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27.07.2020

27.07.2020

Trimble's GEDO Track measurement technology is being used by ScanSurvey A/S to control and document the slab-track installation on the major Follo Line Construction Project.

Several miles of track laid with millimetre precision

When the new Follo line is completed – planned for December 2022 – the travel time from Ski to Oslo will be halved from today. Large parts of the new twin track will be laid in rock, in what will be the Nordic region’s longest railway tunnel. It is a monumental project, with Norwegian railway administrator, Bane NOR, as the project Stakeholder.

The railway tunnel passes under the E6 highway road tunnel, and is close to both oil stocks and other important infrastructure. To achieve this, Acciona Ghella JV, which is the main contractor for this part of the project, had simultaneously used four advanced Tunnel Boring Machines (TBM). The rotating cutter head at the front broke up the rock and a conveyor belt at the rear carried away the loose material. Pre-injected on sections where there could be a risk of leakage were specially built concrete rings, which were installed at the rear of the cutter.

These reinforced rings today form the inside of the tunnel itself.

Currently, the fixed slab track structure is being molded inside this massive construction. The fixed slab tracks will reduce the need for maintenance and the rails will remain fixed, guaranteeing a longer design life and increased reliability. Here, trains will run at top speeds of up to 250 km/h, and the contractor has one shot at installing it correctly within the tight tolerances.

– Sets strict requirements for execution

To document the quality of the work, a Norwegian land survey/geomatics company called Scan Survey are in place. For this job, they have invested in special Trimble GEDO equipment that provides sub-millimetre precision. This is necessary to ensure that trains can maintain both speed, safety and ride quality on the finished railway track.

– Our client is the stakeholder/builder, Bane NOR, but I would say that the work that AGJV has done on this project is impressive. Casting of fixed slab tracks tracks is a completely new method in Norway. This has only been done on one other railway line before. This offers advantages over traditional ballast tracks, but also places strict demands on the design. This is where we intervene with our equipment and our experience, says civil engineer Are Jo Næss in Scan Survey.

He is responsible for all the checks of geomatics-related operations on the project, which includes inspecting all types of land surveys Bane NOR needs. This has required different types of expertise in different parts of the project.

– While the tunnel boring machines were in operation, AGJV measured the tunnel operation and we measured continuously. Then we used, amongst other things, gyro-theodolite to find the absolute position and direction between the Oslo and Ski walls, and took random samples to ensure that the machines were on the right course. At one point, the tunnel passes under a road tunnel at the same location as it passes over Oslo’s largest drainage tunnel, with minimal margin for error.

Creates terrain that matches the map

In addition to the actual tunnel drilling, it is also crucial to install the tracks correctly on the first attempt.

– It is quick to carry out the measurements, but since you cannot adjust fixed tracks in the same way as ballast tracks, it is crucial that it is measured correctly in all three phases. For this, we have invested in a separate Trimble GEDO trolley for track measurement. It allows us to control both where the theoretical/design, future tracks are to be laid, so that they are in accordance with the models, and measure exactly where an existing track is located, Næss explains.

Although it will probably be a while until the next time slab tracks are to be built in Norway, he is happy with both the technique and the expertise Scan Survey has built up on Follobanen. Everything is very transferable to other projects – and there are many of them.

– It is an extensive job to lay tracks, where you have to take responsibility of everything from track geometry to technical infrastructure, and good measurements remain a crucial success factor, he states.