With the XFEL X-ray laser, a large-scale research facility that is unique worldwide has been developed as part of a European collaboration. The X-ray laser is used for research involving high-intensity ultrashort, laser-like X-ray flashes. The facility spans a total length of 3.4 km, beginning at the DESY site in Hamburg and running through an underground tunnel system to Schenefeld in Schleswig-Holstein. In the tunnel structures, the electrons are accelerated. After approx. 2.1 km, the tunnel widens out like a fan, where the electrons made to emit ultra-short X-rays, and opens out into the underground experimentation hall with a total of five individual tube lines. The tunnels were constructed using TBMs with a diameter of five to six metres, while the soil cover varied between six and 30 metres. In addition to the tunnel system, numerous aboveground and underground administrative and research buildings have been built on three operating sites.

The fan-like widening into several tubes resulted in a total length of the shield tunnel system of more than six kilometres. Most of the tunnel and the shaft structures are located up to 20 metres below the groundwater level, hence watertight constructions made of waterproof concrete were used for the foundations of the shaft structures. The excavation pits are up to 40 metres deep and 3,500 m² in size and were constructed using methods minimizing groundwater extraction.

Although the civil engineering work, consisting of shafts, tunnels, and underground experimentation halls, represents merely the shell for the highly complex physical installations, it still has to meet a series of special requirements, such as high temperature stability and a high level of structural stability in order to keep structural and installation deformations and settlements to a minimum. The tunnel was driven “laser-straight” with a tolerance of less than 10 cm and thus follows a tangent to the curvature of the earth. For the installation of the highly technical equipment, such as superconducting accelerator modules, the tunnel was equipped with extensive technical equipment – in some parts with permanent climate control.