Utility tunnel

A utility tunnel, utility corridor, or utilidor is a passage built underground or above ground to carry utility lines such as electricity, steam, water supply pipes, and sewer pipes. Communications utilities like fiber optics, cable television, and telephone cables are also sometimes carried. One may also be referred to as a services tunnel, services trench, services vault, or cable vault. Smaller cable containment is often referred to as a cable duct or underground conduit. Direct-buried cable is a major alternative to ducts or tunnels.

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 18 ft (5.5 m) 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.

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.

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.

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