Twin EPB drives for Florence rail corridor
Twin EPB drives for Florence rail corridor Nov 2009
Ilaria Driussi, Technical Writer
Twin EPB running tunnels are central to the connection of the new Milan-Naples and Turin-Venice high speed rail services to and through the historic city of Florence, Italy. Designed to provide connection to the landmark new high-speed rail station at Belfiore-Macelli, and connecting to the city's main Santa Maria Novella station and other surface rail stations in the area, the new 5.5km of twin running tunnels will start at the Florence Campo di Marte station in the south and end at Florence Rifredi in the north, passing beneath the city centre en-route.
Pic 1

Florence urban rail alignments

The railway project through Florence and its new high-speed rail station is valued at €915 million. Construction of the main civil structures are awarded by Rete Ferroviaria Italiana (RFI), the Italian Railway Network owner, to NODAVIA JV, a group that comprises Coopsette, Ergon Engineering and Contracting Consorzio Stabile S.c.a.r.l., and Coestra. These major structures include a section of new elevated railway to be completed by October 2010; the high-speed underground route beneath the city; and construction of the iconic new railway station, designed by renowned British architect Norman Foster and UK engineering consultant Arup. The rail level at the new station is some 25m below ground surface and will be contained within a concrete box of 454m long x 52m wide with escalators, travelators and lifts providing connections to the ticket zone at mezzanine level and the ground level concourse.

Excavation of the 5.5km long running tunnels has been sub-contracted by NODAVIA to SELI, which will use a 9.4m
Pic 1

Italy's rail network

diameter EPBM to advance through the weak geological formations beneath the city. These comprise river and stream sediments, lake deposits and clay and are made up mainly of sandy or loamy clay, containing several pebbly inclusions of calcareous origins as well as footwalls and layers of sandy or thick clay gravel.
The tunnels will be lined with precast concrete segments in a configuration of six segments, a key and an invert segment in each ring. The gasketed segmental lining design is yet to be completed but will have an internal diameter of 8.3m and an external diameter of 9.1m.
EPBM excavation will continually support the face with sufficient pressure to limit ground settlement and deformations. Given the extreme variability of the soil, the loamy deposits, and the sandy gravel layers in all deposits, it is fundamental for the TBM to operate with adequate working pressure. Grain materials, in particular gravel with a scarce thin matrix, will require the use of special ground conditioning agents and a careful control of the EPB operating parameters to minimize surface settlement.
The new underground high-speed station lies 3km from the southern portal of the twin tunnel alignment. The two one-track tunnels will run at the side of station adits. At the tunnel entrances and exits of the new station, each tunnel will have a larger section in order to include both running tracks and sidetracks. Thirteen cross passages, at between 410m and 490m intervals, and the larger sidetrack cross sections at the station entrances and exits are to be excavated using conventional open-faced methods, supported by soil conditioning and waterproofing technologies.
  • p6

    Tunnel connections to the station

  • p7

    Geological profile

  • p8

    Striking rail station design

The TBM drives will progress along a south-north alignment starting at the Campo di Marte adit and finishing at the Rifredi adit. After completing the first 5.5km drive, the machine will be dismantled inside the Rifredi chamber and transported back to Campo di Marte, where it will be reassembled and launched for the second drive.
The new high-speed services in Florence are due to be inaugurated in mid-2014.


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