Kristof Schuster - Academia.edu (original) (raw)

Papers by Kristof Schuster

Wiley-VCH Verlag GmbH & Co. KGaA eBooks, Jan 4, 2007

Geophysical Journal International, May 26, 1998

In this paper we present newly acquired high-quality wide-angle seismic data of the GRANU95 proje... more In this paper we present newly acquired high-quality wide-angle seismic data of the GRANU95 project and first models of the crustal structure along two profiles (95-A and 95-B) beneath the Saxonian Granulites, a major ellipse-shaped exposure of lower-crustal material within the mid-European Variscan belt in southeastern Germany (Saxony). The crust is subdivided into four layers. The crystalline basement with velocities higher than 6.0 km s−1 is generally reached at shallow depths, with three major sedimentary structures as prominent exceptions where velocities considerably lower than 6.0 km s−1 (as low as 5.1 km s −1) reach as deep as 4 km. The highest upper-crustal velocities (up to 6.5 km s−1) are not seen below the exposed granulites themselves, but at shallow depths (4 km) SW of the exposure. These shallow high velocities correlate well in depth with highly reflective zones observed on three seismic-reflection lines of DEKORP (85-4N, 95-01, 95-02) at their intersection with the seismic-refraction line 95-B, where they appear as a set of NW-SE-trending dome-shaped reflections. On profile 95-A this high-velocity uppercrustal layer (6.3 km s−1) dips from 5 to 9 km beneath the SE margin of the exposed granulites. These results suggest that the granulite dome and its western continuation are widely underlain by a NE-trending antiformal structure (probably a sheet of metabasic rocks) where the exposed felsic granulites form just a local cap on top. Below the upper-crustal high velocities, a layer with decreased velocity (6.2-6.25 km s−1) extends down to an average depth of 15 km along the Variscan strike (95-B) and to 11-16 km depth (slightly dipping towards the SE) perpendicular to the terrane boundaries (95-A). At mid-crustal levels a weak reflection from a layer with a velocity of 6.4-6.6 km s−1 may indicate the classical Conrad discontinuity. At the depth range 22-24 km the velocity jumps to an average value of 7.0 km s−1, thus defining a prominent high-velocity layer in the lower crust, which may be viewed as the well-known laminated lower crust typical of Variscan structures, but with higher average velocity than usually detected. The crust-mantle boundary at about 30-31 km is typical for western Europe and confirms the extensional signature of the West European crust. Below the Moho, poorly constrained upper-mantle velocities of about 7.9-8.0 km s−1 are derived. The high velocities observed in the lower-crustal layer would not exclude the possibility of mantlederived intrusions, but the lack of any sign of an updoming Moho favours the interpretation of a more passively driven extension.

Physics And Chemistry Of The Earth, Parts A/b/c, 2008

Underground excavation induces a disturbed/damaged zone around the opening. In argillaceous rock,... more Underground excavation induces a disturbed/damaged zone around the opening. In argillaceous rock, the excavation disturbed zone may be influenced not only by rock mechanical properties (in situ stress state, rock strength) and excavation methods, but is also strongly controlled by hydro-mechanical properties (desaturation, anisotropy). To characterise the excavation disturbed zone at the Underground Research Laboratory Meuse/Haute-Marne (France), different geoscientific methods,

ASME 2011 14th International Conference on Environmental Remediation and Radioactive Waste Management, Parts A and B, 2011

The evolution of the engineered barrier system (EBS) of geological repositories for radioactive w... more The evolution of the engineered barrier system (EBS) of geological repositories for radioactive waste has been the subject of many research programmes during the last decade. The emphasis of the research activities was on the elaboration of a detailed understanding of the complex thermo-hydro-mechanical-chemical processes, which are expected to evolve in the early post closure period in the near field. It is important to understand the coupled THM-C processes and their evolution occurring in the EBS during the early post-closure phase so it can be confirmed that the safety functions will be fulfilled. Especially, it needs to be ensured that interactions during the resaturation phase (heat pulse, gas generation, non-uniform water uptake from the host rock) do not affect the performance of the EBS in terms of its safety-relevant parameters (e.g. swelling pressure, hydraulic conductivity, diffusivity). The 7th Framework PEBS project (Long Term Performance of Engineered Barrier Systems) aims at providing in depth process understanding for constraining the conceptual and parametric uncertainties in the context of long-term safety assessment. As part of the PEBS project a series of laboratory and URL experiments are envisaged to describe the EBS behaviour after repository closure when resaturation is taking place. In this paper the very early post-closure period is targeted when the EBS is subjected to high temperatures and unsaturated conditions with a low but increasing moisture content. So far the detailed thermo-hydraulic behaviour of a bentonite EBS in a clay host rock has not been evaluated at a large scale in response to temperatures of up to 140°C at the canister surface, produced by HLW (and spent fuel), as anticipated in some of the designs considered. Furthermore, earlier THM experiments have shown that upscaling of thermal conductivity and its dependency on water content and/or humidity from the laboratory scale to a field scale needs further attention. This early post-closure thermal behaviour will be elucidated by the HE-E experiment, a 1:2 scale heating experiment setup at the Mont Terri rock laboratory, that started in June 2011. It will characterise in detail the thermal conductivity at a large scale in both pure bentonite as well as a bentonite-sand mixture, and in the Opalinus Clay host rock. The HE-E experiment is especially designed as a model validation experiment at the large scale and a modelling programme was launched in parallel to the different experimental steps. Scoping calculations were run to help the experimental design and prediction exercises taking the final design into account are foreseen. Calibration and prediction/validation will follow making use of the obtained THM dataset. This benchmarking of THM process models and codes should enhance confidence in the predictive capability of the recently developed numerical tools. It is the ultimate aim to be able to extrapolate the key parameters that might influence the fulfilment of the safety functions defined for the long term steady state.Copyright © 2011 by ASME

Tectonics, 1999

The Saxonian Granulites represent a major exposure of high‐pressure rocks within the mid‐European... more The Saxonian Granulites represent a major exposure of high‐pressure rocks within the mid‐European Variscan belt. The granulites emerge in an extensional dome structure beneath a low‐grade Paleozoic cover. The boundary between the granulites and their cover is a crustal‐scale shear zone with transport top to the SE, juxtaposing high‐pressure (HP) granulites against greenschist‐grade rocks. Seismic reflection and refraction profiling reveal that the granulite dome and its western continuation up to the SW margin of the Bohemian Massif are underlain by a reflective layer up to l s two‐way time (TWT) thickness (∼3.5 km), with P wave velocities Vp generally above 6.0 and up to 7.0 km/s (probably a sheet of metabasic rocks). This layer exhibits a NE trending antiformal structure, in line with the granulite antiform, with an apex at ∼1.2 s TWT. The outcrop of felsic granulite forms a local cap on the NE part of this high‐velocity layer. A magnetotelluric survey has revealed high resistivit...

Geological Society, London, Special Publications, 2000

Major bodies of high-pressure (HP) rocks in the Saxo-Thuringian Belt in East Germany (Saxonian Gr... more Major bodies of high-pressure (HP) rocks in the Saxo-Thuringian Belt in East Germany (Saxonian Granulite Massif, Erzgebirge) are investigated using a variety of geophysical methods (seismic reflection and refraction survey, magnetotelluric studies, gravity modelling). The Saxonian Granulite Massif and the Erzgebirge are not a continuous feature, as can be seen from discontinuous reflections, offset of upper-crustal seismic refraction velocity layers, and crustal resistivity increasing towards the Erzgebirge. Their juxtaposition during the evolution of two Variscan-age thrust wedges may have controlled this geometry. The earlier thrust wedge emplaced the supracrustal Erzgebirge HP nappes from the southeast to the northwest onto the Saxo-Thuringian Basin, whereas the later one propagated southwards and uplifted the Saxo-Thuringian granulites from deeper levels. To the southwest, the granulites are observed at shallow depth as far as the Franconian Line; to the southeast they extend do...

Rock Mechanics and Rock Engineering

<p>Safe as well as sensible economic uses of the subsurface demand both the... more <p>Safe as well as sensible economic uses of the subsurface demand both the comprehensive knowledge of the present state of a system and the understanding of the relevant dynamical processes. In order to facilitate these requirements, adequate characterisation, sufficient monitoring, and conclusive experiments have to be performed. Following this directive, the German Federal Institute for Geosciences and Natural Resources (BGR) has developed, adapted, and successfully employed methods to prospect Opalinus Clay in the Swiss Mont Terri rock laboratory. These methods encompass geoscientific in situ characterisations as well as investigation techniques as part of long-term monitoring programmes from the complementing fields of e.g. micro-seismics, Electrical Resistivity Tomography, micro-structural petrography, geohydrology, and Nuclear Magnetic Resonance. With this expertise, BGR has contributed numerous experiments, which are embedded and coordinated in the long-standing and fruitful cooperation with the partners of the Mont Terri Consortium.</p><p>The knowledge gain, based on now almost 25 years of BGR's engagement in the Mont Terri Project, offers comparison and evaluation of different, complementing methods determining present values and their evolution in time of e.g. moisture, saturation, pressure, deformation, the characterisation of parameter variability, and localisation of heterogeneities. It provides information allowing for programme optimisation of in situ measuring methods concerning penetration, resolution, effort, time, or feasibility. Therefore, the research results can be used for decision-making to refine investigation endevours in regards to specific demands of a certain site or a particular scientific problem not only for Opalinus Clay but also other claystone formations, and in some cases even for non-argillaceous rocks.</p>

EGU General Assembly Conference Abstracts, Apr 1, 2019

at the Underground Rock Laboratory, Mont Terri Dorothee Rebscher, Roman Makhnenko, Franz May, Chr... more at the Underground Rock Laboratory, Mont Terri Dorothee Rebscher, Roman Makhnenko, Franz May, Christophe Nussbaum, Kristof Schuster, Victor Vilarrasa Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany Bundesamt für Landestopografie (swisstopo), Switzerland Institute of Environmental Assessment and Water Research (IDAEA), Spanish National Research Council (CSIC), Spain University of Illinois at Urbana-Champaign, USA

Advances in Geosciences, 2019

Any site selection process for a final repository for high-level and heat producing radioactive w... more Any site selection process for a final repository for high-level and heat producing radioactive waste is a national challenge and has to take into account, among others, regional geological settings. In Germany, the site selection has to restart from zero, and all potential host rocks have to be considered equal, including argillaceous rocks. Therefore, the Federal Institute for Geosciences and Natural Resources (BGR) performs appropriate experiments in the Swiss Mont Terri rock laboratory, which is located in the Jurassic Opalinus Clay. In this paper, activities and results from actual and still ongoing experiments, with participation of BGR, are presented exemplarily. All experiments aim for a contribution to understand particular aspects regarding the behaviour of underground facilities, BGR's focus lies mainly on aspects of the early lifetime of a repository, namely the construction, post-closure transient, and partly post-closure equilibrium phases. It is obvious that for a full understanding of the evolution of a final repository, knowledge and experience of many different groups, their studies and results covering all aspects, have to be included. In this paper, we can only emphasise a few representative examples on geophysical and geotechnical in-situ site investigations, geotechnical mine-by monitoring, laboratory investigations, and modelling aspects. The combined interpretation of these results enhance interpretations and is a prerequisite for a comprehensive understanding of a repository.

Engineering Geology, 2017

Claystones are considered as a geological barrier. However, the properties of claystone may be mo... more Claystones are considered as a geological barrier. However, the properties of claystone may be modified if these are cut by brittle faults and fractures. Investigations of fault rocks are therefore crucial to evaluate the barrier properties of clay rich formations. The present study is dealing with the characterization of naturally and artificially deformed Opalinus Clay of the Mont Terri rock laboratory in NW Switzerland. Complete core sections, covering the artificially excavation damaged zone (EDZ) and several tectonic fault zones, have been studied using a multidisciplinary approach consisting of geophysical, geotechnical, mineralogical/geochemical and lithological/structural data. The fault zones encountered are characterized by a high density of planar discontinuities, which often show slickenside striations. Under the microscope, the fault zones turned out to be pervasively deformed resulting in open veins and pore space, now filled with calcite and celestine. Fault zone reactivation led to very fine-grained, cohesionless fault gouge and fragmentation of the previously formed calcite veins. Packer tests in boreholes reveal excavation induced, enhanced permeabilities up to 3 m borehole depth (1.9 m ┴ to gallery floor). Seismic borehole measurements indicate that seismic attributes, which are typical for undisturbed Opalinus Clay, are not reached until 7.5 m borehole depth (4.8 m ┴ to gallery floor), which is larger than in the usual gallery configuration. We interpret the anomalies in geophysical measurements as well as the elevated permeabilities, measured in the Main Fault (3.6 m to 4.2 m ┴ to gallery floor), to result from an enlarged EDZ, influenced by the presence of the brittle fault structures. The up to two orders of magnitude higher permeability (compared to the intact claystone) most probably results from excavation induced stress and a local reactivation of fault planes. The results suggest that the presence of a fault zone can alter the extent of the EDZ significantly, and thereby affect the rock integrity, at least in the near field of a repository tunnel.

Swiss Journal of Geosciences, 2017

Geologic repositories for radioactive waste are designed as multi-barrier disposal systems that p... more Geologic repositories for radioactive waste are designed as multi-barrier disposal systems that perform a number of functions including the long-term isolation and containment of waste from the human environment, and the attenuation of radionuclides released to the subsurface. The rock laboratory at Mont Terri (canton Jura, Switzerland) in the Opalinus Clay plays an important role in the development of such repositories. The experimental results gained in the last 20 years are used to study the possible evolution of a repository and investigate processes closely related to the safety functions of a repository hosted in a clay rock. At the same time, these experiments have increased our general knowledge of the complex behaviour of argillaceous formations in response to coupled hydrological, mechanical, thermal, chemical, and biological processes. After presenting the geological setting in and around the Mont Terri rock laboratory and an overview of the mineralogy and key properties of the Opalinus Clay, we give a brief overview of the key experiments that are described in more detail in the following research papers to this Special Issue of the Swiss Journal of Geosciences. These experiments aim to characterise the Opalinus Clay and estimate safetyrelevant parameters, test procedures, and technologies for repository construction and waste emplacement. Other aspects covered are: bentonite buffer emplacement, high-pH concrete-clay interaction experiments, anaerobic steel corrosion with hydrogen formation, depletion of hydrogen by microbial activity, and finally, release of radionuclides Editorial handling: A. G. Milnes. This is the introductory paper (including a list of abbreviations and acronyms) to accompany the 20 research papers (papers 1-20) included in the Special Issue.

Swiss Journal of Geosciences, 2017

Repository concepts in clay or crystalline rock involve bentonite-based buffer or seal systems to... more Repository concepts in clay or crystalline rock involve bentonite-based buffer or seal systems to provide containment of the waste and limit advective flow. A thorough understanding of buffer and seal evolution is required to make sure the safety functions are fulfilled in the short and long term. Experiments at the real or near-real scale taking into account the interaction with the host rock help to make sure the safety-relevant processes are identified and understood and to show that laboratory-scale findings can be extrapolated to repository scale. Three large-scale experiments on buffer and seal properties performed in recent years at the Mont Terri rock laboratory are presented in this paper: The 1:2 scale HE-E heater experiment which is currently in operation, and the full-scale engineered barrier experiment and the Borehole Seal experiment which have been completed successfully in 2014 and 2012, respectively. All experiments faced considerable difficulties during installation, operation, evaluation or dismantling that required significant effort to overcome. The in situ experiments show that buffer and seal elements can be constructed meeting the expectations raised through small-scale testing. It was, however, also shown that interaction with the host rock caused additional effects in the buffer or seal that could not always be quantified or even anticipated from the experience of small-scale tests (such as re-saturation by pore-water from the rock, interaction with the excavation damaged zone in terms of preferential flow or mechanical effects). This led to the conclusion that testing of the integral system buffer/rock or seal/rock is needed. Keywords Engineered barrier system Á In-situ experiments Á Bentonite Á Sand-bentonite mixture Á Nuclear waste disposal Editorial handling: P. Bossart and A. G. Milnes. This is paper #12 of the Mont Terri Special Issue of the Swiss Journal of Geosciences (see Bossart et al. 2017, Table 3 and Fig. 7).

Swiss Journal of Geosciences, 2017

The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observe... more The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observed in three in situ heating tests performed in the Mont Terri rock laboratory: HE-B, HE-D and HE-E. The three tests are summarily described; they encompass a broad range of test layouts and experimental conditions. Afterwards, the following topics are examined: determination of thermal conductivity, thermally-induced pore pressure generation and thermally-induced mechanical effects. The mechanisms underlying pore pressure generation and dissipation are discussed in detail and the relationship between rock damage and thermal loading is examined using an additional in situ test: SE-H. The paper concludes with an evaluation of the various thermo-hydro-mechanical (THM) interactions identified in the heating tests. Keywords Temperature effects Á In situ tests Á Coupled THM phenomena Á Numerical analyses Á Heating tests Á Pore pressures Á Nuclear waste disposal Editorial handling: P. Bossart and A. G. Milnes. This is paper #13 in the Mont Terri Special Issue of the Swiss Journal of Geosciences (see Bossart et al. 2017, Table 3 and Fig. 7).

Wiley-VCH Verlag GmbH & Co. KGaA eBooks, Jan 4, 2007

Geophysical Journal International, May 26, 1998

In this paper we present newly acquired high-quality wide-angle seismic data of the GRANU95 proje... more In this paper we present newly acquired high-quality wide-angle seismic data of the GRANU95 project and first models of the crustal structure along two profiles (95-A and 95-B) beneath the Saxonian Granulites, a major ellipse-shaped exposure of lower-crustal material within the mid-European Variscan belt in southeastern Germany (Saxony). The crust is subdivided into four layers. The crystalline basement with velocities higher than 6.0 km s−1 is generally reached at shallow depths, with three major sedimentary structures as prominent exceptions where velocities considerably lower than 6.0 km s−1 (as low as 5.1 km s −1) reach as deep as 4 km. The highest upper-crustal velocities (up to 6.5 km s−1) are not seen below the exposed granulites themselves, but at shallow depths (4 km) SW of the exposure. These shallow high velocities correlate well in depth with highly reflective zones observed on three seismic-reflection lines of DEKORP (85-4N, 95-01, 95-02) at their intersection with the seismic-refraction line 95-B, where they appear as a set of NW-SE-trending dome-shaped reflections. On profile 95-A this high-velocity uppercrustal layer (6.3 km s−1) dips from 5 to 9 km beneath the SE margin of the exposed granulites. These results suggest that the granulite dome and its western continuation are widely underlain by a NE-trending antiformal structure (probably a sheet of metabasic rocks) where the exposed felsic granulites form just a local cap on top. Below the upper-crustal high velocities, a layer with decreased velocity (6.2-6.25 km s−1) extends down to an average depth of 15 km along the Variscan strike (95-B) and to 11-16 km depth (slightly dipping towards the SE) perpendicular to the terrane boundaries (95-A). At mid-crustal levels a weak reflection from a layer with a velocity of 6.4-6.6 km s−1 may indicate the classical Conrad discontinuity. At the depth range 22-24 km the velocity jumps to an average value of 7.0 km s−1, thus defining a prominent high-velocity layer in the lower crust, which may be viewed as the well-known laminated lower crust typical of Variscan structures, but with higher average velocity than usually detected. The crust-mantle boundary at about 30-31 km is typical for western Europe and confirms the extensional signature of the West European crust. Below the Moho, poorly constrained upper-mantle velocities of about 7.9-8.0 km s−1 are derived. The high velocities observed in the lower-crustal layer would not exclude the possibility of mantlederived intrusions, but the lack of any sign of an updoming Moho favours the interpretation of a more passively driven extension.

Physics And Chemistry Of The Earth, Parts A/b/c, 2008

Underground excavation induces a disturbed/damaged zone around the opening. In argillaceous rock,... more Underground excavation induces a disturbed/damaged zone around the opening. In argillaceous rock, the excavation disturbed zone may be influenced not only by rock mechanical properties (in situ stress state, rock strength) and excavation methods, but is also strongly controlled by hydro-mechanical properties (desaturation, anisotropy). To characterise the excavation disturbed zone at the Underground Research Laboratory Meuse/Haute-Marne (France), different geoscientific methods,

ASME 2011 14th International Conference on Environmental Remediation and Radioactive Waste Management, Parts A and B, 2011

The evolution of the engineered barrier system (EBS) of geological repositories for radioactive w... more The evolution of the engineered barrier system (EBS) of geological repositories for radioactive waste has been the subject of many research programmes during the last decade. The emphasis of the research activities was on the elaboration of a detailed understanding of the complex thermo-hydro-mechanical-chemical processes, which are expected to evolve in the early post closure period in the near field. It is important to understand the coupled THM-C processes and their evolution occurring in the EBS during the early post-closure phase so it can be confirmed that the safety functions will be fulfilled. Especially, it needs to be ensured that interactions during the resaturation phase (heat pulse, gas generation, non-uniform water uptake from the host rock) do not affect the performance of the EBS in terms of its safety-relevant parameters (e.g. swelling pressure, hydraulic conductivity, diffusivity). The 7th Framework PEBS project (Long Term Performance of Engineered Barrier Systems) aims at providing in depth process understanding for constraining the conceptual and parametric uncertainties in the context of long-term safety assessment. As part of the PEBS project a series of laboratory and URL experiments are envisaged to describe the EBS behaviour after repository closure when resaturation is taking place. In this paper the very early post-closure period is targeted when the EBS is subjected to high temperatures and unsaturated conditions with a low but increasing moisture content. So far the detailed thermo-hydraulic behaviour of a bentonite EBS in a clay host rock has not been evaluated at a large scale in response to temperatures of up to 140°C at the canister surface, produced by HLW (and spent fuel), as anticipated in some of the designs considered. Furthermore, earlier THM experiments have shown that upscaling of thermal conductivity and its dependency on water content and/or humidity from the laboratory scale to a field scale needs further attention. This early post-closure thermal behaviour will be elucidated by the HE-E experiment, a 1:2 scale heating experiment setup at the Mont Terri rock laboratory, that started in June 2011. It will characterise in detail the thermal conductivity at a large scale in both pure bentonite as well as a bentonite-sand mixture, and in the Opalinus Clay host rock. The HE-E experiment is especially designed as a model validation experiment at the large scale and a modelling programme was launched in parallel to the different experimental steps. Scoping calculations were run to help the experimental design and prediction exercises taking the final design into account are foreseen. Calibration and prediction/validation will follow making use of the obtained THM dataset. This benchmarking of THM process models and codes should enhance confidence in the predictive capability of the recently developed numerical tools. It is the ultimate aim to be able to extrapolate the key parameters that might influence the fulfilment of the safety functions defined for the long term steady state.Copyright © 2011 by ASME

Tectonics, 1999

The Saxonian Granulites represent a major exposure of high‐pressure rocks within the mid‐European... more The Saxonian Granulites represent a major exposure of high‐pressure rocks within the mid‐European Variscan belt. The granulites emerge in an extensional dome structure beneath a low‐grade Paleozoic cover. The boundary between the granulites and their cover is a crustal‐scale shear zone with transport top to the SE, juxtaposing high‐pressure (HP) granulites against greenschist‐grade rocks. Seismic reflection and refraction profiling reveal that the granulite dome and its western continuation up to the SW margin of the Bohemian Massif are underlain by a reflective layer up to l s two‐way time (TWT) thickness (∼3.5 km), with P wave velocities Vp generally above 6.0 and up to 7.0 km/s (probably a sheet of metabasic rocks). This layer exhibits a NE trending antiformal structure, in line with the granulite antiform, with an apex at ∼1.2 s TWT. The outcrop of felsic granulite forms a local cap on the NE part of this high‐velocity layer. A magnetotelluric survey has revealed high resistivit...

Geological Society, London, Special Publications, 2000

Major bodies of high-pressure (HP) rocks in the Saxo-Thuringian Belt in East Germany (Saxonian Gr... more Major bodies of high-pressure (HP) rocks in the Saxo-Thuringian Belt in East Germany (Saxonian Granulite Massif, Erzgebirge) are investigated using a variety of geophysical methods (seismic reflection and refraction survey, magnetotelluric studies, gravity modelling). The Saxonian Granulite Massif and the Erzgebirge are not a continuous feature, as can be seen from discontinuous reflections, offset of upper-crustal seismic refraction velocity layers, and crustal resistivity increasing towards the Erzgebirge. Their juxtaposition during the evolution of two Variscan-age thrust wedges may have controlled this geometry. The earlier thrust wedge emplaced the supracrustal Erzgebirge HP nappes from the southeast to the northwest onto the Saxo-Thuringian Basin, whereas the later one propagated southwards and uplifted the Saxo-Thuringian granulites from deeper levels. To the southwest, the granulites are observed at shallow depth as far as the Franconian Line; to the southeast they extend do...

Rock Mechanics and Rock Engineering

<p>Safe as well as sensible economic uses of the subsurface demand both the... more <p>Safe as well as sensible economic uses of the subsurface demand both the comprehensive knowledge of the present state of a system and the understanding of the relevant dynamical processes. In order to facilitate these requirements, adequate characterisation, sufficient monitoring, and conclusive experiments have to be performed. Following this directive, the German Federal Institute for Geosciences and Natural Resources (BGR) has developed, adapted, and successfully employed methods to prospect Opalinus Clay in the Swiss Mont Terri rock laboratory. These methods encompass geoscientific in situ characterisations as well as investigation techniques as part of long-term monitoring programmes from the complementing fields of e.g. micro-seismics, Electrical Resistivity Tomography, micro-structural petrography, geohydrology, and Nuclear Magnetic Resonance. With this expertise, BGR has contributed numerous experiments, which are embedded and coordinated in the long-standing and fruitful cooperation with the partners of the Mont Terri Consortium.</p><p>The knowledge gain, based on now almost 25 years of BGR's engagement in the Mont Terri Project, offers comparison and evaluation of different, complementing methods determining present values and their evolution in time of e.g. moisture, saturation, pressure, deformation, the characterisation of parameter variability, and localisation of heterogeneities. It provides information allowing for programme optimisation of in situ measuring methods concerning penetration, resolution, effort, time, or feasibility. Therefore, the research results can be used for decision-making to refine investigation endevours in regards to specific demands of a certain site or a particular scientific problem not only for Opalinus Clay but also other claystone formations, and in some cases even for non-argillaceous rocks.</p>

EGU General Assembly Conference Abstracts, Apr 1, 2019

at the Underground Rock Laboratory, Mont Terri Dorothee Rebscher, Roman Makhnenko, Franz May, Chr... more at the Underground Rock Laboratory, Mont Terri Dorothee Rebscher, Roman Makhnenko, Franz May, Christophe Nussbaum, Kristof Schuster, Victor Vilarrasa Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany Bundesamt für Landestopografie (swisstopo), Switzerland Institute of Environmental Assessment and Water Research (IDAEA), Spanish National Research Council (CSIC), Spain University of Illinois at Urbana-Champaign, USA

Advances in Geosciences, 2019

Any site selection process for a final repository for high-level and heat producing radioactive w... more Any site selection process for a final repository for high-level and heat producing radioactive waste is a national challenge and has to take into account, among others, regional geological settings. In Germany, the site selection has to restart from zero, and all potential host rocks have to be considered equal, including argillaceous rocks. Therefore, the Federal Institute for Geosciences and Natural Resources (BGR) performs appropriate experiments in the Swiss Mont Terri rock laboratory, which is located in the Jurassic Opalinus Clay. In this paper, activities and results from actual and still ongoing experiments, with participation of BGR, are presented exemplarily. All experiments aim for a contribution to understand particular aspects regarding the behaviour of underground facilities, BGR's focus lies mainly on aspects of the early lifetime of a repository, namely the construction, post-closure transient, and partly post-closure equilibrium phases. It is obvious that for a full understanding of the evolution of a final repository, knowledge and experience of many different groups, their studies and results covering all aspects, have to be included. In this paper, we can only emphasise a few representative examples on geophysical and geotechnical in-situ site investigations, geotechnical mine-by monitoring, laboratory investigations, and modelling aspects. The combined interpretation of these results enhance interpretations and is a prerequisite for a comprehensive understanding of a repository.

Engineering Geology, 2017

Claystones are considered as a geological barrier. However, the properties of claystone may be mo... more Claystones are considered as a geological barrier. However, the properties of claystone may be modified if these are cut by brittle faults and fractures. Investigations of fault rocks are therefore crucial to evaluate the barrier properties of clay rich formations. The present study is dealing with the characterization of naturally and artificially deformed Opalinus Clay of the Mont Terri rock laboratory in NW Switzerland. Complete core sections, covering the artificially excavation damaged zone (EDZ) and several tectonic fault zones, have been studied using a multidisciplinary approach consisting of geophysical, geotechnical, mineralogical/geochemical and lithological/structural data. The fault zones encountered are characterized by a high density of planar discontinuities, which often show slickenside striations. Under the microscope, the fault zones turned out to be pervasively deformed resulting in open veins and pore space, now filled with calcite and celestine. Fault zone reactivation led to very fine-grained, cohesionless fault gouge and fragmentation of the previously formed calcite veins. Packer tests in boreholes reveal excavation induced, enhanced permeabilities up to 3 m borehole depth (1.9 m ┴ to gallery floor). Seismic borehole measurements indicate that seismic attributes, which are typical for undisturbed Opalinus Clay, are not reached until 7.5 m borehole depth (4.8 m ┴ to gallery floor), which is larger than in the usual gallery configuration. We interpret the anomalies in geophysical measurements as well as the elevated permeabilities, measured in the Main Fault (3.6 m to 4.2 m ┴ to gallery floor), to result from an enlarged EDZ, influenced by the presence of the brittle fault structures. The up to two orders of magnitude higher permeability (compared to the intact claystone) most probably results from excavation induced stress and a local reactivation of fault planes. The results suggest that the presence of a fault zone can alter the extent of the EDZ significantly, and thereby affect the rock integrity, at least in the near field of a repository tunnel.

Swiss Journal of Geosciences, 2017

Geologic repositories for radioactive waste are designed as multi-barrier disposal systems that p... more Geologic repositories for radioactive waste are designed as multi-barrier disposal systems that perform a number of functions including the long-term isolation and containment of waste from the human environment, and the attenuation of radionuclides released to the subsurface. The rock laboratory at Mont Terri (canton Jura, Switzerland) in the Opalinus Clay plays an important role in the development of such repositories. The experimental results gained in the last 20 years are used to study the possible evolution of a repository and investigate processes closely related to the safety functions of a repository hosted in a clay rock. At the same time, these experiments have increased our general knowledge of the complex behaviour of argillaceous formations in response to coupled hydrological, mechanical, thermal, chemical, and biological processes. After presenting the geological setting in and around the Mont Terri rock laboratory and an overview of the mineralogy and key properties of the Opalinus Clay, we give a brief overview of the key experiments that are described in more detail in the following research papers to this Special Issue of the Swiss Journal of Geosciences. These experiments aim to characterise the Opalinus Clay and estimate safetyrelevant parameters, test procedures, and technologies for repository construction and waste emplacement. Other aspects covered are: bentonite buffer emplacement, high-pH concrete-clay interaction experiments, anaerobic steel corrosion with hydrogen formation, depletion of hydrogen by microbial activity, and finally, release of radionuclides Editorial handling: A. G. Milnes. This is the introductory paper (including a list of abbreviations and acronyms) to accompany the 20 research papers (papers 1-20) included in the Special Issue.

Swiss Journal of Geosciences, 2017

Repository concepts in clay or crystalline rock involve bentonite-based buffer or seal systems to... more Repository concepts in clay or crystalline rock involve bentonite-based buffer or seal systems to provide containment of the waste and limit advective flow. A thorough understanding of buffer and seal evolution is required to make sure the safety functions are fulfilled in the short and long term. Experiments at the real or near-real scale taking into account the interaction with the host rock help to make sure the safety-relevant processes are identified and understood and to show that laboratory-scale findings can be extrapolated to repository scale. Three large-scale experiments on buffer and seal properties performed in recent years at the Mont Terri rock laboratory are presented in this paper: The 1:2 scale HE-E heater experiment which is currently in operation, and the full-scale engineered barrier experiment and the Borehole Seal experiment which have been completed successfully in 2014 and 2012, respectively. All experiments faced considerable difficulties during installation, operation, evaluation or dismantling that required significant effort to overcome. The in situ experiments show that buffer and seal elements can be constructed meeting the expectations raised through small-scale testing. It was, however, also shown that interaction with the host rock caused additional effects in the buffer or seal that could not always be quantified or even anticipated from the experience of small-scale tests (such as re-saturation by pore-water from the rock, interaction with the excavation damaged zone in terms of preferential flow or mechanical effects). This led to the conclusion that testing of the integral system buffer/rock or seal/rock is needed. Keywords Engineered barrier system Á In-situ experiments Á Bentonite Á Sand-bentonite mixture Á Nuclear waste disposal Editorial handling: P. Bossart and A. G. Milnes. This is paper #12 of the Mont Terri Special Issue of the Swiss Journal of Geosciences (see Bossart et al. 2017, Table 3 and Fig. 7).

Swiss Journal of Geosciences, 2017

The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observe... more The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observed in three in situ heating tests performed in the Mont Terri rock laboratory: HE-B, HE-D and HE-E. The three tests are summarily described; they encompass a broad range of test layouts and experimental conditions. Afterwards, the following topics are examined: determination of thermal conductivity, thermally-induced pore pressure generation and thermally-induced mechanical effects. The mechanisms underlying pore pressure generation and dissipation are discussed in detail and the relationship between rock damage and thermal loading is examined using an additional in situ test: SE-H. The paper concludes with an evaluation of the various thermo-hydro-mechanical (THM) interactions identified in the heating tests. Keywords Temperature effects Á In situ tests Á Coupled THM phenomena Á Numerical analyses Á Heating tests Á Pore pressures Á Nuclear waste disposal Editorial handling: P. Bossart and A. G. Milnes. This is paper #13 in the Mont Terri Special Issue of the Swiss Journal of Geosciences (see Bossart et al. 2017, Table 3 and Fig. 7).