Design considerations for deep caverns in Opalinus Clay

• Published in: Expanding Underground - Knowledge and Passion to Make a Positive Impact on the World pp. 2114 - 2121
• Main Authors: Morosoli, D., Anagnostou, G., Cantieni, L.
• Format: Book Chapter
• Language: English
• Published: United Kingdom CRC Press 2023; Taylor & Francis Group
• Edition: 1
• Subjects: Load Safety Factors; Full Face Excavation; High Support Pressure; Pore Pressures; Worst Case Convergence; Resistance Principle; Geological Strength Index; Pore Pressure Drops; Overburden; Uniaxial Compressive Strength; Rock Pressure; Entire Service Life; Diameter Caverns; Above Ground; Shotcrete Lining; Opalinus Clay; BIM; BIM Model; Axial Force Distribution; Shotcrete Shell; Consolidated Undrained Triaxial Compression Tests; SEM; Negative Pore Pressures; Intermediate Level Waste; SCL
• DOI: 10.1201/9781003348030-254

The planned radioactive waste repository in Switzerland will be located within a ca. 900 m deep and 100 m thick layer of Opalinus Clay. Low- and intermediate-level waste will be emplaced in caverns with a diameter of 14 m. The great depth of cover and the rather low strength of Opalinus Clay (uniaxial compressive strength in the order of 3-5 MPa) are expected to result in squeezing conditions, which will be demanding to handle on account of the large dimensions of the cavern cross-sections. The paper investigates alterative concepts for the tunnel support, considering the uncertainties and peculiarities of the Opalinus Clay's response to tunnelling - inter alia its very pronounced time-dependency. The development of relevant deformations will not cease even after several decades, while in the presence of a stiff lining the rock pressure would reach very high values within the service life of the caverns (in the order of about 3-4 MPa within a period of 20-30 years after excavation).