Piggyback Tunnels

by John S. Anderson, Project Manager; Frederic R. Harris, Boston,


Serial Information: Civil Engineering—ASCE, 1995, Vol. 65, Issue 6, Pg. 49-51


Document Type: Feature article

Abstract:

Coincidental alignments of the Central Artery Tunnel and the Transitway subway line under the streets of Dewey Square in Boston presented the sponsoring agencies with a rare opportunity for joint construction. The result is an excavation, which will be used to create two transportation tunnels: one carrying automobiles, the other carrying electrically powered subway trains. This spring, a construction joint venture will begin work on cut-and-cover excavations extending approximately 100 ft below grade. On the flow of the excavations, massive concrete sections will be built for an eitht-lane northbound portion of the CA/T. After backfilling the excavation to about 25 ft below grade, the contractor will then cast smaller concrete sections for a second tunnel--the South Boston Piers/Fort Point Channel Transit Project (Transitway). Merging construction of the two projects resulted from negotiations between the Massachusetts Highway Department and the Massachusetts Bay Transportation Authority. The feasibility of joint construction was demonstrated by the advanced design and visualization software programs. Linking construction of the two tunnels also promises significant cost savings (estimated between $20 million and $25 million), since the slurry wall/cut-and-cover excavation will only need to be performed once.

Subject Headings: Tunnels | Excavation | Construction management | Subways | Project management | Joints | Infrastructure construction

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