Mt. Lebanon Tunnel

The Mt. Lebanon Tunnel is a light rail tunnel in Allegheny County, Pennsylvania, also known as the Dormont/Mt. Lebanon Transit Tunnel, part of the Pittsburgh Light Rail system.

Not to be confused with Mt. Washington Transit Tunnel, another tunnel of the Pittsburgh Light Rail system.
Mt. Lebanon Tunnel
South end
Overview
Line
  Red Line – Castle Shannon
  Red Line – South Hills Village
LocationAllegheny County, Pennsylvania
Statusoperational
SystemPittsburgh Light Rail
StartDormont Junction
EndMt. Lebanon
No. of stations0
Operation
ConstructedNew Austrian Tunnelling method
OwnerPort Authority of Allegheny County
OperatorPort Authority of Allegheny County
Technical
Length3,000 feet (910 m)
No. of tracks2
Track gauge5 ft 2+1⁄2 in (1,588 mm)
Electrifiedoverhead catenary

The 3,000-foot (910 m) long tunnel connects the Dormont Junction and Mt. Lebanon stations beneath Washington Road & West Liberty Ave. from Shady Drive East to McFarland Road at a maximum depth of 100 feet (30 m), and runs beneath a cemetery.

The pre-tunnel trolley street line, which ended in 1984, ran from the long-removed Clearview Loop stop on Alfred St. (Mt. Lebanon) to the intersection of McFarland Rd. and Raleigh Ave. (Dormont).

The tunnel was constructed by a technique called the New Austrian Tunnelling method, a tunneling process developed in the early 1960s that has become the primary tunneling practice in Europe. This is the first time that this money-saving technique was used for transit construction in the United States.[1]

The difference with NATM lies in the means of support required to maintain the rock cavity and the configuration of the tunnel structure. With conventional tunneling, support of the rock cavity consists of a rib cage framework of steel beams and horizontal wooden planks. A reinforced steel concrete lining is added to create a perfectly shaped tunnel. With NATM, the rock surrounding the hole becomes the support system. This is done by lining the tunnel cavity with several thin layers of shotcrete, concrete that is blown on under air pressure.[2]

The tunnel has continuous television surveillance.[3]

References
  1. Ozdemir, Levent (17–22 April 2004). North American tunneling: proceedings of the North American Conference Tunneling Conference 2004. CRC Press. p. 473. ISBN 9789058096692.
  2. "Mt. Lebanon Tunnel: What Went Wrong". Tunnels & Tunnelling. 21 (4): 61–62. April 1989.
  3. Joe Grata (10 July 2005). "Getting Around: In Pittsburgh's mini-subway, eyes are always watching". Pittsburgh Post Gazette. Retrieved 1 March 2009.


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