ACCIONA Construction has completed the first of the 45 galleries that will connect the two railway tunnels of the Follo Line project in Norway. These service galleries will be essential for carrying out maintenance work on the main tunnels and are a key element of the safety system. A total of 45 connecting galleries will be constructed, of which 33 will be 25 m long and the other 12 will be 12 m each. This work is expected to take 20 months.
The first gallery was excavated using the borehole expansion method, which breaks up the rock without using explosives, combined with traditional drilling. The hardest part of constructing these sections is coordinating the large number of tasks that have to be simultaneously carried out in the tunnels. The works on the connecting galleries have to be coordinated with the progress of the tunnel boring machines drilling the main tunnels in order to avoid damaging the tunnel rings or interfering with their work.
Fernando Vara, project manager for the work being carried out by the ACCIONA-Ghella consortium, expressed his satisfaction at this first milestone, saying “The rock is extremely hard and presents numerous difficulties. But we are optimistic about construction of the next 44 connecting galleries thanks to the right choice of excavation methods and we are on schedule.”
“Bane NOR has opted for a concept with two separate tunnels and connecting galleries at least every 500 m, which takes into account aspects such as the need to ensure rail traffic continuity, accessibility for maintenance tasks, the length of the tunnel, the geology, the topography and the cost assessment,” explained Anne Kathrine Kalager, head of the Follo Line tunneling project.
This means that maintenance can be carried out on one tunnel while trains continue to use the other. Furthermore, in the event of an incident, having two independent tunnels connected via galleries offers a higher degree of safety.
A total of 6 km of tunnel have already been drilled since the tunnel boring machines began to work in early September 2016. The four machines are working at full capacity.
The Follo Line project consists of a new double-track line between Oslo’s Central Station and the intermodal station in Ski. The project includes a 20 km double railway tunnel, which will be the longest of its type in Scandinavia, and extensive works to Oslo’s Central Station, the new intermodal station in Ski and the necessary diversions to the Østfold main line. The works are scheduled to be completed by December 2021. This is the first part of the inter-city development plan for south east Oslo.