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Civil engineering

Lyyra project

Rock mechanical design for the renovation and enlargement of excavations of an office block

Lyyra was and office block renovation project in the center of Helsinki. The block is located directly above metro tunnels and the northern entrance to the Hakaniemi metro station. Two ventilation shafts and one elevator shaft are part of the block. On the eastern side of the block there is a sewage tunnel and a tram line. On the northern side there is a water tunnel. During the renovation, block’s existing buildings, road and walkway structures were removed. A temporary corridor to the metro entrance was provided and the shafts were protected and supported. One of the ventilation shafts was originally connected to a horizontal tunnel near the surface, but the tunnel part was excavated away during the renovation while still keeping the ventilation flowing. New excavations extended to the boundaries of the block, which meant excavating adjacent to neighbouring building foundations. It was an absolute requirement that at no time during the excavation work can the operation of the metroline, sewage tunnel, water tunnel or tram be compromised.

Rock mechanical design and simulations were done to adjust the excavation and reinforcement sequence so, that work can progress safely and the rock mechanical impact to the environment is minimal. Impact of the building foundation loads was also studied. Among other things, displacements, joint shear/opening and strain on the designed and existing reinforcement structures were monitored during the sequential simulations and critical stages of the excavation were identified. Based on the simulation results, the excavation and reinforcement designs were adjusted accordingly. Simulation results also provided the reference values for on-site displacement and deformation measurements during the excavation.