The City Rail Loop project is a planned urban railway line for commuter trains under the Helsinki city-centre. The triple tunnels run under the very densely-built city-center peninsula. Three underground stations will be built along the new looped railway. The Hakaniemi station will be constructed, with thin jointed rock cover, under extensive existing aboveground infrastructure. The station connects directly into existing underground metro station and adjacent buildings. During the construction these existing facilities should be able to operate normally. In addition, major brittle fault zones intersect the planned station. These pose interesting challenges in the project that were dealt with rock mechanical analysis including the study of the effect of the stress state and excavation sequencing. The analysis were used to guide, and advise the engineering design and layout planning of the station caverns.
The City Rail Loop project, (named 'Pisara'), is a planned urban railway line for commuter trains under the Helsinki city-centre (Figure 1). The railway is roughly 8 kilometers in length, and is a loop-shaped (Pisara = 'droplet' in Finnish). The plan calls for two rail tunnels and an adjoining service tunnel that runs parallel to the rail tunnels. In total, about 25 kilometers of drill and blast tunnels will be excavated. This triple tunnel system runs under the very densely-built city-centre peninsula, which is surrounded by the Baltic Sea on three sides. The tunnel will pass under the sea at a narrow strait on the city's east side. The detailed planning stage of the project takes place in 2015–2017.
Three stations will be built along the new looped railway. The Hakaniemi station is constructed under the extensive existing infrastructure. There is an existing metro station in the immediate vicinity of the planned underground downtown to which the planned Hakaniemi station will connect via underground passages. During the construction these existing facilities should be able to operate normally.