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59-483: The A2 motorway runs a total of 670 km (420 mi). The megaproject began in 1994 and was completed in 2009 at a cost of €5.93 billion ($ 8.27 billion); it was managed by the state-owned company Egnatia Odos, S.A. The route traverses the mountainous Greek regions of Epirus and Macedonia , crossing the Pindos and Vermio mountain ranges, which posed formidable engineering challenges. It includes 76 tunnels (with

118-598: A combined length of 99 km / 61.5 miles) and 1,650 bridges. It is a limited-access highway with sophisticated electronic surveillance measures, SCADA controls for the lighting/tunnel ventilation, and advanced vehicle collision absorption measures. Part of its length, a section of about 360 km (220 mi) from Evros to Thessaloniki , parallels the ancient Roman Via Egnatia , which ran from modern Durrës in Albania to Thessaloniki and thence to Byzantium (now Istanbul , Turkey ). The project has therefore been dubbed

177-634: A high level of innovation and complexity, and are affected by a number of techno-socio-economic and organizational challenges. The OFCCP Mega Construction Project (Megaproject) Program involves projects valued at over $ 35 million. Megaprojects are often affected by corruption, leading to higher cost and lower benefit. According to the European Cooperation in Science and Technology (COST), megaprojects are characterized both by "extreme complexity (both in technical and human terms) and by

236-449: 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 and critical path method . Also, the land needed for excavation and construction staging, and

295-708: A long record of poor delivery". Megaprojects attract significant public attention because of substantial impacts on communities , environment , and budgets , and the high costs involved. Megaprojects can also be defined as "initiatives that are physical, very expensive, and public". Megaprojects include special economic zones , public buildings , power plants , dams , airports , hospitals , seaports , bridges , highways , tunnels , railways , wastewater projects, oil and natural gas extraction projects, aerospace projects, weapons systems , information technology systems, large-scale sporting events and, more recently, mixed use waterfront redevelopments; however,

354-527: A modern Via Egnatia (in Greek , Egnatia Odos / Εγνατία Οδός). However, the parallel is not exact; the original Via Egnatia was much longer (1,120 km / 696 miles) and its western section, from Thessaloniki to the Adriatic Sea, ran much further north than the modern road. The project has raised concerns for the survival of nearby sites of ecological and archaeological significance. The construction of

413-467: 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. There are also several approaches to underwater tunnels,

472-421: A specialized method called clay-kicking for digging tunnels in clay-based soils. The clay-kicker lies on a plank at a 45-degree angle away from the working face and rather than a mattock with his hands, inserts with his feet a tool with a cup-like rounded end, then turns the tool with his hands to extract a section of soil, which is then placed on the waste extract. Clay-kicking is a specialized method developed in

531-434: A tube can be sunk into a body of water, which is called an immersed tunnel. 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. There are two basic forms of cut-and-cover tunnelling: Shallow tunnels are often of the cut-and-cover type (if under water, of

590-747: 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,

649-917: 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 . A tunnel

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708-432: 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

767-483: Is an extremely large-scale construction and investment project . A more general definition is "Megaprojects are temporary endeavours (i.e. projects) characterised by: large investment commitment, vast complexity (especially in organisational terms), and long-lasting impact on the economy, the environment, and society". Megaprojects refer not only to construction projects but also decommissioning projects, which are projects that can reach multi-billion budgets, and have

826-542: Is collective benefits; for example electricity for everybody (who can pay), road access (for those that have cars), etc. They may also serve as a means to open frontiers. Megaprojects have been criticised for their top-down planning processes and their ill effects on certain communities. Large scale projects often advantage one group of people while disadvantaging another, for instance, the Three Gorges Dam in China,

885-505: Is intended to carry both the Istanbul metro and a two-level highway, over a length of 6.5 km (4.0 miles). 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 miles). Although each level offers a physical height of 2.54 m (8.3 ft), only traffic up to 2 m (6.6 ft) tall

944-787: Is often expressed by critics of megaprojects during the planning phase. If the megaproject is delivered in a country with relevant corruption the likelihood and magnitude of having overbudgets increases. One of the most challenging aspects of megaprojects is obtaining sufficient funding. Alan Altshuler and David Luberoff have found that creative and politically adept political leadership is required to secure resources as well as generate public support, mollify critics, and manage conflict through many years of planning, authorization and implementation. Other challenges faced by those planning megaprojects include laws and regulations that empower community groups, contested information and methodologies, high levels of uncertainty, avoiding impacts on neighborhoods and

1003-494: 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." In

1062-401: 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

1121-515: Is that the open building pit is muted after tunnel construction; no roof is placed. 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 160-metre (540 ft) double-deck tunnel section through Yerba Buena Island , the largest-diameter bored tunnel in the world. At construction this was a combination bidirectional rail and truck pathway on

1180-698: Is the Siloam Tunnel , built in Jerusalem by the kings of Judah around the 8th century BC. Another tunnel excavated from both ends, maybe the second known, is the Tunnel of Eupalinos , which is a tunnel aqueduct 1,036 m (3,400 ft) long running through Mount Kastro in Samos , Greece. It was built in the 6th century BC to serve as an aqueduct . In Ethiopia , the Siqurto foot tunnel , hand-hewn in

1239-569: 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. Government funds are often required for the creation of tunnels. When a tunnel is being planned or constructed, economics and politics play

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1298-471: 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. Increased taxes to finance a large project may cause opposition. 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

1357-848: 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

1416-472: The River Mersey at Liverpool was chosen over a massively high bridge partly 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

1475-679: The United Kingdom of digging tunnels in strong clay-based soil structures. This method of cut and cover construction required relatively little disturbance of property during the renewal of the United Kingdom's then ancient sewerage systems. It was also used during the First World War by Royal Engineer tunnelling companies placing mines beneath German lines, because it was almost silent and so not susceptible to listening methods of detection. Tunnel boring machines (TBMs) and associated back-up systems are used to highly automate

1534-610: The canton of Glarus . The borehole has a diameter of 8.03 metres (26.3 ft). 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). This in turn

1593-489: 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

1652-689: The 16th century as a metaphor for a narrow, confined space like the inside of a cask. Some of the earliest tunnels used by humans were paleoburrows excavated by prehistoric mammals. 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. Predecessors of modern tunnels were adits that transported water for irrigation , drinking, or sewerage . The first qanats are known from before 2000 BC. The earliest tunnel known to have been excavated from both ends

1711-638: 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

1770-716: 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 ;

1829-709: 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 AD. 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

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1888-495: The Pindos stretch (i.e. from Grevena to Ioannina ) was delayed due to environmental concerns about the destruction of the habitat of the endangered brown bear. However, a new routing was proposed in 2003, and this part was completed by April 2009. In addition to the main highway, three perpendicular auxiliary highways are under construction connecting the highway to important cities, ports and airports of Macedonia. 94 km of

1947-483: The United States and Germany prevented developments due to environmental and social concerns. More recently, new types of megaprojects have been identified that no longer follow the old models of being singular and monolithic in their purposes, but have become quite flexible and diverse, such as waterfront redevelopment schemes that seem to offer something to everybody. However, just like the old megaprojects,

2006-536: 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)." The word "tunnel" comes from the Middle English tonnelle , meaning "a net", derived from Old French tonnel , a diminutive of tonne ("cask"). The modern meaning, referring to an underground passageway, evolved in

2065-400: 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

2124-502: The concrete mix to improve lining strength. This creates a natural load-bearing ring, which minimizes the rock's deformation . 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 . In pipe jacking , hydraulic jacks are used to push specially made pipes through

2183-409: 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

2242-419: The environment, and attempting to solve a wicked problem . Tunnel A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ventilation openings at various points along the length. A pipeline differs significantly from

2301-441: 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: 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

2360-524: The general economy has been a popular policy measure since the economic crisis of the 1930s. Recent examples are the 2008–2009 Chinese economic stimulus program , the 2008 European Union stimulus plan , and the American Recovery and Reinvestment Act of 2009 . Megaprojects often raise capital based on expected returns—though projects often go overbudget and over time, and market conditions like commodity prices can change. Concern at cost overruns

2419-405: 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 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

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2478-640: 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

2537-435: The inevitable smoke and steam. A major disadvantage of cut-and-cover is the widespread disruption generated at the surface level during construction. This, and the availability of electric traction, brought about London Underground's switch to bored tunnels at a deeper level towards the end of the 19th century. Prior to the replacement of manual excavation by the use of boring machines, Victorian tunnel excavators developed

2596-468: 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

2655-436: The largest hydroelectric project in the world, required the displacement of 1.2 million farmers. In the 1970s, the highway revolts in some Western nations saw urban activists opposing government plans to demolish buildings for freeway route construction, on the basis that such demolitions would unfairly disadvantage the urban working class and benefit commuters. Anti-nuclear protests against proposed nuclear power plants in

2714-629: 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 miles) two-deck road tunnel with two lanes on each deck. Additionally, in 2015 the Turkish government announced that it will build three -level tunnel, also under the Bosporus. The tunnel

2773-428: The most common megaprojects are in the categories of hydroelectric facilities, nuclear power plants, and large public transportation projects. Megaprojects can also include large-scale high-cost initiatives in scientific research and infrastructure, such as the sequencing of the human genome , a significant global advance in genetics and biotechnology . The logic on which many of the typical megaprojects are built

2832-557: The motorway had been built as part of other motorways, before the official project began in 1994. Between 1997 and 2004, 393 km of motorway were built. The main part of the project was completed by 30 May 2009. A final bridge was opened on 10 May 2014 The exits of the completed sections of the A2 motorway: In 2020, EIB and Egnatia Odos are committed to fund treatment of 7000 high risk sites in Greece. Megaproject A megaproject

2891-594: The new ones also foreclose "upon a wide variety of social practices, reproducing rather than resolving urban inequality and disenfranchisement". Because of their plethora of land uses "these mega-projects inhibit the growth of oppositional and contestational practices". The collective benefits that are often the underlying logic of a mega-project, are here reduced to an individualized form of public benefit. Proponents of infrastructure-based development advocate for funding large-scale projects to create long-term economic benefits. Investing in megaprojects in order to stimulate

2950-483: 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

3009-540: 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 ". The vehicles or traffic using a tunnel can outgrow it, requiring replacement or enlargement: 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

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3068-522: 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. Once construction is complete, construction access shafts are often used as ventilation shafts , and may also be used as emergency exits. The New Austrian Tunnelling method (NATM)—also referred to as the Sequential Excavation Method (SEM) —was developed in

3127-490: 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,

3186-482: 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

3245-542: 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

3304-400: 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,

3363-428: 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. 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

3422-575: 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

3481-732: 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 , the world's largest TBM was " Big Bertha ", a 17.5-metre (57.5 ft) diameter machine built by Hitachi Zosen Corporation , which dug the Alaskan Way Viaduct replacement tunnel in Seattle, Washington (US). A temporary access shaft

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