Holma

The hub of the tunnel construction.

MCG’s largest site is in Holma, in southern Malmö. In many ways, the 230,000 m2 area is the heart of the construction process. This is where the tunnel boring machines started their work. This is where the excavation material comes out and this is where the concrete for the tunnel will come from.

The ramp, (the entrance/exit for the tunnel), and the cut-and-cover tunnel are being built at the same time as the support and maintenance units for the tunnel works. The two huge tunnel boring machines (TBMs) were assembled in the trench, before this part of the tunnel was covered and backfilled.

The cut-and-cover tunnel

Where a tunnel is near the surface, it can be simpler and more cost-eff ective, to dig an open trench. Then the tunnel can be built in situ or from pre-abricated sections. Afterwards, the tunnel is covered. The first 360 metres of the tunnel at Holma are built in this way. Most of Holma’s electricity, telephone and water supplies will be carried over the trench on temporary bridges, until the work is finished.

Sealing

As the tunnel boring machines work their way through the limestone rock, the tunnels are sealed and supported permanently by lining the walls with pre-fabricated concrete segments. This is done inside the watertight shields of the tunnel boring machines. This lining technique prevents water getting in.
It was used successfully, for example, in the English Channel tunnel and the Great Belt.

Concrete quality

The quality requirements for the concrete are rigorous. There are special demands caused by the salt water from the Öresund and temperatures that hover around freezing point in winter. The concrete in the tunnel must also resist a temperature of up to 1300 degrees – for three hours. Concrete
does not burn, but when the water in the concrete evaporates, the concrete may burst. Ultimately, the concrete must last for at least 120 years – an impressively long time.