[11/16/2007]
Anna has started the tunnel boring again
After more than two months of service and maintenance one of the two tunnel bore machines in the Citytunnel started to bore again.
– “The second phase between Triangeln and Malmö C, will involve sharper turns and more water than before, but we are well prepared,” says Johan Brantmark, assistant project manager in subproject Tunnels.
When Anna goes back to work in the limestone rock of Malmö, she does it with brand new set of “teeth”. All the cutting discs and scraping irons have been exchanged in the cutter head. Some welding works have also been done on the shield.
The last phase is a little shorter than the first phase. It was about 2,7 kilometres from Holma to Triangeln and it is 1,9 kilometres to Malmö Central station. But the last phase includes new challenges.
“We will bore in tighter turns which are very demanding for the crew of the TBM. They must keep the direction and construct the tunnel rings with the same precision and accuracy as they have done so far,” says Johan Brantmark.
“When we close in on Öresund the limestone rock will also contain more water and we are constructing the tunnel under the channels of Malmö. These circumstances will make the process a little more complicated. But the contractor MCG has great knowledge in tunnel boring and along with our experience from the first phase, I think we are well prepared.
The tunnel distance to Malmö C concern more people who live in Malmö because the machines will bore under more residential houses than before.
“Experience from the first bore phase is that the boring will be noticed. There will be structure-borne sound, which are vibrations that transmit up to the buildings above. But it is difficult to predict how strong the structure-borne sound will be. It is a question of limestone rock hardness, which varies, and how the houses above the construction are built,” says Johan Brantmark.
“The boring will be noticed for a few days while the TBM is passing. We do not want anyone to be taken by surprise. We inform those who may be affected by structure borne sound in advance, says Johan Brantmark.
The second tunnel boring machine, Katrin, will start boring in a few weeks. She is now going through service and maintenance in the rock cavern.