OP Pohjola

The OP Pohjola headquarters is located in the Vallila district of Helsinki at Teollisuuskatu 1. The project involved expanding the current OP Bank Center’s functions by demolishing five buildings constructed in the 1980s, constructing four parking floors, and building new structures.

The excavation was situated between Teollisuuskatu and the operational bank buildings, with a depth of approximately 14 meters, 11 meters of which extended below the groundwater level. Lowering the groundwater level in the vicinity, even temporarily, was prohibited. The soil cover on the Teollisuuskatu side was up to 8 meters thick and was supported by a steel sheet pile wall. The project’s complexity was increased by the constrained space; it was not possible to move the street area’s utilities and cables farther away, and the sheet piles had to penetrate through a rocky surface layer by drilling.

The operational bank building housed the bank’s IT center, which imposed significant constraints on the excavation due to the need to prevent vibrations. The entire side of the excavation adjacent to the building had to be detached to mitigate vibrations, primarily through drilling and partially using diamond sawing. The rock was reinforced by bolting, and its tightness was ensured by grouting. On the eastern end of the excavation, the work extended under the existing building and into the inner courtyard. In these areas, the existing foundations were reinforced with bored piles. As a result of the work, the groundwater level did not decrease, and no movement was observed in the surrounding buildings.

As part of the project, a new type of rock foundation for the tower crane was designed at the request of the crane supplier. The demolition, excavation, and blasting phases were presented in a model. The temporary retaining wall was placed on a side-sloping rock surface that slopes sharply away from the retaining wall. The retaining wall, its anchors, and the rock surfaces were modeled to assess rock stability and the need for reinforcement.