Water Retention Characteristics and State-Dependent Mechanical and Petro-Physical Properties of a Clay Shale

Wild, Katrin M.; Wymann, Linda P.; Zimmer, Sebastian; Thoeny, Reto; Amann, Florian

doi:10.1007/s00603-014-0565-1

Cited by 75 publications

(48 citation statements)

References 33 publications

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“…The initial water contents of the specimens range between 6.95 and 7.34 %, which is comparable with the water content measured on cores right after core extraction (Pearson et al, 2003;Amann et al, 2011;Wild, 2016). The initial saturation was estimated from the initial water content, the bulk dry density, and the porosity of the specimens according to the ISRM-suggested methods (ISRM, 1979).…”

Section: Resultssupporting

confidence: 64%

“…The hydraulic conductivity, for example, varies between 10 −12 m s −1 parallel to bedding and 10 −14 m s −1 normal to bedding (Marschall et al, 2004). The water loss porosity of the shaly facies is in the order of 15-19 % (Bossart, 2005;Amann et al, 2011Amann et al, , 2012Wild et al, 2015;Wild, 2016). The pore water of the Opalinus Clay at the Mont Terri URL can be classified as Na-Cl water and, with regard to its composition, is still close to that of the seawater where the material was deposited (Thury and Bossart, 1999;Pearson et al, 2003).…”

Section: Materials Descriptionmentioning

confidence: 99%

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The response of Opalinus Clay when exposed to cyclic relative humidity variations

2017

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Abstract. Clay shale specimens were exposed to cyclic relative humidity (RH) variations to investigate the response of the material to natural environmental changes. Opalinus Clay, a clay shale chosen as host rock for nuclear waste disposal in Switzerland, was utilized. The specimens were exposed to stepwise relative humidity cycles in which they were alternately allowed to equilibrate at 66 and 93 % relative humidity. Principal strains were monitored throughout the experiments using strain gauges. After each relative humidity cycle, Brazilian tensile strength tests were performed to identify possible changes in tensile strength due to environmental degradation.Results showed that Opalinus Clay follows a cyclic swelling-shrinkage behaviour with irreversible expansion limited to the direction normal to bedding, suggesting that internal damage is restricted along the bedding planes. The Brazilian tensile strength in direction parallel and normal to bedding as well as the water retention characteristic remained unaffected by the RH variations.

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Section: Resultssupporting

confidence: 64%

Section: Materials Descriptionmentioning

confidence: 99%

The response of Opalinus Clay when exposed to cyclic relative humidity variations

2017

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“…More information can be found in e.g. Wild et al (2015) and Bock (2009). The initial conditions imply a fully saturated area of Opalinus Clay.…”

Section: Model Set-upmentioning

confidence: 99%

“…with: the van Genuchten fitting parameters P 0 and R according to Wild et al (2015). The relationship between the relative permeability and the saturation is defined by: where the shape factor m and the effective saturation are given by:…”

Section: Model Set-upmentioning

confidence: 99%

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Coupled hydraulic-mechanical simulation of seasonally induced processes in the Mont Terri rock laboratory (Switzerland)

Ziefle¹,

Matray²,

Maßmann³

et al. 2017

Swiss J Geosci

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This paper focuses on hydraulic-mechanical effects in the Mont Terri rock laboratory (Switzerland) and investigates their impact on pore pressure, the convergence of a niche and the evolution of pre-existing cracks in the wallrock of the niche. A comparison of measurements with numerical simulation results is conducted. The presented in situ measurements include long-term data on temperature, relative humidity, and niche convergence, as well as crackmeter and jointmeter measurements determining the aperture of a bedding-parallel crack. Furthermore, timedomain-reflectometry measurements were carried out in a borehole located in the niche wall close to the crack. They provide information on the water content of the claystone. The numerical simulation is carried out with OpenGeoSys. It contains a 2-dimensional coupled hydraulic-mechanical model considering orthotropy, swelling and shrinkage effects, linear elastic material behaviour and an excavation damaged zone characterized by a zone of lower rock strength. An additional focus is laid on the evolution of cracks in the wallrock of the niche. The presented model approach allows a prediction of the temporal evolution of a desaturated zone incorporating a seasonally influenced part. The comparison with measured water contents yields good agreement. Simulation results and measurements consistently predict a convergence of the niche. The evolution of the crack aperture is influenced by long-term as well as seasonallyinfluenced effects. Due to the convergence of the niche, the long-term trend is characterized by closure of the crack. Furthermore, the seasonally influenced desaturation in winter results in opening of the crack, while the resaturation in the warm and wet summer months leads to closure of the crack. Finally, the comparison of simulation results with measurements indicates qualitative agreement. As a matter of fact, the numerical model seems to represent significant effects concerning the evolution of the crack aperture of a single crack.

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Tonstein als Wirtsgestein: Ein geomechanischer Beitrag über Opalinuston

2016

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Der Opalinuston ist ein prominenter Vertreter der organikhaltigen Tonsteine oder Schiefertone, die in der Schichtenfolge aus Trias und Jura regional ein mehrere Zehnermeter mächtiges, relativ homogenes Schichtpaket bildet. In Abhängigkeit vom Verfestigungsgrad der Pelitgesteine variieren die geomechanischen Parameter Scherfestigkeit, Zugfestigkeit und Durchlässigkeit, die bei einer zu diskutierenden Nutzung als Wirtsgestein für die Lagerung radioaktiver Abfälle auch bautechnische Bedeutung erlangen. Ein Tunnelvortrieb im Opalinuston bot die eher seltene Gelegenheit, Proben aus unverwittert frischen Schiefertonen in größerem Umfang als bei üblichen Bohrungen zu gewinnen. Es werden geomechanische Laborversuche, insbesondere mehrstufige, triaxiale Kompressionsversuche und Hydraulic‐Fracturing‐Versuche an definiert räumlich eingespannten Quaderproben ausgewertet, um Scherfestigkeit, hydraulische Zugfestigkeit sowie Durchlässigkeits‐ bzw. Abdichtungseigenschaften des Opalinustons zu charakterisieren. Einführend wird in diesem Kontext die Bedeutung des Sättigungszustands und dessen Veränderlichkeit diskutiert. Die ermittelten geomechanischen Parameter werden verglichen mit vormals höher und mit ähnlich beanspruchten, äußerlich gleich erscheinenden Pelitgesteinen aus Japan und aus der Schweiz. Clay shale as host rock: a geomechanical contribution about Opalinus clay. The Opalinuston is a prominent rock representing the type of organic clay shales or clay stones within the sequence of Triassic and Jurassic marine sediments in Southern Germany. The rock forms a homogenous unit some ten meters thick. The degree of consolidation of this type of pelitic rock depends mainly on the former load conditions, but is also dependent on the long‐term weathering and even on the present exposition. The geomechanical parameters such as shear strength, tensional strength and permeability vary with the state of consolidation and become important when the use is discussed of such rocks for radioactive waste disposal. A tunneling project at the northern escarpment of the Swabian Alb (Southwest Germany) within the Opalinus clay offered the rare opportunity to obtain fresh unweathered rock samples in greater amounts compared to fresh drilling cores from which geomechanical investigations are usually undertaken. Consequently, the results of geomechanical laboratory testings are presented in order to compare here the results of multistep triaxial compression tests, of hydraulic fracturing laboratory tests and of some other tests for rock characterization with the corresponding results of Opalinus clay sites in Switzerland that were investigated by the Swiss Nagra Company for host rock characterization. After a discussion of the relevant state of fresh Opalinus clay, especially of suction pressure conditions and saturation state, the results of triaxial shear tests are presented. Increasing shear deformation at increasing pressure and unchanged water saturation do not result in a significant strength reduction of the Opalinus clay. The ...

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Water Retention Characteristics and State-Dependent Mechanical and Petro-Physical Properties of a Clay Shale

Cited by 75 publications

References 33 publications

The response of Opalinus Clay when exposed to cyclic relative humidity variations

The response of Opalinus Clay when exposed to cyclic relative humidity variations

Coupled hydraulic-mechanical simulation of seasonally induced processes in the Mont Terri rock laboratory (Switzerland)

Tonstein als Wirtsgestein: Ein geomechanischer Beitrag über Opalinuston

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