What civil engineering work is required for the High-Luminosity LHC?
The new equipment for the High-Luminosity LHC requires civil engineering work to be undertaken on the sites of the ATLAS experiment in Meyrin, Switzerland (LHC Point 1) and the CMS experiment in Cessy, France (LHC Point 5).
On each site, the underground constructions will consist of:
- A shaft around 80 metres deep
- An underground service hall that will notably house cryogenics equipment
- A 300-metre-long tunnel for electrical equipment (power converters)
- Four tunnels measuring around 50 metres in length, connecting the new structures to the accelerator tunnel. These will house specific hardware, such as radiofrequency equipment.
On each site, the surface work consists of constructing five new buildings, representing a total surface area of 2800 m2. These will house the cooling and ventilation equipment, as well as electrical equipment. These buildings will be constructed outside the current site perimeters at Cessy and on a site made available by the Swiss Confederation at Meyrin.
Who is carrying out the work?
Two consortia won the call for tenders for the civil engineering work. Each will employ up to 70 people on each site during peak periods.
What is the work schedule?
Work began in April 2018 and should last four years. The underground work (excavation of shafts, caverns and tunnels) will be carried out first and should be completed in 2021. The surface buildings will be constructed between 2020 and 2022. The surface work will be carried out only on working days.
What will happen to the excavated earth?
Around 100 000 m3 of earth will be excavated to create the underground structures. The excavated material will be analysed on the surface to check its quality. On the Meyrin site, much of the excavated material will be reused to create a platform on which to erect the buildings. The rest will be taken to a treatment centre. At Cessy, almost all of the excavated material will be taken to inert waste storage facilities located less than 20 km from the worksite, to limit the transport distance. On both sites, the topsoil will be reused for landscaping.
How will the work affect traffic?
- Road traffic
During the excavation period, lorries will transport the spoil to treatment or storage centres. A maximum of 10 lorries will come and go on the Meyrin site each day, and 10 to 15 on the Cessy site. Spoil will be transported only during working days (Monday to Friday) and, in Meyrin, during off-peak hours (9.30 a.m. to 12.00 p.m. and 1.00 p.m. to 4.30. p.m.).
- Footpaths and cycle paths
In Meyrin, the footpath linking the Maisonnex sports complex to the Chemin de la Berne (north-north-easterly direction) will be closed while the work is taking place; access to the complex will be possible via the Route de Meyrin and the path along the border.
In Cessy, the pedestrian and cycle path around the site (Chemin du Milieu and Chemin de Mouillets) will stay open and will be sheltered from the worksite.
How will the work affect the environment?
The contracts concluded with the two civil engineering consortia impose environmental restrictions and, notably, the hiring of experts to do environmental monitoring on the worksite.
The noise generated by the work will be limited in order to respect French and Swiss regulations. An acoustic system will monitor noise levels at various times. Measures will be taken to limit noise, such as the construction of a temporary building with noise barriers above each shaft to minimise noise pollution from the excavation, or the installation of mufflers on the ventilation systems for the underground work. Surface work will take place only on working days, during the day.
Host State regulations govern the release of dust into the air while the work is taking place. Measures will be implemented, such as a wheel-washing system for lorries leaving the sites, vehicle speed restrictions and a sprinkler system in dry weather.
A worksite water management plan has been established to prevent pollution. As far as possible, the excavation areas must be protected from rainwater. A water treatment plant will be installed on each site to treat all water coming from the worksite before it is discharged. The water quality will be monitored.
Will there be any long-term environmental impact?
Road traffic will not be affected. When the work is complete, the footpath in Meyrin linking the Maisonnex sports complex to the Chemin de la Berne will be reopened, with the route modified to pass around the new buildings. The footpath in Cessy will remain unchanged.
Both sites will be landscaped and planted with around twenty local tree species.
An acoustic survey of the future facilities has been performed and forms part of the planning permission requirements. Noise emissions will remain below the legal limits. All of the new equipment for the HL-LHC will be installed either in surface buildings with soundproofing or underground.
In Meyrin, a new water retention tank will be installed to regulate the flow of rainwater into the Nant d’Avril stream. A new monitoring station will be set up (CERN has 27 water monitoring stations on its sites and the surrounding areas). A similar tank is already in operation in Cessy, regulating the water released into the Oudar. In Cessy, two water tables are located beneath the experiment site. The work will penetrate only the surface water table: a watertight, circular wall will first be installed to a depth of 15 metres to isolate the water table and make it possible to excavate inside it. The work will not penetrate the deeper water table.