Bedrock gives way to the tunnel

The west metro project has reached its most challenging phase: rock blasting. The project is well on schedule and metro traffic is expected to start as planned towards the end of 2015.

The first phase of the west metro project, the environmental impact assessment phase, was carried out in 2002. This was followed by a cost assessment, geological ground survey, locating the metro on the city plan and detailed project plan. After that, blasting began in Ruoholahti 2009.

Rock blasting is the slowest phase, and work done in the middle of a city slows the project down even more since it cannot be done at night and the blasting must be timed so as not to disturb the residentrs or damage the environment.

Almost all access tunnels and about four kilometres of metro tunnel have now been excavated. Some of the access tunnels wil become service tunnels, and the rest will be landscaped.

“As blasting progresses, test boreholes are drilled, into which water is pumped under pressure. If the rock absorbs more than 60 litres of water per minute, it is so friable that it must be stregthened with injected cement, ” explains Länsimetro Oy’s managing director Matti Kokkinen.

Work on stations and tracks can begin when the blasting is completed, in the summer of 2012. Track work will begin with the substructure, followed by surface structures and track laying. At the same time, the stations will be fitted with 56 different electrical systems, from lighting to track power supply and smoke detection systems.

The last eight months are reserved for the test drives, with the metro line’s external areas, such as escalators, platform areas, station buildings and so on, being completed simultaneously.

“Only one per cent of the work we are doing will be visible above ground,” says Mr Kokkinen.