Geodetic deformation measurement and analysis of the ATLAS experimental cavern at CERN

Caverns for large physics detectors, such as the one for the Large Hadron Collider experiments, sit nearly 100 m underground and measure several tens of meters in length, width and height. The deformation of the cavern base slab over decades has a direct influence on the relative alignment of detectors with respect to the accelerator. The expected long-term movements are larger than the fine adjustment of detectors and accelerators. In this paper, the measured deformations of the ATLAS experiment's main cavern floor and lateral walls over nearly 20 years have been analysed. The measurement series have been performed in various time intervals getting down to half a year. The used measurement techniques, such as the polar method (total station and laser tracker) and precise levelling, allow to obtain sub-millimetre precision. Even if the deformations are significantly (four times) lower compared to the predictions of the civil engineering consultants at the moment of the cavern construction, the measured ones reach values up to 5.0 mm for the base slab and up to 14.7 mm for the lateral walls.