Infrastructure Projects - Construction Technology
A Practical Guide to Construction Techniques and Practice
Welcome to class 5 on cut and cover tunnels. This is a very popular method used in downtown areas, but it's hardly new. It's been used for over 100 years. This photo is about 100 years old or more. It's a photo of the first subway contract to be let in New York City.
The cut and cover technique is very straightforward. You excavate 1/2 of the street. You cover over that excavation, and you can restore traffic over that half while you excavate the second half of the street. This is certainly a useful procedure in busy downtown areas.
This is a stiff leg derrick. It was certainly a helpful tool at the time, but don't think of this as a quaint, historic device. A stiff like derrick is still in use today. It's still a very valuable tool. Back in those days, I imagine it was a hand operated by a winch, but it certainly was good enough to erect the steel in the subway. Now, this is the boom. This three-legged arrangement is the stand.
In the background, there is this tower. I can only speculate that that is some kind of material hoist and I can picture it being used to lift out the excavated material. There is something very captivating about this photo. I would like to acknowledge that it came from the New York Transit Museum, and it is dated 1902. It's remarkable in every aspect.
To begin with, look at the horse-drawn carriage and let that settle in a little bit, because that marks the era. Any mechanical device would have one horsepower. Nevertheless, in 1900, they began construction of 21 miles of subway system. This included 48 stations and two tunnels. They needed to construct tunnels under the East River and the Harlem River. The system ran the full length of Manhattan and had branches into the Bronx and Brooklyn.
Now, as staggering as all that seems, it was accomplished in four and a half years. I find it hard to even say those words, because it just seems unrealistic and way out of my realm of experience. The Big Dig, which is the only mega-project that perhaps had a similar scope, took 13 years. That was built just a few years ago. The original subway system was built, more or less, by hand, They tunneled under two rivers and completed 48 stations. The whole thing is just beyond belief and did it in four and a half years. Now, I've pegged the cost here at 12 plus, or minus billion dollars in today's dollars, but I'm not sure that I have my calculations, right. The project cost 35 million in 1900 and I projected that forward at 6% and got 12 billion.
We will fast forward now into the 21st century. This is a cut-and-cover project being built in lower Manhattan. It's associated with the post 911 re-construction at the World Trade Center. The camera is facing west. And the big open space is the World Trade Center site. Some of the features you may have all read about, and know about is the Deutsche Bank, which was condemned after 9/11 because of extensive damage, but the building is still standing in this photo, which is probably seven years later.
The building is surrounded by controversy and tragedy. These buildings in the background are the world financial center in Battery Park City. This structure is a kind of a shed roof over a temporary entrance to the PATH system. What's being constructed here is a passageway, which will link the existing transit system with the future PATH terminal.
For orientation, this is Church Street, which is running from left to right and the intersecting street here is Day Street. Church Street and Day Street have been completely decked over. You can make out some of the deck panels here in this photo. It's decked over to allow traffic to move back and forth through this very busy site. I waited for the traffic to pass by in order to take a picture which was unobstructed. This is a very busy area and decking over the excavation is certainly the appropriate approach.
I'm standing below the decking, facing west -the same orientation as I had up in the street. I'll just point out some of the features here. All of the utilities have been hung from the decking. The decking not only serves to continuously carry the traffic over the construction, but it's also the support for the utilities.