The assessment of the integrity of the geological barrier for repositories for nuclear waste can be significantly influenced by uncertainties in the model inputs. Hence, the results of these established integrity analyses should be enriched by statistical information. In this contribution, we present preliminary probabilistic results for rock integrity assessment for the generic repository system in clay rock and the developed tools for stochastic analyses.

This contribution gives an overview of how the BARIK constitutive model was developed and tested. BARIK is an extended Hoek–Brown model for fractured crystalline rock that takes up to three fracture systems into account. It gives a numerical value to qualitative integrity criteria to show that the containment-providing rock zone in crystalline host rock is still intact. The BARIK model is a step forward in understanding and modeling the complex behavior of fractured crystalline hard rock.

It has been claimed that, under repository conditions, rock salt may not be as impermeable as usually considered. We present results of fluid permeation tests on natural rock salt at high temperatures and stresses (140 to 180 °C, 18 and 36 MPa) that refute these claims.

A Sandwich shaft sealing system consists of alternating sealing segments (DS) of bentonite and equipotential segments (ES) with a high hydraulic conductivity. Water accessing the system results in swelling of the DS. Within the ES the water is evenly distributed over the cross section of the seal. Thus, swelling is more homogeneous and seal bypass is reduced. At the Mont Terri rock laboratory, this sealing system is tested in connection with the host rock in a large-scale in-situ experiment.

Within the scope of the presentation, a methodical approach for the systematic and structured development and validation of multiphysical material models, which has been successfully tested several times in the meantime, will be introduced and subsequently the concrete application of this methodology will be presented using the example of a material model taking into account the triaxial stress-strain behavior of crushed salt.

The presentation will present the results of the research work for the development, construction and commissioning of the pilot plant as well as successful mechanical-hydraulically coupled tests to demonstrate the functionality of sealing elements made of salt cut bricks.

Since 2013, the search for a site for a HAW-repository has started again in Germany with the entry into force of the first Site Selection Act (StandAG). Compared to repository concepts in steep inclined salt (domes) or in clay or crystalline formations, a repository in bedded salt offers considerable long-term safety advantages due to a site-specific, natural multi-barrier system consisting of the host rock salt (with the ewG) and overlaying sequences of additional salt and salt clay seams.

What is the effect of shearing, holding and effective normal stress on fault gouge permeability, parallel and perpendicular to fault boundaries, as well as on frictional behaviour? Experiments show a pre-shear permeability anisotropy, as well as a decrease in permeability with shear and eff. normal stress, for both fluid flow directions. The results have important implications for pre-existing faults in calcite-rich claystones that seal hydrocarbon reservoirs or potential CO₂ storage reservoirs.

The strength of fault rock plays a central role in determining the distribution of crustal seismicity. We review laboratory work on the physics of fault friction at low shearing velocities carried out at Utrecht University in the past 2 decades. Key mechanical data and post-mortem microstructures can be explained using a generalized, physically based model for the shear of gouge-filled faults. When implemented into numerical fault-slip codes, this offers new ways to simulate the seismic cycle.

A composite flow law model applied to crystal size distributions from the NEEM deep ice core predicts that fine-grained layers in ice from the last Glacial period localize deformation as internal shear zones in the Greenland ice sheet deforming by grain-size-sensitive creep. This prediction is consistent with microstructures in Glacial age ice.

Fast ice flow occurs in deeper parts of polar ice sheets, driven by high stress and high temperatures. Above 262 K ice flow is further enhanced, probably by the formation of thin melt layers between ice crystals. A model applying an experimentally derived composite flow law, using temperature and grain size values from the deepest 540 m of the NEEM ice core, predicts that flow in fine-grained layers is enhanced by a factor of 10 compared to coarse-grained layers in the Greenland ice sheet.

Coal is an important source rock for natural gas recovery, and its frictional properties play a role in induced seismicity. We performed experiments to investigate the frictional properties of bituminous coal, and our results show that the frictional strength of coal became significantly weakened with slip displacement, from a peak value of 0.5 to a steady-state value of 0.3. This may be caused by the development of shear bands with internal shear-enhanced molecular structure.

In Switzerland, the Opalinus Clay (OPA) formation is favored to host a repository for nuclear waste. Thus, we must know its deformation behavior. In this study, we focused on the microstructure of gouge, a thin (< 2 cm), drastically strained clay layer at the so-called Main Fault in the Mont Terri rock laboratory. We suggest that in situ gouge deforms in a more viscous manner than undeformed OPA in laboratory conditions. Moreover, we speculate about the origin and evolution of the gouge layer.

Scaly clay is a well-known rock fabric that can develop in tectonic systems and that can alter the physical rock properties of a formation. However, the internal microstructure and evolution of this fabric remain poorly understood. We examined the scaly microstructure of progressively faulted Opalinus Clay using optical as well as scanning electron microscopy. We show that as little as 1 vol.% in scaly clay aggregates is strained and present an evolutionary model for this.