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The E4 Stockholm Bypass will be 21 kilometres long, and just over 18 kilometres of the E4 Bypass is in tunnels. One particular challenge is in the southern section, where we are blasting tunnels in rock that is beneath Lake Mälaren.
On this page you can read about how we are working in the rock as we construct what is known as the Mälaren Passage, which runs between the shore in Sätra shipyard and the island of Kungshatt.
Mapping and checking the rock
Just over 18 km of the 21 km section of the E4 Stockholm Bypass is in tunnels. The longest section of tunnel runs between Kungens kurva in the south to Lunda in the north and will be 16.5 kilometres long. Before we started work on the tunnels for the E4 Stockholm Bypass, we conducted preliminary studies and analyses. We produced a forecast of the rock’s formation, and then selected the method and technical solution used for us to blast the tunnel. In this project, we give top priority to the safety of the environment and our tunnel workers.
We are prepared at all times to change our approach based on changing conditions, such as changes in the quality of the rock. We therefore map and assess the rock and its quality in the tunnels several times each day as work proceeds.
One method of performing checks is to drill a core, a cut-out, out of the rock where the tunnel is to be created. This core tells us what it looks like inside the rock. It helps us to determine how we should reinforce the rock and adapt the blasts. The method is known as core drilling.
One special challenge when we build beneath Lake Mälaren
There are challenging passages in the southern section of the tunnels in the E4 Stockholm Bypass, where we are blasting the tunnel beneath Lake Mälaren in three places. One place is between the shore in Sätra shipyard and the island of Kungshatt. What is known as the Mälaren Passage is 200 metres wide and is the first place where the E4 Stockholm Bypass passes through rock that is underwater.
In the rock beneath Lake Mälaren there is a well-known regional weakness zone. This is an area about 70 metres below the water’s surface. The inland ice and other large movements that have affected the area have meant that the rock there is of varying quality, with features including cracks with clay in some passages.
The passage beneath Lake Mälaren between the shore in Sätra shipyard and the island of Kungshatt is 200 metres wide.
Because of the weakness zone, we need to reinforce the rock with particular care and proceed a little more slowly. We are constantly adapting our work method so that we can build the tunnel through the weakness zone in a safe, secure way. This means the work will take a little longer.