Swiss Re Next – building on the bed of the lake

The Swiss Re Next project is being followed by employees in Zurich with great interest, and it comes as no surprise that the two information events held in Spring 2013 for the project were fully booked within a very short time. At these events, civil engineers and representatives from the architect's office and building management provided a fascinating insight into the specific challenges on this construction site.

During the Swiss Re Next project, civil engineers will really have to get to grips with the location. After all, the building area has been shaped by the flow of millions of years of water and glaciers as well as climatic change, and until the end of the 19th century was marshland.

As the original building is located on the actual bed of the lake, the civil engineers had to come up with something special when building there in the 1960s. An important, yet invisible part of the building is the excavation enclosure. The strong, approx. 60-cm thick trench wall made from reinforced concrete is designed in the shape of a giant sump, which surrounds the ground around the building being demolished and extends 25 m into the construction ground.

The new development currently being built and its basement floors reinforce the trench wall against the adjacent ground. The trench wall is of superb quality and is also being used as the excavation enclosure for the new building.

The original aim was to fill the bottom floor of the building with concrete, so that the weight of this would distribute the greater load of the new building and there would thus be no reason to install new piles. Other measures have had to be found however, as extra space had to be created for approx. one hundred additional parking spaces. There are now plans to create a pile foundation with a new foundation slab.

Ensuring the balance

The weight of the building decreases continuously as it isdemolished and will increase again during the construction of Swiss Re Next. To prevent the building from floating and to minimise settling, the water table within the trench wall is constantly adjusted using 20 wells with small filters. As the existing building will be completely demolished within the trench wall, a new support solution is required. A strut platform will also be created within the enclosure.

Construction and demolition taking place simultaneously

The new foundation slab will be constructed at the same time as the upper floors of the existing building are being demolished. During this process, the strut platform foundation will be created from the newly built parts. This will help to simplify later building processes and thus save time. Once the building has been demolished to street level, the strut platform will be installed. Only after this has taken place can the remaining bottom floors, not including the foundation slab, be completely demolished. The rest of the existing foundation slab will subsequently be demolished in stages, the pile foundation created and the new foundation slab built.

Pollutants and noise emissions

The original building was constructed at the end of the 1960s with building materials that were state-of-the-art at the time. Some of these materials, e.g. asbestos in fire protection insulation, heavy metals in pipe systems as well as various emollients, are now known to be pollutants. An initial phase will involve these materials being removed from the building in line with the safety measures now in force.

Every effort will naturally be made to keep noise emissions and vibrations as low as possible during the demolition. As a result, demolition hammers will not be used for this work; instead, most of the work will be carried out using cutting tools. Furthermore, self-tapping foundation piles will be used for the pile foundation, instead of driven foundation piles.

Two years building the lower floors, then the only way is up!

The demolition of the original tower should be completed in time for the 150th birthday of Swiss Re on 19 December. Afterwards, work will be carried out on the lower floors until the end of 2014. The upper floors will subsequently be built and the interior fittings installed by 2016. If everything goes according to schedule, the building will be ready for occupation in summer 2017. During the course of the project, information events are being provided on various issues concerning Swiss Re Next. The next event is expected to cover the topics of demolition, recycling and the clean-up of pollutants and will be held in autumn 2013.