utility tunnel

Utility tunnels are common in very cold climates where direct burial below the frost line is not feasible (such as in Alaska, where the frost line is often more than {{convert|18|ft|m|abbr=on}} below the surface, which is frozen year round). They are also built in places where the water table is too high to bury water and sewer mains, and where utility poles would be too unsightly or pose a danger (like in earthquake prone Tokyo). Tunnels are also built to avoid the disruption caused by recurring construction, repair and upgrading of cables and pipes in direct burial trenches.{{cite web |url=http://www.londonpowertunnels.co.uk/why-a-tunnel.asp |title=National Grid - Overview - Why a tunnel? |publisher=National Grid plc |access-date=2013-03-30}}

Utility tunnels are also often common on large industrial, institutional, or commercial sites, where multiple large-scale services infrastructure (gas, water, power, heat, steam, compressed air, telecommunications cable, etc.) are distributed around the site to multiple buildings, without impeding vehicular or pedestrian traffic above ground. Due to the nature of these services, they may require regular inspection, repair, maintenance, or replacement, and therefore accessible utility tunnels are preferred instead of direct burying of the services in the ground.

Utility tunnels range in size from just large enough to accommodate the utility being carried, to very large tunnels that can also accommodate human and even vehicular traffic.

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Utility tunnels are often installed in large industrial plants, as well as large institutions, such as universities, hospitals, research labs, and other facilities managed in common. Shared facilities, such as district heating, use superheated steam pipes routed through utility tunnels. On some university campuses, such as the Massachusetts Institute of Technology, many of the buildings are connected via large underground passages to allow easy movement of people and equipment.

Some municipalities, such as Prague in the Czech Republic, have installed extensive underground utility tunnels, to allow installation and maintenance of utility lines and equipment without disrupting the historic streets above.

Utility tunnels may attract urban explorers, who enjoy investigating hidden complex networks of spaces.

{{Main|Disney utilidor system}}

Some of the largest and most famous utility tunnels are at Disney theme parks. They were first built for Walt Disney World's Magic Kingdom in Florida. Smaller utilidor systems are built under the central section of Epcot's Future World, primarily beneath Spaceship Earth and Innoventions, and formerly at Pleasure Island. Disneyland also has a small utilidor through Tomorrowland. The utilidors are a part of Disney's "backstage" (behind-the-scenes) area. They allow Disney employees ("cast members") to perform park support operations, such as trash removal, out of the sight of guests.

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File:FlinFlon Stack.jpg (in Manitoba, Canada) is built on rock, making excavation costly. The utilidor in the foreground carries municipal sewer and water services and protects piping from freezing in the winter.]]

Utilidors are above-ground enclosed utility conduits that are used in larger communities in the northern polar region where permafrost does not allow the normal practice of burying water and sewer pipes underground. They can in particular be found in Inuvik, Northwest Territories{{cite journal |title=Utilidors in the Canadian North |author=D. J. Gamble, P. Lukomskyj |journal=Canadian Journal of Civil Engineering |volume=2 |issue=2 |date=June 1975 |publisher=Canadian Science Publishing|doi=10.1139/l75-016 |url=https://cdnsciencepub.com/doi/10.1139/l75-016}} and Iqaluit, Nunavut.{{cite journal |title=Nunavut Urban Futures: Vernaculars, Informality and Tactics (Research Note) |author=Lola Sheppard |journal=Études Inuit Studies |volume=44 |issue=1-2 |date=2020 |publisher=Centre interuniversitaire d’études et de recherches autochtones (CIÉRA) |url=https://id.erudit.org/iderudit/1081808ar |doi=10.7202/1081808ar |issn=0701-1008|doi-access=free }} Not all older homes are connected, and these must rely on trucks to deliver water and remove sewage. Most homes in rural Alaska (off the road system) are not equipped with plumbing and require fresh water and waste to be transported by personal vehicle such as snowmobile or four-wheeler ATV. Villages with utilidors are considered more advanced.

Utilidors may also be used to carry fuel lines, such as natural gas. They are not normally used to carry wiring for electric, telephone, and television service, which are usually suspended from poles.

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The advantages of utility tunnels are the reduction of maintenance manholes, one-time relocation, and less excavation and repair, compared to separate cable ducts for each service. When they are well mapped, they also allow rapid access to all utilities without having to dig access trenches or resort to confused and often inaccurate utility maps.

One of the greatest advantages is public safety. Underground power lines, whether in common or separate channels, prevent downed utility cables from blocking roads, thus speeding emergency access after natural disasters such as earthquakes, hurricanes, and tsunamis.

The following table compares the features of utility networks in single purpose buried trenches vs. the features of common ducts or tunnels:

class="wikitable" ! Utility tunnels ! Direct burial

Higher initial capital cost for construction of tunnels |Cheaper initial capital cost of burying individual infrastructure

Easy location of infrastructure |Difficult location of infrastructure

Fast maintenance and replacement |Slow maintenance and replacement

Less roadworks and traffic as maintenance can be done without disruption of traffic |Increased roadworks and traffic

Reduced manholes on roads. Single manhole for all infrastructure |Large numbers of manholes for various infrastructure types

Easy to coordinate between different infrastructure |Hard to coordinate projects between infrastructure providers

Easy access for maintenance, upgrades and expansion of infrastructure |Huge labour costs for regular re-burial

Easy access for maintenance |Roads constantly need to be excavated for repair of various utilities.

Reduced future maintenance costs |Increased risk of disruption

Shared initial capital costs between infrastructure providers (ie, water, gas, electric) |Risk of damage to co-located infrastructure (eg: pipes, wiring & cables)

Reduced impact from outages due to increased maintenance speed |

The low thermal conductivity of air in tunnels allows heat transmission with less insulation and cheaper standoffs. |

Reduced excavation and labour costs |

Many examples of utility tunnels are found in Japan, where government officials have sought ways to reduce the catastrophic effects of earthquakes in their tectonically active country. Their use, however, is not limited to that country, and there are many examples of such utility tunnels. These include:

• Incorporated with Xinyi[http://www.maa.com.tw/en/markets/infra_cud.asp "Infrastructures: Common Utility Duct"]. MMA Group. 2006. Retrieved November 30, 2014. and Sonshan MRT rapid transit lines in Taipei, Taiwan.{{citation needed|date=November 2014}}
• Azabu-Hibiya Common Utility Duct in Tokyo, Japan[http://www.bigempire.com/sake/underground_tokyo.html "Tokyo Underground"]. Big Empire. Retrieved November 30, 2014.
• Minatomirai District lines in Yokohama, Japan[http://www.yokohama-landmark.jp/office/english/p08.html]. The Landmark Tower. {{webarchive|url=https://web.archive.org/web/20090704042636/http://www.yokohama-landmark.jp/office/english/p08.html|date=July 4, 2009}}
• Portions of the Chicago Tunnel Company's abandoned network of tunnels are leased to utility companies for use as common utility ducts for electrical, communication and HVAC lines. The tunnels lie approximately forty feet below the street surface and run under all streets in the central business district, except where they were displaced by rapid transit tunnels.{{citation needed|date=November 2014}}
• Poundbury in Dorset, England, a planned community built on land belonging to King Charles as Duke of Cornwall, incorporates common utility ductsMitchell, Sandy (May 2006). [https://web.archive.org/web/20060421175900/http://www7.nationalgeographic.com/ngm/0605/feature3/index.html "Prince Charles–not your typical radical"]. National Geographic
• The Dartford Cable Tunnel allows high voltage electricity line to cross the River Thames.{{citation needed|date=November 2014}}
• The Utility Tunnels in Qatar built on the Lusail, 15 km north of Doha, is approximately 14–15 km in length.{{citation needed|date=November 2014}}
• The old Beacon Hill Tunnel in New Kowloon, Hong Kong, a disused railway tunnel which now carries a towngas pipeline
• Tunnels of Hongkong Electric{{cite web |url=http://www.hkelectric.com/NR/rdonlyres/2D3E993F-1BD1-4BA5-BDCD-CB1D504DA3DF/0/TunnelFactSheet24September2007.pdf |title=Archived copy |access-date=2013-10-17 |url-status=dead |archive-url=https://web.archive.org/web/20131017122249/http://www.hkelectric.com/NR/rdonlyres/2D3E993F-1BD1-4BA5-BDCD-CB1D504DA3DF/0/TunnelFactSheet24September2007.pdf |archive-date=2013-10-17 }}
• Utility Tunnel in GIFT City, Gandhinagar, India[http://www.financialexpress.com/article/economy/gujarat-international-finance-tec-city-a-smart-gift/53955/ "Gujarat International Finance Tec-city: A Smart GIFT"]

File:Schiffbau tunnel.jpg|Stark utility tunnel in Zurich, Switzerland

File:Fernwärmetunnel Köln (2).jpg|District heating tunnel beneath the Rhein River in Cologne, Germany

File:Heatpipe tunnel copenhagen 2009.jpg|District heating tunnel in Copenhagen, Denmark

File:Utility tunnel.jpg|Red arrow marks a prefabricated element of a utility tunnel already placed in the trench

File:Haifa Utility tunnel.JPG|A newly built utility tunnel in Haifa, Israel

File:Kolektory Praha, 48.jpg|Tunnel in Prague is shared by pipes and cables

File:Interior view of utilidor passageway link between building nos. 101 and 102 showing waveguides on left and cable tray system on right sides. Note fire suppression water supply piping HAER AK-30-A-102.tif|Utility passageway between two buildings of a Ballistic Missile Early Warning System site in Alaska.

File:Connecting-houses.jpg|Utilidors connecting houses in Inuvik, Northwest Territories, Canada

File:Utility Tunnel GIFT City.jpg|Utility Tunnel in GIFT City Gandhinagar, India

File:Barrow High School 2007-12-08.jpg|A utilidor system is used in Utqiaġvik, Alaska due to extensive permafrost underlying the city. At right foreground is a portion of the utilidor crossing Okpik Street overhead, adjacent to Barrow High School.

{{Commons category|Utility tunnels}}

• Dartford Cable Tunnel
• Tunnel
• Underground city
• Utility vault
• Wayfinding (urban or indoor)

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Category:Tunnels

Category:Subterranea (geography)