Inset (Czechia)

​In order to place experiments in real geological conditions, a new section of the already active generic underground research facility Bukov (Bukovská et al. 2019) is recently being constructed. It is located in the central Bohemian Massif, in former uranium mine Rožná, at c. 550 m below the surface. During the excavation of new tunnels and laboratory chambers, a complex of geomechanical, structural, geological, hydrogeological and geophysical measurements and monitoring activities is continuously performed. The main objectives of this in-situ characterization project are to understand and 3D visualize the structural record and its hydrogeological systematics. Other objectives are to determine the excavation damage zones, the effect of blasting, the physical and mechanical properties of the rocks, and testing the excavation and drilling methodology. The laboratory is situated mostly in the intensively deformed paragneiss, high-grade amphibolites and migmatites, typical for the European Variscan belt. Geological observations have revealed a complex polyphase deformational pattern of metamorphic foliations, strongly influencing the superposed fault and fracture systems, hydrogeological conditions and rock mass properties. Based on multidisciplinary research of borehole and tunnel data, possible problematical geological structures are identified and investigated. Finally, all obtained data and experience will serve to development of work-flows of documentation and rock-mass suitability classification system during building of the future real deep geological repository. The construction will be completed in 2024 and the underground research facility will become part of the national planning and siting strategy for the deep underground repository for high-level radioactive waste. The data from this research will contribute to the understanding of the geology of the region and will be used for experiments addressing long-term safety and technical feasibility. Such results from the depth can allow correlation and validation of data collected from surface research (Soejono et al. 2021) in the potential sites for deep geological repository construction.  Bukovská, Z., Soejono, I., Vondrovic, L., et al., 2019. Characterization and 3D visualization of underground research facility for deep geological repository experiments: A case study of underground research facility Bukov. Czech Republic. Eng. Geol. 259, 105186. https://doi.org/10.1016/j.enggeo.2019.105186 Soejono, I., Bukovská, Z., Levá, B., et al., 2021. Interdisciplinary geoscientific approach to radioactive waste repository site selection: the Březový potok site, southwestern Czech Republic. J. Maps 17, 741–749. https://doi.org/10.1080/17445647.2021.2004942

Abstract The warehouse halls were founded on backfill sediment, which were 4 to 6 meters thick. Beneath them were the loess and saturated Cretaceous sands. During heavy rains, there were two large landslides that hit the local road. It was therefore necessary to carry out a rapid design of remedial steps (stabilization) without the time to carry out drilling exploration survey. During fieldwork (mapping, geodetic measuring of landslides and sampling of soil) it was found that most of the warehouse halls did not have solved the drainage of rainwater from roofs and roads and there occurred long cracks in the floors of the halls. Laboratory soil tests served as inputs for stability calculations. Reverse analysis (landslide condition) derived residual geotechnical parameters of the soil. The proposal for redevelopment consisted of changing the slope geometry, building a loading bench and brand new drainage of surface water along the slope (it was missing on the top). It was also recommended to replace the subsoil – saturated loess – under the floors of the warehouse halls.