LEP tunnel movements at point 1 caused by LHC civil engineering

The excavation of underground openings causes the surrounding ground to move towards the newly created opening. The magnitude of the movement is dependant of various factors, such as the shape and the size of the excavation, the geotechnical ground conditions, the in-situ ground stress, the distance from the excavation, etc. The excavation technique and the rock support measures are to be adapted to the prevailing ground conditions to limit the displacements to an acceptable level. From the output of the numerical analyses for the design of the underground structures, data can be obtained to determine the predicted movements. For the particular case of the LHC excavations at Point 1 in close proximity to the existing LEP tunnel, a facility had to be designed and installed in the LEP tunnel to allow adjustments of the machine alignment to compensate for the tunnel movements. The design was based on the predicted displacements, and the adequacy of the facility has been validated during excavation.