Gubrist tunnel: Easing the pressure at a bottleneck
With more than 120,000 vehicles per day, Zurich’s northern bypass road is currently one of Switzerland’s busiest road sections. The result: regular traffic jams and accidents. The general redevelopment and expansion of the Gubrist tunnel to add a third tunnel tube are designed to boost capacity and make the route safer.
Federal Roads Office (FEDRO)
Largest excavation diameter in Switzerland
The 3.3 km long Gubrist tunnel with two single-direction tunnels was opened in 1985. As part of the building project “A1 North Bypass Zurich”, a third tunnel tube with three traffic lanes will be constructed by 2022. Afterwards, the two existing tunnel tubes will be redeveloped with two lanes each. The construction of the third tunnel tube is setting new standards in tunnel construction. At a width of 16 m, the new tube will have the largest excavation diameter that has ever been tunnelled in Switzerland.
3D laser scanning surveys
The expert surveyors from Basler & Hofmann have created a precise fixed point grid as a basis so that the roadheader can make its way through the rock as the tunnelling progresses. During the construction work, checks are performed at regular intervals to make sure the machine is on the right path. As a basis for project planning of the restoration of the existing tunnel tubes, the latter were scanned entirely with laser scanners. In comparison to using tachymeters for measurements, laser scanning is much faster – a key advantage, as this means that traffic in the tubes is held up less.
Construction management services and staff function with senior construction supervision responsibility for lot 2 (new build of the 3rd tube) and lot 3 (renovation of tubes 1 and 2) for project planning, tendering and implementation.
Principal surveyor: 3D laser scanning as the basis for renovation of the existing tunnels. Measurement of the road surface area, exhaust air, fresh air and service ducts over a combined length of around 25 km. Creation of 3D models, 3D axes and cross profiles.
Creation of a fixed-point grid in the areas around both portals of the third tube. Checks of tunnelling progress and main fixed reference points below ground. Comparison of actual-versus-target for newly excavated cross-sections. Breakthrough monitoring. Stacking out the tunnel profile and performing control measurements on the portals.