The Northern Link (Norra länken)

The Swedish Road Administration (Vägverket) are planning to build The Northern Link in Stockholm. In connection to that they need to produce some information material for the general public. Something which can show what the affected areas might look like during the building process, as well as describe some of the techniques used. Here below I am showing some of the illustrations I produced for their information material. For complete and official information you are referred to their website www.vv.se.

Roslagstull The Northern Link can in short be described as a number of underground tunnels in which the major part of the passing through traffic will be handled. Here, at Roslagstull, the planned tunnel will pass just a few meters below the ground surface - stretching from the picture's bottom left corner to the top right. At this particular location they found it practical to dig an open air shaft down to the tunnel. In order to not disturb the traffic too much they decided to build two temporary bridges straight across the shaft, letting the traffic flow as usual while the tunnel is being built underneath it.

The National City Park at Bellevue must remain untouched during the construction. Because of that they have planned to dig a shaft right outside the park. From that shaft they would then dig under the park a tunnel which would emerge on the other side of the park, leaving the surface unaffected. The dashed line behind the building crane is showing planned direction of the tunnel. Please note the tree in it's "balcony" on the left side of the shaft. The tunneling must be performed with the greatest caution, leaving the environment as untouched as possible. Because of this they planned to perform some tests with different digging methods to establish what would be the optimal solution. One of these methods is called "Pipe Jacking".

Pipe Jacking Four powerful and synchronized jacks are hoisted down the shaft. Their task will be to push the reinforced concrete pipes into the shaft wall.

While the pipe is being pressed, a machine is digging it's way in the end of the tunnel. The dirt is being removed through the pipes in small railed wagons which are hoisted up to the ground level. In front of the first pipe, there is a steel shield which is protecting the digging machine from gravel and possible cave-ins.

When one pipe is fully mounted, the jack is put in reverse, leaving room for a new pipe to be lowered into position. Then the jack can continue to push the pipes further into the shaft wall.

Pilot Tunnel The method tests also includes the digging of a Pilot Tunnel. For this they will not use pipe jacking. Floor, walls and ceiling will consist of narrow steel sheets (blue) supported by bow-shaped girders (yellow).

A Thin steel sheets are being pressed into the shaft wall, giving shape to the tunnel profile. The first pair of girders are mounted into it's place. The tunnel face is being supported by a log wall which continuously will be moved forward as the digging is progressing.
B The digging is continuing and new girders are being erected as far as the steel sheets reach.
C New sheets are being pressed into place, leaving some over-lap to the previous sheets. The log wall is preventing the tunnel face from caving in.

D After approximately 15 meters the digging is finished and the log wall is being disassembled.
E Several coats of shotcrete is sealing the tunnel's ceiling, walls and floor. After that they can evaluate if the digging method is suitable for the characteristics of this type of soil.

Jet Grouting A lot of the work will be performed in waterlogged ground because of the high groundwater level. One way of keeping the water away from the digging area is by using Jet Grouting. A pipe is being brought down in the ground. At a certain level the pipe is stopped and a special "milk shake" of cement and water is sprayed with high pressure from a number of nozzles at the tip of the pipe. At the same time, the pipe starts rotating and is slowly being brought back towards the surface again. At a certain level the flushing is stopped and the pipe is pulled all the way out, leaving a rough underground "cylinder" of cement. The pipe is moved and the whole procedure is repeated so that the two cylinders merge under ground.

Underground Tub Using high precision, it is possible to build a whole plate of these merged cylinders under ground. See arrow at bottom left. Along the plate's edges you can build higher cylinders which will form a kind of palisade of cement pillars. When all four sides of the plate has a wall of joined pillars, you can start excavate soil and water from the area, leaving an underground cement "tub". After additional sealing the tub will be able to keep the ground water away from the digging area.

Material: The customer supplied a number of text documents, pictures and building plans, explaining the different techiques and drilling details.
Tools: Scanner, Illustrator and PhotoShop.

Click on any of the images to return