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TBM launched for Brenner exploratory tunnel 07 Oct 2015

Patrick Reynolds for TunnelTalk

The latest TBM on the Brenner Base Tunnel project is officially launched for excavation of the 15km-long stage of the central exploratory tunnel on the record-breaking rail scheme being developed in the Alps between Austria and Italy.

Tulfes-Pfons TBM will bore 15km of exploratory tunnel
Tulfes-Pfons TBM will bore 15km of exploratory tunnel

Project developer BBT-SE also reports it has received approval of a major tranche of the total €1.18 billion of European Union funding towards the scheme. The project is also funded by Austria and Italy.

With a total length along the axis of 64km, the rail tunnel will be the world’s longest when it opens in 2026. Between the Innsbruck and Fortezza portals the straight-run of the route along the main axis is 55km.

JV contractor Strabag/Salini-Impregilo officially launched the 7.93m diameter Herrenknecht TBM on the Tulfes-Pfons Lot (T-PL) at the end of September. The JV was awarded the contract by BBT-SE in mid-2014 and began early drill+blast excavations soon after.

Excavation of the T-PL involves work in a number of locations in the complex layout at the northern end of the scheme, near Innsbruck in Austria. The works also call for significant use of both TBM and drill+blast to perform a total of 38km of tunnelling.

Geology along the alignment is mostly quartz phyllite, although the TBM will also pass through shale.

View along NATM tunnel on the Tulfes-Pfons Lot
View along NATM tunnel on the Tulfes-Pfons Lot

Nicola Meistro, a manager in Salini-Impregilo’s domestic operations division, told TunnelTalk that the challenges posed by the geology include: optimising against the high abrasivity of the quartz phyllite; and crossing the fault zone between the quartz phyllite and shale.

The TBM section of the T-PL is focused on the 15km portion of the exploratory tunnel from the Ahrental adit, southwards towards the border with Italy, but going as far as Steinbach and just short of the Wolf adit. On the same (Austrian) side of the border, one more stretch of the exploratory tunnel will remain to be excavated, from the Wolf adit onward. This will be completed as part of a larger package to follow that will also include works for the 8.1m i.d. running tunnels.

For the T-FL, NATM drill+blast excavation totals approximately 23km, accounting for the majority of tunnelling on the contract. This includes the rescue tunnel that links to the main tunnels, the main tunnels/connection tunnels, and the emergency station tunnel at Innsbruck.

7.93m Herrenknecht TBM assembly
7.93m Herrenknecht TBM assembly
NATM works on Tulfes-Pfons Lot
NATM works on Tulfes-Pfons Lot
Official TBM launch ceremony on Tulfes-Pfons Lot
Official TBM launch ceremony on Tulfes-Pfons Lot

The underground works have more than 23 different tunnel cross-sections, the largest up to 250m2. The maximum dimensions are for widths and heights up to approximately 20m and 15m, respectively, said Meistro.

BBT-SE reports that just over 5km of the drill+blast headings on the T-FL Lot have been excavated, opening up the different sections from a number of access adits. All T-FL works are scheduled to be completed by March 2019.

Salini Impregilo and Strabag are also working together on a separate contract, with other companies, at the southern, Italian end of the project, at the Isarco River Underpass near Fortezza station. Work started on this section in late 2014. The soft ground in the area calls for different construction techniques – jet grouting to strengthen the local soil, and also ground freezing to excavate below the river.

On the matter of funding, Italy recently formally approved a further tranche of €920 million, clearing the way for further procurement to proceed on the Italian side between the Mules adit and the border with Austria.

The remaining main tunnel works on the Italian side – in the section known as “Mules (Mauls) 2 and 3” – involve approximately 14km of exploratory tunnel excavation and a total of 36km of headings for the main tunnels, said BBT-SE. These works are set to take about nine years.

The main tunnels will run about 70m apart and are to be connected every 333m by cross passages. Multifunctional emergency stations, with direct access to the surface, will be located at 20km intervals.

Earlier works on the Italian side involved both TBM boring and drill+blast excavation for the exploratory tunnel, as well as opening up short sections of the main tunnels. BBT-SE is to commence procurement in 2016 for the main tunnels on the Austrian side, to the border. This Lot is estimated at €1.8 billion, and includes the last section of exploratory tunnel on the Austrian side, from Steinbach south to the border.

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