The Matinkylä station is the end station of the West Metro. The bedrock in the Matinkylä area is mainly densely jointed granite with open horizontal fractures. The station hall is 23m wide, 9m high and 230m long rock cavern. The span of the track switching halls is 21 m, the height 9m and the length 100 m. Due to the numerous weakness zones, the large span, the thin rock roof and the horizontal rock stress field, the numerical analysis was carried out consisting of both 2D and 3D numerical analysis. The analysis showed that the maximum displacement is expected to be about 20 mm. An extensive monitoring system was installed. During the construction phase it was noticed that the closure of the walls was about 8 mm, the maximum rising of the ground surface was about 15 mm, cracks appeared in the shotcrete at the roof arc and leakages appeared due to the rock displacements.

1. Description of the West Metro

The West metro is an extension of the Helsinki metro line to the city of Espoo. The length of the tunnel line is 13.9 km with two parallel tunnels excavated in rock (Fig. 1). The rail tunnels are connected to each other at the intervals of 100m to 150 m.

Nine access tunnels have been made for construction and maintenance purposes and fifteen vertical shafts for smoke exhaust, pressure equalization, emergency exits and technical installations. All tunnels shafts and stations are excavated using the drill and blast method, and reinforced with rock bolts and shotcrete.

The Matinkylä station is the western end terminal station. The Matinkylä contracts covered the excavation of two 1.8 km long metro tunnels, a service tunnel, two track switching halls (located before and after the station hall) as well as a station including passenger and technical shafts of the station, two shafts along the line, and open excavations for the station.

The span of the station and track switching halls is about 23 m, the height of walls is 6.3m and the total height varies from 9m (track switching hall) to 12m (station hall). Each one of these halls is 200m long. The excavation was made in three stages. The width of each stage rage from 7 to 8mand the maximum length of each blasting round was 5 m.

The platform will be approximately 30m below the ground level, and there are escalator shafts located in both east and west end of the station.

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