Observations of heterogeneous pore pressure distributions in clay-rich materials

Cuss, R.J.; Harrington, J.F.; Graham, C.C.; Sathar, Shanvas; Milodowski, Antoni E.

doi:10.1180/minmag.2012.076.8.26

Cited by 8 publications

(2 citation statements)

References 13 publications

(16 reference statements)

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“…Larger fractures did form along pre-existing shear zones, always showing slickenlines on the fracture walls if separated. Such larger fractures in mudstones were interpreted as artefacts from unloading and/or from desiccation (Dehandschutter et al, 2005;Houben, 2013). Other artefacts were not observed.…”

Section: Methodsmentioning

confidence: 99%

Microstructures and deformation mechanisms in Opalinus Clay: insights from scaly clay from the Main Fault in the Mont Terri Rock Laboratory (CH)

2017

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Abstract. The Main Fault in the shaly facies of Opalinus Clay is a small reverse fault formed in slightly overconsolidated claystone at around 1 km depth. The fault zone is up to 6 m wide, with micron-thick shear zones, calcite and celestite veins, scaly clay and clay gouge. Scaly clay occurs in up to 1.5 m wide lenses, providing hand specimens for this study. We mapped the scaly clay fabric at 1 m–10 nm scale, examining scaly clay for the first time using broad-ion beam polishing combined with scanning electron microscopy (BIB-SEM). Results show a network of thin shear zones and microveins, separating angular to lensoid microlithons between 10 cm and 10 µm in diameter, with slickensided surfaces. Our results show that microlithons are only weakly deformed and that strain is accumulated by fragmentation of microlithons by newly formed shear zones, by shearing in the micron-thick zones and by rearrangement of the microlithons.The scaly clay aggregates can be easily disintegrated into individual microlithons because of the very low tensile strength of the thin shear zones. Analyses of the microlithon size by sieving indicate a power-law distribution model with exponents just above 2. From this, we estimate that only 1 vol % of the scaly clay aggregate is in the shear zones.After a literature review of the hypotheses for scaly clay generation, we present a new model to explain the progressive formation of a self-similar network of anastomosing thin shear zones in a fault relay. The relay provides the necessary boundary conditions for macroscopically continuous deformation. Localization of strain in thin shear zones which are locally dilatant, and precipitation of calcite veins in dilatant shear fractures, evolve into complex microscale re-partitioning of shear, forming new shear zones while the microlithons remain much less deformed internally and the volume proportion of the µm-thick shear zones slowly increases. Grain-scale deformation mechanisms are microfracturing, boudinage and rotation of mica grains, pressure solution of carbonate fossils and pore collapse during ductile flow of the clay matrix. This study provides a microphysical basis to relate microstructures to macroscopic observations of strength and permeability of the Main Fault, and extrapolating fault properties in long-term deformation.

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Section: Methodsmentioning

confidence: 99%

Microstructures and deformation mechanisms in Opalinus Clay: insights from scaly clay from the Main Fault in the Mont Terri Rock Laboratory (CH)

2017

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“…The discussion of the far field begins with an introduction to geosphere research studies for the UK geological disposal programme by Simon Norris of the NDA (Norris, 2012). There follow papers on: observations of stable high-pressure differentials in clay-rich materials; implications for the concept of effective stress by Robert Cuss (BGS) and co-workers (Cuss et al, 2012); coupled hydro-mechanical-chemical process modelling in argillaceous formations by Alexander Bond (Quintessa Ltd) and co-workers (Bond et al, 2012); a comparison of a postclosure transient criticality models with the Oklo natural reactors by Robert Mason (AMEC) and co-workers (Mason et al, 2012a); the consequences of hypothetical post-closure criticality by Robert Mason (AMEC) and co-workers (Mason et al, 2012b); critical stress theory applied to repository concepts; the importance of the stress tensor and stress history in fracture flow by Robert Cuss (BGS) and co-workers (Sathar et al, 2012); the comparison of discrete fracture network and equivalent continuum simulations of fluid flow through two-dimensional fracture networks for the DECOVALEX-2011 project by Colin Leung (Imperial College, London) and coworkers (Leung et al, 2012); radionuclide diffusion into undisturbed and altered crystalline rocks by Václava Havlová (Nuclear Research Institute) and co-workers (Havlová et al, 2012); and the adsorption and diffusion of Sr in simulated rock fractures by Roy Wogelius (The University of Manchester) and co-workers (Ohe et al, 2012).…”

Section: Section 4: Geosphere (Far Field)mentioning

confidence: 99%

Geological disposal of radioactive waste: underpinning science and technology

Evans

2012

Mineral. mag.

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The Royal Society of Chemistry, the Geological Society, the Institution of Civil Engineers, the Nuclear Institute, the Institution of Chemical Engineers, the Royal Academy of Engineering and the Mineralogical Society organized a wideranging conference themed around the geological disposal of radioactive waste from 18 th À20 th October 2011 at the Burleigh Court Conference C e n t r e , L o u g h b o r o u g h U n i v e r s i t y , Loughborough, UK. One of its principal objectives was to showcase and publish research relevant to radioactive waste storage and disposal. The event was supported by the Nuclear Decommissioning Authority (NDA) and the Energy Generation and Supply Knowledge Transfer Network (KTN) for the Nuclear Sector, and kindly sponsored by AMEC and the National Nuclear Laboratory (NNL). The conference brought together scientists, engineers and other interested specialists to discuss the chemical, biological, geological, hydrological, materials, engineering and other scientific and technological challenges associated with the long-term management of radioactive waste in the UK. The scientific committee peerreviewed all abstracts received prior to the conference, and determined those best for oral and poster presentation. Papers presented in this issue of Mineralogical Magazine were subsequently subjected to a detailed and independent peer-review process.

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Gas migration in pre-compacted bentonite under elevated pore-water pressure conditions

Graham

Harrington

Sellin

2016

Applied Clay Science

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6 Pre-compacted bentonite has long been proposed as a primary component of an Experiments also show the potential for gas entry into the buffer to occur as a result of 23 declining pore-water pressure conditions. As such, the influence of significant deviations 24 from hydrostatic conditions (for example, resulting from glacial loading) should not be 25 neglected when considering gas interaction with the buffer over long timescales.26

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Observations of heterogeneous pore pressure distributions in clay-rich materials

Abstract: Abstract

Cited by 8 publications

References 13 publications

Microstructures and deformation mechanisms in Opalinus Clay: insights from scaly clay from the Main Fault in the Mont Terri Rock Laboratory (CH)

Microstructures and deformation mechanisms in Opalinus Clay: insights from scaly clay from the Main Fault in the Mont Terri Rock Laboratory (CH)

Geological disposal of radioactive waste: underpinning science and technology

Gas migration in pre-compacted bentonite under elevated pore-water pressure conditions

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