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65-585: The Flat Rock Tunnel is an active railroad tunnel located on Norfolk Southern 's Harrisburg Line near Manayunk , Pennsylvania , United States. The tunnel was built by the Reading Railroad for its line along the Schuylkill River . Construction of the tunnel started in 1836 and it opened in 1840. In 1858-9 the Flat Rock and Black Rock Tunnels were widened to accommodate the wider rolling stock from

130-660: 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

195-536: A 20 feet deep ditch in the ground, covered over by large rock slabs, which were then hidden in the foliage. It is narrower than the tunnel, but can still be walked by a human for most of its length. In addition to the (3 ft high) exit near the Siloam pool, the channel has several small outlets that watered the gardens facing the Kidron Valley. Similar to the qanats of ancient Persia, the canal or culvert, carved into

260-449: 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

325-461: 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,

390-421: 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

455-626: A time when Jerusalem was preparing for an impending siege by the Assyrians, led by Sennacherib . Since the Gihon Spring was already protected by a massive tower and was included in the city's defensive wall system, Jerusalem seems to have been supplied with enough water in case of siege even without this tunnel. According to Aharon Horovitz, director of the Megalim Institute, the tunnel can be interpreted as an additional aqueduct designed for keeping

520-434: 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

585-710: 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,

650-432: 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

715-563: A water tunnel in his time. Scientific support for this, however, came from radiocarbon dates of organic matter contained in the original plastering as well as radiometry ( uranium-thorium dating of speleothems ). The dates were challenged in 2011 by new excavations that suggested an earlier origin in the late 9th or early 8th century BC. The tunnel leads from the Gihon Spring to the Pool of Siloam . If indeed built under Hezekiah, it dates to

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780-472: 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. Siloam tunnel The idea of dating the tunnel to Hezekiah's period was derived from the Biblical text that describes construction of

845-470: Is clear from the tunnel itself that several directional errors were made during its construction. Recent scholarship has discredited the idea that the tunnel may have been formed by substantially widening a pre-existing natural karst . How the Israelite engineers dealt with the difficult feat of making two teams digging from opposite ends meet far underground is still not fully understood, but some suggest that

910-500: 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

975-487: 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

1040-401: 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

1105-515: 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

1170-673: 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

1235-560: Is used to distribute the water. The Bible verses relating to a tunnel in Hezekiah's time are these: "As for the other events of Hezekiah’s reign, all his achievements and how he made the pool and the tunnel by which he brought water into the city, are they not written in the book of the annals of the kings of Judah?" ( 2 Kings 20:20 ) "When Hezekiah saw that Sennacherib had come and that he intended to wage war against Jerusalem, he consulted with his officials and military staff about blocking off

1300-556: 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

1365-495: The Lebanon Valley Branch . The spacing between the tracks was increased from 4 feet (1.2 m) to 6 feet (1.8 m). The widening of the tunnel was the first project to employ electric detonation of multiple explosive charges. Railroad 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

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1430-556: The Pool of Siloam may have been "dug by King Hezekiah" and in 1884 following the discovery of the Siloam inscription wrote that: "The inscription thus appears to belong to the later period of the Hebrew monarchy, and may very well be considered to agree with the Biblical account of Hezekiah's preparations for Sennacherib's siege." The ancient city of Jerusalem , being on a mountain, is naturally defensible from almost all sides, but suffers from

1495-464: 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

1560-797: 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

1625-466: 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

1690-665: 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

1755-591: 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

1820-486: 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

1885-474: The 12 inch (30 cm) altitude difference between its two ends, which corresponds to a 0.06 percent gradient, the engineers managed to convey the water from the spring to the pool. According to the Siloam inscription , the tunnel was carved out of the living rock by two teams, one starting at each end of the tunnel and then meeting in the middle. The inscription is partly unreadable at present, and may originally have conveyed more information than this. It

1950-689: 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

2015-638: 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

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2080-687: 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 ;

2145-601: The City of David, that it was great; And you gathered together the waters of the lower pool. You also made a reservoir between the two walls for the water of the old pool. But you did not look to its Maker, Nor did you have respect for him who fashioned it long ago." ( Isaiah 22:11 ) Excavation work in the tunnel by Ronny Reich of the University of Haifa and Eli Shukron of the Israel Antiquities Authority has cast doubt over

2210-527: The Gihon Spring halfway to the Siloam Pool area, but by a more direct route, was found. This channel is now known as the Middle Bronze Age channel , on account of its estimated age. Ronny Reich determined that it was constructed around 1800 BC, in the Middle Bronze Age , and thus that the spring's water had already been diverted many centuries before Hezekiah. As originally constructed, it is understood as

2275-691: 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

2340-462: The Pool of Siloam would have fully disappeared into a karstic system located right outside the southern tip of the city walls. In contrast to that, the previous water system did release all the water not used by the city population into the Kidron Valley to the east, where besieging troops could have taken advantage of it. The curving tunnel is 583 yards (533 m; about 1 ⁄ 3 mile) long and by using

2405-581: 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

2470-459: The attribution of the tunnel to the reign of Hezekiah. They believe the evidence points to a date several decades earlier, in the last part of the 9th century or early part of the 8th century BC. They note that the biblical passage connecting Hezekiah to the construction of waterworks doesn't specify a place in the city, and suggest it might refer to waterworks in the Mamilla area. The revised dating

2535-400: 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

2600-583: The city walls. The Bible says that King Hezekiah (c. 8th century BC), fearful that the Assyrians would lay siege to the city, blocked the spring's water outside the city and diverted it through a channel into the then Pool of Siloam. Since 1997, it is now known that the earlier Warren's shaft system had already heavily fortified the Gihon Spring. Warren's shaft is not an aqueduct, and requires those desiring water to travel up and down it themselves—an arrangement that Hezekiah seemingly must have considered inadequate. In 1899, an ancient channel, also leading from

2665-498: 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

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2730-591: The drawback that its major source of fresh water, the Gihon Spring , is on the side of the cliff overlooking the Kidron Valley . This presented a major military weakness, as the city walls, if high enough to be defensible, must necessarily leave the Gihon spring outside, leaving the city without a fresh water supply in case of siege. This weakness was removed by the Canaanites, who built a very strongly fortified tower around

2795-412: The entire outflow of the spring inside the walled area, which included the downstream Pool of Siloam, with the specific purpose of withholding water from any besieging forces. Both the spring itself, and the pool at the end of the tunnel, would have been used by the inhabitants as water sources. Troops positioned outside the walls wouldn't have reached any of it, because even the overflow water released from

2860-409: 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

2925-441: 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

2990-405: 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

3055-636: 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

3120-435: 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

3185-468: 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

3250-607: 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

3315-483: 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

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3380-540: 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

3445-510: 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

3510-485: 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,

3575-482: 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

3640-409: The rock, led from a main water source, and was meant to channel the current to a lower place where water was needed for agricultural purposes. The well-like vertical shaft ( Warren's Shaft ), connected by a gently sloping tunnel, is thought to have provided ventilation, light and access to the underground water channel for construction and maintenance. At its outlet, a network of dams, gates and channels

3705-528: 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

3770-463: The spring and connected it to the city walls on the slope by an additional wall, which carried a well-protected corridor. A Canaanite tunnel already collected the spring water since ca. 1800 BC and led it southwards through the bedrock. It released the water onto the fields in the Kidron Valley through several openings, and ended in an open reservoir. While allowing for important farming, this arrangement also made water available to besieging troops outside

3835-400: 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,

3900-422: 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 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

3965-428: 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

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4030-499: The two teams were directed from above by sound signals generated by hammering on the solid rock through which the tunnelers were digging. The tunnel was first described in modern times by Franciscus Quaresmius in 1625. It was later explored in 1838 by the American biblical scholar Edward Robinson , and in 1865 by Charles Warren . Neither Quaresmius nor Robinson identified the tunnel with Hezekiah, but in 1871 Warren suggested that

4095-492: The water from the springs outside the city, and they helped him. They gathered a large group of people who blocked all the springs and the stream that flowed through the land. 'Why should the kings of Assyria come and find plenty of water?' they said." ( 2 Chronicles 32:2–4 ) "It was Hezekiah who blocked the upper outlet of the Gihon spring and channeled the water down to the west side of the City of David. He succeeded in everything he undertook." ( 2 Chronicles 32:30 ) "You also saw

4160-566: 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

4225-701: 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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