Boring of accelerator tunnel completed
The tunnel boring machine TULA reached its goal in the last week of July. A few days later, the tunnel builders installed the last concrete ring of the tunnel tube for the accelerator. What will happen next?
On 27 July 2011 at around 22:00, the tunnel boring machine TULA (TUnnel for LAser) was outside the wall of its reception shaft. It then just had to slowly drill through the 1.50-metre-thick diaphragm wall of the construction pit and pass through the round “TULA window” in the adjoining wall of the injector building. With a “landing precision” of one millimetre, TULA arrived in its travel-out panel on the western wall of the injector building on the DESY-Bahrenfeld site.
The construction of the 2010-metre-long tunnel was not yet finished, however. Six reinforced concrete rings—the last of which connects the tunnel with the hall—were still missing. While TULA inched its way onto the large steel jack (the “shield cradle”) that was installed in the hall especially for this purpose, the tunnel builders assembled the last concrete rings. On Saturday, 6 August 2011, the boring of the tunnel tube for the superconducting accelerator of the European XFEL was finally completed!
What happens next? After more than 400 days of service for European XFEL, TULA has now completed its job. In the coming days, it will be dismantled inside the injector building so that it can be transported in parts through the narrow shaft back to the surface. At the end of August, TULA will return to the manufacturer by ship, as some of its components may be reusable, while others have at least a high scrap value. In parallel, the dismantling of the infrastructure needed for the tunnel boring machine (catwalk, supply pipes, cables, and finally the tracks of the tunnel railway) has already started. The dismantling is expected to take until mid-September. The tunnel construction also includes fitting the tunnel tube with a stable, flat floor. This will be completed in January 2012. With the help of a special vehicle, the substructure will be constructed from precast concrete elements weighing six tonnes each. The stable floor panels will then be laid on top of this substructure.
Joint news of the European XFEL GmbH and Deutsches Elektronen-Synchrotron DESY, a research centre of the Helmholtz association