Crown Bridges alliance, Helsinki
A former industrial area, the Rotermanni block in central Tallinn, was transformed into a modern shopping, entertainment, corporate and residential area.
We constructed a two-level parking hall in this culturally and historically valuable project where both the earth and the old structures above ground are fragile. The parking hall was constructed under three business, office and residential buildings which were still under construction. Some of them had old protected facades.
The area, only 500 metres from Tallinn Bay, is a former seabed with soft, weak layers of earth. In addition, the groundwater level is unusually high, only 1.5–2 metres below ground.
The base slab of the parking hall is almost seven metres below the groundwater level, which means that the enormous water pressure had to be considered during the construction. We installed permanent sheet pile walls around the excavation, which was the first time this has ever been done in such an underground parking hall project in Estonia. We also had to consider how we would keep the excavation dry.
We had to keep the vibration as low as possible in order to not damage the buildings in the vicinity. We used a low-vibration compression method when installing the sheet piles and monitored the situation by installing vibrographs in the nearby buildings.
An old 53-metre chimney in brick directly above the parking hall required special measures as well. We transferred the chimney’s load to strata that would bear the load better with excavation piles that also functioned as a solid retaining wall.