Rockfall protection for tunnel construction
January 9, 2025 | Lucia Reinsprecht
Airy, airy! For anyone who isn't free from giddiness, just looking down would be enough to feel uncomfortable. Let alone moving around fearlessly on a wooden post anchored in the scaffolding on a rock face. From the topmost working level, there is a 70-metre drop to the ground below, which is roughly equivalent to the 20th floor of a high-rise building.
Physical fitness
On seven horizontally mounted scaffolds, which extend across the vertical rock face at ten-metre intervals, the Felbermayr specialised civil engineering workers move as nimbly as others at ground level. Secured and concentrated working there all day long is reserved for only a few. “This requires mental and physical fitness as well as rope training in order to be able to secure yourself and others,” emphasizes project manager Markus Winkler. “Access to the workplace was via a fixed rope route that we have set up. Twice a day, you had to climb up and down because it also goes down for the lunch break. For shorter breaks in between, platforms were set up where it was easy to move around.”
71 large drill holes
The team consists of between seven and 15 people worked on the up to 30-metre-long concrete reinforcements since the summer of 2024. This required 71 large anchor holes with a diameter of 120 mm to be drilled into the rock of the Venter stock. “These drill holes are between 12 and 25 metres deep, adding up to a total borehole depth of 1.1 kilometres,” the project manager informed us. By the way, it took a whole day to descend to a depth of 25 metres. A drill truck and a crane made the work on the lower three cross beams easier. The 75 mm thick steel anchors with double corrosion protection were pressed along their entire length and finally fixed in the mountain by means of cement injection.
Partly overhanging wall
Drilling for the large anchors is not enough: A fixed rope route, construction site equipment, scaffolding and elaborate concrete formwork required countless smaller securing points. All of this is “rock-hard labour”. “Individual components are perfectly routine and standard work for us, but due to the altitude and steepness of the terrain, with some overhanging walls, this was a very challenging project for us,” summarises Winkler.
Hundreds of helicopter flights
A project that also boasts impressive figures: “In terms of cubic volume, we kept to a total of around 230 cubic metres, or 575 tonnes of concrete,” the experienced site manager informs us. This material was flown up by helicopter in two-minute intervals and immediately poured into the formwork. “Three to four flights were required per cubic metre. The helicopter flew for almost three hours for the 25 cubic metres of the uppermost beam.” In the event of ice formation or the onset of winter, work would be stopped immediately:“If it freezes, we have no business on the wall,” Winkler emphasises, referring to the exorbitant increase in the risk of danger.
Preparatory work for rescue tunnelsThe seven concreted beams will then secure the wall rock over a large area and permanently. Once completed, monitoring sensors should help to identify potential hazards in good time. The seven-kilometrelong, single-tube Landecker Tunnel in the direction of the Reschen Pass marks the beginning of the A12 Inntal motorway and was opened in 2000. Securing the rock face is the first step in the construction of a rescue tunnel and is therefore also to be regarded as an advance safety measure for further work.
