28 March 2021 Railway Gazette International

RESILIENT INFRASTRUCTURE Track

slab

Construction of a long single-bore tunnel to alleviate capacity problems in the Bergen

Opened for traffic with the timetable change on December 13, the 7·8 km Ulriken tunnel in western

Norway is set to bring a step-change in performance on Bane Nor’s Bergen Line, helping to eliminate a critical bottleneck close to the Atlantic port city. But it also points to the future, as the first implementation of slab track on the national rail network.

�e 100 year old Bergen Line is one of the country’s most important rail corridors, providing an east-west connection between the coastal region and the capital for both passengers and freight. Much of the line is single track, although there has been a steady programme of improvements over many years.

�e railway leaves Bergen through a lengthy tunnel under the Ulriken mountain, which starts at Fløen, just 1·3 km from the terminus. �e Fløen – Arna bore was completed in 1964, shortening the railway by no less than 16 km and cutting the journey time between Bergen and Arna by 40 min.

Traffic volumes have increased steadily over the years, and by 2009 the

Arna – Fløen section had become the busiest single-track line in northern Europe, according to Bane Nor, carrying no less than 126 trains per day.

A decision was taken in 2009 to double-track the line, boring a second tunnel parallel to the 1964 structure, along with 16 connecting cross-passages at 500 m intervals to provide an emergency evacuation route. �e project saw the first use of a tunnel boring machine for rail tunnel in Norway, with a 9·3 m diameter Herrenknecht TBM starting work from Arna in December 2015 and completing the main drive in around 18 months. A 800 m section at the Arna end was excavated using traditional methods to accommodate an extension of the station’s passing tracks.

Top: Arna station

has been rebuilt as

part of the double-

tracking project;

this view looks east

towards Mount

Arnanipa.

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Torbjørn

Søderholm,

Midt Utbygging division; Alexej von Glasenapp, Senior

and Javier Cabeza

Railway Gazette International March 2021 29

Track RESILIENT INFRASTRUCTURE

‘The main reasons for the new tunnel were to enhance flexibility, to

increase the frequency of trains between

and to carry more freight by rail’Torbjørn Søderholm, Project Manager, Bane Nor

Below: Completed

slab track in the

Ulriken tunnel.

Bottom: Construction

of the in-situ

concrete slab.

�e NKr4·6bn project has been managed by Bane Nor’s Vest/Midt Utbygging division, with Project Director Hans-Egil Larsen and Project Manager Torbjørn Søderholm overseeing five teams responsible for the various disciplines.

According to Søderholm, ‘the main reasons for the new tunnel were to enhance flexibility, to increase the frequency of trains between Bergen and Arna from 30 min to 15 min, and to carry more freight by rail. Now we have the new tunnel available, we can refurbish the old bore, which will retain its ballasted track. And once that is completed we will have a double-track section able to accommodate more regional and inter-regional trains.’

Competitive tenderingBane Nor’s budget for major projects has been increased considerably in recent years, and it is considering whether to use more ballastless track in future schemes. Ballastless track was specified for the Ulriken tunnel, and is also being installed on the Follobanen project near Oslo (RG 6.19 p49).

‘We wanted to understand the ballastless track technology and benefit from the know-how of experienced construction companies’, Søderholm explains. ‘Our Bergen-based project team realised at an early stage that it was crucial to enter in dialogue with European suppliers of track systems in order to attract qualified companies to participate in the tender. A!er a prequalification phase, we usually aim at shortlisting five to seven participants for several rounds of negotiation. In general, we usually have a combination of qualitative and price elements, to be considered when evaluating the best offer. And in our case the trackwork contract UUT 31 included both design and installation of the slab track.’

A!er an extended negotiation process, Spanish construction company Azvi SAU was awarded the contract in February 2019. �e Sevilla-based company had more than 100 years of experience in railway

construction and had been involved in building almost 500 km of high speed line since 1987.

Ballastless track designOn straight sections, the slab track was specified with a maximum depth of 460 mm between the top of the rail and the bottom of the structural slab, compared to 770 mm for a comparable ballasted trackform. �e saving of 310 mm allowed Bane Nor and its contractors to optimise the design of the tunnel cross-section.

To meet the requirement, Azvi and Bane Nor decided to use the Rheda 2000® track system from PCM Rail.One. �is is one of the most widely used ballastless track systems for high speed and high performance railways, having been installed on more than 4 500 single track-km across Europe, the Middle East and Asia.

Rheda 2000® is assembled from prefabricated twin-block concrete sleepers and lattice girders, concreted into an in-situ concrete base to form a monolithic track structure. �e B355.3 sleepers can easily be modified to suit any local requirements.

�e use of twin-block sleepers enables a fairly conventional installation process, with the sleepers serving as a temporary tie rod to keep the rails to gauge during the work. �e foundation

provided by the concrete base allows loaded construction vehicles to use the track without difficulty before the rails are accurately positioned and secured in place. �is meant that it was possible to lay the track in single-sleeper mode or using pre-assembled track panels.

A transition zone design was developed to ensure a smooth ride between the slab track in the tunnel and the ballasted tracks at each end. �is consists of customised transition sleepers with special fastenings; a guard rail is also provided to reduce the risk of derailments and provide additional safety.

Highlights and challengesCompleting the tracklaying to a fairly tight schedule posed a number of challenges, particularly around the complex logistics and co-ordination required to manage the work inside a single-bore tunnel, with only a 3·4 m wide access road, given that several contractors were working on different disciplines at the same time. �ese constraints demanded very detailed planning as well as rigorous performance by the teams from both Bane Nor and Azvi in order to meet the project deadlines.

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RESILIENT INFRASTRUCTURE Track

30 March 2021 Railway Gazette International

Positioning of track

components using

the robotic vehicle.

to reduce vibration

uses a Rheda 2000®

mass-spring system

with Pandrol FCA

fastenings.

�e main track construction activities included the transport and distribution of rails and sleepers along the tunnel, pouring of the concrete track panels, li�ing the track and shuttering a�er fine alignment, the finish concreting and flash-butt welding of the rails.

Azvi developed two innovations for the project: a robotic positioning device and a very precise procedure for pumping concrete.

As well as minimising the amount of manual work, the positioning machine brought greater efficiency in the track li�ing phase. It also ensured a high level of accuracy in positioning and reduced the risk of possible errors.

�e concrete pumping procedure ensured that work could meet the estimated daily performance needed to achieve the targets. Using an experienced installation team, Azvi laid an average of approximately 150 m of slab track per day throughout the tracklaying phase.

�e project required the use of concrete containing synthetic fibres for added reinforcement, while a special frost-resistant concrete was used in the area close to the tunnel portal at Fløen.

One major engineering task was the design and installation of a section of floating slab track to mitigate noise and vibration where the tunnel passes under the Haukeland hospital. �ere is less surface covering on the Fløen side of the mountain, and the hospital is located just above a 600 m long curve in the tunnel.

Azvi’s Engineering Department adapted the Rheda 2000® design into a mass-spring system, using Pandrol elastomer mats under the track slab. �e Pandrol FCA fastening system was also adopted for this section, giving a total depth for the trackform of approximately 546 mm on the outside of the canted curve.

Project supervisionBane Nor’s construction division worked closely with the contractors throughout the project, undertaking supplier audits and quality checks. ‘For an important project like the Arna – Fløen line, and considering that the slab track elements are fairly new to Bane Nor, we felt that it was important to visit the suppliers and sub-suppliers to ensure the highest level of quality, production processes and supply chain considerations’, says Søderholm.

Health and safety were also extremely important. ‘We try the utmost to reduce the number of accidents and to reduce the risk of any incidents occurring’, he says. ‘You have to bear in mind that tunnel projects are especially challenging from a logistics perspective, and there are many movements, which need to be handled professionally.

‘�e Covid-19 pandemic also posed a big challenge to the project over a period of about six months. Due to the new regulations, foreign staff working for the construction companies had to quarantine for a time when returning from a trip abroad. We were able to work very well with Azvi to deal with this and ensure that the project could proceed without any significant interruptions.

‘Bane Nor and Azvi implemented extra measures to reduce the contamination risk for the construction workers on site, and this co-operation has been very satisfactory. Azvi was able to achieve all of the specified milestones including opening the railway on December 13 as scheduled.’

Lessons learnedSøderholm says Bane Nor has learned a number of important lessons from the Ulriken tunnel scheme. ‘Having a good project information management system is particularly important when introducing multi-disciplinary projects of this type’, he explains. ‘�e Tilos Planning & Schedule so�ware helped us to estimate and calculate process times and the detailed locations. �e detailed planning tool adds a lot of value in tunnel projects.

‘We are currently changing our organisation structure to become more like a matrix. It is more and more important to establish best practice and to learn from experienced teams. However, with all the safety measures needed to reduce the risk of contamination during the coronavirus pandemic, we had to keep the number of physical meetings and visits to a minimum. Our colleagues in other areas and departments have been very eager to learn more about our experience.’

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Cost of

Ulriken tunnel

project

4.6NKrbn