The Bothnia Line in Sweden is keeping its project promises as it moves “from vision to reality”. The SEK10.9bn (US$ 1.44bn) mega project to construct a 190km high-speed freight and passenger coastal railway parallel to the Gulf of Bothnia, linking Umeå, regarded as the “capital” of north Sweden, to Nyland, was given approval to proceed in 1997 by the state, municipalities and county councils. By mid 2004, 25 bridges, 20km of track and 4.3km of tunnels in rock had been completed, with a further 33.7km of tunnel either being constructed or mobilised (see Table 1).
Despite the Bothnia Line’s dual intent, it is the freight service that has proved to be the driving factor of the project, due to the extensive mining and timber operations in this northern region, together with the state’s desire to move freight transport from roads to rail for environmental reasons.
With the majority of the population of northern Sweden concentrated along the coast, the new line will also serve to knit together the coastal communities. The scheme is Sweden’s biggest infrastructure project since World War II, replacing the 110 year old mainline that runs inland along a route that was planned as much to protect it from a perceived Russian threat as for speed and efficiency of travel. In addition, the project is the first railway to be built in accordance with Sweden’s stringent new Environmental Code.
Construction began in 1998 under the watchful eye of Botniabanan AB, the organisation set up to fulfil the client role for the scheme, which consists of 91% state and 9% municipality factions. A total 130 major contracts will be administered throughout the construction process, both traditional and turnkey terms are used as appropriate. The National Rail Administration will lease the line once it has been commissioned. Current plans are for all tunnelling work to be completed by 2007.
Camp Skanska
With the necessary environmental permits in place the design and build turnkey contract E3541, between Offersjön and Bjällstaån, was awarded to Skanska Sverige AB on 24 September 2003. This SEK1.3bn (US$171M) section runs for 32km from Offersjön, north of the Ångerman river, to Bjällsta, southwest of Örnsköldsvik, through two tunnels and twelve bridges as well as extensive embankment works. The tunnels have a combined length of 11km and when completed will be the longest tunnels in Sweden, at 6km and 5km respectively.
A more direct alignment for this stretch would have shadowed the E4 trunk road, but it would have necessitated even more, up to 75%, of the line being in tunnel and, apart from cost, there were felt to be security concerns with this approach.
To the south of Botniabanan’s headquarters in Örnsköldsvik (Eagle’s Shields Bay), in an area aptly described as the middle of nowhere, is what is becoming known as “Camp Skanska”, the site office location for contract E3541. Here you will find offices, stores, accommodation blocks and workshops that are semi self-sufficient for the 55 staff, 80 labour force and 80 sub-contractors. The contract scope includes 25km of access roads for cars to link the different work locations, even tree felling and clearance for this, let alone the actual Bothnia Line embankments, is a sizeable body of work in its own right.
There are two main tunnels in this contract, the 5km Björnböle tunnel and the 6km Namntall tunnel, together with a further 11km of parallel service tunnels. Anders Östberg is the production manager for the Björnböle tunnel, with additional responsibility for the drill rigs and blast design. He described the single-track rail tunnel as having a cross sectional area of 62m2 and the service tunnel as being 28m2 in face area. The service tunnel facilitates maintenance and also serves as a rescue / egress tunnel with connections by means of 10m long cross passages at approximately 450m intervals.
Skanska’s method involves driving a 610m access tunnel at a gradient of 1:10 down towards the middle of the Björnböle tunnel. Breaking into both the running and service tunnels gives four faces for simultaneous production. The tunnels will also be driven from the southern portal, which gives six faces in total that can be excavated. The northern portal will not be used for driving, as this is not expected to be required for optimal use of the tunnel crews. For the longer Namntall tunnel, a similar approach will be adopted, although the access tunnel will only be 570m long and in this case it is feasible to drive from both the northern and southern portals.
Six Atlas Copco Rocket Boomer face drilling rigs will be used for development of the tunnels, with each rig covering two faces. Skanska is using three of the older Atlas Copco Rocket Boomer 353 rigs and three Rocket Boomer XL3C rigs. On the XL3Cs, the middle boom has been equipped with rod handling for longer holes such as may be required for grouting or probing and also for rockbolting.
Mechanical scaling is carried out by the subcontractor Hedins of Sweden, using modified hydraulic excavators. Hedins has also equipped its excavators with a drill boom and an Atlas Copco 1838 drill for rockbolting. Mucking out is by the sub-contractor Euromining with Volvo 330 and CAT 980 wheel-loaders to 50t Volvo trucks.
At the time of T&TI’s site visit in early June, only the cut had been fired for the first round in the northern face of the Björnböle tunnel, work was ongoing to lower the bench, mesh and shotcrete at the southern portal.
At the time, it was hoped that the tunnels could get underway by the end of August and this was confirmed by Skanska’s project manager, Jan Stattin, in mid-August who said tunnelling works had got underway for the rail and service tunnels at three locations, but that the “start of tunnelling, close to the surface, is always hampered by extra strengthening works and other complications.” He went on to add that approximately 750m had been excavated in total in the two access tunnels. Progress in these is according to programme and “rather good” rock quality, as predicted, was being encountered.
While the Stranneberg Tunnel (T&TI October 2002, p16) on the Bothnia Line may have required the use of jet-grouting and ground freezing, Stattin reported that grouting on the Skanska contract was progressing as expected using cementitious pregrouting and that the required watertightness was being achieved in the tunnels. Indeed, during the visit it was commented that the tunnels were dry enough to permit the use of ANFO as the column charge in blastholes.
The work cycle for the Skanska crews runs on dayshift from 6am until 5pm, seven days a week, on a seven days on/seven days off rotation. On the dayshift, drilling, charging and blasting is carried out, together with shotcrete and grout operations.
Generally 40mm-70mm of shotcrete containing steel fibres is applied to the roof as a strengthening measure. Nominal spot bolting is expected, in the region or one or two grouted bolts per metre of tunnel. Ventilation is by means of 90kW Swedvent fans, initially only a single fan, uprated to a pair of fans when the headings are far enough advanced for losses to warrant it. The nightshift is taken up with scaling and mucking out.
Environmental controls
As mentioned, the Bothnia Line is subject to strict environmental controls. Water from the tunnels is re-used for drilling, but not grouting or shotcreting. Before being released to watercourses, it is filtered through carbon and sand. At the time of T&TI’s visit, some of the filtration system was still to be commissioned, therefore all the water had to be stored and taken offsite for processing and disposal.
Despite the remote locations of the worksites, the quality of the discharges are “as important here as any other part of Sweden,” said Stattin. Regulations denote the minimal amount of grouting to be carried out for tunnel water control, but Skanska is providing extra grout cover in the roof to limit water leaks onto the caternary wire once the tunnels are in operation.
Regarding blast vibration restrictions, Stattin said the only limits in place were in order to maintain the effectiveness of the pregrouting operations. In terms of time, the contractor is free to blast at any time; the only limits are technical restrictions. Skanska is aiming for a safely achievable work cycle that will give a 5.4m round in both the rail tunnel and the service tunnel every day for each drill rig. If not, pregrouting is performed, which is scheduled for every third round.
In a typical round in the rail tunnel 48mm diameter blastholes, with 104mm diameter reamer holes in the cut, are drilled to give a specific charge-weight of 1.4kg/m3. NONEL detonators are used to initiate the blast, with igniter cord used for the smoothwall holes and cartridge emulsion as the primer for the ANFO. Generally the round pulls to approximately 5.4m having been drilled to 6m, giving a pull efficiency of 89%.
Östberg said it was hoped that 7.5m rounds could be trialled. Skanska was involved in trials roughly ten years ago for long drift rounds of 7.5m, but at the time, the test was not positive enough for the change in method to be adopted. Stattin said the newly purchased Atlas Copco XL3C drill rigs provided the possibility of longer rounds but no decision had yet been made.
Talking about the older Atlas Copco 353 drill rigs on the project, Stattin praised their longevity saying “you can use them as long as you maintain them”, though he did add the caveat that it “will cost a lot in the end.” When asked if he would upgrade the 1838 drills on the rigs with the new 3038 drills that are said to drill up to 50% faster, Stattin said that in terms of the work cycle, drilling speed was not that important overall, when compared to mucking out and ground support. He advocated reliability and cheaper costs to maintain as being more important considerations for him as project manager.
Related Files
Table 1: Bothnia Line tunnels from south to north
Cross section through the Björnböle railway and service tunnels
Widening the Åsberget tunnel – see box
