Grain-scale deformation mechanisms and evolution of porosity in experimentally deformed Boom Clay

Schuck, Bernhard; Desbois, Guillaume; Urai, János

doi:10.1016/j.jsg.2019.103894

Cited by 12 publications

(16 citation statements)

References 89 publications

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“…Subsequently, the surfaces of the subsamples were polished using the BIB surface polishing procedure (Leica TIC3X) using a low-incident Ar ion beam angle (10.5 • at 7 kV for 45 min followed by 4.5 • at 5 KV for 4 h and for some selected subsamples followed by 4.5 • at 5 kV for 18 h, similarly to e.g. Schuck et al, 2020;Laurich et al, 2018;Oelker, 2019). The BIB-polished surfaces were imaged with an SEM (Zeiss Supra 55) after surface coating with a 7 nm thick tungsten layer (Leica EM ACE600).…”

Section: Sample Preparation For Image Analysis and Bib-semmentioning

confidence: 99%

“…Houben et al (2013Houben et al ( , 2014 give an overview of the microstructure of the pristine material (unfaulted shaly OPA). SEM-based studies (scanning electron microscopy) have shown that the microfabric consists of larger sub-millimetre domains embedded in a matrix of sub-parallel platy clay aggregates (Klinkenberg, 2009;Houben et al, 2013Houben et al, , 2014Seiphoori et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…Micromechanisms of deformation in clay-rich rocks are complex (e.g. Desbois et al, 2016Desbois et al, , 2017Chandler et al, 2016;Forbes Inskip et al, 2018;Gehne et al, 2020;Nejati et al, 2020;Schuck et al, 2020). Early macroscopic studies on experimentally deformed shales by compressive loading show that failure is accompanied by shear faulting both across and in-plane of anisotropy, plastic flow or slip along the plane of anisotropy, or kinking (McLamore and Gray, 1967).…”

Section: Introductionmentioning

confidence: 99%

“…The deformation behaviour of shales or clay-rich materials can be brittle, ductile, or a combination of both. Underlying micromechanisms are cataclasis, granular flow, frictional sliding, and crystal plasticity (Morgenstern and Tchalenko, 1967;Handin et al, 1963;Maltman, 1987;Logan et al, 1979Logan et al, , 1987Wang et al, 1980;Lupini et al, 1981;Rutter et al, 1986;Blenkinsop, 2000;Desbois et al, 2016Desbois et al, , 2017Schuck et al, 2020). Additionally, Ibanez and Kronenberg (1993) distinguished deformation modes based on the loading direction with respect to bedding.…”

Section: Introductionmentioning

confidence: 99%

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Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

et al. 2021

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Abstract. A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical tests have been performed to characterise the bulk mechanical, hydro-mechanical, and failure behaviour of Opalinus Clay, important questions remain about micromechanisms: how do microstructural evolution and deformation mechanisms control the complex rheology? What is the in situ microstructural shear evolution, and can it be mimicked in the laboratory? In this contribution, scanning electron microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated–undrained triaxial compression test at 4 MPa confining stress followed by argon broad ion beam (BIB) polishing. Axial load was applied (sub-)perpendicular to bedding until the sample failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the centimetre to micrometre scale showed that the samples exhibited shear failure and that deformation localised by forming a network of micrometre-wide fractures, which are oriented with angles of 50∘ with respect to horizontal. In BIB–SEM at the grain scale, macroscale fractures are shown to be incipient shear bands, which show dilatant intergranular and intragranular microfracturing, granular flow, bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed, indicating only localised permanent deformation. Thus, micromechanisms of deformation appear to be controlled by both brittle and ductile processes along preferred deformation bands. Anastomosing networks of fractures develop into the main deformation bands with widths up to tens of micrometres along which the sample fails. Microstructural observations and the stress–strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates, while bulk measurement shows compaction, with an inferred major effect on permeability by an increase in hydraulic conductivity within the deformation band. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows partial similarity and suggests that during long-term deformation additional solution–precipitation processes operate.

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Section: Sample Preparation For Image Analysis and Bib-semmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

et al. 2021

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“…Previous studies were limited to macro-and mesoscale structures, due to difficult sample preparation of OPA (e.g., Klinkenberg et al 2009;Amann et al 2012;Kaufhold et al 2013Kaufhold et al , 2016. More recent studies applied ion beam preparation tools like BIB/FIB (broad and focused ion beam) for the use of scanning electron microscopy (SEM) imaging, to resolve mineral and pore fabrics of shales and clays at the micro-scale (Keller et al 2011(Keller et al , 2013aLoucks et al 2012;Houben et al 2014;Laurich et al 2014Laurich et al , 2017Laurich et al , 2018Desbois et al 2017Desbois et al , 2018Philipp et al 2017;Schuck et al 2020). Desbois et al (2018) described the microstructures of deformed shaly OPA samples from triaxial experiments conducted by Amann et al (2012), revealing localized deformation with dilatant microcracking and cataclastic fabrics, dominated by granular flow and bending of phyllosilicates outside of the shear zone.…”

Section: Introductionmentioning

confidence: 99%

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

et al. 2021

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The mechanical behavior of the sandy facies of Opalinus Clay (OPA) was investigated in 42 triaxial tests performed on dry samples at unconsolidated, undrained conditions at confining pressures (pc) of 50–100 MPa, temperatures (T) between 25 and 200 °C and strain rates ($$\dot{\varepsilon }$$ ε ˙ ) of 1 × 10–3–5 × 10–6 s−1. Using a Paterson-type deformation apparatus, samples oriented at 0°, 45° and 90° to bedding were deformed up to about 15% axial strain. Additionally, the influence of water content, drainage condition and pre-consolidation was investigated at fixed pc–T conditions, using dry and re-saturated samples. Deformed samples display brittle to semi-brittle deformation behavior, characterized by cataclastic flow in quartz-rich sandy layers and granular flow in phyllosilicate-rich layers. Samples loaded parallel to bedding are less compliant compared to the other loading directions. With the exception of samples deformed 45° and 90° to bedding at pc = 100 MPa, strain is localized in discrete shear zones. Compressive strength (σmax) increases with increasing pc, resulting in an internal friction coefficient of ≈ 0.31 for samples deformed at 45° and 90° to bedding, and ≈ 0.44 for samples deformed parallel to bedding. In contrast, pre-consolidation, drainage condition, T and $$\dot{\varepsilon }$$ ε ˙ do not significantly affect deformation behavior of dried samples. However, σmax and Young’s modulus (E) decrease substantially with increasing water saturation. Compared to the clay-rich shaly facies of OPA, sandy facies specimens display higher strength σmax and Young’s modulus E at similar deformation conditions. Strength and Young’s modulus of samples deformed 90° and 45° to bedding are close to the iso-stress Reuss bound, suggesting a strong influence of weak clay-rich layers on the deformation behavior.

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Mechanisms of Rock Deformation

Bhattacharya

2022

Structural Geology

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Grain-scale deformation mechanisms and evolution of porosity in experimentally deformed Boom Clay

Cited by 12 publications

References 89 publications

Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

Mechanisms of Rock Deformation

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