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A complex, highly coupled hydraulic-mechanical behavior characterizes claystone. The physical understanding of the related effects is of great importance concerning the stability during the construction phase as well as for the safety assessment of the integrity of a potential repository for high-level nuclear waste. The underground research laboratory (URL) Mont Terri, Switzerland, provides the unique possibility to conduct in-situ experiments in the Opalinus clay for a broad international community. The experiment on the influence of humidity on the cyclic and long-term deformation behavior (CD-A experiment) is conducted in the new part of the URL, which is currently under construction. To compare the coupled hydraulic-mechanical effects under different conditions, the construction of two parallel oriented niches is planned in summer 2019. These niches have a length of 11 m and a diameter of 2.3 m and no shotcrete support. The first niche remains under "natural conditions". Here, the atmospheric conditions are characterized by a seasonal change in air humidity and temperature. This will lead to a desaturation of the claystone around the niche. The second niche is locked. In this area, the air conditions imply a high humidity and the desaturation of the claystone will be avoided as much as possible.In both niches, a geological characterization of drill cores and of rocks exposed in the niches will be carried out. Furthermore, measurements of the related parameters are planned for at least 10 years. The measuring program includes long-term measurements of the air humidity, the temperature, the deformation (extensometer), the convergence of the niches, the pore water pressure (piezometer) and the water content (Taupe). Furthermore, periodic measurements of the permeability, electrical resistivity (ERT), and nuclear magnetic resonance (NMR) on the niche walls as well as petrophysical analyses of drilled cores are planned. Seismic borehole measurements will also be carried out. The measuring program will be accompanied by the numerical simulation of the coupled hydraulic-mechanical effects in the vicinity of the niches. The comparison of the measurements with simulations considering different model approaches should support the identification of significant physical effects of the complex coupled material behavior.This contribution will focus on the concept of the measurement program and numerical pre-simulations carried out with OpenGeoSys. Furthermore, the possibilities of an integrated visualization of numerical results in a complex geotechnical setting will be presented. [ABSTRACT FROM AUTHOR]

Understanding all processes with relevance to the whole lifetime of a final repository for high-level radioactive waste (HLW) is an extraordinary challenge, but essential for the creation of repositories worldwide and a part of licensing procedures in Germany. To this end, BGR performs various experiments in national and international underground facilities. As claystone is a potential host rock for a HLW-repository in Germany, too, BGR also performs experiments in Opalinus Clay at Mont Terri Rock Laboratory in Switzerland. BGR is one of 19 consortium partners from nine countries in the Mont Terri Project since its creation in 1996. Experiments are performed in close collaboration and exchange between the partners in order to avoid doubling. All results and experiences are made available immediately to all partners and later to the public. The experiments cover the full evolution of a HLW-repository. BGR experiments mainly cover the early repository evolution (up to several 1000 years), comprising construction period (desaturation), canister emplacement period (temperature pulse), post-closure transient phase (temperature decrease, ongoing re-saturation), and post-closure equilibrium phase.We focus exemplarily on some selected topics of more than 20 years of BGR's participation in the Mont Terri rock laboratory.• After a site selection process, one of the first steps is an in-situ site characterization. BGR developed different high-resolution geophysical tools which allow a precise rock characterization with geophysical parameters, dynamic elastic moduli, characterization of Excavation Damaged/disturbed Zone (ED/dZ) features at different stages of the evolution and long-term emplacement experiment monitoring for barrier integrity assessments.• With the extension of the rock laboratory extensive investigations have started regarding the more stable sandy facies of the Opalinus Clay. In advance of the excavation, a section of the planned gallery has been instrumented with different sensors to observe the coupled hydromechanics processes due to excavation. The measurement results will be the basis of computational simulations to determine the property values of the sandy facies.• Hydraulic characterization is another focus of our research. Permeability measurements were performed in the near-field around an excavation, in the undisturbed rock zone, in the zone with wet-spots, and in the transition area between different geological units. Additionally, a coupled thermal-hydro-mechanical (THM) code was developed in cooperation with UFZ Leipzig to analyse coupled HM (Mine-By experiment) and THM processes (Heater Test).• Mechanical parameters of Opalinus Clay were studied in triaxial tests in Kármán cells. Young's modulus was found to exhibit a significant dependency on the confining pressure as well as a strong anisotropy regarding value and type of functional dependency.Despite enormous efforts of all partners involved and the hitherto obtained vast, interdisciplinary knowledge, various important technical and scientific questions remain as of yet unanswered. While undisturbed rock regions and new experimental space became quite rare, add-on excavations started in 2018. With the scheduled doubling of the Mont Terri laboratory space in late 2019, synergies will open up between research on safe options for nuclear waste repositories and new studies on further potential uses of the subsurface. [ABSTRACT FROM AUTHOR]