverpool was chosen over a
massively high bridge for defence reasons: it was feared 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
under the Mersey.

Water-crossing tunnels built instead of bridges include the Holland Tunnel and Lincoln
Tunnel between New Jersey and Manhattan in New York City, the Queens-Midtown Tunnel between
Manhattan and the borough of Queens on Long Island, and the Elizabeth River tunnels
between Norfolk and Portsmouth, Virginia, the 1934 River Mersey road Queensway Tunnel,
the Western Scheldt Tunnel, Zeeland, Netherlands, and the North Shore Connectortunnel
in 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 51.5-kilometre or 32.0-mileChannel Tunnel),
aesthetic reasons (preserving the above-ground view, landscape, and scenery), and also for weight
capacity reasons (it may be more feasible to build a tunnel than a sufficiently strong bridge).
Some water crossings are a mixture of bridges and tunnels, such as the Denmark to Sweden
link and the Chesapeake Bay Bridge-Tunnel in Virginia.
There are particular hazards with tunnels, especially from vehicle fires when combustion gases
can asphyxiate users, as happened at the Gotthard Road Tunnel in 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 in 1944, killing 426 passengers.

Cost estimates and overruns[edit]
Government funds are a major factor in the creation of tunnels.[7] When a tunnel is in the process of
being constructed, economics and politics play a large factor in the decision making process. This
division of the project is part of the construction/project management aspect of civil engineering. The
project duration must be identified using a work breakdown structure (WBS) and critical path
method (CPM). Understanding the amount of time the project requires, the amount of labors and
materials needed is a crucial part of the project. Also, the amount of land that will need to be
excavated and the proper machinery that is needed is also very important. Since infrastructures
require millions, or even billions of dollars, acquiring these funds can be challenging.
The need for an infrastructure such as a tunnel must be identified. Political issues are bound to
occur as it was shown in 2005 when the US House of Representatives approved a $100 million
federal grant to build a tunnel in the New York Harbor. However, the Port Authority of New York and
New Jersey was aware of this bill and had never asked for a grant or for such a project. [8] The current
state of the economy reflects on the amount of money the government can give for public projects.
Since taxpayers money goes to projects such as the creation of tunnels, or any other infrastructures,
increasing taxes may cause issues.[9]

Construction[edit]
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 ground water 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 shape of the tunnel and appropriate risk management.
There are three basic types of tunnel construction in common use:


Cut-and-cover tunnels, constructed in a shallow trench and then covered over.



Bored tunnels, constructed in situ, without removing the ground above. They are usually of
circular or horseshoe cross-section.



Immersed tube tunnels, sunk into a body of water and sit on, or are buried just under, its bed.

Cut-and-cover[edit]

Cut-and-cover construction of theParis Métro in France

Cut-and-cover is a simple method of construction for shallow tunnels where a trench is excavated
and roofed 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 tunnelling 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 backfilled 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. Then a shallow excavation allows
making the tunnel roof of precast beams or in situ concrete. The surface is then reinstated
except for access openings. This allows early reinstatement of roadways, services and other
surface features. Excavation then takes place under the permanent tunnel roof, and the base
slab is constructed.

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

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

A tunnel boring machine used to excavate the Gotthard Base Tunnel(Switzerland), the world's longest tunnel.

Tunnel boring machines (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 quick and cost effective alternative to laying surface rails and roads.
Expensive compulsory purchase of buildings and land, with potentially lengthy planning inquiries, is
eliminated.
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 pressurised compartments at the front end, allowing them to be used in difficult
conditions below the 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 pressurised
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 air lock/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 in Switzerland. The borehole has a diameter of 8.03 metres (26.3 ft).[10] The
four TBMs used for excavating the 57-kilometre (35 mi) Gotthard Base Tunnel, in Switzerland, had a
diameter of about 9 metres (30 ft). A larger TBM was built to bore the Green Heart Tunnel (Dutch:
Tunnel Groene Hart) as part of the HSL-Zuid in the Netherlands, with a diameter of 14.87 metres
(48.8 ft).[11] This in turn was superseded by the Madrid M30 ringroad, Spain, and the Chong
Ming tunnels in Shanghai, China. All of these machines were built at least partly byHerrenknecht. As
of August 2013, the world's largest TBM is "Big Bertha", a 57.5-foot (17.5 m) diameter machine built
by Hitachi Zosen Corporation, which is digging the Alaskan Way Viaduct replacement
tunnel in Seattle, Washington (US).[12]

Shafts[edit]

1886 illustration showing the ventilation and drainage system of the Mersey railway tunnel

A temporary access shaft 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. [6]
Once construction is complete, construction access shafts are often used as ventilation shafts, and
may also be used as emergency exits.

Sprayed concrete techniques[edit]
The New Austrian Tunneling Method (NATM) was developed in the 1960s, and is the best known
of a number of engineering solutions that use calculated and empirical real-time measurements to
provide optimised safe support to the tunnel lining. The main idea of this method is to use the

geological stress of the surrounding rock mass to stabilize the tunnel itself, by allowing a measured
relaxation and stress reassignment into the surrounding rock to prevent full loads becoming imposed
on the introduced support measures. Based on geotechnicalmeasurements, an optimal cross
section is computed. The excavation is immediately protected by a layer of sprayed concrete,
commonly referred to as shotcrete, after excavation. Other support measures could include steel
arches, rockbolts and mesh. Technological developments in sprayed concrete technology have
resulted in steel and polypropylene fibres being added to the concrete mix to improve lining strength.
This creates a natural load-bearing ring, which minimizes the rock'sdeformation.

Illowra Battery utility tunnel, Port Kembla. One of many bunkers south of Sydney.

By special monitoring the NATM method is very flexible, even at surprising changes of
the geomechanical rock consistency during the tunneling work. The measured rock properties lead
to appropriate tools for tunnel strengthening. In the last decades also soft ground excavations up to
10 kilometres (6.2 mi) became usual.

Pipe jacking[edit]
Main article: Pipe jacking
In Pipe jacking hydraulic jacks are used to push specially made pipes through the ground behind a
TBM or shield, commonly used to create tunnels under existing structures, such as roads or
railways. Tunnels constructed by pipe jacking are normally small diameter tunnels with a maximum
size of around 3.2m.

Box jacking[edit]
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 20m. A cutting head is normally used at the front of the box being jacked and excavation is
normally by excavator from within the box.

Underwater tunnels[edit]

Shark tunnel at the Georgia Aquarium

Main article: Undersea tunnel
There are also several approaches to underwater tunnels, the two most common being bored
tunnels or immersed tubes, examples areBjørvika Tunnel and Marmaray. Submerged floating
tunnels are a novel approach under consideration; however, no such tunnels have been constructed
to date.

Temporary way[edit]
During construction of a tunnel it is often convenient to install a temporary railway, particularly to
remove excavated spoil, often narrow gaugeso 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 thepermanent way at
completion, thus explaining the term "Perway".

Enlargement[edit]

A utility tunnel in Prague

The vehicles or traffic using a tunnel can outgrow it, requiring replacement or enlargement. The
original single line Gib Tunnel near Mittagongwas replaced with a double-track tunnel, with the
original tunnel used for growing mushrooms.[citation needed] The Rhyndaston Tunnel was enlarged using a
borrowed TBM so as to be able to take ISO containers.
The 1836 double-track mile-long tunnel from Edge Hill to Lime Street in Liverpool was totally
removed, apart from a 50-metre section at Edge Hill. Four tracks were required. The tunnel was
converted into a very deep four-track cutting, with short four-track tunnels in places. Train services
were not interrupted as the work progressed. Photos of the work in progress: [13][14] There are other
occurrences of tunnels being replaced by open cuts, for example, the Auburn Tunnel.

Tunnels can also be enlarged by lowering the floor.[citation needed]

Open building pit[edit]
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[edit]


Drilling and blasting



Hydraulic splitter



Slurry-shield machine



Wall-cover construction method.

Variant tunnel types[edit]
Double-deck and multipurpose tunnels[edit]

The upper level traffic lanes throughYerba Buena Island, part of the San Francisco – Oakland Bay Bridge

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 double-deck tunnel through Yerba Buena Island, the
largest-diameter bored tunnel in the world.[15] 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 the UK, the 1934 Queensway Tunnel under the River
Mersey between 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
used for cables, pipes and emergency accident refuge enclosures.
In China, the Lion Rock Tunnel, built in the mid 1960s connecting New Kowloon and Sha Tin in Hong
Kong, carries a motorway and anaqueduct. A recent double-deck tunnel with both decks for motor

vehicles is the Fuxing Road Tunnel in Shanghai. Cars travel on the two-lane upper deck, and
heavier vehicles on the single-lane lower level.
Multipurpose tunnels exist that have more than one purpose. The SMART Tunnel in Malaysia is the
first multipurpose flood control tunnel in the world, used both to convey traffic and
occasional flood waters in Kuala Lumpur.
Common utility ducts or utility tunnels are 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[edit]

The 19th century Dark Gate in Esztergom, Hungary

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 South Coast railway line, protects the line
from rockfalls.

Safety and security[edit]
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 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 shafts and powered fans to remove toxic exhaust
gases during routine operation. Rail tunnels usually require fewer air changes per hour, but still may
require 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.
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 tunnel in Boston, Massachusetts, may have a
dedicated 24-hour manned operations center which monitors and reports on traffic conditions, and
responds to emergencies.[16] 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.

Examples of tunnels[edit]
In history[edit]
This section needs additional citations for verification. Please help improve this
article by adding citations to reliable sources. Unsourced material may be challenged
and removed. (March 2013)
See also: History of rapid transit

The three eastern portals of Liverpool Edge Hill tunnels, built into a hand dug deep cutting. The left tunnel with tracks
is the short 1846 second Crown Street Tunnel, next on the right partially hidden by undergrowth is the 2.03 km
(1.26 mi) 1829 Wapping Tunnel, to the right again hidden by undergrowth, is the original short 1829 Crown Street
Tunnel.

A short section remains of the 1836 Edge Hill to Lime Street tunnel inLiverpool. This is the oldest rail tunnel in the
world still in active use.

The 1,659-foot (506 m)Donner Pass Summit Tunnel (#6) was in service from 1868 to 1993.

Liverpool Lime Street Approach. The original two track tunnel was removed to create a deep cutting. The road
bridges seen across the cutting are solid rock and in effect a series of short tunnels.

A late 19th-century pneumatic rock-drilling machine, invented by Germain Sommeiller 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. [17][18] Some well
known ancient and modern tunnels are briefly introduced below:


The world's oldest underwater tunnel is claimed

[19]

to be the Terelek kaya tüneli under Kızıl

River, a little south of the towns of Boyabatand 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 on a rock
face nearby, it is assumed to have had a defence purpose.


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 360 m
(1,180 ft), and its length is 45 km (28 mi).[20]



One of the first known drainage and sewage networks in form of tunnels was constructed at
Persepolis in Iran at the same time as the construction of its foundation in 518 B.C.. 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 rubbles 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.[21]



Hezekiah's Tunnel was built before 701 BCE for water as a defense against siege attacks.



The Eupalinian aqueduct on the island of Samos (North Aegean, Greece) was built in 520
BCE by the ancient Greek engineer Eupalinosof 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. 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 1.030 km long (3,380 ft) and visitors can still enter
it Eupalinos tunnel.



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.



Sapperton Canal Tunnel on the Thames and Severn Canal in England, dug through hills,
which opened in 1789, was 3.5 km (2.2 mi) long and allowed boat transport of coal and other
goods. Above it runs the Sapperton Long Tunnel which carries the "Golden Valley" railway line
between Swindon and Gloucester.



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.



The Derby Tunnels in Salem, Massachusetts were built in 1801 utilizing the first US National
Guard unit to build and hide the dirt in 5 ponds in a park in town. The tunnels were built to
smuggle imports that President Thomas Jefferson had ordered local militias to help the Custom
House in each port collect. 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 hid 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.[citation needed]



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, for
self-propelled steam engines on rails.



The Montgomery Bell Tunnel in Tennessee, an 88 m long (289 ft) water diversion tunnel,
4.50 m × 2.45 m high (14.8 ft × 8.0 ft), 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, England. 0.0321 km (105 ft) long. Built in the late
1820s, the exact date is unknown. This is the first tunnel in the world that runs under a railway
line. The construction of the Liverpool to Manchester Railway ran over a horse-drawn tramway
from the Sutton collieries to the Liverpool to Warrington turnpike road. It was decided to bore a

tunnel 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. [22]


Crown Street Station, Liverpool, England, 1829. Built by George Stephenson, a single track
tunnel 266 m long (873 ft), 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 rail tunnel running under streets in the world. [23][24]



The 2.03 km (1.26 mi) 1829 twin track Wapping Tunnel in Liverpool, England, was the first
rail tunnel bored under a metropolis. Currently disused since 1972, the tunnel runs from Edge
Hill in the east of the city to the south end Liverpool docks being used only for freight. The tunnel
was to be a part of the Merseyrail network, with work started and abandoned because of costs.
The tunnel is still in excellent condition and is still being considered for reuse
by Merseyrail system, maybe with an underground station cut into the tunnel for Liverpool
university. The river portal is opposite the new Liverpool Arena being ideal for a serving station. If
reused it will be the oldest used underground rail tunnel in the world and oldest part of any
underground metro system.[24][25][26]



1836, Lime St Station tunnel, Liverpool. A two track rail tunnel, 1.811 km (1.125 mi) long was
bored under the metropolis from Edge Hill in the east of the city to Lime Street. In the 1880s the
tunnel was converted to a deep open to the atmosphere cutting four tracks wide, the only
occurrence of a major tunnel being removed. A short section of the original tunnel still exists at
Edge Hill station, giving the tunnel the distinction of being the oldest rail tunnel in the world still in
use, and the oldest in use under streets.[27]



The 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 2.9 km (1.8 mi).



The 1.1 km (0.68 mi) 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 Thames Tunnel, built by Marc Isambard Brunel and his son Isambard Kingdom
Brunel opened in 1843, was the first underwater tunnel and the first to be built using a tunnelling
shield. Originally used as a foot-tunnel, it was a part of the East London Line of theLondon
Underground until 2007, then being the oldest section of the network. From 2010 the tunnel
became a part of the London Overground system.



The 3.34 km (2.08 mi) Victoria Tunnel/Waterloo Tunnel in Liverpool, England, opened in
1848, being bored under a metropolis. The tunnel was initially used only for rail freight and later
freight and passengers serving the Liverpool ship liner terminal, the tunnel runs from Edge Hill in
the east of the city to the north end Liverpool docks. 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 2,375 m (1.476 mi) long Victoria section was originally
cable hauled and the shorter 862 m (943 yd) Waterloo section was locomotive hauled, two
separate names were given, the short section being named the Waterloo Tunnel. In 1895 the
two tunnels were converted to locomotive haulage. Used until 1972, the tunnel is still in excellent
condition, being considered for reuse by the Merseyrail system. Stations being cut into the
tunnel are being considered. Also, reuse by a monorail system from the proposed Liverpool
Waters redevelopment of Liverpool's Central Docks has been proposed. [28][29]



The vertex tunnel of the Semmering railway, the first Alpine tunnel, was opened in 1848 and
was 1.431 km (0.889 mi) long. It connected rail traffic between Vienna, the capital ofAustroHungarian 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 3.25 km (2.02 mi) long.



The oldest underground sections of the London Underground were built using the cut-andcover method in the 1860s, and opened in January 1863. What are now theMetropolitan,
Hammersmith & City and Circle lines were the first to prove the success of a metro or subway
system.



On June 18, 1868, the Central Pacific Railroad's 1,659-foot (506 m) Summit Tunnel (Tunnel
#6) at Donner Pass in the California 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 theSouthern Pacific Railroad closed it
and transferred all rail traffic through the 10,322-foot (3,146 m) long Tunnel #41 (aka "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, 13.7 km (8.5 mi) long. At that time it was
the longest in the world.



The third Alpine tunnel, the Gotthard Rail Tunnel opened in 1882 and was the longest rail
tunnel in the world, measuring 15 km (9.3 mi).



The 1882 Col de Tende Road Tunnel, at 3.182 km (1.977 mi) long, was one of the first long
road tunnels under a pass, running between France and Italy.



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 3.12 mi (5.02 km) in length. The under river section is 0.75 mi (1.21 km) in length,
and was the longest underwater tunnel in world in January 1886.[30][31]



The rail Severn Tunnel was opened in late 1886, at 7.008 km (4.355 mi) long, although only
3.62 km (2.25 mi) 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.[32]



Built from 1890 to 1940, the section of London Underground's Northern line from Morden to
East Finchley was the longest railway tunnel in the world at 27.8 km (17.3 mi) in length.



St. Clair Tunnel, also opened later in 1890, linked the elements of the Greathead tunnels on
a larger scale.[32]



In 1906 the fourth Alpine tunnel opened, the Simplon Tunnel, linking Paris to Milan. It is
19.7 km (12.2 mi) long, and was the longest tunnel in the world until 1982.



The 1927 Holland Tunnel was the first underwater tunnel designed for automobiles. The
construction required a novel ventilation system.



In 1945 the Delaware Aqueduct tunnel was completed, supplying water to New York City in
the US. At 137 km (85 mi) it is the second longest tunnel in the world.



In 1988 the 53.850 km (33.461 mi) 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[edit]
Main article: List of tunnels by length



The Thirlmere Aqueduct in North West England, United Kingdom is sometimes considered
the longest tunnel, of any type, in the world at 154 km (96 mi), though the aqueduct's tunnel
section is not continuous.[dubious – discuss]



The Gotthard Base Tunnel will be the longest rail tunnel in the world at 57 km (35 mi). It will
be totally completed in 2016.



The Seikan Tunnel in Japan is the longest undersea rail tunnel in the world at 53.9 km
(33.5 mi), of which 23.3 km (14.5 mi) is under the sea.



The Channel Tunnel between France and the United Kingdom under the English Channel is
the second-longest, with a total length of 50 km (31 mi), of which 39 km (24 mi) is under the sea.



The Lötschberg Base Tunnel opened in June 2007 in Switzerland was the longest land rail
tunnel, with a total of 34.5 km (21.4 mi).



The Lærdal Tunnel in Norway from Lærdal to Aurland is the world's longest road tunnel,
intended for cars and similar vehicles, at 24.5 km (15.2 mi).



The Zhongnanshan Tunnel in People's Republic of China opened in January 2007 is the
world's second longest highway tunnel and the longest road tunnel in Asia, at 18 km (11 mi).



The longest canal tunnel is the Rove Tunnel in France, over 7.12 km (4.42 mi) long.

Notable[edit]

The Big Dig road vehicle tunnel in Boston

The Gerrards Cross tunnel in England, completed in 2010. Looking west towards the station in March 2005, showing
the extent of construction three months before a small section collapsed

The eastern portal of the abandoned Sideling Hill Tunnel in 2009.



Williamson's tunnels in 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.



Gerrards Cross railway tunnel, in England, opened in 2010, is notable in that it was built in a
railway cutting, that was first opened around 1906. This arguably is the longest ever tunnel in
construction taking 104 years.[dubious – discuss] The tunnel was built using the cut-and-cover method
with prefabricated forms in order to keep the busy railway operating. A branch of
the Tesco supermarket chain occupies the space above the railway tunnel with an adjacent
railway station. During construction, a portion of the tunnel collapsed when the soil cover was
added. The prefabricated forms were covered with a layer of reinforced concrete after the
collapse.[33]



Moffat Tunnel, opened in 1928 in Colorado, straddles the Continental Divide. The tunnel is
10.0 km (6.2 mi) long and at 2,816 m (9,239 ft) above sea level is the highest active railroad
tunnel in the US (Tennessee Pass, currently inactive, andAlpine Tunnel are higher).



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,Tuscarora Mountain, Kittatinny Mountain,
and Blue Mountain) remain in active use, while the other three (Laurel Hill, Rays Hill,
and 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 Fredhälls road tunnel was opened in 1966, in Stockholm, Sweden, and the New Elbe
road tunnel opened in 1975 inHamburg, Germany. Both tunnels handle around 150,000 vehicles
a day, making them two of the most trafficked tunnels in the world.



The Honningsvåg Tunnel (4.443 km (2.76 mi) 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, USA, is a part of the larger Big Dig completed
around 2007, carries approximately 200,000 vehicles/day under the city along Interstate 93, U.S.
Route 1, and Massachusetts Route 3, which share a concurrency through the tunnels. The Big
Dig replaced Boston's old badly deteriorated I-93 elevated highway.



Stormwater Management And Road Tunnel or SMART Tunnel, is a storm drainage and road
structure opened in 2007 inKuala Lumpur, Malaysia. The 9.7 km (6.0 mi) tunnel is the longest
stormwater tunnel in South East Asia and second longest in Asia.



The Eiksund Tunnel[34] on national road Rv 653 in Norway is the world's deepest subsea road
tunnel, measuring 7.776 km (4.832 mi) long, with deepest point at −287 m (−942 ft) below the
sea level, opened in February 2008.



The Fenghuoshan tunnel (date of completion unknown) on Qinghai-Tibet railway is the
world's highest railway tunnel, about 4.905 km (3.05 mi) above sea level.



The La Linea Tunnel in Colombia, will be (2013) the longest, 8.58 km (5.33 mi), mountain
tunnel in South America. It crosses beneath a mountain at 2,500 m (8,202.1 ft) 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 Chicago Deep Tunnel Project is a network of 175 km (109 mi) of tunnels designed to
reduce flooding in the Chicago area. Started in the mid-1970s, the project is due to be
completed in 2019.



New York City Water Tunnel No. 3,[35] started in 1970, has an expected completion date of
2020, and will measure more than 97 km long (60 mi).

Mining[edit]
Main article: Mining

Former tunnel used for coal mining in New Taipei, Taiwan.

The use of tunnels for mining is called drift mining.

Military use[edit]
See also: Sapper
Some tunnels are not for transport at all but rather, are fortifications, for
example Mittelwerk and Cheyenne Mountain. Excavation techniques, as well as the construction of
underground bunkers and other habitable areas, are often associated with military use during armed
conflict, or civilian responses to threat of attack. One of the strangest uses of a tunnel was for the
storage of chemical weapons[36][37] [2].

Secret tunnels[edit]
This section needs additional citations for verification. Please help improve this
article by adding citations to reliable sources. Unsourced material may be challenged
and removed. (January 2014)
Main articles: Secret passage and Smuggling tunnel

Door to a compartment where runaway slaves would sleep, on the Underground Railroad

Secret tunnels have given entrance to or escape from an area, such as the Cu Chi Tunnels or
the 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, such as illegal drugs and weapons.
Elaborately engineered 1,000-foot (300 m) 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.
[38]

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. [38] Secret tunnels
have also been used by thieves to break into bank vaults and retail stores after hours. [39][40]
The actual usage of erdstall tunnels is unknown but theories connect it to a rebirth ritual.

Natural tunnels[edit]

View through a natural tunnel in South Korea



Lava tubes are partially empty, cave-like conduits underground, formed during volcanic
eruptions by flowing and cooling lava.



Natural Tunnel State Park (Virginia, USA) features an 850-foot (259 m) natural tunnel, really
a limestone cave, that has been used as a railroad tunnel since 1890.



Punarjani Guha 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 tunnel in the middle of the
hat, letting light come through. The 160 metres (520 ft) long, 35 metres (115 ft) wide, and 20
metres (66 ft) high tunnel is believed to be the hole after an arrow by the troll Hestmannen, the
hill being the hat of the troll-king of Sømna trying to save the beautiful Lekamøya from the arrow
(more likely to be the work of ice). The sun shines through the tunnel during two short periods
every year.[41]



Small "snow tunnels" are created by voles, chipmunks and other rodents for protection and
access to food sources. For more information regarding tunnels built by animals, see Burrow

Accidents[edit]


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 - 1996

See also[edit]


Cattle creep



Megaproject



Structure gauge — measure of maximum physical clearance in a tunnel



Tree tunnel



Tunnels in popular culture

Notes and references[edit]
1.

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PART 9: BD 78/99: DESIGN OF ROAD TUNNELS. The Department for Transport. 1999.

2.

Jump up^ NFPA Standard for Safeguarding Construction, Alteration, and Demolition
Operations. National Fire Protection Association.

3.

Jump up^ "Tunnelling". tunnellersmemorial.com. Retrieved 2010-06-20.

4.

Jump up^ Bickel. (1995). Tunnel engineering handbook, 2nd edition. CBS Publishers.

5.

Jump up^ Powers, P.J. (2007). Construction de-watering and groundwater control.
Hoboken, NJ: John Wiley & Sons Inc.

6.

^ Jump up to:a b United States Army Corps of Engineers. (1978). Tunnels and shafts in
rock. Washington, DC: Department of the Army.

7.

Jump up^ "Capital Projects Funds". Cord.edu. Retrieved 2013-04-19.

8.

Jump up^ Chan, Sewell (2005-08-03). "$100 Million for a Tunnel. What Tunnel?". The
New York Times.

9.

Jump up^ "Encouraging U.S. Infrastructure Investment - Council on Foreign Relations".
Cfr.org. Retrieved 2013-04-19.

10.

Jump up^ "Tunnels & Tunnelling International". Tunnelsonline.info. Retrieved 2013-0419.

11.

Jump up^ "The Groene Hart Tunnel". Hslzuid.nl. Retrieved 2013-04-19.

12.

Jump up^ Johnson, Kirk (December 4, 2012). "Engineering Projects Will Transform
Seattle, All Along the Waterfront". The New York Times.

13.

Jump up^ http://i34.tinypic.com/23ixthy.jpg

14.

Jump up^ http://i36.tinypic.com/16k1ahx.jpg

15.

Jump up^ "San Francisco-Oakland Bay Bridge". Bay Area Toll Authority.

16.

Jump up^ Johnson, Christine M.; Edward L. Thomas (October 1999). "A Case Study
Boston Central Artery/Tunnel Integrated Project Control System, Responding to incidents Rapidly
and Effectively". Metropolitan Transportation Management Center: 12. Retrieved 4 April2014.

17.

Jump up^ Klaus Grewe, 1998, Licht am Ende des Tunnels – Planung und Trassierung
im antiken Tunnelbau, Verlag Philipp von Zabern, Mainz am Rhein.

18.

Jump up^ Siamak Hashemi, 2013, The Magnificence of Civilization in Depths of Ground
(A Review of Underground Structures in Iran – Past to Present), Shadrang Printing and
Publishing Co., Tehran.

19.

Jump up^ Blogcu http://terelek.blogcu.com/terelek-kaya-tuneli/319497

20.

Jump up^ UNESCO World Heritage Centre – World Heritage List: Qanats of Gonabad,
Date of Inscription 2007, Reference No. 5207, At: http://whc.unesco.org/fr/listesindicatives/5207

21.

Jump up^ Schmidt, E.F., 1953, Persepolis I – Structures, Reliefs, Inscriptions; The
University of Chicago Oriental Institute Publications, Volume LXVIII, The University of Chicago
Press.

22.

Jump up^ "Bourne's Tunnel at Sj5033491804 - Saint Helens - St Helens England". British Listed Buildings. Retrieved 30 September 2014.

23.

Jump up^ "Liverpool's Historic Rail Tunnels". The Liverpool Wiki. 1999-02-22.
Retrieved2013-04-19.

24.

^ Jump up to:a b "Subterranea Britannica: Sites:". Retrieved 30 September 2014.

25.

Jump up^ "Wapping Tunnel". Retrieved 30 September 2014.

26.

Jump up^ Maund, T.B. (2001). Merseyrail electrics: the inside story. Sheffield: NBC
Books.OCLC 655126526.

27.

Jump up^ http://www.hows.org.uk/personal/rail/incline/lls.htm

28.

Jump up^ "Victoria Tunnel". Retrieved 30 September 2014.

29.

Jump up^ "Waterloo Tunnel". Retrieved 30 September 2014.

30.

Jump up^ "Mersey Railway Tunnel". Retrieved 30 September 2014.

31.

Jump up^ http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=1151

32.

^ Jump up to:a b Robie S. Lange (February 1993). "National Register of Historic Places
Inventory-Nomination: St. Clair River Tunnel / St. Clair Railroad Tunnel". National Park Service.

33.

Jump up^ "Costain finishes Gerrards Cross tunnel rebuild". Retrieved 30
September 2014.

34.

Jump up^ [1][dead link]

35.

Jump up^ "City Water Tunnel No. 3". Web.archive.org. Archived from the original on
2007-06-21. Retrieved 2013-04-19.

36.

Jump up^ "Glenbrook Tunnel - Alcatraz Down Under - History Channel". Youtube.com.
Retrieved2013-04-19.

37.

Jump up^ Author lifts lid on chemical wartime history - Local News - News - General Blue Mountains Gazette

38.

^ Jump up to:a b Audi, Tamara (Jan 31, 2013). "Drug Tunnels Have Feds Digging for
Answers". Wall Street Journal. Retrieved 2014-10-04.

39.

Jump up^ Colchester, Max (March 31, 2010). "Thieves Drill Into Paris Bank Vault". Wall
Street Journal. Retrieved 2014-10-04.

40.

Jump up^ Evans, Peter (Oct 3, 2014). "Where ‘Criminal Underworld’ Is More Than a
Euphemism".Wall Street Journal. Retrieved 2014-10-04.

41.

Jump up^ Warholm, Harald (Nov 10, 2014). "The hobby photograph has waited tree
years for this rare shot of the Torghatten mount". nrk.no. Retrieved 2014-11-13.

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