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tunnel 在英语-中文（简体）词典中的翻译

tunnelnoun [ C ] uk

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/ˈtʌn.əl/ us

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/ˈtʌn.əl/

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B1 a long passage under or through the ground, especially one made by people

隧道；地道；坑道

The train went into the tunnel.

火车驶入隧道。

the tunnel

the long passage through which football, rugby etc. players walk to get to the pitch

（足球或橄榄球等比赛时球员走向球场的）球员通道

更多范例减少例句The tunnel was dug with the aid of heavy machinery.Ten miners were trapped underground when the roof of the tunnel fell in.The road goes over the mountains, not through a tunnel.It is not practicable to complete the tunnel before the end of the year.A tunnel entrance was found within the precincts of the prison camp.

tunnelverb [ I or T ] uk

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/ˈtʌn.əl/ us

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/ˈtʌn.əl/ -ll- or US usually -l-

to dig a tunnel

开凿隧道;挖地道

The decision has not yet been made whether to tunnel under the river or build a bridge over it.

还没有决定是在河底挖掘隧道还是在河上建桥。

The alternative is to tunnel a route through the mountain.

另一个办法是挖一条穿山隧道。

He was trapped in a collapsed building but managed to tunnel his way out.

他被困在倒塌的楼房下，但他想办法挖地道出来了。

Tunnel - Wikipedia

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1Terminology

2History

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2.1Antiquity and early middle ages

3Geotechnical investigation and design

Toggle Geotechnical investigation and design subsection

3.1Choice of tunnels versus bridges

3.2Project planning and cost estimates

4Construction

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4.1Cut-and-cover

4.2Boring machines

4.3Clay-kicking

4.4Shafts

4.5Sprayed concrete techniques

4.6Pipe jacking

4.7Box jacking

4.8Underwater tunnels

4.9Temporary way

4.10Enlargement

4.11Open building pit

4.12Other construction methods

5Variant tunnel types

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5.1Double-deck and multipurpose tunnels

5.2Covered passageways

5.3Underpass

6Safety and security

7Examples

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7.1In history

7.2Longest

7.3Notable

8Mining

9Military use

10Secret tunnels

11Natural tunnels

12Major accidents

13See also

14References

15Bibliography

16External links

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Tunnel

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From Wikipedia, the free encyclopedia

Underground passage made for traffic

This article is about underground passages. For other uses, see Tunnel (disambiguation).

"Underpass" redirects here. For the John Foxx song, see Underpass (song). For a tunnel for pedestrians, see Subway (underpass).

Tunnel in Col du Galibier, France

Tunnel in Fort de Mutzig, France

Decorated portal to a road tunnel in Guanajuato, Mexico

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

Tunnel on the Taipei Metro in Taiwan

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

A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is enclosed except for the portals, 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 the tunnel. Some tunnels are used as sewers or aqueducts to supply water for consumption or for hydroelectric stations. 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 as wildlife crossings, are built to allow wildlife to cross human-made barriers safely. Tunnels can be connected together in tunnel networks.

Terminology[edit]

An entrance of the Rantaväylä Tunnel in the northern part of Tampere, Pirkanmaa, Finland

A fabric tunnel in Moulvibazar District, Bangladesh

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, in the United Kingdom, a road tunnel 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]

History[edit]

See also: History of water supply and sanitation

This section needs expansion. You can help by adding to it. (March 2013)

Joralemon Street Tunnel on 1913 postcard, part of the New York City Subway system

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.

Antiquity and early middle ages[edit]

Predecessors of modern tunnels were adits that transported water for irrigation, drinking, or sewerage. The first qanats are known from before 2000 B.C.

The Tunnel of Eupalinos is a tunnel aqueduct 1,036 m (3,399 ft) long running through Mount Kastro in Samos, Greece, built in the 6th century BC to serve as an aqueduct. It is the second known tunnel to have been excavated from both ends, after the Siloam tunnel in the neighbourhood of Silwan in eastern Jerusalem.

In Ethiopia, the Siqurto foot tunnel, hand-hewn in the Middle Ages, crosses a mountain ridge.

In the Gaza Strip, the network of tunnels was used by Jewish strategists as rock-cut shelters, in first links to Judean resistance against Roman rule in the Bar Kokhba revolt during the 2nd century CE.

Geotechnical investigation and design[edit]

Main article: Geotechnical investigation

A major 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 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.[3]

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.[4] A very effective but expensive technology is ground freezing, 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.[5]

Choice of tunnels versus bridges[edit]

This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2021) (Learn how and when to remove this template message)

The Harbor Tunnel in Baltimore, USA, which carries I-895, 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. However, both navigational and traffic considerations may limit the use of high bridges or drawbridges 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 urban Hong Kong, this is a strong factor in favor of a tunnel. 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.

The 1934 Queensway Tunnel under the River Mersey at Liverpool was chosen over a massively high bridge for defense reasons; it was feared that aircraft could destroy a bridge in times of war, not merely impairing road traffic but blocking the river to navigation. 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. In Hampton Roads, Virginia, tunnels were chosen over bridges for strategic considerations; in the event of damage, bridges might prevent US Navy vessels from leaving Naval Station Norfolk.

Water-crossing tunnels built instead of bridges include the Seikan Tunnel in Japan; 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; the Detroit-Windsor Tunnel between Michigan and Ontario; 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 Connector tunnel in Pittsburgh, Pennsylvania. The Sydney Harbour Tunnel was constructed to provide a second harbour crossing and to alleviate traffic congestion on the Sydney Harbour Bridge, without spoiling the iconic view.

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-mile Channel 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. 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[edit]

Government funds are often required for the creation of tunnels.[6] 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 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 (WBS) and critical path method (CPM). Also, the land needed for excavation and construction staging, and the proper machinery must be selected. Large infrastructure projects require millions or even billions of dollars, involving long-term financing, usually through issuance of bonds.

The costs and benefits 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 was not aware of this bill and had not asked for a grant for such a project.[7] Increased taxes to finance a large project may cause opposition.[8]

Construction[edit]

Main article: Tunnel 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[edit]

Cut-and-cover construction at Saint-Michel on Paris Métro Line 4 (c. 1910)

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.[9]

There are two basic forms of cut-and-cover tunnelling:

Bottom-up method: A trench is excavated, with ground support as necessary, and the tunnel is constructed in it. The tunnel may be of in situ concrete, precast concrete, precast arches, or corrugated steel arches; in early days brickwork was used. The trench is then carefully back-filled and the surface is reinstated.

Top-down method: Side support walls and capping beams are constructed from ground level by such methods as slurry 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. 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.[10] 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 workman is dwarfed by the cutting end of a tunnel boring machine used to excavate the Gotthard Base Tunnel (Switzerland), the world's longest railway 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 a 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. 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 TBMs, the bentonite slurry and earth-pressure balance types, have pressurized 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 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 located south of Linthal in the canton of Glarus. The borehole has a diameter of 8.03 metres (26.3 ft).[11] 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).[12] 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 by Herrenknecht. As of August 2013[update], the world's largest TBM was "Big Bertha", a 57.5-foot (17.5 m) diameter machine built by Hitachi Zosen Corporation, which dug the Alaskan Way Viaduct replacement tunnel in Seattle, Washington (US).[13]

Clay-kicking[edit]

Clay-kicking is a specialized method developed in the United Kingdom of 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, the kicker extracts a section of soil, which is then placed on the waste extract.

Used in Victorian civil engineering, the method found favor in the renewal of Britain's ancient sewerage systems, by not having to remove all property or infrastructure to create a small tunnel system. During the First World War, the system was used by Royal Engineer tunnelling companies to put mines beneath the German Empire lines. The method was virtually silent and so not susceptible to listening methods of detection.[14]

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.[5]

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 Tunnelling method (NATM)—also referred to as the Sequential Excavation Method (SEM)[15]—was developed in the 1960s.

The main idea of this method is to use the geological stress of the surrounding rock 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 measurements, an optimal cross section is computed. The excavation is protected by a layer of sprayed concrete, commonly referred to as shotcrete. 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.[15]

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

By special monitoring 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 strengthening.[15]

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. 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 3.2 metres (10 ft).

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 20 metres (66 ft). 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.

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 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[edit]

During construction of a tunnel it is often convenient to install a temporary railway, particularly to remove 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[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 Mittagong was replaced with a double-track tunnel, with the original tunnel used for growing mushrooms.[16][17]

The 1832 double-track one-mile (1.6 km)-long tunnel from Edge Hill to Lime Street in Liverpool was near totally removed, apart from a 50-metre (55 yd) 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.[18][19] 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.[20] 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.[21]

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 through Yerba 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 540-foot (160 m) double-deck tunnel section through Yerba Buena Island, the largest-diameter bored tunnel in the world.[22] 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 5.4 km (3.4 mi) two-deck road tunnel with two lanes on each deck.[23]

Additionally, in 2015 the Turkish government announced that it will build three-level tunnel, also under the Bosporus.[24] The tunnel is intended to carry both the Istanbul metro and a two-level highway, over a length of 6.5 km (4.0 mi).

The French A86 Duplex Tunnel [fr] 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 10 km (6.2 mi). Although each level offers a physical height of 2.54 m (8.3 ft), only traffic up to 2 m (6.6 ft) 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, China, a 2.8 km (1.7 mi) two-tube double-deck tunnel was built starting in 2002. In each tube of the Fuxing Road Tunnel [zh] both decks are for motor vehicles. In each direction, only cars and taxis travel on the 2.6 m (8.5 ft) high two-lane upper deck, and heavier vehicles, like trucks and buses, as well as cars, may use the 4.0 m (13 ft) high single-lane lower level.[25]

In the Netherlands, a 2.3 km (1.4 mi) two-storey, eight-lane, cut-and-cover road tunnel under the city of Maastricht was opened in 2016.[26] Each level accommodates a full height, two by two-lane highway. The two lower tubes of the tunnel carry the A2 motorway, which originates in Amsterdam, through the city; and the two upper tubes take the N2 regional highway for local traffic.[27]

The Alaskan Way Viaduct replacement tunnel, is a $3.3 billion 1.76-mile (2.83 km), double-decker bored highway tunnel under Downtown Seattle. Construction began in July 2013 using "Bertha", at the time the world's largest earth pressure balance tunnel boring machine, with a 57.5-foot (17.5 m) cutterhead diameter. After several delays, tunnel boring was completed in April 2017, and the tunnel opened to traffic on 4 February 2019.

New York City's 63rd Street Tunnel under the East River, between the boroughs of Manhattan and Queens, was intended to carry subway trains on the upper level and Long Island Rail Road commuter trains on the lower level. Construction started in 1969,[28] and the two sides of the tunnel were bored through in 1972.[29] The upper level, used by the IND 63rd Street Line (F train) of the New York City Subway, was not opened for passenger service until 1989.[30] The lower level, intended for commuter rail, saw passenger service after completion of the East Side Access project, in late 2022.[31]

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 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, carries a motorway but also serves as an aqueduct, featuring a gallery containing five water mains lines with diameters between 1.2m and 1.5m below the road section of the tunnel.[32]

Wuhan's Yangtze River Highway and Railway Tunnel is a 2.59 km two-tube double-deck tunnel under the Yangtze River completed in 2018. Each tube carries 3 lanes of local traffic on the top deck with one track Wuhan Metro Line 7 on the lower deck.[33][34][35]

Mount Baker Tunnel has three levels. Bottom level is to be used by Sound Transit light rail. Middle level is used by car traffic. Top layer is for bicycle and pedestrian access.

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 2.5 mi (4.0 km) 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.[36]

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[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 Illawarra railway line, protects the line from rockfalls.

Underpass[edit]

tunnel - 搜索词典

el - 搜索词典 Rewards网页图片视频学术词典地图更多航班我的必应笔记本tunnel美 [ˈtʌn(ə)l] 英 ['tʌn(ə)l] n.地下通道；地道；隧道；（动物的）洞穴通道v.开凿隧道；挖地道网络坑道；隧道技术；管道复数：tunnels 过去式：tunnelled 过去式：tunneled 现在分词：tunneling 现在分词：tunnelling 搭配同义词反义词adj.+n.long tunnel,underground tunnel,underwater tunnel,carpal tunnel,utility tunnelv.+n.dig tunnel,tunnel open,build tunneln.bridgev.excavate,burrow,dig,mine,channeln.passageway,subway,shaft,underpass,hole权威英汉双解英汉英英网络释义tunnel显示所有例句n.1.地下通道；地道；隧道a passage built underground, for example to allow a road or railway/railroad to go through a hill, under a river, etc.a railway/railroad tunnel铁路隧道the Channel Tunnel英吉利海峡隧道2.（动物的）洞穴通道an underground passage made by an animalv.1.[i][t]开凿隧道；挖地道to dig a tunnel under or through the groundThe engineers had to tunnel through solid rock.工程师须要在坚实的岩石中开凿隧道。The rescuers tunnelled their way in to the trapped miners.救援人员挖地道通向那些被困的矿工。n.1.隧道;地道;坑道;管道,烟道,风洞;【矿】石巷,平峒v.1.在...凿隧道[掘坑道]2.凿隧道通过3.凿隧道[掘坑道]4.运过坑道 (through) 进隧道 (into)1.在...凿隧道[掘坑道]2.凿隧道通过3.凿隧道[掘坑道]4.运过坑道 (through) 进隧道 (into)n.1.an underground passage through which vehicles travel; an underground passage made by animalsv.1.to dig a tunnel1.隧道隧道(Tunnel) 是指一种协议封装到另外一种协议中以实现互联目的。对于采用隧道技术的设备来说，在起始端(隧道入口处)，将I…ipv6.tsinghua.edu.cn|基于6014个网页2.地道穴字的解释---在线新华字典 ... 动物的窝〖 den〗地道〖 tunnel〗水道〖 watercourse〗 ... xh.5156edu.com|基于1309个网页3.通道13.通道(Tunnel)：是作为两个连接中继的中介程序。一旦激活，通道便被认为不属于HTTP通讯，尽管通道可能是被一个HTTP …iask.sina.com.cn|基于695个网页4.坑道英语词汇的奥秘 ... brothel 妓院 tunnel 隧道，坑道 channel 航道，海峡 ... word.langfly.com|基于372个网页5.隧道技术说的隧道技术（tunnel）。在Linux下的IPv6协议栈是支持隧道技术的。www.newsmth.net|基于272个网页6.管道 (4) 管道(Tunnel)设备:有2个HT接口,可扩展其他类型总线。管道设备两侧的总线号保持不变,这是它与HT桥的主要区别。www.chinaaet.com|基于147个网页7.隧道窑陶瓷英语词汇_专业词汇_专业英语_食品伙伴网 ... 窑: kiln 隧道窑: tunnel 印花: stamping ... www.foodmate.net|基于103个网页8.隧道二极管技术文章 - tanghongy的日志 - 网易博客 ... TRIAC 三端双向可控硅开关 TUNNEL 隧道二极管 UNLJUNC-N N 型单结晶体管 ... tanghongy.blog.163.com|基于79个网页更多释义收起释义例句释义:全部全部,地下通道地下通道,地道地道,隧道隧道,洞穴通道洞穴通道,开凿隧道开凿隧道,挖地道挖地道,坑道坑道,隧道技术隧道技术,管道管道类别:全部全部,口语口语,书面语书面语,标题标题,技术技术来源:全部全部,字典字典,网络网络难度:全部全部,简单简单,中等中等,难难更多例句筛选收起例句筛选1.Almost every structure in the wind tunnel was a one-of-a-kind installation.几乎所有的风洞结构是一对的一类安装。www.bugutang.com2.The Queen was accompanied on her train journey through the historic tunnel by one of her Rolls-Royce cars which was placed on the train.女王陪同她火车穿越历史隧道的一个她的劳斯莱斯汽车放在火车上。www.p4pp.com3.The reflection on his face in the train window when they went through a tunnel was a little sinister.当他们穿过隧道时，车窗上反映出他的面部，有点儿凶神恶煞的样子。4.It would be like a near-death experience where you see the light at the end of the tunnel, but it's a total death experience.这就像体验濒临死亡的感觉，你看到了隧道尽头的光明，不过这可是一个完整的死亡体验。www.ted.com5.Nancy Drew: I found a tunnel and I'm going in. If I don't come back in 10 minutes, that means something bad has happened. Corky: laughs.南茜·朱尔：我发现了一条地道，现在就进去。如果我10分钟之内没有回来，就意味着我出事了。考基：真好笑。blog.sina.com.cn6.Being able to detect damage to a bridge or tunnel and report it automatically would be very useful.能发觉损坏的桥或隧道并主动把其记录下来，这举动将会非常有用。www.ecocn.org7.Thick pipes protrude from the ceiling, and a window in the front room opens onto nowhere, just another gray tunnel wall beyond it.粗壮的管道从天花板上突出来，前屋的窗户外不过是另一堵灰色的隧道墙壁。www.bing.com8.Granin told me that I should be able to get there from the mountains to the north through an underground tunnel .告诉我，穿过这座山北部的地下隧道就可以到那里。www.bing.com9.The long- term monitoring of secondary tunnel lining stress and strain is always a focus problem in geotechnical engineering field.隧道二次衬砌应力、应变状态的长期监测，一直是国内外岩土工程界关注的焦点。dictsearch.appspot.com10.Many suffocated trying to crawl out of the tunnel, Mr. Zhou said. Only three or four survived.周先生说，许多被窒息的工人企图爬出矿井，只有三四人死里逃生。www.bing.com12345© 2024 Microsoft隐私声明和 Cookie法律声明广告帮

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tunnel是什么意思_tunnel的翻译_音标_读音_用法_例句_爱词霸在线词典

el是什么意思_tunnel的翻译_音标_读音_用法_例句_爱词霸在线词典首页翻译背单词写作校对词霸下载用户反馈专栏平台登录tunnel是什么意思_tunnel用英语怎么说_tunnel的翻译_tunnel翻译成_tunnel的中文意思_tunnel怎么读,tunnel的读音,tunnel的用法,tunnel的例句翻译人工翻译试试人工翻译翻译全文简明柯林斯牛津tunnel高中/CET4/CET6/考研/TOEFL/IELTS英 [ˈtʌnl]美 [ˈtʌnl]释义常用高考讲解n.隧道，地道v.挖隧道，挖地道大小写变形:Tunnel点击人工翻译，了解更多人工释义词态变化复数: tunnels;第三人称单数: tunnels;过去式: tunnelled;过去分词: tunnelled;现在分词: tunnelling;实用场景例句全部隧道地道打通隧道挖掘隧道a railway/railroad tunnel铁路隧道牛津词典the Channel Tunnel英吉利海峡隧道牛津词典The engineers had to tunnel through solid rock.工程师须要在坚实的岩石中开凿隧道。牛津词典The rescuers tunnelled their way in to the trapped miners.救援人员挖地道通向那些被困的矿工。牛津词典...two new railway tunnels through the Alps.穿过阿尔卑斯山的两条新的铁路隧道柯林斯高阶英语词典…the motorway tunnels under the Hudson river.哈得孙河下的高速公路隧道柯林斯高阶英语词典The rebels tunnelled out of a maximum security jail...叛乱者挖地道逃离了戒备最为森严的监狱。柯林斯高阶英语词典The caterpillars tunnel into the fruit to grow and mature.毛虫钻入果实，并在其中生长为成虫。柯林斯高阶英语词典Chris: I'm just looking at the safety instruction manual.克里斯: 我只是在翻阅安全指南手册.期刊摘选If a train entered this tunnel, itwould draw in fresh air behind it.如果火车开进这条隧道, 它会抽进新鲜冷空气.《用法词典》The train passed through a tunnel.火车通过了一条隧道.《简明英汉词典》The exit of the tunnel is concealed.地道的出口开在隐秘的地方.《现代汉英综合大词典》They drove a tunnel through the rock.他们凿通一条穿过岩石的隧道.《简明英汉词典》Recently, there has again been great interest in the idea of a Channel Tunnel.近来, 对英吉利海峡隧道的念头有了很大兴趣.《用法词典》Now they can construct tunnel systems without hindrance.现在他们可以顺利地建造隧道系统了.《简明英汉词典》To build this tunnel we had to cut through the solid rock.为了修建这条隧道,我们必须凿开坚硬的岩石.《简明英汉词典》They hollowed out a tunnel through the mountain.他们挖通了穿山隧道.《简明英汉词典》They will hole a tunnel through the mountain.他们将穿山打隧道.《简明英汉词典》They came out of the tunnel and thankfully breathed the fresh air.他们走出地道,贪婪地吸着新鲜空气.《简明英汉词典》A worker put a prop against the wall of the tunnel to keep it from falling.一名工人用东西支撑住隧道壁好使它不会倒塌.《简明英汉词典》A mouse dug a tunnel under the lawn.老鼠在草地下打了洞.《简明英汉词典》I escaped by means of a secret tunnel.我通过一条秘密通道逃跑了.《简明英汉词典》The ferry service of bygone days has been replaced by that tunnel.往日的渡口已被那个隧道取代.《现代汉英综合大词典》The project has been going on for months but at last we can see the light at the end of the tunnel.这个项目已进行了很长时间,但我们终于看到了成功的希望.《简明英汉词典》The roof of the new tunnel hasn't been properly supported; It'shows signs of falling in.新隧道的顶部支撑得不好, 已显出坍塌的迹象.《简明英汉词典》The tunnel is a brilliant feat of engineering.这条隧道是工程方面的光辉业绩。《牛津高阶英汉双解词典》He passed down the tunnel.他穿行在隧道中。柯林斯例句The Channel Tunnel project is the biggest civil engineering project in Europe.英吉利海峡隧道是欧洲最大的土木工程。柯林斯例句收起实用场景例句英英释义Noun1. a passageway through or under something, usually underground (especially one for trains or cars);"the tunnel reduced congestion at that intersection"2. a hole in the ground made by an animal for shelterVerb1. move through by or as by digging;"burrow through the forest"2. force a way through收起英英释义词根词缀后缀: -el表名词,"人或物等等"adj.novel 新奇的,新颖的nov新的+el人或物等等→n.[长篇]小说 adj.新奇的,新颖的n.kennel 狗舍,狗窝 kenn=can+el人或物等等→狗舍,狗窝channel 海峡,水道;信道,波道;路线,途径chann=can管道+el人或物等等→n.海峡,水道;信道,波道;路线,途径chisel 凿子 chis挖+el人或物等等→n.凿子 v.用凿子刻,雕,凿colonel [陆军]上校colon=column柱子+el人或物等等→像柱子一样站着的人→上校wastrel 败家子,挥霍无度的人wastr=waste浪费+el人或物等等→n.败家子,挥霍无度的人model 样式,型;模范;模型,原型;模特 mod模式+el人或物等等→n.样式,型;模范;模型,原型;模特 v.模仿novel [长篇]小说 nov新的+el人或物等等→n.[长篇]小说 adj.新奇的,新颖的parcel 包裹,邮包,部分 parc部分+el人或物等等→n.包裹,邮包,部分 v.打包,捆扎,分配personnel 全体人员,全体职员;人事[部门]person人+el人或物等等→personnel全体人员sentinel 哨兵;看守人sent感觉,警觉+in+el人或物等等→n.哨兵;看守人tunnel 隧道,山洞tunn管道+el人或物等等→n.隧道,山洞v.kennel 置于狗窝kenn=can+el人或物等等→狗舍,狗窝chisel 用凿子刻,雕,凿chis挖+el人或物等等→n.凿子 v.用凿子刻,雕,凿model 模仿mod模式+el人或物等等→n.样式,型;模范;模型,原型;模特 v.模仿parcel 打包,捆扎,分配parc部分+el人或物等等→n.包裹,邮包,部分 v.打包,捆扎,分配词组搭配light at the end of the tunnel见 light收起词组搭配同义词n.洞穴passageundergroundcavegrottocavern其他释义subwaycouchdigburrowcavedengrottogrubcavern行业词典公路科技隧道冶金学隧道医学隧道：贯穿实体的通道，长短不一，除两端开放以供进、出外，完全封闭土木工程隧道水利隧道挖筑在山体内或地面以下的长条形的通道。煤炭隧道在地层中开凿的两端有地面出入口的水平通道。常用俚语tunnel(黑社会用语)藏身匿迹You have to find a good place for tunneling yourself.你一定要找一处让自己藏身匿迹的好地方。释义词态变化实用场景例句英英释义词根词缀词组搭配同义词行业词典常

TUNNEL | English meaning - Cambridge Dictionary

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English (UK)

English

Meaning of tunnel in English

tunnelnoun [ C ] uk

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/ˈtʌn.əl/ us

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/ˈtʌn.əl/

Add to word list

B1 a long passage under or through the ground, especially one made by people: The train went into the tunnel.

vasiliki/E+/GettyImages

the tunnel

the long passage through which football, rugby etc. players walk to get to the pitch

efks/iStock/Getty Images Plus/GettyImages

More examplesFewer examplesThe tunnel was dug with the aid of heavy machinery.Ten miners were trapped underground when the roof of the tunnel fell in.The road goes over the mountains, not through a tunnel.It is not practicable to complete the tunnel before the end of the year.A tunnel entrance was found within the precincts of the prison camp.

SMART Vocabulary: related words and phrases

Ditches, dams & tunnels

cut

cutting

dam

dam something up

dike

ditch

dyke

groin

groyne

ha ha

inspection chamber

spillway

subway

the Channel Tunnel

the Chunnel

trench

tunneller

underpass

You can also find related words, phrases, and synonyms in the topics:

Sports venues

tunnelverb [ I or T ] uk

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/ˈtʌn.əl/ us

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/ˈtʌn.əl/ -ll- or US usually -l-

to dig a tunnel: The decision has not yet been made whether to tunnel under the river or build a bridge over it. The alternative is to tunnel a route through the mountain. He was trapped in a collapsed building but managed to tunnel his way out.

SMART Vocabulary: related words and phrases

Digging

borer

break ground idiom

burrow

dig

dig (yourself) in

dig someone/something out

drill

excavate

excavator

fork

furrow

grub

grub something up/out

plough

plough something back/in

prospect

redrill

root something out/up

sink

steam shovel

See more results »

You can also find related words, phrases, and synonyms in the topics:

Ditches, dams & tunnels

Related words

tunneller

tunneler

(Definition of tunnel from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

tunnel | American Dictionary

tunnelnoun [ C ] us

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/ˈtʌn·əl/

Add to word list

a long passage under or through the earth, esp. one made for vehicles: The train entered the tunnel.

tunnelverb [ I/T ] us

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/ˈtʌn·əl/ -l- | -ll-

to dig a tunnel: [ I ] Earthworms digest organic matter as they tunnel. [ T ] The people trapped in the collapsed building had to tunnel their way out.

(Definition of tunnel from the Cambridge Academic Content Dictionary © Cambridge University Press)

Examples of tunnel

tunnel

Termites tunnelled slowly in the dry sand, but diverted their tunnelling into the wet sand once it had been discovered.

From the Cambridge English Corpus

Both are usually estimated using data derived by scanning tunneling microscopy from different surface specimens.

From the Cambridge English Corpus

The percentage of stem tunnelled, internodes bored and cobs damaged did not significantly vary among treatments in the insecticide-treated plots (table 5).

From the Cambridge English Corpus

The arenas were typically explored to their edges after four days, with all solid objects and gaps interconnected with many tunnels.

From the Cambridge English Corpus

Of course new food sources will be discovered and the laboratory studies of tunnelling behaviour may yield valuable insights into this process.

From the Cambridge English Corpus

Extract-treated sand barriers deterred tunnelling completely for 2-4 days at the higher extract concentrations tested, although partial penetration was seen in succeeding days.

From the Cambridge English Corpus

Dynamically controlled protein tunneling paths in photosynthetic reaction centers.

From the Cambridge English Corpus

The rolling and tunnelling dung beetle species used in this study, were selected for their large size and/or abundance.

From the Cambridge English Corpus

The three chambers were connected in series by two, 4 cm in diameter, tunnels which only permitted the adolescents to shuttle between the chambers.

From the Cambridge English Corpus

The number of tunnels was determined as the number of points where termites were excavating.

From the Cambridge English Corpus

We need to detect the nuclear products of the weak interaction if we are to search for resonant tunneling at low energy.

From the Cambridge English Corpus

Physical models and simulators, such as wind tunnels, are also commonly used to analyze the behavior of designs when the mathematics required are formidable.

From the Cambridge English Corpus

A good example is the use of wind tunnels to evaluate the aerodynamic proper ties of vehicles under various conditions.

From the Cambridge English Corpus

The theory can be tested using wings with various cross-sections in wind tunnels.

From the Cambridge English Corpus

The experimental apparatus was designed to mimic natural foraging tunnels of termites and to allow for rapid and simple sampling of feeding sites.

From the Cambridge English Corpus

See all examples of tunnel

These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors.

Collocations with tunnel

tunnel

These are words often used in combination with tunnel.Click on a collocation to see more examples of it.

access tunnelThere was no access tunnel; the sphere had to be loaded and unloaded while on deck.

From Wikipedia

This example is from Wikipedia and may be reused under a CC BY-SA license.

dark tunnelWe are going through a long dark tunnel and no one can see the light.

From the Hansard archive

Example from the Hansard archive. Contains Parliamentary information licensed under the Open Parliament Licence v3.0

drainage tunnelOften thought to be a railway tunnel, it was actually constructed only as a drainage tunnel so that water can be removed from the farmlands.

From Wikipedia

This example is from Wikipedia and may be reused under a CC BY-SA license.

See all collocations with tunnel

What is the pronunciation of tunnel?

Translations of tunnel

in Chinese (Traditional)

隧道, 地道, 坑道…

in Chinese (Simplified)

隧道, 地道, 坑道…

in Spanish

túnel, túnel [masculine]…

in Portuguese

túnel, túnel [masculine]…

in more languages

in Marathi

in Japanese

in Turkish

in French

in Catalan

in Dutch

in Tamil

in Hindi

in Gujarati

in Danish

in Swedish

in Malay

in German

in Norwegian

in Urdu

in Ukrainian

in Russian

in Telugu

in Arabic

in Bengali

in Czech

in Indonesian

in Thai

in Vietnamese

in Polish

in Korean

in Italian

बोगदा…

トンネル, 穴（あな）…

tünel, tünel kazmak/açmak…

tunnel [masculine], galerie [feminine], tunnel…

túnel…

tunnel, een tunnel graven…

सुरंग, भूमिगत पथ…

બોગદું…

tunnel, grave sig igennem…

tunnel, gräva en tunnel…

terowong, membuat terowong…

der Tunnel, untertunneln…

tunnel [masculine], underjordisk gang [masculine], tunnel…

سرنگ…

тунель, підземний хід, прокладати тунель…

тоннель, прокладывать тоннель…

సొరంగం…

نَفَق…

সুড়ঙ্গ…

tunel, vykopat tunel…

terowongan, membuat terowongan…

อุโมงค์, ขุดอุโมงค์…

đường hầm, xây dựng đường hầm…

tunel, przekopywać lub kopać (tunel), wykopać tunel…

터널…

galleria, tunnel, (scavare un tunnel)…

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tuning fork

tuning peg

Tunisia

Tunisian

tunnel

tunnel vision

tunneler

tunnelled

tunneller

More meanings of tunnel

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wind tunnel

flesh tunnel

tunnel vision

the Channel Tunnel

carpal tunnel syndrome

carpal tunnel, at carpal tunnel syndrome

light at the end of the tunnel idiom

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Idioms and phrases

light at the end of the tunnel idiom

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Home Geology Branches Engineering Geology Tunnel Construction

Engineering Geology

Tunnel Construction

Modified date: 23/04/2023

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Introduction to tunnel construction involves understanding the purpose, history, and basics of tunnel construction.

A tunnel is an underground passageway that is excavated through soil, rock or both. Tunnels are used for transportation, water conveyance, sewage, and utility conduits. They have a long history of use, dating back to ancient civilizations, and have become increasingly important in modern society for transportation and infrastructure development.

Tunnel Boring Machine (TBM) )that is being moved inside an underground tunnel.

The basics of tunnel construction involve a series of steps that include surveying and site investigation, tunnel design, excavation and construction, and final finishing work. These steps must be carefully planned and executed to ensure the safety and durability of the tunnel, as well as to minimize the impact on the surrounding environment.

Tunnel construction also involves the use of specialized equipment and techniques, such as tunnel boring machines, explosives, and support systems, which require skilled workers and engineers. The construction process must also take into account potential hazards such as groundwater, soil instability, and the risk of collapse.

Overall, tunnel construction is a complex and demanding process that requires careful planning, execution, and monitoring to ensure the successful completion of the project.

ContentsPurpose and types of tunnelsHistorical background of tunnel constructionSite investigation and geological considerationsImportance of site investigationMethods of site investigationGeological factors affecting tunnel constructionRock mass classification systemsTunnel designDesign parameters and considerationsTypes of tunnel linings and support systemsTunnel drainage systemsVentilation and lightingTunnel excavation and construction methodsDrill and blast methodTunnel boring machine (TBM) methodCut-and-cover methodNew Austrian Tunneling Method (NATM)Tunnel support systemsRock bolting and shotcretingSteel arches and ribsReinforced concrete liningsTunnel construction challenges and solutionsWater inflows and dewateringGeological and geotechnical hazardsEnvironmental impacts and mitigation measuresTunnel maintenance and rehabilitationMonitoring and maintenance of tunnelsCase studies of tunnel construction projectsLessons learned from failed tunnel construction projectsReferences

Purpose and types of tunnels

Tunnels are underground passageways constructed through a variety of rock or soil materials. The purpose of tunnels varies, and they can be used for transportation, water supply, sewage, hydroelectric power, mining, and other purposes.

Tunnels can be broadly classified into the following categories based on their purpose:

Transportation tunnels: These tunnels are constructed for vehicular traffic, rail transport, and pedestrian use. Examples include road tunnels, railway tunnels, and pedestrian walkways.

Utility tunnels: These tunnels are used to carry pipes, cables, and other utility services, such as water, gas, electricity, and telecommunications.

Mining tunnels: These tunnels are constructed in mining operations for the extraction of minerals and ores.

Hydroelectric power tunnels: These tunnels are used to convey water to hydroelectric power plants, where the force of the water is used to generate electricity.

Sewage tunnels: These tunnels are used to transport sewage from one location to another, usually from a treatment plant to a discharge point.

The type of tunnel chosen for a specific project will depend on its intended purpose, as well as the geological and environmental conditions of the site.

Historical background of tunnel construction

The history of tunnel construction dates back thousands of years, with early examples of tunnels used for irrigation, mining, and transportation purposes. The ancient Greeks and Romans were known for their tunnel engineering, with tunnels used for aqueducts, sewage systems, and transportation. In the Middle Ages, tunnels were built for defensive purposes, such as secret escape routes or to conduct surprise attacks on enemy fortresses.

Historical background of tunnel construction

In the modern era, tunnel construction advanced significantly with the introduction of drilling and blasting techniques in the 1800s. The development of the tunnel boring machine (TBM) in the mid-1900s further revolutionized tunnel construction by allowing for faster and more efficient excavation. Today, tunnels are built for a wide range of purposes, including transportation (such as roads, railways, and subways), water conveyance, mining, and storage.

Site investigation and geological considerations

Site investigation and geological considerations are critical aspects of tunnel construction projects. A thorough site investigation is necessary to determine the geological and geotechnical conditions at the proposed tunnel location, as well as to identify any potential geological hazards that may affect the construction and operation of the tunnel. The geological conditions at the site can have a significant impact on the tunnel design, construction methods, and overall project cost.

Site investigation typically involves a combination of geological mapping, geophysical surveys, and drilling to obtain soil and rock samples for laboratory testing. Geological mapping involves the study of surface rock formations and their characteristics, including their orientation, strength, and permeability. Geophysical surveys use non-invasive techniques to investigate subsurface rock formations and detect any anomalies that may indicate the presence of geological hazards such as faults, fractures, and groundwater. Drilling provides a more detailed understanding of the subsurface conditions by obtaining soil and rock samples for laboratory testing.

Geological considerations during tunnel construction include the type and strength of the rock or soil through which the tunnel is being excavated, the presence of groundwater and its flow characteristics, the possibility of seismic activity, and the potential for geological hazards such as landslides and rockfalls. The geological conditions may also impact the choice of tunneling method, such as the use of a tunnel boring machine versus drill and blast methods.

Overall, a thorough site investigation and understanding of the geological conditions at the tunnel location are critical for the safe and successful construction of a tunnel.

Importance of site investigation

Site investigation is an important aspect of tunnel construction as it helps to identify potential geological hazards and other factors that could affect the construction process. A thorough site investigation can help to determine the characteristics of the soil and rock, the presence of groundwater, and the potential for seismic activity. This information can be used to develop an appropriate design for the tunnel, as well as to identify any potential risks or challenges that may need to be addressed during the construction process. Additionally, a site investigation can help to identify any potential environmental or social impacts of the project, which can be addressed through appropriate mitigation measures. Overall, a site investigation is a critical step in the tunnel construction process, as it provides important information for the design and construction of a safe and effective tunnel.

Methods of site investigation

There are several methods that can be used for site investigation for tunnel construction. Some of the common methods are:

Desk study: A desk study involves a review of existing literature, geological maps, and reports, and any other relevant information about the site.

Geophysical survey: This involves the use of various geophysical techniques to obtain information about the subsurface, such as seismic surveys, ground penetrating radar, resistivity surveys, and electromagnetic surveys.

Boreholes: Boreholes are drilled into the ground to obtain samples of soil and rock for laboratory testing. They can also be used to obtain in-situ measurements of groundwater pressure and permeability.

Trial pits: Trial pits are excavations made to provide a visual inspection of the subsurface, and can be used to obtain soil samples for laboratory testing.

Field mapping: Field mapping involves the mapping of the surface geology, geological structures, and any surface features that could affect the tunnel construction.

Instrumentation: Various instruments can be installed to measure the performance of the ground during the construction of the tunnel. These instruments can include inclinometers, piezometers, and strain gauges.

The methods used for site investigation will depend on the specific site conditions and the requirements of the project.

Geological factors affecting tunnel construction

Geological factors play a significant role in the feasibility and design of a tunnel construction project. Some of the important geological factors that affect tunnel construction include:

Rock or soil type: The type of rock or soil through which a tunnel is constructed will significantly impact its design, stability, and construction method.

Rock mass quality: The quality of the rock mass, including its strength, stability, and deformation characteristics, can affect tunnel design, excavation method, and support requirements.

Geological structures: Geological structures such as faults, joints, bedding planes, and folds can significantly affect tunnel design, excavation method, and support requirements.

Groundwater: The presence and flow of groundwater can affect tunnel construction by increasing the risk of water ingress and causing instability of the surrounding rock or soil.

Seismicity: Tunnels constructed in seismically active regions must be designed to withstand the stresses and strains caused by earthquakes.

Slope stability: The stability of the surrounding slopes and hillsides can impact tunnel construction and safety.

Environmental considerations: Tunnels constructed in environmentally sensitive areas must be designed to minimize their impact on the surrounding ecosystem.

Overall, a detailed site investigation is crucial for understanding the geological factors that may impact tunnel construction and developing an appropriate tunnel design and construction plan.

Rock mass classification systems

Rock mass classification systems are used to evaluate the quality of rock masses and assess their suitability for tunnel construction. These systems take into account a variety of factors, including rock strength, discontinuities, joint spacing, weathering, and groundwater conditions.

One commonly used rock mass classification system is the Rock Mass Rating (RMR) system, which was developed by Bieniawski in 1973. RMR assigns numerical values to different parameters such as uniaxial compressive strength, spacing of discontinuities, and groundwater conditions. The values are then combined to give an overall rating for the rock mass, which can be used to predict the difficulty of tunneling through the rock.

Another commonly used rock mass classification system is the Q system, which was developed by Barton et al. in 1974. The Q system uses similar parameters to the RMR system, but places more emphasis on the orientation and persistence of discontinuities.

Other rock mass classification systems include the Geological Strength Index (GSI) system, which was developed by Hoek in 1994, and the Tunneling Quality Index (TQI) system, which was developed by Grimstad and Barton in 1993.

Tunnel design

Tunnel design is the process of determining the most effective and efficient means of excavating a tunnel based on the geologic conditions and intended use of the tunnel. The design process generally involves the following steps:

Establish the purpose of the tunnel: The purpose of the tunnel should be clearly defined in order to determine the appropriate size, shape, and alignment of the tunnel.

Geologic and geotechnical investigation: This step involves collecting data on the geologic and geotechnical characteristics of the site, such as rock type, strength, and stability, groundwater conditions, and the presence of any faults or other geologic features that could impact the design and construction of the tunnel.

Tunnel alignment: The tunnel alignment is based on factors such as the intended use of the tunnel, the geologic and topographic conditions of the site, and any environmental considerations. Factors that influence the alignment of a tunnel include the presence of faults or other geologic features, the location of surface structures, and the need to minimize environmental impacts.

Tunnel cross-section: The tunnel cross-section is determined by the purpose of the tunnel, the anticipated traffic or other loads, and the geologic conditions. The cross-section can be circular, elliptical, horseshoe-shaped, or other shapes depending on the site conditions.

Support system: The support system is designed to stabilize the tunnel during and after excavation. The support system can include rock bolts, shotcrete, steel ribs, and/or concrete lining.

Ventilation and drainage: Ventilation and drainage systems are designed to ensure safe and efficient operation of the tunnel. Ventilation systems are used to remove exhaust gases and provide fresh air for workers and passengers, while drainage systems are used to remove water from the tunnel and prevent flooding.

Construction methods: Various construction methods can be used for tunnel excavation, including drill and blast, tunnel boring machines (TBMs), and sequential excavation methods (SEM). The selection of the appropriate construction method depends on the geologic conditions, the intended use of the tunnel, and the available equipment and resources.

Cost estimation: The final step in the tunnel design process is to estimate the cost of construction based on the design specifications, the selected construction method, and the anticipated site conditions.

Overall, tunnel design is a complex process that requires the expertise of geologists, engineers, and other specialists to ensure safe and efficient construction of tunnels that meet the intended purpose.

Design parameters and considerations

The design of a tunnel depends on a number of factors, including:

Purpose of the tunnel: The design of the tunnel will depend on its intended use. For example, a highway tunnel will have different design requirements than a tunnel used for water transport.

Site conditions: The geology and topography of the site will influence the design of the tunnel. Factors such as rock strength, water inflow, and ground support requirements will all need to be considered.

Tunnel dimensions: The diameter of the tunnel, its length, and its alignment will all need to be determined based on the site conditions and the purpose of the tunnel.

Excavation method: The method used to excavate the tunnel will also influence the design. Methods such as drill and blast, tunnel boring machines (TBM), and cut-and-cover will have different requirements.

Ventilation: The design of the tunnel will need to include provisions for ventilation to ensure the safety of workers and users of the tunnel.

Drainage: The tunnel design will also need to include provisions for drainage to manage groundwater inflow and prevent flooding.

Fire protection: Fire protection measures will need to be incorporated into the design of the tunnel to ensure the safety of users.

Traffic and safety systems: Traffic and safety systems such as lighting, signage, and emergency phones will also need to be included in the design.

Environmental considerations: The design of the tunnel will need to consider the potential impact of construction and operation on the environment and take steps to minimize these impacts.

Types of tunnel linings and support systems

Example tunnel support scheme including tendon support (rock bolts/cable bolts), umbrella arch support (forepoles/spiles), steelsets/girders, and shotcrete lining.

There are several types of tunnel linings and support systems used in tunnel construction, and the choice of which one to use depends on a variety of factors including the geological conditions, the purpose of the tunnel, the method of construction, and the budget. Some of the most common types of tunnel linings and support systems include:

Shotcrete lining: This is a concrete layer sprayed onto the rock or soil to provide support and prevent collapse. It is often used in soft ground tunnels and can be applied quickly.

Steel rib support: Steel ribs are used to support the tunnel walls and roof. The steel ribs can be pre-fabricated and quickly installed, making them a popular choice in hard rock tunnels.

Cast-in-place concrete lining: This involves pouring concrete into the tunnel cavity to form a permanent lining. It is often used in larger tunnels with high traffic volumes.

Tunnel boring machines (TBMs): TBMs can be used to excavate tunnels and provide support at the same time. As the TBM advances, concrete segments are installed behind it to form a lining.

Ground freezing: This method involves freezing the surrounding ground to form a temporary support system. It is often used in tunnels that pass through water-bearing soil or rock.

Rock bolts and mesh: This method involves drilling holes into the rock and installing steel bolts to provide support. Wire mesh is also used to help stabilize the rock and prevent debris from falling into the tunnel.

Fiber-reinforced shotcrete: This is similar to shotcrete lining but with the addition of fiber reinforcement to increase strength and durability.

The choice of lining and support system is often a trade-off between cost, speed of construction, and the specific geological conditions encountered during excavation.

Tunnel drainage systems

Tunnel drainage systems are essential for removing water that may enter the tunnel during construction and operation. There are various types of tunnel drainage systems, including:

Dewatering wells: These are installed near the tunnel to intercept and collect groundwater before it enters the tunnel. Dewatering wells can be either permanent or temporary.

Drainage galleries: These are drainage systems built into the tunnel lining that collect water and channel it to a sump or pump station.

Sumps: These are chambers built at low points in the tunnel where water can collect and be pumped out.

Pumps: Pumps are used to remove water from the tunnel sumps and drainage galleries and discharge it to the surface or to a water treatment facility.

The type of drainage system used depends on the geology and hydrology of the area, as well as the construction method and tunnel alignment. Proper design and installation of tunnel drainage systems are important to ensure the safety and long-term durability of the tunnel.

Ventilation and lighting

Ventilation and lighting are important aspects of tunnel construction to ensure safety, maintain proper air quality, and provide visibility for workers and users. Ventilation systems are designed to provide a steady flow of fresh air into the tunnel while removing stale air, dust, and harmful gases. The ventilation system is usually composed of a network of ventilation ducts, fans, and air quality monitoring systems.

Ventilation system for tbm tunnels

Lighting is also an essential aspect of tunnel construction, particularly for safety and visibility. Lighting systems are usually designed to provide adequate illumination for drivers, pedestrians, and workers in the tunnel. The lighting system can be composed of various types of lights, such as fluorescent, LED, and incandescent lights, depending on the specific requirements and conditions of the tunnel. The design of the lighting system should also consider energy efficiency and environmental impact.

Tunnel excavation and construction methods

Tunnel excavation and construction methods vary depending on the geological conditions, tunnel length and diameter, and other factors. Here are some of the most common tunnel excavation and construction methods:

Drill and blast method: This method involves drilling boreholes into the rock face, then blasting the rock using explosives. The resulting debris is removed by loading and hauling equipment.

Tunnel boring machine (TBM) method: This method uses a machine that excavates the tunnel while simultaneously installing the tunnel lining. TBMs can be used for both hard rock and soft ground tunnels.

New Austrian Tunnelling Method (NATM): This method involves excavating the tunnel in small sections, then supporting the excavated section with a temporary lining, such as sprayed concrete or rock bolts, before moving on to the next section.

Cut and cover method: This method is used for shallow tunnels and involves excavating a trench, constructing the tunnel, and then backfilling the trench.

Sequential excavation method (SEM): This method involves excavating the tunnel in small sections, using ground support and reinforcement measures to control deformation and stabilize the tunnel.

Shield tunneling: This method uses a shield or a similar specialized piece of equipment to excavate and support the tunnel at the same time.

The choice of the excavation method depends on various factors such as tunnel length, diameter, geology, groundwater conditions, available resources, and environmental considerations.

Drill and blast method

The drill and blast method is a traditional technique used for the excavation of tunnels and involves drilling holes into the rock or soil, filling the holes with explosives, and then detonating the explosives to fragment the rock or soil. The fragmented rock or soil is then removed using machinery or manual labor.

In the drill and blast method, a series of holes are drilled into the rock or soil face using specialized equipment such as rock drills or tunnel boring machines. The holes are typically spaced at regular intervals and arranged in a pattern designed to achieve the desired excavation profile. Once the holes are drilled, they are loaded with explosives, which are then detonated using a remote trigger.

After the explosion, the fragmented rock or soil is removed using excavators or loaders, and the tunnel is stabilized using a support system. The support system may include rock bolts, steel arches, or concrete linings, depending on the nature of the rock or soil and the requirements of the project.

The drill and blast method can be highly effective for excavating tunnels in hard rock, but it can also be time-consuming and expensive, particularly in densely populated areas where noise and vibration from blasting may be a concern.

Tunnel boring machine (TBM) method

The Tunnel Boring Machine (TBM) method is a popular technique used for excavating tunnels in a variety of geological conditions. A TBM is a large cylindrical machine that can excavate through various types of soil and rock by using a rotating cutterhead with disc cutters, which can excavate the tunnel face while simultaneously installing the tunnel lining.

Tunnel boring machine

The TBM method is generally preferred for tunnels that are long and straight, as it is less labor-intensive and can work at a much faster rate than other tunneling methods. The TBM method is also preferred in urban areas where there is a need to minimize the impact on the surrounding community, as it produces less noise, vibration, and dust than other methods.

The TBM method typically involves the following steps:

Excavation of the launch shaft: A large pit is excavated at the starting point of the tunnel where the TBM will be assembled.

TBM assembly and launch: The TBM is assembled at the bottom of the launch shaft and then launched into the tunnel alignment.

TBM excavation: The TBM excavates the soil or rock in front of it while simultaneously installing precast concrete segments or other tunnel lining materials.

Muck removal: The excavated material, or “muck,” is transported out of the tunnel using a conveyor belt or a slurry pipeline.

Tunnel lining installation: Once the TBM has excavated a certain length of the tunnel, the precast concrete segments or other tunnel lining materials are installed behind the TBM.

TBM retrieval: When the TBM reaches the end of the tunnel, it is disassembled and retrieved from the tunnel using the same launch shaft.

Cut-and-cover method

The cut-and-cover method is a technique used for the construction of shallow tunnels or underground structures. In this method, a trench is excavated in the ground and the structure is built inside it. The trench is then covered back with the excavated material or a precast concrete slab.

Cut-and-cover method

This method is suitable for constructing tunnels in urban areas or areas where surface traffic is a concern. It is also an effective technique for constructing underground railway stations, pedestrian walkways, and stormwater drainage tunnels. However, the method has some limitations, such as the high cost of construction, disruption to surface traffic during excavation, and limitations on the depth of excavation.

New Austrian Tunneling Method (NATM)

The New Austrian Tunneling Method (NATM) is a method of tunnel construction that was developed in the 1960s in Austria. It is also known as the sequential excavation method (SEM). NATM involves excavating the tunnel in small sections or “drifts,” usually around 3-4 meters in length, and then immediately reinforcing the excavated section with a layer of shotcrete and rock bolts or steel ribs. The surrounding rock or soil provides additional support. This method allows for flexibility in adapting to the geological conditions encountered during excavation and is particularly suitable for soft or unstable ground. NATM also has the advantage of being relatively fast and economical, since it does not require the extensive use of heavy machinery. However, it requires a high level of skill and expertise from the construction team to be effective.

Tunnel support systems

Tunnel support systems are used to stabilize the ground and prevent collapse during tunnel excavation. The choice of support system depends on a variety of factors, including the geology of the ground, the type of tunnel being constructed, and the excavation method being used. Some common types of tunnel support systems include:

Rock bolts: These are long, steel rods that are inserted into boreholes and grouted into place. They provide reinforcement and stabilization of the rock mass by transferring the loads between the rock blocks.

Shotcrete: This is a spray-on concrete mixture that is applied to the exposed rock surface to form a thin shell, which acts as a temporary support until the final lining is constructed.

Steel arches: These are pre-fabricated or custom-fabricated steel arches that are used to support the roof and walls of the tunnel.

Reinforced concrete: This is a common lining material for tunnels. Reinforced concrete is cast in place or prefabricated off-site and then installed in the tunnel.

Steel ribs and lagging: This is a method of tunnel support in which steel ribs are installed and then wooden lagging is placed between them. The lagging helps to hold the ground in place until the final lining is constructed.

Ground freezing: This is a method of support used in soft ground conditions where the soil is frozen using liquid nitrogen or other refrigerants. This creates an ice wall around the tunnel, which provides temporary support until the final lining is installed.

The choice of support system depends on the geological conditions, excavation method, and the design of the tunnel. The support system must provide temporary support during excavation and construction, and also long-term support to maintain the stability of the tunnel throughout its life.

Rock bolting and shotcreting

Rock bolting and shotcreting are two common techniques used for tunnel support in underground construction.

Rock bolting involves drilling holes into the rock face and inserting steel bolts into the holes, which are then grouted in place. The bolts help to support the rock and prevent it from collapsing.

shotcreting

Shotcreting, on the other hand, involves spraying a layer of concrete onto the rock face using a high-pressure hose. The concrete provides additional support and helps to prevent rock falls.

Both techniques can be used in conjunction with other support systems, such as steel ribs or mesh, to provide additional reinforcement to the tunnel walls and roof. The specific support system used will depend on the geology of the tunnel and the design requirements.

Steel arches and ribs

Steel arches and ribs are commonly used in tunnel construction to provide additional support to the tunnel lining. They are usually made of steel or a combination of steel and concrete and are installed along the tunnel walls to provide additional strength and stability to the rock mass.

Steel arches are generally used for shallow tunnels with a span of less than 10 meters, whereas steel ribs are used for larger tunnels with a span of more than 10 meters. The steel arches or ribs are typically installed in a pre-determined pattern and are held in place using rock bolts, which are long, steel rods that are anchored into the rock surrounding the tunnel.

The use of steel arches and ribs is particularly useful in unstable rock formations, where the rock mass has a tendency to deform or collapse. The arches or ribs can help to redistribute the load and provide additional support to the tunnel lining, which helps to ensure the stability and safety of the tunnel.

Reinforced concrete linings

Reinforced concrete linings are commonly used for tunnel construction as they provide a durable and strong structural support. Reinforced concrete linings are typically used in tunnels with large diameter and higher stability requirements. The lining provides resistance to external loads, supports the load of the overlying ground, and protects the tunnel from water ingress and corrosion.

The process of constructing a reinforced concrete lining involves the following steps:

Erecting formwork: The formwork, which is a temporary structure, is erected to the shape and size of the tunnel cross-section.

Placing reinforcing steel: Reinforcing steel is placed inside the formwork according to the design requirements.

Pouring concrete: Once the reinforcing steel is in place, concrete is poured into the formwork. The concrete mix design is typically designed to achieve high strength and durability.

Curing: After the concrete is poured, it needs to be cured for a specific period of time to achieve its design strength. Curing can be done through wet curing or by applying curing compounds to the concrete surface.

Stripping the formwork: Once the concrete has achieved sufficient strength, the formwork is removed, revealing the hardened concrete lining.

Reinforced concrete linings can be designed in various shapes and sizes depending on the tunnel alignment and geological conditions. In some cases, precast concrete segments are used, which are manufactured offsite and assembled inside the tunnel using specialized equipment.

Tunnel construction challenges and solutions

Tunnel construction can present many challenges that need to be addressed to ensure successful completion of the project. Some of the common challenges in tunnel construction include:

Geotechnical conditions: The geological conditions of the site can greatly affect the construction process, making it more challenging to excavate the tunnel. For example, tunnels constructed through hard rock formations are easier to excavate than those constructed through soft soil.

Groundwater: Groundwater can pose a challenge during tunnel construction, as it can weaken the tunnel support systems and cause instability. Adequate drainage and dewatering systems must be installed to prevent flooding and damage to the tunnel.

Ventilation: Ventilation is crucial in tunnel construction to provide fresh air and remove dust, fumes, and gases that can accumulate in the tunnel. Proper ventilation is necessary for the safety of workers and the efficient operation of equipment.

Limited space: The limited space in the tunnel can make it difficult to maneuver heavy equipment and materials, which can slow down the construction process. Innovative solutions, such as remote-controlled equipment and robotic systems, can help mitigate this challenge.

Safety: Tunnel construction can be dangerous due to the risks of collapse, rock falls, flooding, fires, and explosions. Stringent safety measures must be implemented to protect workers and the public.

To address these challenges, tunnel construction projects require careful planning and execution. Modern technologies such as computer-aided design, simulation models, and real-time monitoring can aid in the planning and execution of tunnel construction projects. Additionally, experienced tunneling professionals who understand the geology and engineering of tunnels can help to identify potential challenges and develop effective solutions.

Water inflows and dewatering

During tunnel construction, one of the main challenges is dealing with water inflows. Water can seep into the tunnel from surrounding rock formations or from groundwater. This can lead to issues such as flooding, instability of the excavation, and erosion of the tunnel lining.

To manage water inflows, a dewatering system is often put in place. This involves installing pumps and drainage systems to remove water from the tunnel as it is being excavated. The dewatering system can be designed to manage both groundwater and surface water inflows.

In some cases, grouting may also be used to reduce water inflows by filling voids and fractures in the surrounding rock mass. Additionally, a waterproof membrane or lining can be installed to prevent water from entering the tunnel in the first place.

Other challenges during tunnel construction can include dealing with difficult geological conditions, such as fault zones or highly fractured rock. These challenges can be addressed through careful site investigation, appropriate excavation methods, and effective support systems.

It’s important to note that each tunnel construction project is unique and may present its own set of challenges, requiring tailored solutions to overcome them.

Geological and geotechnical hazards

Geological and geotechnical hazards are common challenges encountered during tunnel construction. These hazards can include rock bursts, squeezing ground, fault zones, high water inflows, gas emissions, and other adverse geological and geotechnical conditions.

Rock bursts occur when stresses in the rock mass exceed the strength of the rock, causing sudden and violent failure. Squeezing ground occurs when the rock mass deforms under high confining pressures, leading to convergence of the tunnel walls. Fault zones can be problematic because they can contain loose and weak materials, which may require additional support measures.

High water inflows can also pose challenges during tunnel construction. Dewatering methods may be necessary to control water ingress into the tunnel. Gas emissions, such as methane, can also be hazardous and require careful monitoring.

Solutions to these challenges include careful site investigation and planning to identify potential hazards, the use of appropriate tunnel support systems, and the implementation of effective dewatering and ventilation systems. Additionally, the use of advanced technologies such as 3D modeling and computer simulations can help identify potential hazards and optimize the design of the tunnel support system. Regular monitoring during construction can also help to detect and address potential hazards before they become a serious problem.

Environmental impacts and mitigation measures

Tunnel construction can have a range of environmental impacts, including:

Habitat destruction and fragmentation: Tunnel construction can cause the fragmentation and loss of habitat for a variety of flora and fauna.

Soil erosion and sedimentation: The excavation and construction activities can lead to soil erosion and sedimentation, which can harm aquatic ecosystems.

Water pollution: Tunnel construction can lead to the release of pollutants into nearby water sources, which can harm aquatic organisms.

Air pollution: Tunnel construction can release dust, exhaust fumes, and other pollutants into the air, which can harm human health and the environment.

Noise pollution: Tunnel construction can generate high levels of noise, which can disturb nearby residents and wildlife.

To mitigate these impacts, a range of measures can be taken, including:

Habitat restoration: Efforts can be made to restore habitat in areas that have been affected by tunnel construction.

Erosion and sediment control: Measures such as silt fences and sediment ponds can be used to prevent soil erosion and sedimentation.

Water treatment: Water can be treated before it is discharged to remove pollutants.

Air pollution control: Measures such as dust suppression and the use of low-emission vehicles and equipment can be employed to reduce air pollution.

Noise barriers and insulation: Barriers and insulation can be used to reduce the amount of noise that reaches nearby residents and wildlife.

Monitoring and compliance: Regular monitoring can be carried out to ensure that environmental standards are being met, and any issues that arise can be addressed promptly.

Tunnel maintenance and rehabilitation

Tunnel maintenance and rehabilitation are important aspects of tunnel management to ensure their safe and efficient operation over their design life. Some of the key activities involved in tunnel maintenance and rehabilitation are:

Routine inspection and monitoring: Regular inspection and monitoring of tunnel structures, linings, and support systems are necessary to detect any signs of deterioration or damage.

Cleaning and debris removal: Regular cleaning of the tunnel and removal of debris, sediment, and other obstructions from drainage systems, access tunnels, and ventilation systems is important to ensure smooth and safe operation.

Repairs and maintenance: Repairs and maintenance activities such as grouting, crack filling, and replacement of damaged or corroded components are essential to maintain the integrity of the tunnel structure.

Upgrades and modernization: Upgrades and modernization of tunnel systems such as lighting, ventilation, and communication systems may be required to improve safety and efficiency.

Rehabilitation and strengthening: Rehabilitation and strengthening of tunnel structures may be necessary due to deterioration or changes in the tunnel’s usage.

Risk management and emergency preparedness: Risk management and emergency preparedness plans are important to ensure the safety of tunnel users and to minimize the impact of any incidents or accidents.

Overall, tunnel maintenance and rehabilitation activities require careful planning and execution to ensure their effectiveness and to minimize disruption to tunnel users.

Monitoring and maintenance of tunnels

Monitoring and maintenance of tunnels are critical to ensure the safety and longevity of the tunnel structure. Regular monitoring can help identify signs of deterioration or damage, which can be addressed before they become major problems. Some common methods of monitoring tunnels include visual inspections, instrumentation, and non-destructive testing.

Visual inspections involve physically inspecting the tunnel for signs of wear and tear, such as cracks, leaks, and damage to the lining or support systems. Instrumentation involves installing sensors to measure various parameters such as temperature, humidity, water pressure, and ground movement. Non-destructive testing techniques such as ground penetrating radar, ultrasonic testing, and magnetic particle inspection can also be used to assess the integrity of the tunnel structure.

Maintenance activities can include cleaning the tunnel, repairing damage or leaks, and replacing worn-out or damaged components such as lighting, ventilation systems, and support systems. Rehabilitation may be necessary to address more significant damage or deterioration, and can involve techniques such as grouting, shotcreting, or applying a new lining.

Overall, regular monitoring and maintenance are critical to ensure the long-term safety and functionality of tunnels, and can help prevent costly repairs or even catastrophic failures.

Case studies of tunnel construction projects

There are many examples of significant tunnel construction projects around the world. Here are a few notable ones:

Channel Tunnel: Also known as the “Chunnel,” this tunnel connects the United Kingdom and France beneath the English Channel. It is 31.4 miles long, making it the longest underwater tunnel in the world. The tunnel consists of two parallel rail tunnels and a service tunnel.

Gotthard Base Tunnel: This tunnel, located in Switzerland, is currently the longest railway tunnel in the world, measuring 35.5 miles in length. It is a key part of the New Rail Link through the Alps, which connects Zurich and Milan.

Alaskan Way Viaduct Replacement Tunnel: This tunnel, located in Seattle, Washington, replaced an aging elevated freeway that was vulnerable to earthquakes. The tunnel is two miles long and carries State Route 99 beneath downtown Seattle.

Crossrail: This is a major new railway line currently under construction in London, England. It includes a 13-mile twin-bore tunnel that will run beneath the city and connect 40 stations.

Hong Kong-Zhuhai-Macau Bridge: This bridge-tunnel project connects the cities of Hong Kong, Zhuhai, and Macau in China. It includes a 4.2-mile tunnel section that runs beneath the South China Sea.

These projects all presented unique challenges in terms of geology, site conditions, and construction methods. They are good examples of the importance of careful planning, site investigation, and design in the successful construction of tunnels.

Lessons learned from failed tunnel construction projects

Lessons learned from failed tunnel construction projects can help engineers and construction professionals avoid similar mistakes in the future. Some common reasons for tunnel construction failures include poor site investigation, inadequate design and planning, insufficient support systems, and unforeseen geological or geotechnical conditions.

For example, the collapse of the tunnel being constructed for the Big Dig highway project in Boston, Massachusetts, in 2006 was due to a combination of factors, including inadequate site investigation, faulty design, and poor construction practices. As a result, the construction team had to undertake extensive remediation work to address the issues, leading to significant delays and cost overruns.

Similarly, the construction of the Crossrail project in London was delayed and faced cost overruns due to unexpected geological and geotechnical conditions. The project encountered challenging ground conditions, including sand, gravel, and clay layers, which required additional support and reinforcement measures.

Lessons learned from such incidents can include the need for rigorous site investigation and testing, better communication between designers and construction teams, the implementation of more robust safety protocols, and the use of advanced technologies and equipment to monitor and manage construction activities.

References

Bell, F. G. (2007). Engineering geology and construction. Spon Press.

Hoek, E., & Bray, J. (2014). Rock slope engineering: civil and mining. CRC Press.

Krampe, J., Müller, J., & Neumann, F. (2017). Underground Engineering: Planning, Design, Construction, and Operation of the Underground Space. Springer.

National Ground Water Association. (2019). Groundwater and Wells. CRC Press.

Novakowski, K. S., & Wilkin, R. T. (2011). Groundwater and soil remediation: process design and cost estimating of proven technologies. John Wiley & Sons.

Robery, P. C. (2013). Introduction to tunnelling. CRC Press.

Rojek, J. (2015). Tunnelling and tunnel mechanics: a rational approach to tunnelling. CRC Press.

Terzaghi, K., Peck, R. B., & Mesri, G. (1996). Soil mechanics in engineering practice. John Wiley & Sons.

Williams, D. J. (2013). Geotechnical engineering of embankment dams. CRC Press.

Yilmaz, I. (2010). Seismic data analysis: processing, inversion, and interpretation of seismic data. Society of Exploration Geophysicists.

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How Tunnels Work

By: William Harris

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Up NextHow Subways WorkHow Bridges WorkDiscover.com Transatlantic TunnelAt its most basic, a tunnel is a tube hollowed through soil or stone. Constructing a tunnel, however, is one of the most complex challenges in the field of civil engineering. Many tunnels are considered technological masterpieces and governments have honored tunnel engineers as heroes. That's not to say, of course, that some tunnel projects haven't encountered major setbacks. The Central Artery/Tunnel Project (the "Big Dig") in Boston, Massachusetts was plagued by massive cost overruns, allegations of corruption, and a partial ceiling collapse that resulted in a fatality. But these challenges haven't stopped engineers from dreaming up even bigger and bolder ideas, such as building a Transatlantic Tunnel to connect New York with London.

In this article, we'll explore what makes tunnels such an attractive solution for railways, roadways, public utilities and telecommunications. We'll look at the defining characteristics of tunnels and examine how tunnels are built. We'll also look at the "Big Dig" in detail to understand the opportunities and challenges inherent to building a tunnel. Finally, we'll look at the future of tunnels.Tunnel Image Gallery

Image

courtesy Daniel Schwen/used under Creative Commons Attribution-ShareAlike License

The Gotthard Base Tunnel, a railway tunnel under construction in Switzerland. See more pictures of tunnels.

Tunnel Basics

A tunnel is a horizontal passageway located underground. While erosion and other forces of nature can form tunnels, in this article we'll talk about man made tunnels -- tunnels created by the process of excavation. There are many different ways to excavate a tunnel, including manual labor, explosives, rapid heating and cooling, tunneling machinery or a combination of these methods.

Some structures may require excavation similar to tunnel excavation, but are not actually tunnels. Shafts, for example, are often hand-dug or dug with boring equipment. But unlike tunnels, shafts are vertical and shorter. Often, shafts are built either as part of a tunnel project to analyze the rock or soil, or in tunnel construction to provide headings, or locations, from which a tunnel can be excavated.

The diagram below shows the relationship between these underground structures in a typical mountain tunnel. The opening of the tunnel is a portal. The "roof" of the tunnel, or the top half of the tube, is the crown. The bottom half is the invert. The basic geometry of the tunnel is a continuous arch. Because tunnels must withstand tremendous pressure from all sides, the arch is an ideal shape. In the case of a tunnel, the arch simply goes all the way around.

Tunnel engineers, like bridge engineers, must be concerned with an area of physics known as statics. Statics describes how the following forces interact to produce equilibrium on structures such as tunnels and bridges:

Tension, which expands, or pulls on, material

Compression, which shortens, or squeezes material

Shearing, which causes parts of a material to slide past one another in opposite directions

Torsion, which twists a material

The tunnel must oppose these forces with strong materials, such as masonry, steel, iron and concrete.

In order to remain static, tunnels must be able to withstand the loads placed on them. Dead load refers to the weight of the structure itself, while live load refers to the weight of the vehicles and people that move through the tunnel.

We'll look at the basic types of tunnels next.

Contents

Types of Tunnels

Tunnel Planning

Tunnel Construction: Soft Ground and Hard Rock

Tunnel Construction: Soft Rock and Underwater

The Big Dig

Types of Tunnels

There are three broad categories of tunnels: mining, public works and transportation. Let's look briefly at each type.

Mine tunnels are used during ore extraction, enabling laborers or equipment to access mineral and metal deposits deep inside the earth. These tunnels are made using similar techniques as other types of tunnels, but they cost less to build. Mine tunnels are not as safe as tunnels designed for permanent occupation, however.

Photo courtesy National Photo Company Collection/Library of Congress Prints and Photographs Division

A coal miner standing on the back of a car in a mine tunnel in the early 1900s. Notice that the sides of the tunnel are shored up with timber.

Public works tunnels carry water, sewage or gas lines across great distances. The earliest tunnels were used to transport water to, and sewage away from, heavily populated regions. Roman engineers used an extensive network of tunnels to help carry water from mountain springs to cities and villages. These tunnels were part of aqueduct systems, which also comprised underground chambers and sloping bridge-like structures supported by a series of arches. By A.D. 97, nine aqueducts carried approximately 85 million gallons of water a day from mountain springs to the city of Rome.

Photo courtesy Eric and Edith Matson Photograph Collection/Library of Congress Prints and Photographs Division

A Roman aqueduct that runs from the Pools of Solomon to Jerusalem

Before there were trains and cars, there were transportation tunnels such as canals -- artificial waterways used for travel, shipping or irrigation. Just like railways and roadways today, canals usually ran above ground, but many required tunnels to pass efficiently through an obstacle, such as a mountain. Canal construction inspired some of the world's earliest tunnels.

The Underground Canal, located in Lancashire County and Manchester, England, was constructed from the mid- to late-1700s and includes miles of tunnels to house the underground canals. One of America's first tunnels was the Paw Paw Tunnel, built in West Virginia between 1836 and 1850 as part of the Chesapeake and Ohio Canal. Although the canal no longer runs through the Paw Paw, at 3,118 feet long it is still one of the longest canal tunnels in the United States.

Photo courtesy Kmf164/

Creation Commons Attribution Share-alike License

Traveling through the Holland Tunnel from Manhattan to New Jersey

By the 20th century, trains and cars had replaced canals as the primary form of transportation, leading to the construction of bigger, longer tunnels. The Holland Tunnel, completed in 1927, was one of the first roadway tunnels and is still one of the world's greatest engineering projects. Named for the engineer who oversaw construction, the tunnel ushers nearly 100,000 vehicles daily between New York City and New Jersey.

Tunnel construction takes a lot of planning. We'll explore why in the next section.

Tunnel Planning

Almost every tunnel is a solution to a specific challenge or problem. In many cases, that challenge is an obstacle that a roadway or railway must bypass. They might be bodies of water, mountains or other transportation routes. Even cities, with little open space available for new construction, can be an obstacle that engineers must tunnel beneath to avoid.

Photo courtesy Japan Railway Public Corporation

Construction of the Seikan Tunnel involved a 24-year struggle to overcome challenges posed by soft rock under the sea.

In the case of the Holland Tunnel, the challenge was an obsolete ferry system that strained to transport more than 20,000 vehicles a day across the Hudson River. For New York City officials, the solution was clear: Build an automobile tunnel under the river and let commuters drive themselves from New Jersey into the city. The tunnel made an immediate impact. On the opening day alone, 51,694 vehicles made the crossing, with an average trip time of just 8 minutes.

Sometimes, tunnels offer a safer solution than other structures. The Seikan Tunnel in Japan was built because ferries crossing the Tsugaru Strait often encountered dangerous waters and weather conditions. After a typhoon sank five ferryboats in 1954, the Japanese government considered a variety of solutions. They decided that any bridge safe enough to withstand the severe conditions would be too difficult to build. Finally, they proposed a railway tunnel running almost 800 feet below the sea surface. Ten years later, construction began, and in 1988, the Seikan Tunnel officially opened.

How a tunnel is built depends heavily on the material through which it must pass. Tunneling through soft ground, for instance, requires very different techniques than tunneling through hard rock or soft rock, such as shale, chalk or sandstone. Tunneling underwater, the most challenging of all environments, demands a unique approach that would be impossible or impractical to implement above ground.

That's why planning is so important to a successful tunnel project. Engineers conduct a thorough geologic analysis to determine the type of material they will be tunneling through and assess the relative risks of different locations. They consider many factors, but some of the most important include:

Soil and rock types

Weak beds and zones, including faults and shear zones

Groundwater, including flow pattern and pressure

Special hazards, such as heat, gas and fault lines

Often, a single tunnel will pass through more than one type of material or encounter multiple hazards. Good planning allows engineers to plan for these variations right from the beginning, decreasing the likelihood of an unexpected delay in the middle of the project.

Once engineers have analyzed the material that the tunnel will pass through and have developed an overall excavation plan, construction can begin. The tunnel engineers' term for building a tunnel is driving, and advancing the passageway can be a long, tedious process that requires blasting, boring and digging by hand.

In the next section, we'll look at how workers drive tunnels through soft ground and hard rock.

Tunnel Construction: Soft Ground and Hard Rock

Workers generally use two basic techniques to advance a tunnel. In the full-face method, they excavate the entire diameter of the tunnel at the same time. This is most suitable for tunnels passing through strong ground or for building smaller tunnels. The second technique, shown in the diagram below, is the top-heading-and-bench method. In this technique, workers dig a smaller tunnel known as a heading. Once the top heading has advanced some distance into the rock, workers begin excavating immediately below the floor of the top heading; this is a bench. One advantage of the top-heading-and-bench method is that engineers can use the heading tunnel to gauge the stability of the rock before moving forward with the project.

Notice that the diagram shows tunneling taking place from both sides. Tunnels through mountains or underwater are usually worked from the two opposite ends, or faces, of the passage. In long tunnels, vertical shafts may be dug at intervals to excavate from more than two points.

Now let's look more specifically at how tunnels are excavated in each of the four primary environments: soft ground, hard rock, soft rock and underwater.

Soft Ground (Earth)

Workers dig soft-ground tunnels through clay, silt, sand, gravel or mud. In this type of tunnel, stand-up time -- how long the ground will safely stand by itself at the point of excavation -- is of paramount importance. Because stand-up time is generally short when tunneling through soft ground, cave-ins are a constant threat. To prevent this from happening, engineers use a special piece of equipment called a shield. A shield is an iron or steel cylinder literally pushed into the soft soil. It carves a perfectly round hole and supports the surrounding earth while workers remove debris and install a permanent lining made of cast iron or precast concrete. When the workers complete a section, jacks push the shield forward and they repeat the process.

Marc Isambard Brunel, a French engineer, invented the first tunnel shield in 1825 to excavate the Thames Tunnel in London, England. Brunel's shield comprised 12 connected frames, protected on the top and sides by heavy plates called staves. He divided each frame into three workspaces, or cells, where diggers could work safely. A wall of short timbers, or breasting boards, separated each cell from the face of the tunnel. A digger would remove a breasting board, carve out three or four inches of clay and replace the board. When all of the diggers in all of the cells had completed this process on one section, powerful screw jacks pushed the shield forward.

In 1874, Peter M. Barlow and James Henry Greathead improved on Brunel's design by constructing a circular shield lined with cast-iron segments. They first used the newly-designed shield to excavate a second tunnel under the Thames for pedestrian traffic. Then, in 1874, the shield was used to help excavate the London Underground, the world's first subway. Greathead further refined the shield design by adding compressed air pressure inside the tunnel. When air pressure inside the tunnel exceeded water pressure outside, the water stayed out. Soon, engineers in New York, Boston, Budapest and Paris had adopted the Greathead shield to build their own subways.

Hard Rock

Tunneling through hard rock almost always involves blasting. Workers use a scaffold, called a jumbo, to place explosives quickly and safely. The jumbo moves to the face of the tunnel, and drills mounted to the jumbo make several holes in the rock. The depth of the holes can vary depending on the type of rock, but a typical hole is about 10 feet deep and only a few inches in diameter. Next, workers pack explosives into the holes, evacuate the tunnel and detonate the charges. After vacuuming out the noxious fumes created during the explosion, workers can enter and begin carrying out the debris, known as muck, using carts. Then they repeat the process, which advances the tunnel slowly through the rock.

Fire-setting is an alternative to blasting. In this technique, the tunnel wall is heated with fire, and then cooled with water. The rapid expansion and contraction caused by the sudden temperature change causes large chunks of rock to break off. The Cloaca Maxima, one of Rome's oldest sewer tunnels, was built using this technique.

The stand-up time for solid, very hard rock may measure in centuries. In this environment, extra support for the tunnel roof and walls may not be required. However, most tunnels pass through rock that contains breaks or pockets of fractured rock, so engineers must add additional support in the form of bolts, sprayed concrete or rings of steel beams. In most cases, they add a permanent concrete lining.

We'll look at tunnel driving through soft rock and driving underwater next.

Tunnel Construction: Soft Rock and Underwater

Photo courtesy City and County of Denver

A TBM boring head showing the disk cutters

Tunneling through soft rock and tunneling underground require different approaches. Blasting in soft, firm rock such as shale or limestone is difficult to control. Instead, engineers use tunnel-boring machines (TBMs), or moles, to create the tunnel. TBMs are enormous, multimillion-dollar pieces of equipment with a circular plate on one end. The circular plate is covered with disk cutters -- chisel-shaped cutting teeth, steel disks or a combination of the two. As the circular plate slowly rotates, the disk cutters slice into the rock, which falls through spaces in the cutting head onto a conveyor system. The conveyor system carries the muck to the rear of the machine. Hydraulic cylinders attached to the spine of the TBM propel it forward a few feet at a time.

TBMs don't just bore the tunnels -- they also provide support. As the machine excavates, two drills just behind the cutters bore into the rock. Then workers pump grout into the holes and attach bolts to hold everything in place until the permanent lining can be installed. The TBM accomplishes this with a massive erector arm that raises segments of the tunnel lining into place.

Photo courtesy Department of Energy

A TBM used in the construction of Yucca Mountain Repository, a U.S. Department of Energy terminal storage facility

Underwater

Tunnels built across the bottoms of rivers, bays and other bodies of water use the cut-and-cover method, which involves immersing a tube in a trench and covering it with material to keep the tube in place.

Construction begins by dredging a trench in the riverbed or ocean floor. Long, prefabricated tube sections, made of steel or concrete and sealed to keep out water, are floated to the site and sunk in the prepared trench. Then divers connect the sections and remove the seals. Any excess water is pumped out, and the entire tunnel is covered with backfill.

Photo courtesy Stephen Dawson/Creative Commons Attribution Share-alike License

The British end of the Channel Tunnel at Cheriton near Folkestone in Kent

The tunnel connecting England and France -- known as the Channel Tunnel, the Euro Tunnel or Chunnel -- runs beneath the English Channel through 32 miles of soft, chalky earth. Although it's one of the longest tunnels in the world, it took just three years to excavate, thanks to state-of-the-art TBMs. Eleven of these massive machines chewed through the seabed that lay beneath the Channel. Why so many? Because the Chunnel actually consists of three parallel tubes, two that carry trains and one that acts as a service tunnel. Two TBMs placed on opposite ends of the tunnel dug each of these tubes. In essence, the three British TBMs raced against the three French TBMs to see who would make it to the middle first. The remaining five TBMs worked inland, creating the portion of the tunnel that lay between the portals and their respective coasts.

Photo courtesy Eric and Edith Matson Photograph Collection/

Library of Congress Prints and Photographs Division

Inside a Holland Tunnel ventilation tower

Unless the tunnel is short, control of the environment is essential to provide safe working conditions and to ensure the safety of passengers after the tunnel is operational. One of the most important concerns is ventilation -- a problem magnified by waste gases produced by trains and automobiles. Clifford Holland addressed the problem of ventilation when he designed the tunnel that bears his name. His solution was to add two additional layers above and below the main traffic tunnel. The upper layer clears exhaust fumes, while the lower layer pumps in fresh air. Four large ventilation towers, two on each side of the Hudson River, house the fans that move the air in and out. Eighty-four fans, each 80 feet in diameter, can change the air completely every 90 seconds.

We'll look at the "Big Dig" next.

The Big Dig

Now that we've looked at some of the general principles of tunnel building, let's consider an ongoing tunnel project that continues to make headlines, both for its potential and for its problems. The Central Artery is a major highway system running through the heart of downtown Boston, and the project that bears its name is considered by many to be one of the most complex -- and expensive -- engineering feats in American history. The "Big Dig" is actually several different projects in one, including a brand-new bridge and several tunnels. One key tunnel, completed in 1995, is the Ted Williams Tunnel. It dives below the Boston Harbor to take Interstate 90 traffic from South Boston to Logan Airport. Another key tunnel is located below the Fort Point Channel, a narrow body of water used long ago by the British as a toll collection point for ships.

Before we look at some of the techniques used in the construction of these Big Dig tunnels, let's review why Boston officials decided to undertake such a massive civil-engineering project in the first place. The biggest issue was the city's nightmarish traffic. Some studies indicated that, by 2010, Boston's rush hour could last almost 16 hours a day, with dire consequences both for commerce and quality of life for residents. Clearly, something had to be done to relieve traffic congestion and make it easier for commuters to navigate the city. In 1990, Congress allocated $755 million to the massive highway improvement project, and a year later, the Federal Highway Administration gave its approval to move ahead.

Photo courtesy Massachusetts Turnpike Authority

The Ted Williams Tunnel

The Big Dig kicked off in 1991 with construction of the Ted Williams Tunnel. This underwater tunnel took advantage of tried-and-true tunneling techniques used on many different tunnels all over the world. Because the Boston Harbor is fairly deep, engineers used the cut-and-cover method. Steel tubes, 40 feet in diameter and 300 feet long, were towed to Boston after workers made them in Baltimore. There, workers finished each tube with supports for the road, enclosures for the air-handling passages and utilities and a complete lining. Other laborers dredged a trench on the harbor floor. Then, they floated the tubes to the site, filled them with water and lowered them into the trench. Once anchored, a pump removed the water and workers connected the tubes to the adjoining sections.

The Ted Williams Tunnel officially opened in 1995 -- one of the few aspects of the Big Dig completed on time and within the proposed budget. By 2010, it is expected to carry about 98,000 vehicles a day.

A few miles west, Interstate 90 enters another tunnel that carries the highway below South Boston. Just before the I-90/I-93 interchange, the tunnel encounters the Fort Point Channel, a 400-foot-wide body of water that provided some of the biggest challenges of the Big Dig. Engineers couldn't use the same steel-tube approach they employed on the Ted Williams Tunnel because there wasn't enough room to float the long steel sections under bridges at Summer Street, Congress Street and Northern Avenue. Eventually, they decided to abandon the steel-tube concept altogether and go with concrete tunnel sections, the first use of this technique in the United States.

The problem was fabricating the concrete sections in a way that allowed workers to move into position in the channel. To solve the problem, workers first built an enormous dry dock on the South Boston side of the channel. Known as the casting basin, the dry dock measured 1,000 feet long, 300 feet wide and 60 feet deep -- big enough to construct the six concrete sections that would make up the tunnel. The longest of the six tunnel sections was 414 feet long, the widest 174 feet wide. All were about 27 feet high. The heaviest weighed more than 50,000 tons.

The completed sections were sealed watertight at either end. Then workers flooded the basin so they could float out the sections and position them over a trench dredged on the bottom of the channel. Unfortunately, another challenge prevented engineers from simply lowering the concrete sections into the trench. That challenge was the Massachusetts Bay Transportation Authority's Red Line subway tunnel, which runs just under the trench. The weight of the massive concrete sections would damage the older subway tunnel if nothing were done to protect it. So engineers decided to prop up the tunnel sections using 110 columns sunk into the bedrock. The columns distribute the weight of the tunnel and protect the Red Line subway, which continues to carry 1,000 passengers a day.

Photo courtesy City and County of Denver

The tunnel-jacking process

The Big Dig features other tunneling innovations, as well. For one portion of the tunnel running beneath a railroad yard and bridge, engineers settled on tunnel-jacking, a technique normally used to install underground pipes. Tunnel-jacking involves forcing a huge concrete box through the dirt. The top and bottom of the box support the soil while the earth inside the box was removed. Once it was empty, hydraulic jacks pushed the box against a concrete wall until the entire thing slid forward five feet. Workers then installed spacer tubes in the newly-created gap. By repeating this process over and over, engineers were able to advance the tunnel without disturbing the structures at the surface.

Today, 98 percent of the construction associated with the Big Dig is complete, and the cost is well over $14 billion. But the payoff for Boston commuters should be worth the investment. The old elevated Central Artery had just six lanes and was designed to carry 75,000 vehicles a day. The new underground expressway has eight to ten lanes and will carry about 245,000 vehicles a day by 2010. The result is a normal urban rush hour lasting a couple of hours in the morning and evening.

To see how the Big Dig compares to other tunnel projects, see the table below.

Tunnel

Location

Length

Years to Build

Opened

Cost

Railway Tunnels

Seikan Tunnel

Japan

33.5 mi (53.9 km)

1988

$7 billion

Channel Tunnel

England-France

30.6 mi (49.2 km)

1994

$21 billion

Apennine Tunnel

Italy

11.5 mi (18.5 km)

1934

Hoosac Tunnel

United States

4.75 mi (7.6 km)

1873

$21 million

Motor-Traffic Tunnels

Laerdal Tunnel

Norway

15.2 mi (24.5 km)

2000

$125 million

St. Gotthard Road Tunnel

Switzerland

10.1 mi (16.2 km)

1980

Bridge-Tunnel Complexes

Chesapeake Bay Bridge-tunnel

United States

17.6 mi (28.3 km)

3.5

1964

$200 million

Øresund Bridge and Tunnel

Denmark-Sweden

9.9 mi (16 km)

2000

$3 billion

The Future of Tunneling

As their tools improve, engineers continue to build longer and bigger tunnels. Recently, advanced imaging technology has been available to scan the inside of the earth by computing how sound waves travel through the ground. This new tool provides an accurate snapshot of a tunnel's potential environment, showing rock and soil types, as well as geologic anomalies such as faults and fissures.

While such technology promises to improve tunnel planning, other advances will expedite excavation and ground support. The next generation of tunnel-boring machines will be able to cut 1,600 tons of muck per hour. Engineers are also experimenting with other rock-cutting methods that take advantage of high-pressure water jets, lasers or ultrasonics. And chemical engineers are working on new types of concrete that harden faster because they use resins and other polymers instead of cement.

With new technologies and techniques, tunnels that seemed impossible even 10 years ago suddenly seem doable. One such tunnel is a proposed Transatlantic Tunnel connecting New York with London. The 3,100-mile-long tunnel would house a magnetically-levitated train traveling 5,000 miles per hour. The estimated trip time is 54 minutes -- almost seven hours shorter than an average transatlantic flight.

For lots more information about tunnels and related topics, check out the links on the next page.

Lots More Information

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tunnel 在英語-中文（繁體）詞典中的翻譯

tunnelnoun [ C ] uk

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/ˈtʌn.əl/ us

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/ˈtʌn.əl/

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B1 a long passage under or through the ground, especially one made by people

隧道；地道；坑道

The train went into the tunnel.

火車駛入隧道。

the tunnel

the long passage through which football, rugby etc. players walk to get to the pitch

（足球或橄欖球等比賽時球員走向球場的）球員通道

更多範例减少例句The tunnel was dug with the aid of heavy machinery.Ten miners were trapped underground when the roof of the tunnel fell in.The road goes over the mountains, not through a tunnel.It is not practicable to complete the tunnel before the end of the year.A tunnel entrance was found within the precincts of the prison camp.

tunnelverb [ I or T ] uk

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/ˈtʌn.əl/ us

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/ˈtʌn.əl/ -ll- or US usually -l-

to dig a tunnel

開鑿隧道;挖地道

The decision has not yet been made whether to tunnel under the river or build a bridge over it.

還沒有決定是在河底挖掘隧道還是在河上建橋。

The alternative is to tunnel a route through the mountain.

另一個辦法是挖一條穿山隧道。

He was trapped in a collapsed building but managed to tunnel his way out.

他被困在倒塌的樓房下，但他想辦法挖地道出來了。

相關詞語

tunneller

tunnel的例句

tunnel

Termites always chose to explore gaps thoroughly before they began tunnelling in the sand.

來自 Cambridge English Corpus

A method invented earlier in scanning tunnelling microscopy was applied to measure the motion of the cantilever.

來自 Cambridge English Corpus

The rolling and tunnelling dung beetle species used in this study, were selected for their large size and/or abundance.

來自 Cambridge English Corpus

Likewise, severity of borer damage, as evidenced by the % stem tunnelled and % cob damaged, was directly proportional to numbers of attacking larvae.

來自 Cambridge English Corpus

The theory can be tested using wings with various cross-sections in wind tunnels.

來自 Cambridge English Corpus

There was also evidence in a number of places that cercariae, tunnelling horizontally beneath the stratum corneum, led to its separation from the underlying epidermis.

來自 Cambridge English Corpus

The classical trajectory calculations do not account for tunneling transitions allowed by quantum mechanics.

來自 Cambridge English Corpus

A high value means a high computational cost in the calculation of the successive dynamic tunnels.

來自 Cambridge English Corpus

示例中的觀點不代表劍橋詞典編輯、劍橋大學出版社和其許可證頒發者的觀點。

tunnel的翻譯

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隧道, 地道, 坑道…

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túnel, túnel [masculine]…

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tunnel [masculine], galerie [feminine], tunnel…

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tunnel, grave sig igennem…

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tunnel, gräva en tunnel…

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terowong, membuat terowong…

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der Tunnel, untertunneln…

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tunnel [masculine], underjordisk gang [masculine], tunnel…

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سرنگ…

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тунель, підземний хід, прокладати тунель…

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тоннель, прокладывать тоннель…

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tunel, vykopat tunel…

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terowongan, membuat terowongan…

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อุโมงค์, ขุดอุโมงค์…

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đường hầm, xây dựng đường hầm…

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tunel, przekopywać lub kopać (tunel), wykopać tunel…

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galleria, tunnel, (scavare un tunnel)…

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an answer or reaction

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