A Frontier-Kemper-Tutor Perini joint venture (JV) has been awarded the design-build contract for the $1.18 billion Manhattan Tunnel (MT), a critical 700-foot leg of the $16 billion, 3.86-kilometre Hudson Tunnel Project (HTP) to improve rail infrastructure between New York and New Jersey.
Set to begin this spring and be completed in 2029, construction on the MT, which runs under the west side of Manhattan, faces a host of challenges, including navigating around major utility lines that connect to the city above it.
“It’s a relatively short section of the Hudson Tunnel Project but an incredibly complicated, complex job, particularly given the unknowns and the knowns underneath the ground,” says Stephen
Sigmund, chief of public outreach with Gateway Development Commission (GDC), the public authority overseeing the two-tunnel HTP and associated work.
Sigmund says extensive geotechnical borings, sonar surveys and map assessments have been crucial to chart locations of the maze of sewer, water and electrical utilities that run beneath the area.
An excavation accident that cuts an electrical line could shut power off to 60,000 residents. Heavy equipment damaging the 19th century bulkhead could be even worse, he says.
“If portions of the bulkhead collapsed, it would allow the river to flood the west side of Manhattan.”
The soil conditions consist largely of landfill from the 19th century and while the team does not anticipate discovering significant historical artifacts that could delay the project for an archeological assessment, “you don’t know everything until you are down there.”
Mini tunnel boring machines with drill heads and excavation shovels will remove material over the 700-foot length of the MT before lightweight concrete is placed for reinforcement to accommodate the “gigantic” tunnel boring machines that will be employed to excavate under the Hudson River.
The access shaft to the Manhattan Tunnel — a 30-foot-wide-by-98-foot-deep hole — will be dug largely with conventional excavation equipment. Once the entire project is completed in 2035, the shaft will serve as ventilation port for the tunnels crossing the river.
The project involves a cut and cover tunnelling section that connects to Penn Station. To minimize city disruptions, much of the work was completed by 2018, prior to the development of Hudson Yards East, says Sigmund.
Overall the construction program from New Jersey in the west to New York in the east includes about three kilometres above ground connecting under one of the busiest roadways in New Jersey. It drops 80 to 250 feet deep under the Palisades.
Sigmund says under the Hudson River portion of the big excavation the ground will be stabilized with a lightweight concrete box partly because as the tunnel runs up near the riverbed along the shoreline the soil “has a consistency of chocolate pudding.”
He says Gateway calls the HTP “the most urgent infrastructure project in the country because it is a critical fracture point of the entire northeast corridor for a section of the nation that produces 20 per cent of its GDP.
“It is an enormous challenge. I joke at public affairs that I have an honorary degree in engineering after six years of doing this.”
The HTP will replace the existing 115-year-old tunnel, which faces frequent delays for repairs, often disrupting schedules for many of its 200,000 daily passengers.
“If even one of the existing two tubes was taken out for rehabilitation before the new tunnels were built the cost to the national economy would be $16 billion…and it would release two million tons of CO2 into the atmosphere,” Sigmund says.
The Manhattan Tunnel is expected to create roughly 15,000 jobs. Overall the HTP will create almost 100,000 jobs through the course of the next decade.
Funding consists of about 70 per cent federal grants and 30 per cent low-interest Railroad Rehabilitation and Improvement Financing loans that are repaid by the state of New Jersey and New York and the Port Authority of New York City and New Jersey.
The Gateway Development Commission was created through the enactment of parallel legislation by the States of New York and New Jersey in July 2019.
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