Experiment 5. ELSA

ELSA is a programme of laboratory and in-situ experiments that will be used to further develop the reference shaft seal for the German disposal concept for a repository in salt rock and to develop a reference shaft seal for a repository in clay host rocks.

The ELSA Project is divided into three phases:

• Phase 1:  Boundary conditions and requirements for shaft seals in salt and clay host rocks
• Phase 2:  Development of shaft seal concepts and testing of functional elements of shaft seals in laboratory tests and in small-scale in-situ tests, including testing and calibration of mathematical models of material behaviour.
• Phase 3:  A large-scale demonstration test of particular sealing components and adjustment of the sealing concept.  The main requirements of the test are to demonstrate technical feasibility and long-term effectiveness.  It has not yet been determined which components will be tested within this phase of the ELSA project.

The following tests during Phase 2 of ELSA contribute to development of shaft sealing concepts and designs to conduct the large-scale tests in Phase 3:

• Tests regarding the technical feasibility of filling columns made of compacted rock salt (crushed salt or pre-compacted material).
• Investigations regarding the suitability of calottes (concave sections) made of basalt as an additional element in gravel columns to improve packing density.
• Abutments made of MgO concrete cast in situ.
• Further development of treatment methods for the EDZ and the interfaces between concrete and the surrounding rock mass based on grout injection.
• Further development of the design and construction of bitumen or asphalt seals.
• Additional studies on bentonite seals in clay formations focussing on the placing of equipotential elements within the bentonite plug.
• Generation of models to analyse the properties of the material as well as the loading and flow processes at the various construction stages.

In addition to these investigations, the laboratory programme of GRS (Lava and Lasa projects) will address sealing materials planned to be utilised in the shaft seals as well. The programme aims at providing experimental data needed for the theoretical analysis of the long-term behaviour of MgO and cement based salt concrete in interaction with the host rock and fluids. The data gained will be needed to show the long-term preservation of the required hydraulic conductivity of the seals.