«Laila» drills her way under Oslo

In a large rock hall underground at Stubberud, we are waiting for a train. The train will take us to the tunnel boring machine «Laila», which is drilling one of the tunnels for Oslo’s new water supply. The City of Oslo’s Water and Sewerage Department is the client. 

Personnel, equipment, and concrete elements are transported to the machine by train. The masses that are excavated are removed by conveyor belt. Both train tracks and conveyor belts must be extended as the work progresses. 

By mid-June, the tunnel boring machine (TBM) had drilled one kilometer on its way between Alna and Huseby.

«So far, we have made progress of 10 meters per day. The goal is to work much faster, but a lot of injection has limited us,» says Fabio Moizo. 

He is the TBM Manager and works for the joint venture AF Ghella. Fabio has previously worked with TBMs in Brisbane, Australia, and on the Follobanen. Now he makes sure «Laila» is working as expected. 

At the front of the tunnel boring machine is a drill head with a diameter of just over seven meters. In the drill head, there are openings for drill strings. Here, long holes are drilled in a shield formation for the injection of cement slurry. This is done for sealing and stabilizing the rock before the actual drilling. 

As the work progresses, the tunnel is lined with concrete segments. The concrete segments have six different patterns and are equipped with waterproof seals. The elements are locked into each other, and then fill material is injected into the layer between the rock and concrete elements. The result is a finished tunnel that meets strict requirements for water intrusion. 

The tunnel boring machine is actually a 200-meter-long tunnel factory. The train arrives at a part of the TBM called the back rig. Here there are offices and dining barracks. 

We move forward along a platform that runs along the side of the machine and come to a section that resembles a workshop. This is the part where the conveyor belt is extended as the tunnel gets deeper. A little further ahead is the operator cabin from which the large machine is controlled. 

15-16 people are working on the TBM this day. They make sure that «Laila» gets a little closer to the goal, which is a mountain hall at Huseby. Here ends another tunnel, namely the 19-kilometer tunnel that will transport raw water from Holsfjorden. At Huseby, the water will be treated in a large underground water treatment plant. The water is then distributed in pipes through the tunnel system that JV AF Ghella is in the process of building. 

Presently, lake Maridalsvannet supplies 90 percent of Oslo’s population with drinking water. A failure in vital parts of the system can have serious consequences. Therefore, a complete backup water supply is now being built. The entire facility is to be completed in 2028. 

• This article was originally published in July 2024.