Speaker
Description
This contribution highlights research conducted on sealing elements for underground repositories, with a focus on bentonite-based barrier systems for shaft and drift sealing. A central challenge in this field is the reliable transfer of laboratory-scale material data to full-scale repository applications. While in-situ experiments provide valuable insights, their limited controllability of boundary conditions restricts systematic analysis. This gap is addressed through semi-technical scale laboratory experiments that combine realistic dimensions with controlled testing environments.
A key research infrastructure is a cylindrical steel pressure cell with an inner length of 1.90 m and a diameter of 0.80 m, designed for fluid pressures up to 20 MPa. Since the late 1990s, this facility has been used to investigate bentonite seals and multilayer “sandwich” sealing systems consisting of bentonite sealing segments and sandy to silty equipotential segments. These systems are pressurized with saline solutions representative of mining environments to simulate repository conditions. The bentonite swells upon hydration, generating sealing pressure, while fluid injection, moisture migration, and stress development are continuously monitored.
The experimental setup allows both vertical and horizontal operation, enabling simulations of shaft and drift seals. A comprehensive sensor network records axial and radial stresses, isotropic pressures, pore pressures, moisture distribution, and in-situ displacements. Advanced measurement techniques, including earth pressure transducers, TDR sensors, and novel deformation monitoring systems, provide detailed spatial and temporal data on the evolving hydro-mechanical behavior.
The facility effectively bridges the scale gap between small-scale laboratory tests and in-situ experiments, offering stress levels and material volumes relevant for practical applications. It is particularly valuable for studying layered sealing systems and bentonite–sand mixtures and is currently used in major research initiatives such as the Mt. Terri Sandwich project and EURAD-2 ANCHORS.
Experimental investigations are complemented by coupled thermo-hydro-mechanical numerical simulations. These models account for partial saturation, swelling behavior, wall friction, and structural heterogeneities that influence fluid flow and stress development. The development of digital twins of the experimental setups enables systematic testing of mechanistic hypotheses and improves interpretation of complex sensor data. Combined with small-scale and in-situ modeling, this integrated approach enhances the predictive capability for long-term repository sealing performance.