Page 10 - TunnelTalk Annual Review 2012

TBMs to excavate Norway’s Oslo-Ski Follo Line
Shani Wallis, TunnelTalk
escape connections every 1,000m. Single- track parallel tunnels of 70m2 with cross passages at 500m intervals would fulfil the operating safety requirements and drill+blast or TBM excavation would have been appropriate for the tunnels. The final decision might have been left to the successful EPC construction group but after consideration, the client specified TBM excavation.
TBMs of more than 10m diameter will be needed to create the minimum 9.1m i.d. of tunnels designed for 250km/hr high-speed train services. A bolted and gasketed precast concrete segmental lining is also specified as part of the TBM excavation operation to meet strict specifications for the control of ground water inflows. Using single or double shield TBMs and erecting the segmental lining as excavation progresses also adds programme advantages to the TBM method for the long drives.
The one central working site eliminates up to five additional access adits that would have been needed to divide drill+blast of the long running tunnels. As many as eight headings of about 2km each were needed to complete excavation within the same planned TBM excavation programme.
Drill+blast will be used on the project for approximately a third of the rock excavation required. This includes excavation of the central working access adit of up to 1,000m long and the emergency cross-passages between the two TBM drives. Drill+blast is also likely to be used for excavation of the final 2.8km of the twin running tunnels on the approaches to the Oslo Central Station. The alignment through the Ekeberg Hill passes beside existing road tunnels and other underground infrastructure. Final decisions about the most appropriate method of this excavation are under consideration.
The most significant factors to influence the choice of TBM as the primary method of construction, as explained in a statement by Jernbaneverket, are the tunnel’s length, the character of the rock, and a limitation of the number of access adits. Design life expectancy was another noted advantage. According to the Jernbaneverket statement, “it is now an internationally accepted norm that tunnel constructions, such as those on the new Follo Line, are designed for a life expectancy of 100 years or more. The industrialised process that the TBM method enables is a reliable guarantee of high quality work.”
The selection of TBM excavation for the new tunnel reignites an expertise that Norway dominated in the 1980s, primarily in the field of long TBM tunnel excavations for hydroelectric projects. Through alliance building with international contractors, it is expected that the use of TBM technology will also re-establish TBM excavation skills within the Norwegian tunnel construction sector to strengthen the competiveness of Norwegian contractors within tunnelling both at home and abroad. n
References
• Direct twin-tube route for Oslo-Ski railway - TunnelTalk, October 2010
Table 1. Facts about the Follo Line Project
22km of new double track line between Oslo and Ski
19.5km in twin tube tunnels with cross-passages every 500m
Construction scheduled to commence in 2014; completion scheduled in 2019
Designed for 250km/hr
Potential start of a high-speed link between Norway and the Continent via Sweden
An estimated 150,000 passengers daily are anticipated
Top: Oslo-Ski twin-tube TBM railway route; Bottom: underground link to Oslo Station
TBM excavation with a precast concrete segmental lining is specified for majority excavation of the new twin-tube, 20km-long railway tunnel between Oslo and Ski in Norway. The decision by the National Rail Administration, Jernbaneverket, paves the way for national and international bidding of an EPC (engineer, procure, construct) contract to build Norway’s longest railway tunnel to date.
The announcement in favour of TBM excavation combines the social, environmental, time and cost advantages that mechanical excavation can offer over drill+blast. The new 22km-long double track Follo Line between Oslo Central Station and the public transport hub at the town of Ski runs 20km through twin tunnels beneath the commuter suburbs and rural towns south east of Oslo. The issues of construction traffic, noise, vibration and protection of the groundwater table were major concerns.
TBM excavation confines construction to one mid-point access adit at a secluded rural site at Åsland. From here the specification is to use four TBMs, two in each opposite direction, to complete drives of up to 10km each, south to the
tunnel portals at Langhus and north to Bækkelaget.
With the decision made to specify TBM excavation and a precast concrete lining, the project schedule is to have preparatory works and the prequalification process for the main contract begin in 2013. Award of the EPC contract and start of main works are scheduled for 2014 and services are programmed to open in 2019.
In announcing the method of construction, Harald V Nikolaisen, Director of Infrastructure Construction at the Norwegian National Rail Administration, invited interested parties to a project meeting in November 2012. Construction groups will compete for an envisaged five major EPC contracts including the TBM tunnel excavation works and the system wide operating services.
The decision in favour of TBM excavation is taken after extensive study and following an earlier decision by the client to rule out a single-tube, double- track tunnel of 118m2. The single tube design would have required either escape adits to the surface at regular intervals, or a parallel 25m2 service tunnel with
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