Pittsburgh-based Trumbull Corp. is working in joint venture with Japanese construction leader Obayahi's east coast U.S. division to construct twin 1.2-mile tunnels under the Allegheny River in Pittsburgh. The companies are serving as general contractors on the North Shore Connector project. Work includes launch and receiving pits for tunnel boring machines, utility removal, relocation and replacement, and underpinning highway SR 65 pier bents.
The construction of the twin tunnel project is to extend the Allegheny County Port Authority's light rail transit system 1.2 miles from the Gateway Subway Station underneath Stanwix Street and the Allegheny River to the river's north shore.
To construct the tunnel, Trumbull will cut and cover the tunnel, including the station shell, while it creates the launch and receiving pits for the tunnel-boring machine. In addition, extensive excavation, shoring of the excavated tunneling pits, soil stabilization, monitoring of buildings adjacent to the alignment, tunneling using the tunnel boring machine, placement of the precast tunnel lining, placement of a cast-in-place secondary liner, controlled fill and replacement of sidewalks and streets will be performed.
The removal and replacement of existing retaining walls and foundation elements on the south shore of the Allegheny River also must be done.
"The North Shore Connector is a significant regional investment that will support the revitalized downtown Pittsburgh and north shore venues in addition to enhancing development opportunities," Trumbull says. "It will also enable the [Port] Authority to construct future extensions of the [light rail] to other destinations within Allegheny County, thus making it a catalyst for future development opportunities throughout the region."
The North Shore Connector
The cost for the project is $ 156 million and scheduled to be completed in 2011. The project will extend the Pittsburgh trolley line tothe Pirates' PNC Park and the Steelers' Heinz Field, both located in the north shore area.
With the digging of the tunnel complete, parts of the 500-tunnel boring machine will be scrapped, while other components are shipped back to Herrenknecht AG of Germany, which produced the machine. Concrete has been poured to flatten the tunnel floor and prepare the tubes necessary for light rail tracks. Pipelines that moved air, water and debris to and from the digging machine also will be removed upon completion.
A total of 110,000 square feet of cutter soil mixed (CSM) walls were constructed during excavation for the pits of the tunnel-boring machine. According to Nicholson Construction, which performed excavation support on the project, the CSM technique mixes in-situ soils with grout to make a soil mix wall and is reinforced with soldier beams. The wall was 60 feet deep and extended 3 feet into the bedrock.
A Wealth of Services
Formed in 1955, Trumbull has been a contributor to both the local Pittsburgh and regional construction market. It offers services in general contracting and construction management, and says it has managed more than $2 billion of quality services to both government and private clients. Headquartered in Pittsburgh, the company operates a regional office in St. Albans, W.Va., and establishes project control centers wherever it performs large construction projects.
"By completing some of the most challenging projects in our region, on time and with a constant focus on owner cooperation and partnering, Trumbull has earned its unequaled reputation in the heavy highway construction industry," it says. "Trumbull Corp. offers our clients a wealth of services, and our professionals work with you to determine what type of services will best meet your needs."