ACCIONA Construction took part at Rail Live 2019, one of the most important international events for the railway sector.Fernando Vara, Follo Line project manager for the ACCIONA Ghella Joint Venture (AGJV), gave a presentation at the event in which he examined the main challenges of managing such a highly complex infrastructure project.
The Follo Line is the largest transport project carried out in Norway to date.It is part of the inter-city development plan for south-east Oslo, which is improving and developing the country’s transport infrastructures and includes construction of a twin 19.5 km railway tunnel between the city of Oslo and the town of Ski.
Logistics challenges – four TBMs drilling simultaneously, starting from the same point
The tunnel was excavated using a pioneering method in the country, with four double-shield tunnel boring machines (TBMs) simultaneously drilling and starting from the same point, in conjunction with traditional drilling and blasting methods.
Starting from Asland, two of these machines excavated north towards Oslo and the other two drilled south towards Ski.The project also included excavation work using conventional methods with two caverns for assembling the TBMs, rescue tunnels, an escape tunnel and two transport tunnels.
The TBMs used were 150 metres long and weighed 2,400 tons each, and were especially designed for the hardness of the Norwegian rock.Each one has drilled a ten-metre diameter tunnel for a distance of nine kilometres, which was then simultaneously lined with concrete segmental rings.A total of 140,000 concrete segments have been installed, which were manufactured at a plant next to the works site and transported into the tunnel on custom vehicles.
Geological challenges – the hardness of the Norwegian rock
Excavation of the tunnel was completed on 26 February.One of the greatest challenges in this phase of the project was the extreme hardness of the rock, which made drilling work difficult, combined with ground weakness in other zones.
The cutting discs on the head of the TBM penetrate the rock and the excavated material is then carried along the tunnel on an underground conveyor belt until it reaches the outside.As the cutting head drills through the rock, the rear section of the TBM installs the tunnel lining rings.
A total of nine million tonnes of rock were excavated and some of this material was reused to manufacture the lining rings, contributing to the overall sustainability of the project.
“We have faced important challenges related to the ground conditions and we are proud to be part of such a demanding TBM project”, said Fernando Vara.
All of this is in addition to the complexity of managing a team that, at its peak, consisted of 1,200 people with 25 different nationalities.
The design project produced by ACCIONA Engineering incorporated important improvements and innovations.A continuous monitoring procedure was put in place to determine the strain-deformation conditions of the excavation work at any given time, as well as a new database that allowed documentation to be delivered and accessed systematically.
A monitoring and control system was also developed for the four TBMs that provided first-hand information about the progress of the construction work and enabled supplementary measures and solutions to be proposed. Furthermore, the new methodology of systematically applying pre-grouting meant that the initial conditions of the underground excavation work changed as little as possible, reducing the economic and timing impacts of works stoppages.
Minimising the environmental impact and the potential effects on traffic and the local community has been one AGJV’s priorities throughout the project.
Next phase – railway installation works
Now that the tunnel excavation work has been completed, AGJV will carry out all the railway installation works, except for the signalling systems.The planning phase for these activities has already begun and the concreting works, preparation of the tunnel walls and the catenary systems, and the walkways and the technical rooms will all be carried out in the coming months.The telecommunications systems, installation of the tracks and the power supply and ventilation systems also form part of the project.
The project is scheduled to be completed by December 2021.