Figure 1. One vertical core drilling tests of 2025, this one in October. Photos: Thomas Bauler and Henry De Maynard / CERN

By Thomas Bauler and Henry De Maynard (CERN)

2025 was once again an important and strategic year for the High-Luminosity LHC (HiLumi LHC) Project as a whole, including for Work Package 17 (WP17), responsible of infrastructure, logistics and civil engineering.

2025 was the last full year to advance the installation of major infrastructure before the start of Long Shutdown 3 (LS3). This race against time has seen many accomplishments throughout the year, with much work completed by the various sub-WPs for WP17.

Figure 2. Location of HiLumi underground galleries in 2D and 3D. CERN

Vertical cores to connect HiLumi LHC galleries to the LHC tunnel

In the last two year-end technical stops (YETS), 2024-2025 and 2025-2026, WP17.1  carried out drilling tests for the vertical cores that will connect the new HiLumi LHC underground service galleries to the LHC tunnel. 28 vertical cores, 14 at Point 1 and 14 at Point 5 and each with a final diameter of around 1 m and a length of around 7 m, will allow the routing of new powering, control and cryogenic supply equipment installed in the HiLumi LHC galleries to the systems in the LHC tunnel.

The procurement procedure launched in January 2025 and lasting several months evaluated the different methodologies proposed by bidders – including hand mining, coring, drilling and wire cutting. Field tests were strongly valuable to reduce uncertainties and refine excavation methods and equipment, including optimisation measures, like the use of prefabricated metallic linings instead of concrete to help simplify and accelerate the installation. The contract was awarded to a joint venture of three Swiss contractors after approval in June 2025.

Thanks to the selected methodology and increased resources, the expected LHC intervention time for this work was reduced from 8.5 months to 5.5 months from start to end in both points, saving valuable time in the intense LS3 schedule. The tests performed during the most-recent successfully completed YETS , and coordination with CERN teams, aimed to validate the approach and ensure a successful execution during LS3.

Electrical distribution, cooling & ventilation, alarm & access, logistics and operational safety

Figure 3. UR 15 in HiLumi LHC underground at Point 1 in February (above) and November (below) 2025. Photos: Thomas Bauler (above) and Florence Thompson (below) / CERN

WP17.1 also successfully completed the construction of the Point 5 electrical substation.

WP17.2 completed the installation of general services on the surface and underground. All of the water-cooled cables have been installed, and the lights are operational in the underground.

Concerning WP17.3, the SF buildings are commissioned, and the SU buildings are in the process of commissioning. The major installation works for this sub-WP were completed, including those of the piping, insulation, ventilation and smoke extraction ducts.

Safety of the construction site was reinforced thanks to the work of WP17.4 with the installation of the fire detector, already functional in the surface buildings, and oxygen-deficiency hazard (ODH) detection. The PAD and MAD systems (Personnel and Material Access Device systems for personnel and material access to the underground galleries) have been installed and the evacuation systems have been commissioned.

Under WP17.10 the doors for the two underground caverns of Point 1 and 5 were delivered.

Last but not least, in operational safety, WP17 has continued to provide safety coordination (with Michel Bonnet as Health & Safety Officer) between many HiLumi LHC WPs when their activities overlap with the HiLumi LHC sites at Points 1 and 5, offering rigorous reporting of the worksite and sharing accumulated knowledge about safety and coordination across the HiLumi LHC Project. For example, with the ongoing cryogenics (WP9) installations which started last year.

Worksite coordination is done in close synergy between WP15 and WP17 as both WPs are overseeing installations in the galleries.

2026 missions

2026 promises to be an interesting year for WP17, above all due to the start of LS3 in July. WP17.2 will be finalising the installation of the Point 5 electrical substations and overseeing major cabling campaigns – including the installation of the air-cooled cables – in the HiLumi LHC galleries. WP17.3 has the mission of finishing the commissioning of the SF and SU buildings as well as the installation of manifolds for the pipes of radio-frequency devices in the UA. 

Before the start of LS3, WP17.5 must put in service the PAD/MAD access systems. During this year, the sub-work package will finish the installation of the smoke extraction control system. Finally, WP17.10 will install the doors in the underground caverns as well as the panelling in the UR to ensure safe access to the cable trays. 

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