Opalinus Clay is considered a potential host rock for radioactive waste disposal. The Jurassic claystone formation is composed of several facies and subfacies types, which are characterized by varying amounts of quartz, carbonates (cements and fossils) and clay minerals. To provide samples for ongoing experimental and numerical studies, a complete core section was drilled in the Mont Terri rock laboratory. The lithological and structural variability (including tectonic fault structures) from borehole BAD-2 was investigated using a multidisciplinary approach including high-resolution geoelectric in situ borehole measurements, mineralogical/geochemical and (micro)structural analyses.The lithological–compositional variability was captured by successfully applying a modified subfacies approach, which is independently confirmed by the geochemical data and ERT (Electrical Resistivity Tomography) measurements. The variability on the cm to dm scale perpendicular to bedding can be determined based on the mean resistivity and variation of amplitude. In particular, the facies transitions could be precisely located. The new results suggest that both shaly facies types form the homogenous part of the investigated section, whereas the sandy facies and especially the carbonate-rich sandy facies represent the more heterogeneous lithofacies types of the Opalinus Clay. The varying resistivity can be attributed to differences in clay mineral and carbonate content. Regarding the structural variability, brittle faults were observed with varying frequency throughout the investigated section. Most fault planes occur in the shaly facies types, some of them concentrate along heterogeneities on the subfacies scale. The striking reproducibility of the measurements and observations was confirmed by a comparison with boreholes drilled in parallel, indicating a rather low compositional–structural variability parallel to bedding. The applied multidisciplinary approach is well suited to depict the vertical and lateral variability of a claystone formation, allowing an assessment of the degree of homogeneity/heterogeneity based on the subfacies concept.
Abstract. A potential repository site for high-level radioactive waste should ensure the
highest possible safety level over a period of one million years. In addition
to design issues, demonstrating the integrity of the barrier is essential as
it ensures the long-term containment of radioactive waste. Therefore, a
multi-disciplinary approach is necessary for the characterization of the
surrounding rock and for the understanding of the occurring physical
processes. For site selection, however, the understanding of the respective
system is essential as well: Do fault zones exist in the relevant area? Are
these active and relevant for interpreting system behavior? What is the role
of the existing heterogeneities of the claystone and how do these
site-dependent conditions influence the physical effects? To answer these
questions, the site-selection procedure requires underground exploration,
which includes geophysical and geological investigations on milli- to
decameter scales. Their results serve as the basis for numerical
modelling. This combined, multi-disciplinary interpretation requires extensive
knowledge of the various methods, their capabilities, limitations, and areas
of application. In the cyclic deformation (CD-A) experiment in the Mont Terri rock laboratory,
the hydraulic–mechanical effects due to excavation and the climatic
conditions within the rock laboratory are investigated in two niches in the
Opalinus Clay. The twin niches differ mainly with regard to the relative
humidity inside them, but are also characterized by different boundary
conditions such as existing fault zones, the technical construction of the
neighboring gallery, etc. In order to gain insights into the relevance of the
individual influences, comparative studies are being carried out on both
niches. The presented results provide a first insight into the initial
experimental years of the CD-A long-term experiment and illustrate the
benefits of multi-disciplinary investigations in terms of system understanding
and the scale dependency of physical effects. Amongst other effects, the
assessment of the impact of heterogeneities on the deformation behavior and
the evolution of pore water pressure is very complex and benefits from
geological interpretation and measurements of for example deformation, water
content, and pore pressure. The numerical modeling allows statements about the
interaction of different processes and thus enables an interpretation of the
overall system, taking into account the knowledge gained by the
multi-disciplinary investigation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.