The Large Hadron Collider (LHC) is the most recent and powerful particle accelerator constructed on the CERN site. The LHC consists of a 27 km circular tunnel, about 100 m underground, with eight sites positioned around the tunnel’s circumference. High-Luminosity LHC (HL-LHC) is a project aiming to upgrade the LHC to maintain scientific progress and exploit its full capacity.
The HL-LHC project foresees new underground infrastructures to be placed on the inner side of the existing LHC ring, at an average distance of approx. 50 m from the LHC axis either at Point 1 (Meyrin, Switzerland), where the A Toroidal LHC ApparatuS (ATLAS) is located, and Point 5 (Cessy, France), where the Compact Muon Solenoid (CMS) is situated. These new underground infrastructures will be located approx. 6–7 m above the level of the existing LHC tunnel crown. They consist of the following main structures: new shafts (PM17 & PM57), service caverns (US17/UW17 & US57/UW57), power-converter galleries (UR15 & UR55), service galleries (UA17, UL17, UA13, UL13 & UA57, UL57, UA53, UL53), and vertical linkage cores to the existing LHC tunnel and escape exits (UPR13/UPR17 & UPR53/UPR57). The shafts connect the surface buildings with the underground facilities (cavern and tunnels). It is approx. 60-m deep with a constant internal diameter of the final lining of 9.80 m. The thickness of the final lining varies from 0.50 m (typical cross section) to 0.80 m (junction with cavern). The cavern is located at the bottom of the shaft. It is approx. 50-m long, 15-m wide and 11.2-m high (internal dimension). It will house the cryogenic equipment and services. The power-converter gallery links the cavern with four 50-m long transversal service galleries. This power-converter gallery is approximately 300-m long, starting from the cavern. It will mainly house the power converters and the current feed boxes of the superconducting magnets. The UA service galleries will house the radiofrequency equipment of the crab-cavities and the UL service galleries will house the cryogenic distribution system and the superconducting links. At the extremity of each UA service gallery, personnel safety exits, called UPR, provide additional evacuation paths towards the LHC tunnel.
As mentioned, the construction sites are located near to the ATLAS site (Point 1) and CMS site (Point 5). Both sites are equipped with the typical installations for underground works, such as ventilation, water treatment plant, excavation equipment, site accommodations, workshop, lift installation, etc.
On each Point, the following buildings are foreseen on the surface:
1. Head Shaft Building (SD): Steel frame structure with dimensions of 22 m by 35 m housing one cold box for the cryogenic system. The building is about 16-m high.
2. Ventilation Building (SU): Reinforced concrete structure with dimensions of nearly 22 m by 30 m. The building is about 13-m high. The SU building will host the necessary cooling and ventilation systems for the HL-LHC underground infrastructures.
3. Electrical Building (SE): The SE building will host the necessary electrical systems for the HL-LHC infrastructures. The steel frame structure is moment resisting in the transverse direction while the longitudinal stability is ensured with cross bracings.
4. Cooling Towers (SF): Reinforced concrete structure with dimensions of nearly 18 m by 30 m housing 3 cooling towers. This building is about 12-m high. The SF building will host the cooling tower structures that are required to extract the heat loads form the machines for the HL-LHC infrastructures. The cooling towers exhausts will be built with curved formwork tools.
5. Compressor Building (SHM): Reinforced concrete structure with dimensions of nearly 16 m by 50 m. The building is about 11-m high. The SHM building will host the compressors for the cryogenic equipment required for the HL-LHC infrastructures.
The Eurocodes represented the main set of reference norms for the design and assessment of the structural safety for all foreseen surface buildings and underground infrastructures.