THE CONSTRUCTION LOT IN FIGURES
Reinforced concrete retaining wall for the new railway line
Preliminary tunnel “Silltal tunnel” through the Bergisel eastern slope
Two tunnel tubes, each approx. 130 m long, for the “Viller Berg” tunnel stretch
Railway bridges over the Sill, one for the east and one for the west track
Contractor: PORR Bau GmbH Tiefbau, Tyrolean branch Kematen
Contract value: 59.5 million euros
COMPLETED
Tunnel excavation for this construction lot was completed in May 2022. The remaining work was completed in December 2024.
EXCAVATION DATA
- Excavation 120 m
- Length 120 m
- Cross-section 100 m²
- Excavation 130 m
- Length 130 m
- Cross-section 100 m²
ABOVE-GROUND WORK
Most of the work in this construction lot did not take place deep inside the mountain, but above ground. Following the north portal, two railway bridges, a reinforced concrete retaining wall next to the Sill, a new road access bridge into the Sill Gorge and a pedestrian bridge over the Sill were constructed. In addition, extensive slope stabilisation work was carried out and numerous hydraulic engineering measures were implemented. A total of 350 metres of river engineering work was carried out to ensure flood protection and enable upstream fish passage in the river.
COMPLETED WORK
- Construction of the two northern portals of the BBT, the two tunnel tubes of the ‘Viller Berg’ tunnel section and the two ‘Silltal-tunnel’ preliminary tunnels through the Bergisel eastern slope.
- Creation of hiking trails connecting the construction lot with the existing network of paths in the Sill Gorge. The existing hiking trail on the orographic left bank of the river was also renovated.
- Construction of a viewing platform on the Silltal tunnel, from which the northern portals of the Brenner Base Tunnel can be viewed at close range.
EXCAVATION METHODS
DRILL AND BLAST: At the northern portal of the BBT in the Sill Gorge near Innsbruck, around 50 metres of tunnel were initially excavated using excavators, pipe roofs and other consolidation measures until solid rock was reached and conventional blasting could be used to continue the work. In May 2022, the two tunnel sections running through the ‘Viller Berg’ in construction lot H21 were completed, the 120-metre-long main east tunnel and the 130-metre-long main west tunnel . This marked the completion of tunnel excavation for this construction lot. The breakthrough between the two Austrian construction lots ‘H21 Sill Gorge’ and ‘H41 Sill Gorge-Pfons’ took place in the east main tunnel on 17 September 2024.
TUNNELLING USING CUT AND COVER: The 130-metre-long Silltal tunnel was constructed using the cut and cover technique through the eastern slope of the Bergisel. To do this, around 60,000 m³ of material was first removed from the slope. The next step was to build an artificial concrete tunnel. The concrete structure was then covered over with the previously removed material and planted with typical local tree and shrub species. This restored the appearance of the Sill Gorge to its original state as far as possible.
PECULIARITIES OF THE CONSTRUCTION LOT
After completing e construction work, extensive re-vegetation measures were carried out and the network of paths in the Sill Gorge was expanded. This allowed the course of the Sill River near Innsbruck to be widened and, after 500 years, upstream fish passage was restored. The population now has access to a natural recreational area just outside the city. In spring 2025, the newly created network of hiking trails was opened to the public. By the end of 2024, almost all structures had been greened and the cover fill had been re-vegetated. In order to take into account the special location of the site on the outskirts of the city, the construction work was carried out over a 5-day week without night shifts to protect residents from noise.