Author: Oskar Hannler

Drilling and blasting work is currently being performed at a total of 61 underground fronts, in various directions. This concerns the building of track tunnels where the trains will run, but also service tunnels and connecting cross tunnels.

A front is the point at which the machines are about to penetrate the rock, in order to first seal the area around the tunnel and then drill holes for the explosives. After the blast, the front will have moved forwards a few more metres.

Here you can read more about all the different tunnels and spaces we are building, both longitudinally and transversely.

Where the most – and least – blasting work is taking place

One of the areas where construction is taking place on the most fronts at the same time is eastern Södermalm, where tunnels are being drilled and blasted at 8 fronts towards both the north and the south. The southbound tracks branch off towards Söderort and Nacka, which means that five tunnels are being worked on at the same time (track tunnels and a service tunnel).

In Barkarby, there are currently only three active tunnel fronts. This is because the space that has been excavated almost reaches the whole way between Akalla and Barkarby. Some blasting work remains to be done in some of the existing tunnels at Akalla station. This work will continue throughout 2023.

Number of fronts right now:

Here you can see how many tunnel fronts are being built at each location, and you can also click through to the progress map, where you can see how much has been blasted out of each section:

Blue Line to Barkarby Number of tunnel fronts: 3

Progress map

Yellow Line to Arenastaden  Hagastaden: 8 Södra Hagalund: 3 Arenastaden: 1 (work tunnel)

Progress map

Blue Line to Nacka Sickla: 5 Järla: 5 Nacka: 6

Progress map.

Blue Line to Söderort  Gullmarsplan: 7 Sockenplan: 3

Progress map

Blue Line to Södermalm Blasieholmen: 3 Östra Södermalm: 8 Hammarby Sjöstad: 5

Progress map

Expanded depot in Högdalen 4 fronts

Progress map

Metro to Älvsjö Planning for the new line is underway

“The public spaces visible to passengers are really only a fraction of what’s being built,” Malin Harders explains.

All the new metro lines and stations will be built underground, and there is an entire system of tunnels and spaces needed to enable everything to work as it should.

“When we build the rail tunnels, we need space for more than just the trains. We also need space for various types of installations, such as for electricity and lighting, as well as for a bunch of concrete structures. This is why the tunnels are blasted larger than their final size.”

Like an underground house

According to Harders, building a station is a bit like building a house, only below ground. The first construction phase involves blasting out large caverns. Then there are large numbers of concrete structures to be built, some of which are cast in situ while others are prefabricated. Stations usually have three levels: the platform where you wait for the trains, then the escalators to the mezzanine level, and from there the escalators up to ground level.

All stations need special rooms for technical installations.

“The tunnels are also equipped with a range of installations and signalling systems that take up space. We also build walkways inside the tunnels. These provide access to service tunnels running parallel to almost all rail tunnels, which can be used to evacuate in an emergency.”

Different types of tunnels

The service tunnels are smaller than the rail tunnels and are asphalted so that service vehicles can use them. This is a type of tunnel not found in the existing metro system but that is needed now due to new legal requirements.

To be able to move between the rail tunnels and the service tunnels, cross tunnels are also built at regular intervals along the entire length of the tunnels.

The stations also need escalator shafts. Moreover, alongside most escalators, there should also be space for an inclined lift.

Like a bicycle pump

Pressure relief shafts are being built at all stations as well. These are needed to equalise the air pressure on the platform.

“A metro train running through a tunnel acts a bit like a bicycle pump. The train is constantly pushing the air in front of it and that air has to go somewhere, otherwise you’d be blown over when standing on the platform. We also build ventilation shafts to route air up or down between the tunnels and ground level for ventilation,” Harders explains.