The FAIR (Facility for Antiproton and Ion Research) particle accelerator is being built at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt. In the accelerator facility, particles will be accelerated to almost the speed of light and made available for basic physical research with outstanding intensity and quality. The central structure of the entire facility, as well as the northern facility area, is the 1.1-kilometre-long, 40-metre-wide tunnel for the SIS100 ring accelerator. It is complemented by structurally connected, above- and below-ground facility components, such as accelerator and experimental structures, operational and supply structures, as well as various transfer sections and storage rings.

PORR realised the construction of the circular accelerator tunnel, as well as nine above- and underground buildings for experiments, operations and supply facilities in the northern construction field. A total of up to 550 employees were involved in the project from planning to realisation, including PDE Integrale Planung, PORR Special Civil Engineering and PORR Structural Engineering. Thanks to the work carried out shoulder to shoulder, a wealth of expertise and the promise of ‘Construction from a single source’, PORR made a unique megaproject possible.

Different areas of expertise pose different challenges

It was not only the logistics of the large amount of earth that posed a challenge for this project. The large number of pipes required for the supply and disposal facilities of the particle accelerator also presented the pipeline construction team with new challenges. The planning of the piping system for the FAIR project followed the principle ‘form follows beam’ in order to design the system to be compact. Only necessary components were installed in the tunnel, while ventilation and exhaust pipes, as well as cable protection pipes, were laid outside in the sand bed. The high complexity resulted from the three-dimensional geometry and the quantity of pipes that had to be measured, welded and laid. A 3D model was used as the basis for the laying. Numerous lines were routed up to 13 metres high and embedded in compacted layers. 4,400 metres of HDPE wound pipe and 3,000 metres of heat-resistant C-steel pipe were laid for the ventilation. In addition, 100,000 metres of cable protection conduits were installed. Furthermore, around 2,500 electrical conduits were connected in a water pressure-tight manner, and expansion joints allowed for vertical displacements.

The construction materials sector also showed full pioneering spirit in the project: the three-cell tunnel was built using the open reinforced concrete construction method. It is a frame structure with massive components. These include the 6.35-metre-thick ceiling with a span of 29 metres, which was constructed in formwork on supporting scaffolding. The special thing about this is that the entire structure is 18 metres below ground and will later be completely buried. A major challenge was the wall axis on which the ceiling rests, with a degree of reinforcement of up to 750 kilograms per cubic metre of concrete. PORR mastered this challenge by using a self-compacting concrete that was specially developed for this project together with a concrete manufacturer.

Completion of an impressive construction project

The structural work in the FAIR construction field north is now largely complete. In addition to the final concrete and backfilling work, the construction site facilities, which have grown steadily in recent years, must be dismantled, packed and removed. Partial acceptance has already been achieved for seven of the nine buildings.

Project manager Thomas Kühnert is also very satisfied with the construction process as work draws to a close: ‘PORR's major benefits in these projects are its ability to handle many trades in parallel and its comprehensive knowledge of concrete and how to process it. The FAIR project has come this far because everyone involved has contributed their full range of experience and developed an extraordinary feedback culture.’