ABSTRACT
To ensure long-term safe confinement of high-level radioactive waste in a repository in saliniferous formations geological barriers in combination with geotechnical barriers are demanded to be permanently tight against fluids. As a consequence, an essential aspect of underground disposal is to demonstrate that connections between biosphere and lithosphere, i.e. shafts, boreholes and drifts, created during the excavation of underground cavities can be sealed sufficiently tightly. An essential element of the sealing system required for this purpose is the shaft closure. All shaft closure concepts developed so far include sealing and support elements in repository shafts, but differ in the arrangement of these construction elements and the materials used for this purpose. To ensure both, redundancy and diversity of a sealing system currently proposed and investigated materials for the construction of sealing elements are: clay/bentonite, asphalt/bitumen, crushed salt and salt-/sorel concrete. In addition to the materials mentioned above, a research project funded by the Federal Ministry for Economic Affairs and Energy is investigating the possibility of integrating a layer of salt cut bricks into the shaft closure system as a long-term sealing element with the option of enabling shortly after installation a long-term healing of the geological barrier. The following article first documents laboratory investigations into the geomechanical-geohydraulic effectiveness of a closure element made of salt cut bricks. For this purpose, chapter 2 presents the development and construction of a test facility able to investigate a cylindrical specimen made of salt-cut bricks characterized by a length of 1,5m and a diameter of 0,75m. Chapter 3 describes work on the configuration and fabrication of salt cut bricks and addresses issues of spatial arrangement of salt cut bricks to avoid axially continuous joints in the specimen. Chapter 4 document special boundary conditions, which have to be consider in case of installing, implementation of tests and removal of large-scale test specimens made of salt cut bricks. Finally, chapter 5 presents the results of mechanically-hydraulically coupled tests to demonstrate and prove the functionality and suitability of sealing elements made of salt cut bricks.
