The work and the technique: New York subway, linea F, USA

Works to build Line 131 A the fact that it was located in a highly dense and populated area was the most difficult thing that the Joint Venture made of Italian companies Impresit, Girola and Lodigiani (that later made up Webuild) had to face.  

The project foresaw building four lines, on two levels. In Lot 5A, the excavation works of a tunnel were carried out with the traditional method, with explosives, also being careful to constantly monitor the vibrations near the foundations of the overlooking buildings. To avoid excessive noise and other types of discomfort, a system to load excavation rubble onto trucks directly in the tunnel, was put in place: these trucks were raised to street level with a lifting system that was capable of carrying up to 40 tons.

In Lot 5B, the continuation of the previous one, works were carried out from Third Avenue to Franklyn D. Roosvelt continuing with an already existing tunnel beneath East River, towards Queens. To avoid using explosives with their consequent vibrations, for the first time in New York, it was decided to use a TBM of the Robbins-type, with a diameter going from 6.20 to 6.70 metres, working on 3 shifts with an advancement that averagely was equal to 7.40 metres/day, with a peak of 26.50 metres/day.

Among the other things done to make the works not impact the lives of residents, was maintaining the normal road mobility in the open, with the use of steel girders and concrete slabs capable of supporting the weight of heavy vehicles. Also, the attention placed in making sure that the underground services, like the sewage system, the phone connections, the electric grid, and the gas one, but also the vapour tubing system that in New York is used to heating by pressure the entire city remained the same as usual, without any interruption at all.

Works ended in 1984. They were carried out by trying to keep the reliability of the New York metro the same, as it is the only one that runs 24/7 all year round.