New York is the centre of attention for the construction industry at present. But the post 11 September rebuild of lower Manhattan is not the only major project due over the next few years.
In mid-town Manhattan another giant scheme is underway, this time to restructure the vast Grand Central Terminal (GCT), New York's primary railway station. First preparation contract has been let and design work is getting to grips with the detail.
There are to be eight new platforms at GCT and an additional passenger concourse, new entrances and exits. New railway lines will run along the skyscraper lined Park Avenue - one of the world's most prestigious cityscapes. And a new twin track train will cross the East river.
But work will catch none of the public attention of the World Trade Center, despite a price tag of more than $4bn, because it will all be underground.
The East Side Access (ESA) project will run entirely in tunnel from the 63rd Street East river tunnel to just before Grand Central at around 50th Street, where the two lines will fan out into four tunnels. Each of the four tunnels will in turn split into upper and lower tunnels to terminate in two twin level station chambers to be excavated beneath the existing 20ha station complex.
On the far side of the river in Queens, the river tunnel tracks will fan up and out into five different lines running under the multiple tracks of the Harold Interlocking, one of the US's busiest train junctions. They will rise on the far side through cuttings to tie into existing lines.
These connections are with the Long Island Rail Road (LIRR) network which services the major residential zones of the island, which is also the location of John F Kennedy airport.
Every day around half a million people move between Manhattan and Long Island, with every form of transport at - or over - capacity. The area accounts for the majority of New York State's traffic jams, the subways are crowded and the 740 daily LIRR trains which travel the 180km length of the island are full.
Not only that, the existing LIRR route to Manhattan terminates at Penn station on the west side while the growing number of white collar office jobs are concentrated on the east side, adding 30 minutes to commuters' journeys as they retrace their steps by subway.
The ESA scheme should alleviate these problems, increasing LIRR capacity by around 45%. An additional 300 of the system's 1,800 passenger capacity trains will run into Grand Central.
Plans for expanded connections are not new. The first schemes were drawn up 30 years ago by the Metropolitan Transport Authority, owner and operator of the city's buses, subways and LIRR. The $600M 63rd Street tunnel, through which the trains will run, was completed in the 1970s, although funding troubles at the time meant no trains used it until 1989.
Today, the subway system runs through the tunnel, but the bottom cells of the 2.6km long double deck immersed tube are unused, says John Moss of consultant Hatch Mott McDonald.
The UK owned firm is working as specialist tunnel consultant to the ESA's main project manager Parsons Brinckerhoff.
'One of our tasks is to drain, repair and inspect the lower level, which was intended for the LIRR trains, ' he says. 'It was flooded for a long while and was leaking and without any maintenance.'
Both tunnel ends - currently sealed with bulkheads - will be connected to new tunnel as part of the access project.
On the GST side, this will be a twin bore through the famously hard schists of Manhattan Island. Each 6m internal diameter tunnel, driven by hard rock TBM, will curve round on to the line of Park Avenue and then run down to 50th Street before curving in under the station's tracks and platforms to about half way down its length.
The tunnels will be driven to the end point of the 400m long station caverns and the machines will then be brought back to form the Y junctions and the upwards running tunnels to give four train platforms in each cavern.
'Caverns will be excavated outwards from the tunnels, using them as pilot tunnels for a drill and blast operation, ' says Moss. 'It is much better to 'slash cut' from an existing excavation than to burn cut into virgin rock because the rock has somewhere to go during the blast.'
That means less noise and vibration. Both are significant issues, since the work aims to create caverns just 30m below GCT and that in turn means working just below some very significant skyscraper buildings.
'When GCT was built in the 19th century, it was open to the sky and so were the track approaches and platforms, ' says Moss. Some of the first air-rights buildings were built over the 10 block long station early in the century and it is now mainly under cover.
'We also have some pile foundations coming down to around 15m above us, ' he adds.
Excavation and tunnelling in the Manhattan schist should be relatively straightforward. But the material can have pockets of foliation and 'there have been some significant collapses', says Moss. 'You cannot find the weak areas by boreholes, but need exploratory drilling from the machine as you go.'
On the Queens side, the bedrock slopes away steeply with much softer alluvial deposits above and the tunnels will mainly be driven using EPB machines. But it does not slope fast enough and there will also be sections of mixed face with the lower part in hard rock and the top in water bearing sand and gravel.
'And the rock is actually better quality here than in Manhattan, ' adds Moss. 'It makes these tunnels quite complex.'
A 350m long 'trapezium' box will be built by cut and cover to bring the tracks out of the river tunnel and into six 600m long drives where the track connections fan out.
Each of these must pass under the continuously busy tracks of the Harold Interlocking junction and so they must be driven by machine, though a short end section of each will again use cut and cover methods where the tunnel emerges into a cutting.
'It is a very complex issue to organise this job so that the tunnels can pass under this very busy junction without disrupting the service, ' says Moss. Some of the tracks are used to carry trains into the adjacent Sunnyside rail yard for daytime storage. Here the tunnels will emerge with virtually zero cover close by operational rail tracks.
However, the huge railroad facility does have one big advantage for the tunnellers. In disposing of the muck, every tonne will pass through the river tunnel and on to trains to be hauled away.
All this is due to happen in the next 10 years. Currently, the MTA is holding its breath because federal funding talks are still in progress. Money has been forthcoming for design work and around $14M was recently allocated for initial works.
But although one contract has been let, clearing some existing non-LIRR rail platforms at Grand Central to make room for the new LIRR concourse area, the major elements of the project cannot go ahead without federal backing.
New York will know in six months if the project will go full steam ahead. Fingers are crossed that the city will not have to wait another 25 years.