Construction of stations and shafts
In Line C’s sections T4, T5 and T6A, 11 underground stations were built, which may be divided into three types:
- 6 box stations, in which the entire work is contained within the perimeter diaphragm walls. This type of station was used in all cases where there were no space limits at street level.
- 3 hammer-type stations, where only the atrium level and the inclined shafts linking to the platforms are contained inside the perimeter diaphragm walls. In this case, the platforms are made in a polycentric tunnel with traditional excavation in expansion starting from the TBM tunnel. This station type was used in all cases in which road-level constraints made it indispensable to reduce the size of open-cut excavations.
- 2 stations with mixed system, in which only a part of the work is contained inside the perimeter diaphragm walls while a portion of the platforms is made in a polycentric tunnel with traditional excavation in expansion starting from the TBM tunnel.
In all cases, once the perimeter diaphragm walls are built, excavation proceeds top-down, which consists of building the slabs in progression with the excavation, so as to counter the perimeter diaphragm walls and reduce impacts behind.
Upon reaching the excavation bottom, progress continues, if necessary, with the completion of the platforms by traditional excavation in expansion starting from the TBM tunnel.
In all other cases, perimeter linings are built with the function of waterproofing the work.
The construction of shafts between sections starts with the building of the sheet piles retaining the excavation of the surface locations and the deep shaft for linkage with the line tunnels. Upon reaching the excavation bottom, progress continues with the excavation of adits providing connection with the line tunnels by traditional blind hole excavation.
In some cases, such as for the Malatesta TBM shaft, given the future presence of an important switching park needed for the line’s railway operation, it was necessary to build a box structure between diaphragm walls having dimensions comparable to those of a real station.