Skanska managed three contracts – totaling nearly $1 billion – as part of a joint venture to improve central artery traffic in Boston with the renowned project commonly called “The Big Dig.” The Massachusetts Highway Department conceived the project to reroute Interstate 93, the principal controlled-access highway through the heart of Boston, into a 3.5 mile tunnel under the city.
The scope of the first contract included:
· demolition and removal of existing roadway viaducts
· construction of approximately six miles of temporary and permanent roadways, six viaducts and twelve bridges
· excavation and excavation support
· construction of grade slabs on piles, traffic control systems, storm drainage, two stormwater pump stations, utility relocation and landscaping
The second contract included the construction of thousands of feet of cut-and-cover tunnels; boat sections; viaducts; and jacked tunnels underneath active railroad tracks and roadway lanes.
Skanska used several methods to complete the work, including decking systems, temporary bridges and underpinning of the elevated Central Artery viaduct. The Skanska team chose segmental precast concrete as the method of construction for the viaducts.
The construction of the tunnel and boat sections required a combination of slurry walls, sheet piling and soil stabilization using a freezing technique. Excavation depths for utilities ranged up to 25 feet and extended through fill silts, sands and various clays and soils.
