The project
Geotechnical, hydrogeological and geoenvironmental ground investigations have been carried out as part of a feasibility project supporting the Future Circular Collider study at CERN, the European Laboratory for Particle Physics. Structural Soils have carried out the work in France as part of a consortium with the additional support from RSK Group businesses CAN, RSK Acoustics, Central Alliance, Irish Drilling, Drilling Supplies and RSK France.
Project background
An international collaboration is conducting a feasibility study for a new Future Circular Collider, a proposed next-generation collider expected to be around three times the size of the existing Large Hadron Collider. This study explores the potential of the Future Circular Collider to push the boundaries of high-energy physics. The consortium led by Structural Soils includes French geophysics specialist Smart Seismic Solutions (S3) and Italian deep drilling specialist Geotec SPA.
Structural Soils has carried out site investigations for CERN in the Haute-Savoie area of France. The work has examined the geology of the area with the enhanced level detail required to support the goals of the feasibility study. The site investigation examined critical areas to reduce any uncertainty surrounding the geological conditions, focusing on reviewing and quantifying potential construction risks. This included identifying suitable, consistent tunnelling strata, investigating potential high water pressures within the strata and ascertaining the levels of natural gas in the ground.
Multidisciplinary approach/strategy
Working alongside Structural Soils, CAN has assisted with the supply of equipment, RSK Acoustics carried out noise and vibration monitoring, Central Alliance tasked with mobilisation planning, Irish Drilling supported with provision of drilling equipment, Drilling Supplies provided consumables and RSK France giving health and safety support. The opportunity to tender for the project arose from the need for an experienced business to manage a contract of this size and supply background resources. Structural Soils were selected for its record in managing contracts, lab testing and reporting with additional support from sister companies in the RSK Group.
Challenges
During the work, geologies new to Structural Soils were encountered which are unique to the local environment. The surface geology was found to comprise high water bearing Quarternary/glacial deposits underlain by the typically alpine geology of “Molasse” a thinly interbedded mudstones and sandstones, which is the preferred tunneling medium. In some areas the Molasse was underlain by karstic Limestones which were significantly stronger and had greater water bearing potential. The limestones present increased challenges for construction because of their greater strength, which makes tunnelling harder and the potential for high volume water ingress into the tunnels is much greater.
The properties of the underlying geology were such that there was a risk of encountering natural hyrdocarbons at depth. Mitigation measures therefore needed to be taken to manage the risk of ground gas. This included ongoing monitoring for gases, wearing of personal gas alarms and ultimately employment of gas flares to enable safe works in areas where ground gas was potentially present.
Working in a different country presented a unique set of challenges in terms of navigating the logistics of the project and collaborating with partners in a different language. Unforeseen changes and access restrictions led to last-minute scheduling changes, resulting in the geophysical and drilling works being carried out at the same time. This presents a particular challenge as the two methods of investigation are not entirely compatible! The project also had to manage completing the works in the winter period, when the weather in this part of Europe is colder than we are used to in the UK and there are increased risks associated with snow/ice and day light working hours are reduced.
Solutions
As part of the work, Structural Soils produced a realistic geological underground model along with a geological profile for every location. This will provide a template for future main site investigations and the work will support plans for future civil engineering underground works. This will also contribute to the input required for the next European Strategy Update for Particle Physics in 2026/2027.
Working closely with local and regional stakeholders as well as CERN’s health and safety representatives and environmental specialists ensured that all activities were conducted responsibly and sustainably in line with national regulations and permitting, with safety and environmental care as top priorities. A ‘one team’ approach will ensure that this first phase of works aids the team in any future phases of work planning.
Impact
Through the course of the works, which began on site in September 2024 and was completed in June 2025, our engineers confirmed the ground conditions present at the locations investigated to aid with the design of the optimum tunnel alignment and inform future studies by CERN.
The project pushed the Structural Soils team’s capability to now include competency in; overseas project management, experience of working in and leading a consortium, deep rotary drilling, deep lugeon testing and geologging, and improved all processes when it comes to the complexities of drilling at these significant depths.
