Stability Analysis of Large Underground Caverns of Unprecedent Dimensions at Depth

The European Spallation Source Neutrino Super Beam (ESSnuSB) is a long-term particle physics project focused on neutrino research. A crucial component of this is the Far Detector (FD), a massive underground facility to host scientific instruments. The FD will consist of two large caverns with a total volume of 960,000 m3, accommodating 1 million m3 of ultra-pure water for the water Cherenkov experiment. These cylindrical caverns, measuring 78 m in diameter and 100 m in height, are to be located at a depth of 1,000 m underground. For the conceptual study, the Zinkgruvan mine, which is optimally located circa 360 km from Lund, where the European Spallation Source (ESS) will generate the neutrino beam, is chosen as the candidate site. For stability assessment of the caverns a3D numerical simulation was conducted to determine an optimal location, ensuring a 250-meter offset from mining operations. The conceptual design study involved 2D and 3D numerical analyses to assess cavern stability under high-stress conditions, ensuring feasibility and structural integrity. The research also aimed to evaluate risks, refine engineering requirements, and estimate costs for construction, making this project a significant advancement in underground research infrastructure.