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Helsinki Central Railway Station

A landmark in the center of Helsinki, the railway station was built in the early 20th century and founded on wooden piles, as was common practice at the time. This method is no longer used due to the risk of pile decay. If the tops of the piles remain below the water table in an oxygen-free environment, decay does not occur. However, if the groundwater level drops below the tops of the wooden piles, decay begins. Due to the risk of decay, the groundwater level in central Helsinki has been monitored since the 1970s, and the water level has been maintained by infiltrating rainwater into the ground.

Geotechnical design tasks related to changes in the operation of the railway station have been carried out in phases across the entire building. From 2017 to 2021, a hotel was constructed in the eastern wing, and since 2020, modifications have been made to the western and southern wings.

At the beginning of the design process, it was necessary to determine whether the old wooden piles could be utilized. Over the years, extensive studies had been conducted on this subject, and the data indicated that, apart from surface decay, the wooden piles were in relatively good condition and had not deteriorated over the past 30 years. No settlements had been observed either. Additional samples were taken to further assess the condition of the piles.

The design solution was to utilize the existing piling and to ensure its preservation by constructing groundwater management and monitoring systems. New heavy structures and the new extension were founded on driven steel piles. Temporary excavations extending below the groundwater level were made watertight using steel sheet piles and working concrete. The construction work was successfully completed without lowering the groundwater level or causing damage to the surrounding environment.

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