Boston’s “Big Dig” I-90 Fort Point Channel Crossing ($300 Million)

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LOCATION
Boston, Suffolk County, MA

CLIENT
Massachusetts Highway Department, MA

DESCRIPTION
ARRO was responsible for the specialist design of the concrete immersed tube tunnel (ITT) for the Fort Pierce Channel Crossing, including detailed design and design support services during constructions.

The Fort Point Channel Crossing was a vital link between the Massachusetts’ Turnpike (I-90) extension and Boston’s Logan Airport. ARRO was responsible for the specialist design of the concrete immersed tube tunnel (ITT) for the Fort Pierce Channel Crossing, including detailed design and design support services during constructions.

The immersed tube tunnels consisted of six units; the largest of which was 400 feet long by 160 feet wide and displaced 55,000 tons while floating.  Other features:

  • I-90 traffic was contained within separate parallel tubes, each consisting of three units
  • The two western units support a multi-story ventilation building and highway viaduct
  • The ventilation building and highway viaduct foundation were integral with the immersed tube tunnel and were floated into position with the two western units
  • The two center units were placed five feet above the MBTA Red Line tunnel.
    • To avoid additional load on the MBTA tunnel, the center sections were built on a system of caissons.
    • Due to the oblique angle of the MBTA tunnel, the center units will have unsupported lengths of 110 feet
  • The two eastern units support a new seawall and have 25 feet of earth fill-over in one-third of their length.
  • ARRO designed coffer dam, using multiple 65 foot diameter and 65 foot high circular cell walls to enclose the casting basin used to construct the ITTs.