The excavation of the shafts and caverns for the ATLAS and CMS experiments of the LHC will start whilst LEP and the SPS are running. This will be at a period when LEP should be at its peak performance and the SPS will be providing beams for LEP, fixed target physics and LHC test beams. Simulations show that movements of the machine tunnels can be expected during the excavation and it is essential that this does not affect the performance of the SPS and LEP. These movements are of sufficient amplitude to prevent machine operation if no precautions are taken. This preliminary report outlines the problems and suggests what actions should be taken to ensure efficient operation of the SPS and LEP during the critical period
