Mayor Michael Bloomberg, Deputy Mayor for Economic Development Robert C. Lieber and Metropolitan Transportation Authority Chairman and CEO Jay H. Walder recently announced the completion of the first phase of the Number 7 subway extension at the Hudson Yards in Manhattan which includes the second of two tunnel boring machines having reached the southern wall of the 34th Street Station cavern after mining a combined 2,900 ft from its starting point at 26th Street under 11th Avenue.

The 7 Line extension project which is being managed by the MTA, will help transform the Hudson Yards into a 24-hour, mixed-use community containing commercial, residential, retail, open space and recreational uses and will introduce subway service to this Midtown West neighborhood, fostering transit oriented development in one of Manhattan’s most underserved and underdeveloped areas.

Funding for the project is being provided by the city after the creation of two local development corporations; the Hudson Yards Infrastructure Corporation which is contributing $2.1 billion to the project and the Hudson Yards Development Corporation which is overseeing planning and development in the Hudson Yards.

The city council approved the Bloomberg Administration’s plan for re-zoning the Hudson Yards including the Eastern Rail Yards in January 2005 and now the city council will vote on the plan for the Western Rail Yards, which would complete the public approvals process for the development of the area.

“It’s been a half century since the city government expanded its subway system, but that drought will soon be at an end,” said Mayor Bloomberg in a statement. “Too often, government falls victim to the temptation to abandon long-term infrastructure projects amidst short-term downturns and that’s why big things never get done. The redevelopment of the Hudson Yards has been talked about for decades, but with the expansion of the number 7 Line, its potential will finally be realized,” added Bloomberg.

Last summer, the tunnel boring machines were launched from the underground assembly chamber located at 26th Street but the first 300 ft of tunneling had its complications- a section of soft ground between 27th and 28th Streets required a technique called “ground freeze” to reinforce the ground, allowing the machines to pass through as if it were solid rock. As the tunnel boring machines mine, they place pre-cast concrete lining rings along the excavated tunnel, making up the permanent linear of the finished tunnel. The new service will terminate at the new 34th Street station but the tunnels will continue to 25th Street allowing for the storage of trains.

One tunnel boring machine has already started mining north of the station cavern toward 42nd Street while the other is being pulled through the cavern and will begin mining in a few weeks. Tunneling north from 34th Street also presents unique challenges because the tracks will run under the 8th Avenue Subway, Amtrak/NJ TRANSIT tunnels,  the former New York Central Line tunnels, the Lincoln Tunnel and the Port Authority Bus Terminal and ramps. Excavation and underpinning of the 8th Avenue Subway Line is underway to allow the new tunnels to tie into the existing 7 Line tracks at Times Square.

Construction of the tunnels and the 34th Street Station cavern is being done by S3II Tunnel Constructors, a joint venture of J.F. Shea Construction, Inc., SKANSKA USA Civil Northeast, Inc., and Schiavone Construction Co., Inc. who was awarded a $1.14 billion contract for the work in December 2007.

“Committing to the expansion of our mass transportation system is only more important to the success of our city in these tough economic times,” said Manhattan Borough President Scott M. Stringer.

Tunneling will be completed in the spring of 2010, when work will commence on station entrances and finishes, as well as support facilities such as ventilation and traction power substations. The new service is scheduled to open in December 2013.