During the spring and summer, freezing has taken place by pumping coolant into approximately 40 meter long pipes in the tunnel under Mårtensdal. The area consists of soft rock, and in order to be able to blast more safely, the rock is therefore frozen to at least -5 °C.
– We have reached about a third of the distance in one tunnel tube and have just started the other, says construction manager Mathias Tisjö Brinck.
This video shows the tunnel and the frozen mountain. Notice ice crystals on the tunnel walls:
It has been a bit of a slow start to this section as we had problems getting the shotcrete to stick to the frozen surface. Now, however, we have found a method that seems to work and hope that the rest will go on without problems.
Unattended train operation means, for example, that no driver’s cab is needed, but the passengers can see the tunnel during the trip. The solution already exists today in many places in the world, with Copenhagen being the closest.
– Exactly which trains we will buy in is not yet clear, but what we do know is that they will be customized according to our needs. Both in terms of number and furnishings, we are planning for the expected number of passengers by 2060. An advantage of unattended train operation is that it is easier to add more trains if necessary, says Johan Brantmark, director of the metro to Älvsjö.
Giant drill
The new yellow line between Fridhemsplan and Älvsjö will be separate from the rest of the metro system. That is why it can be built in a different way.
– The constructions that are underway now are all extensions, where we add some stations to existing lines. Then we need to build for the same type of train and the same signaling system. On the Yellow Line, we can do things differently – and then we must take advantage of the technological development that has taken place, says Johan Brantmark, director of the metro to Älvsjö.
In addition to unattended train operation, the metro to Älvsjö will be built using a different technique than the rest of the metro system – it will be bored with a large boring machine.
Smaller stations
The stations will also be smaller, with platforms 75 meters long instead of today’s 145 meters. This will allow us to run shorter trains with more frequent departures as it is more logical and causal and make the total travel time and waiting time shorter.
About 250 unique concrete structures will be built along the four-kilometre stretch from Akalla to Barkarby. These include tunnel walls, utility buildings, pump pits, station buildings, escalator shafts, ticket halls and ventilation towers above ground.
“The production principle is the same for all structures,” says Christer Vestergren, construction manager for concrete and steel structures.
Christer Vestergren.
The wooden formwork is built, the rebar is put in place and the concrete is poured. After three or four days, the concrete has hardened and the formwork can be removed.
“We don’t pour concrete where doors, gates or pipes are to be installed. In such places we create cavities, voids inside the formwork.”
A concrete wall with openings for wiring and doors, for example.A ventilation tower for the new metro has already been erected at the old airfield in Barkarby.
40 concrete works under way
The rough concrete surfaces might not look that great, but they will rarely be visible in the finished metro. However, concrete provides the foundations for the escalators, ticket halls and platforms to be built later on.
While the last tunnels are being blasted for the Blue Line to Barkarby, some 40 concrete works are also under way. The next phase will then begin: kitting out the stations and tunnels with, for example, power, tracks, escalators, lifts, floors and other surfaces.
“But we won’t be finished before then. There will be some overlap in the work. That’s how the metro extension has been planned,” says Christer.
Getting all the pieces of the puzzle in place requires effective coordination, planning and logistics, which is a challenge when working in a tunnel under the ground. “In a tunnel, you always have a roof overhead. When building above ground, there’s usually a tall crane on hand to help move the heavy rebar. Getting the construction materials in place takes a lot longer in the tunnels.”
“You could say that we’ve already decided on the circulation, we know where the tracks will be. Now we need to decide on the best place for the depot, the heart that keeps the trains running,” says Johan Brantmark, head of the west department, which is responsible for building the metro line between Fridhemsplan and Älvsjö.
This autumn will see the start of a study on the best location, and there are many options on the table.
“We’re looking into whether the best solution is to expand an existing depot or to build a brand-new one. If we decide on a brand-new depot, it needs a good location close to the tracks, somewhere that’s easy for the trains to access,” says Henrik Unosson, project manager for the depot for the new metro line.
It’ll be several years before you even start construction, so why do you need to decide on the depot location so early?
“Finding a good location takes time, as does designing a depot. A depot needs to work well for many years, it’s a fundamental part of the system for keeping the metro trains running. We may need to make changes and minor adjustments to the new line. This is why it’s important to take our time looking at both the location and the design early and thoroughly,” says Henrik.
The procurements of all major rock contracts are now either complete or in progress. Those in progress are the Hammarby kanal, Slakthusområdet, Järla in Nacka, Södra Hagalund and the underground connection track between the depot in Högdalen and the tracks towards Farsta. All are expected to be completed in the spring of 2022.
– It’s clear that we’re on our way to a new stage. Focus next year is on procurement in construction, installations and BEST – everything that will make the tunnels to a metro, says procurement manager Iveta Sandström.
Iveta Sandström, procurement manager.
Approximately half of the total sum of procurements in kronor is completed. The charts below show what percentage is done, what is in progress and how many are left to do.
