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Civil engineering

Keilaniemi underground parking facility

A large underground parking facility below high rise buildings and next to and partly above an operating metro station at Keilaniemi.

A large underground parking facility was designed as part of the development of the Keilaniemi area in Espoo, Finland. The parking facility is located below high-rise buildings and next to and partly above an operating metro station. Simulations were performed in several stages and in tandem with rock engineering design. The designs were updated based on the simulation findings to limit the rock mechanical impact to the environment, mitigate risks related to the damage of existing structures and to ensure that work can progress safely. It was an unconditional requirement that at no time during the excavation work can the operation of the metroline be compromised. The optimized layout of the parking cavern consists of two main caverns, one auxiliary cavern, 5 shafts and two vehicle accesses.

The simulation geometry included the new parking facility, the existing metro station and tunnels and all the known foundation excavations of existing buildings. The rock surface topography was interpreted from surveyed outcrops, the existing excavations and from percussion drillings in the Keilaniemi area. Rock quality, rock joint orientations and properties were interpreted from systematic geological surveys from metro and core drillings through the volume of the new parking cavern. Intact rock properties were based on rock samples tested in the laboratory and the in-situ stress field on two stress measurements done during the design phase of the metro. Uncertainties related to the stress measurements were mitigated by running sensitivity analyses with variations of the stress field. Rock reinforcement structures were based on the designs of the metro and the new parking facility.

Numerical simulations were performed with 3DEC to describe the behaviour of a blocky rock mass. Natural jointing of the rock mass was implemented with a DFN. The simulated excavations and installation of the reinforcements of the Keilaniemi area were done sequentially according to the true order of construction as closely as possible. Existing and new building foundation loads were also considered. Several aspects were monitored during the sequential simulations including but not limited to displacements, joint shear/dilation and strain of the designed and existing reinforcement structures, while critical stages of excavation were identified. The excavation and reinforcement designs were adjusted accordingly based on the simulation results. Simulation results also provided reference values for on-site displacement and deformation measurements during the excavations.