CERN, HL-LHC Project: numerical modelling and design challenges for the new underground facilities at Point 5

The most powerful underground particle accelerator, known as Large Hadron Collider (LHC), is located at CERN on the border between Switzerland and France. The High-Luminosity (HL-LHC) Project will increase existing facilities with new underground and shallow structures at Point 1 (ATLAS, Switzerland) and Point 5 (CMS, France). The new underground structures include a shaft, a wide cavern, 500 meters of galleries and some vertical linkage cores. This paper presents the main challenges of the Project at Point 5 describing the design and construction issues encountered for the underground structures, together with the key role of the numerical modelling in the design. The main challenges of the construction were related to the following: i) meeting the tight schedule of design and construction ii) defining design criteria i.e. calculating expected excavation-induced vibrations and minimizing the disturbance effects on the LHC where experiments were in progress; iii) excavating within a complex rock mass with several known challenging characteristics; iv) assessing the potential impact of the excavation works on the nearby existing underground structures. The excavation of the main underground works was successfully completed without any critical impact on the nearby existing underground structures. The construction phase is on track for completion within the stipulated contractual Construction Programme. The completion of the entire works is scheduled for September 2022.