In video – CERN seeks to reuse millions of cubic meters of excavated materials

The future circular collider at CERN is expected to span 91 kilometers in circumference, which means an equally massive amount of rock will need to be excavated — and somehow reused or repurposed. The research center is currently testing solutions to give a second life to the molasse (the soft sedimentary rock) extracted from the ground.

It caused controversy as soon as it was announced some time ago — because of its sheer size, but above all due to its environmental impact. The new collider will stretch 91 kilometers in length and will be buried on average 200 meters below the surface. That means all that material will have to be excavated. But what can be done with all that rock?

According to estimates, CERN will need to excavate over 6.3 million cubic meters of rock. The NGO Noé21 claims that once brought to the surface, the total volume will reach 8.5 million cubic meters, since compact rock expands when exposed to air — the equivalent of roughly three pyramids of Khufu, extracted from eight different sites over eight years.

To respond to criticism, CERN has launched research to reuse a large portion of the excavated material. Journalists were invited to a test site just across the border in France, part of a project called OpenSkyLab — literally “open-sky laboratory.” According to CERN, the ground beneath the Greater Geneva area consists of 95% molasse, a type of soft sandstone once used to build many of Geneva’s historical buildings. CERN researchers showed how they aim to repurpose this molasse, giving it new life.

At present, no industrial-scale process exists for recycling molasse. Most of it ends up as sterile backfill or in landfills. CERN hopes to transform about one quarter of the excavated materials into substrate — fertile soil that could be used locally for landscaping, reclaiming industrial wastelands, roadside vegetation, or even growing fiber-producing plants, such as apple trees and vines.

Excavation is expected to begin in the mid-2040s, in two phases: first with an electron–positron collider, then a proton–proton collider. According to CERN, the accelerator will pave the way for unprecedented precision measurements, going beyond the Standard Model. With its proton–proton configuration, the Future Circular Collider (FCC) will reach energies eight times higher than those of today’s LHC.

By Artiom Missiri, published in Le Temps, October 11, 2025, 08:00 / Updated October 11, 2025, 09:17.