The “Big Dig,” Boston’s Central Artery/Tunnel (CA/T) project, the nation’s largest, most complex, and technically challenging highway project, has opened for traffic and most of the final phases of facility construction are now underway. Over the years, EarthWorks has featured many CA/T projects and this wrap-up helps to bring into perspective the magnitude of the effort. As a team member on many CA/T contracts, Haley & Aldrich helped develop engineering technologies and solutions that met project needs, and will be applied to other projects for years to come. Key project roles included area geotechnical consultant for the airport and Ted Williams Tunnel; and section design consultant for many of the mainline tunnel sections. For a separate testing section contract, Haley & Aldrich completed projects covering caisson load testing, tension element testing, soil stabilization, and field sampling and testing; the results of which were used throughout the program.

Haley & Aldrich was a team member on the following CA/T contracts:

• 1A: I-90 South Boston Interchange: 1,600-ft cut-and-cover highway tunnel and 9,700-ft surface roadway.
• 4A & 24A: BMIP Tunnel and Central Maintenance Facility: I-90 vent building and cut-and-cover tunnel connection to the Third Harbor Tunnel, and vehicle storage and repair facility.
• 5A: I-90 Immersed Tube Tunnel: Twin-barrel, 3,848-ft immersed tube tunnel under Boston Harbor required underwater rock cut and deep retained excavation for adjacent tunnels.
• 7A: I-90 Bird Island Flats Tunnel and Vent Building: 2,800-ft cut-and-cover tunnel; 600-ft, four-lane depressed highway; tunnel approaches; ventilation building; and East Boston electrical substation.
• 7B: Porter Street Outfall: Relocation of combined sewer outfall and part of a storm drain.
• 7C: I-90 East Boston Toll Plaza and Facilities: Toll plaza complex, support buildings, and administration offices; involved interface of the buildings with adjacent tunnels.
• 7D: I-90 Logan Airport Interchange: Interchange roadway and 8-span viaduct structure including traffic signals, lighting, utility installations, elevated ramp, and retained fill structures.
• 9A: I-93/I-90 Interchange, I-93 Northbound: The largest deep soil mixing project ever undertaken in the U.S. This project required 60 to 70-ft-deep excavations in soft clay, and tunnel jacking to construct four multi-lane tunnels beneath very active railroad tracks.
• 11A: I-93 Northbound Tunnel, Atlantic Avenue Section: 2,000-ft cut-and-cover highway tunnel; creative methods used to construct 200-ft section mined in soil and bedrock under active subway tunnel.
• 12A: I-93/Massachusetts Avenue Interchange: Piles were driven in highly variable soil conditions for foundations to support mainline viaducts, two bridges, and elevated frontage roads.
• 14B: Utility Relocations: Analysis, design, and installation of systems to support utilities during mainline tunnel construction.
• 15A1,2: I-93 Central Artery, North to Causeway: 2,900-ft mainline tunnel with excavation up to 120 ft deep and 270 ft wide.
• 15A3, 16A: Haymarket Parking Garage: Parking garage built over a subway station involving drilling foundations through the active platform and track areas.
• 17B: Aquarium Station: A complex design of two intersecting tunnels: the MBTA Blue Line tunnel and station, and the underground CA/T tunnel.
• 18A: I-93 Kneeland Street to Congress Street, Southbound: Refurbishing air intake structures, new Dewey Square Tunnel Intake Structure, 400-ft tunnel extension, and utility relocations.
• 19D: Charles River Bridges: Leonard P. Zakim Bridge, a 10-lane-wide, cable-stayed mainline bridge; and the Storrow Drive Connector Bridge, a four-lane, single deck bridge. Designed to control effects of construction and lateral loading on a subway tunnel directly under the bridge’s north tower.
• 19E: Leverett Circle/Storrow Drive Connectors: Two highway interchange tunnels under commuter rail station, tunnel under a rapid transit station, cut-and-cover tunnel and viaducts, a temporary bridge, and an underground ventilation building.
• 21H: Water Transportation Docking Facilities: Water transportation docking facilities were built at the Charles River Dam.