The new Bothnia railway project in Sweden’s mid-north has had its share of troubles. At its northern end a 10km section of the line is still awaiting final clearance for bridge construction as environmental objections continue over protected sea bird migration grounds. At the south end work has been underway but has taken much longer than expected, particularly on its long tunnels.
Main contractor Skanska originally hoped to hole through on two tunnels, one of 6km length and one of 5.2km, around spring last year. But progress on both, and particularly the northern of the two, has been more difficult than anticipated it says, with numerous awkward ground fractures and soft patches to get through in the rock. Drilling for the basic drill & blast excavation has been held up and the rock support required has been consistently heavier than anticipated.
The southern Namntal tunnel at 6km long finally holed through in October in its southern drive and November in the northern drive. In early January this year some 300m or so remained to be driven on the 5.2km long Björnböles tunnel to the north with completion due in early spring.
The tunnels carry the line through a well-known and exceptionally picturesque section of the new route known as the High Coast, famous for holidaying and walking in the long summer daylight close to the Arctic Circle. Just here the track swings away from the Baltic Sea coastal alignment taken for most of the 192km route (see box). It heads inland in order to miss the more difficult mountain sections and minimise overall tunnelling costs, explains spokesman Gunnar Sundgren for the client Botniabanan, a specially created government company overseeing the project.
Even on this less undulating route the project needs several long tunnels to take the line to its southern end point at Nyland, including these two and a smaller but respectable 3.3km tunnel outside Nyland. Skanska’s pair will create record length tunnels, which are both the project’s longest and also the longest railway tunnels in Sweden.
In all Skanska Sweden has four tunnels on the route, which total 22km, with each of the major 8.6m high x 8.4m wide bores for the single-track mainline accompanied by a smaller service and emergency tunnel running parallel alongside. Both modern safety considerations and ease of power supply and maintenance made the secondary bores a necessity says Sundgren. They have approximately half the 63m2 cross-section of the bigger tunnels and a height of 6.2m with a 5.2m width. Cross-passages are also being driven to link the main and service tunnels at 500m intervals.
Skanska’s US$171M contract also includes a number of fairly large bridges, two of them just over 100m in length, and some embankment work. Running from Lake Offer to the Bjällsta River, this section is 32km long, making it the biggest contract on the line, which has otherwise been broken into relatively small sections for letting. But it made sense to put the two tunnels into the one package as they are just 3km apart on the highest section of the line, some 230m up. Economies of scale and organisation would apply, says Sundgren.
The contractor was given an outline design specification for the project but carries out detail design work itself under the contract, using sister company Skanska Technik for the detail design work. Scandia Consult is the client’s consultant and produced the tender design.
Geology and support
Like the rest of Sweden the region is primarily one of hard and ancient rock, all part of the Baltic shield and with a geology dating back billions rather than millions of years. The northern Baltic coast is a little unusual for Sweden however, explains Skanska geologist Linda Lindström with a preponderance of Grey Wacke hard sedimentary rock. “It is about 1.8bn years old and has had one or two metamorphoses. It is penetrated with pegmantite and there has been a major granite intrusion,” she says.
The rock is tilted at about 70°-80° – “that probably happened about 1.4M years ago” – and has a large number of fracture and shear zones, frequently filled with sediments like clay/graphite mixtures and sand and silt. “These can be anything from 10mm wide to over 1m,” she says. “I think most were formed when the tilting occurred.”
It is these zones that Skanska says have caused significant difficulties in progressing the work, slowing up drilling and causing deviations sometimes on the drill pattern as bits have caught in the discontinuities. Particularly in the more northern Björnböles tunnel, which overall has lower cover than the Namntal, the fractures and fissures have been a significant factor in slowing progress says Skanska project manager Kjell Isaksson.
It means not only slower drilling but also the need to install much more rock support than expected he says. “It is a lot worse than we supposed from the original information,” says Isaksson.
“We thought it would need only a class one support for the majority of the tunnel, around 90% of it, but out of 10,705m so far we have only used class one on 338m – that is around 3%.”
The design allows for four main classes of support with a special category for specific situations. “There were two other additional heavy classes for the areas of low overburden near the entrances” adds Isaksson. Class 3 has been used for 56% of the tunnel he says and class “two and half” the second category with additional spot bolting – for 24% while the heaviest was used on 15% of the length.
Tunnel construction
Skanska has worked the tunnels with two faces at either end for the south tunnels and an additional four faces starting approximately in the centre from an access adit, working north and south. On the northern tunnel there were just six faces initially, starting from the south and again from a central access point working in each direction. A final two faces have been added in recent months as part of efforts to catch up delays.
The fourteen faces were drilled using six Atlas Copco rigs, three older Rocket Boomer 353 rigs and three new XL3C computerised machines. “There was also a WL3C rental rig being used,” adds Atlas Copco local representative Stig Fredriksson who has regularly visited the site throughout the work, working closely with onsite Atlas Copco maintenance staff.
Faces were mostly drilled to 6m and gave a 5.5m advance. For mucking out, and follow on rockbolting and shotcreting, the job was divided into five main zones, with three teams from subcontractor Euromining for removing the spoil. They had a Volvo 330 and two Caterpillar 988 loaders. The machines were allocated after a morning progress and planning meeting according to need, making the 3km-4km journey between different tunnels as required.
“It was fairly straightforward early on,” says Skanska production engineer Mattias Widenbrant “though the logistics took a little more organising further in.”
Drilling crews work around the clock, following a decision to put on a night shift some time back, again in an effort to catch up on schedule and recover some of the contract delays.
Spoil has been stockpiled at various sites in the area and some of it is crushed for the outside embankments and as ground replacement for boggy areas on the external works. “But part will remain until the next local road job requires it,” says Isaksson “because we cannot use all of it.” The rock quality is not sufficient for the stringent demands of the top ballast layers for the track he explains.
Water control
Some of the most difficult work has been in the follow on grouting. For rail purposes leakage has to be kept to minimum and an initial target of 7l/100m/minute was set for water ingress.
This has since been revised says Isaksson, to a 20l criterion, although it has not been passed by the Swedish “Water Court” which has to ratify an application from the client for changed levels. On an informal basis, following indications that the decision will be approved, the contractor is allowed currently to work to a 14lt/100m/minute limit.
But the tight limits meant grouting was particularly difficult early on says Widenbrant, responsible for grouting and shotcrete work. The contractor had anticipated being able to work with some eight boreholes, primarily in the ceiling of the tunnel where stopping the leakage is most important, but in many areas was forced to use up to 22 boreholes around the entire perimeter. These are up to 24m long.
“The fractured zones have been harder to grout and we had water inflows of 50l/minute in some places,” says Widenbrant. “With so much water coming in we could not push in the grouting plugs by hand and had to hold them with the machine booms.”
The clay in some fissures has been particularly difficult, he says, because it will only allow a maximum 45 bar grouting pressure before breaking through. A change in the grout cement used helped progress, with Rheocem 650 from UGC BASF having better penetration and going off slightly faster.
Waterproofing also requires a drainage lining in many sections of the tunnels if there is any dripping. This is not because of icy conditions causing build-up of dangerous icicles – though that can be a problem near the tunnel entrances – but because of erosion. Dripping literally wears away the catenary. “I was surprised, because rain is not problem on power lines outside” says Isaksson. “But the unvarying position of a drip means long term damage can build up over years.”
Any drip with a rate greater than once a minute has to be guided down the tunnels walls to the track-bed drainage using waterproofing panels. These are 40mm thick foam panels from Skumtech in Norway, which cover the tunnel wall to 400mm below the gravel tunnel base. The panels are 8m long and 2.5m high and overlapped for as much of the tunnel length as required before being shotcreted.
Contiguous lining with the foam is also carried out at the tunnel’s entrances where cold air can affect the tunnel. In this region that could mean -30°C, though so far this winter a freakishly warm -4°C has been recorded.
The cold air has whistled through the southern tunnel since hole through but small lengths have deliberately been left unblasted on the Björnböles main and service drives in the south until completion of the north end drives. “It means we can keep significantly higher temperatures inside the tunnel for completion of work,” says Isaksson.
Current progress
Apart from waterproofing, there is also completion of the gravel track bed to be done and assorted finishing works.
“We completed most of the external works, bridges, embankment and grade level in late October last year,” says Isaksson. As T&TI was going to press, there was just 170m left of the main tunnel to blast and 120m on the service tunnel. “Drainage is in progress on the Namntal tunnel and trackbed following on and we have just begun drainage on the Björnböles,” he says. There is also an element of the electrical work to be done.
“The track laying contractor begins works in August on the Namntal and we finish the work on the Björnböles a bit later, in time for the track contractor to start in the middle of October this year.”
Originally the tunnels were due in spring last year with the external works completed as they were. “But there are contracts on either side of us which are not ready yet, so the overall timescale is not affected by our completion,” he maintains. “I think tracklaying is about the same as it was originally.”
Undoubtedly there will be a protracted discussion to follow. Skanska maintains that the tender information did not prepare it for the difficulties it encountered. But client Botniabanan simply comments that it thinks the contractor did not mobilise fast enough.
Isaksson adds that, at the very least “they are getting two very good tunnels.”
And eventually a very good railway, it is hoped, once track and electrical contractors to move in. Trains should be running on this section by 2010.
Alignment of the southern section of Sweden’s Bothnia Rail Project Figure 1 – Map Improving connections through Sweden
The new Bothnia line will give some 350,000 of Sweden’s 8M population a much needed improvement to their lives by linking them together. Transport has been awkward between the string of coastal towns along the northern Baltic coast, either by winding road or sea vessel, and new 250km/hr high-speed trains will almost halve travel times. Connections to high-speed lines further south from Sundsvall will also cut times to Stockholm.
The line will also improve freight links to the giant Kiruna iron ore mines in the north, and to increasingly important long-distance links through Norway, Finland and Russia for container traffic. Until now these trains ran through the unpopulated inland forests, the main line sited there when it was built in the 1900’s because of fears that the Russian Tsar’s battleships could bombard trains. But the route is mountainous and winding, with trains limited to 1000t capacity; on the new coastal flat 1400t can be pulled. A second stage project for another 200km Bothnia section northwards would improve this even more, if it gets the go ahead.
The first new line runs from Nyland north to the university town of Umeå and will open in sections; an initial coastal link from the town of Örnsköldvik at the midway point to Husum northwards should see test trains this year and be open for freight next year. It will service a large paper mill and generate initial revenue by routing trains through to the existing main line.
The line south should open in 2010 and the last part to Umeå is currently expected to take until 2011 because of environmental holdups.
There are fourteen other tunnels on the route, though most are simple and relatively short at up to 600m. There are also extended areas of rock cutting drill and blast activity and 140 bridges and viaducts including one of 1000m length over the Ångermanälven.
Works also include seven stations and a major 7km diversion around the biggest town on the line, the 112,000 strong Umeå. Some 22 double tracked areas will allow passing of trains without disrupting timetables.
The special Botniabanan company was set up to carry out the US$1,877M (SEK 13,200M) project at the end of the 1990’s. It is 93% government owned and 7% by the local municipalities and funds the work with long-term bank loans.
