X‐ray Micro CT for Studying Strain Localization in Clay Rocks under Triaxial Compression

Bésuelle, Pierre; Viggiani, Gioacchino; Lenoir, Nicolas; Desrues, Jacques; Bornert, Michel

doi:10.1002/9780470612187.ch2

Cited by 34 publications

(21 citation statements)

References 25 publications

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“…It is worth noting that the specimen was scanned while the strain held constant, which unavoidably causes some amount of axial stress relaxation during scanning. However, this relaxation is relatively small in the view of the complete stress-strain relationship of samples 3 and 4 (Figures 4a and 5a) and can be ignored [29]. The loading device was specifically designed for a CT scanner with a rigid frame, which is generally similar to the conventional testing system except for its much smaller size and a confining cell that is transparent to the X-ray.…”

Section: Methodsmentioning

confidence: 99%

“…It is worth noting that the specimen was scanned while the strain held constant, which unavoidably causes some amount of axial stress relaxation during scanning. However, this relaxation is relatively small in the view of the complete stress-strain relationship of samples 3 and 4 (Figures 4a and 5a) and can be ignored [29]. Additionally, in order to get the progressive failure characteristics of shale, the pauses during the loading process were necessary and the relaxation was unavoidable.…”

Section: Methodsmentioning

confidence: 99%

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Study on the Progressive Failure Characteristics of Longmaxi Shale under Uniaxial Compression Conditions by X-ray Micro-Computed Tomography

Duan

et al. 2017

Energies

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Abstract:To investigate the deformation-failure process of Longmaxi shale under uniaxial compression conditions from the mesoscopic and macroscopic points of view, novel X-ray micro-Computed Tomography (micro-CT) equipment combined with unique loading apparatus was used. Cylindrical shale samples (4 mm in diameter and 8 mm in height) were produced to perform a series of uniaxial compression tests. CT scanning images at different time points during the loading process were obtained to study the characteristics of the progressive failure. In addition, stereograms were reconstructed and vertical slices were selected to explain the failure mechanism. From the results of the testing the low-density area, local per-peak cracks, numerous post-peak cracks and secondary cracks consecutively appeared in the CT images. Vertical and inclined fissures in the samples could be observed from the stereograms' surfaces and from internal slices. The cracking indicates that the failure process of shale is progressive and the failure mechanism of shale under uniaxial compression is mainly tension destruction or comprehensive tension-shear destruction.

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Section: Methodsmentioning

confidence: 99%

“…It is worth noting that the specimen was scanned while the strain held constant, which unavoidably causes some amount of axial stress relaxation during scanning. However, this relaxation is relatively small in the view of the complete stress-strain relationship of samples 3 and 4 (Figures 4a and 5a) and can be ignored [29]. Additionally, in order to get the progressive failure characteristics of shale, the pauses during the loading process were necessary and the relaxation was unavoidable.…”

Section: Methodsmentioning

confidence: 99%

Study on the Progressive Failure Characteristics of Longmaxi Shale under Uniaxial Compression Conditions by X-ray Micro-Computed Tomography

Duan

et al. 2017

Energies

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“…It is now generally recognized that the material anisotropy is originated from particle scale as a consequence of particle spatial arrangement, also known as the internal structure. Experimental techniques including photo-elastic testing (Oda and Conishi 1974a, b;Oda et al 1985) and X-Ray computer tomography (BŽsuelle et al 2006;Takemura et al 2007) have been employed to obtain particle-scale information.…”

Section: ! Introductionmentioning

confidence: 99%

Experimental investigation on the deformation characteristics of granular materials under drained rotational shear

Yang

et al. 2015

Geomechanics and Geoengineering

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Abstract:! This paper presents an experimental investigation revisiting the anisotropic stress-strainstrength behaviour of geomaterials in drained monotonic shear using Hollow Cylinder Apparatus. The test program has been designed to cover the effect of material anisotropy, preshearing, material density and intermediate principal stress on the behaviour of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. This paper explains phenomenological observations based on recently acquired understanding in micromechanics, with attention focused on strength anisotropy and deformation non-coaxiality, i.e., non-coincidence between the principal stress direction and the principal strain rate direction. The test results demonstrate that the effects of initial anisotropy produced during sample preparation is significant. The stress-strain-strength behaviour of the specimen shows strong dependence on the principal stress direction. Pre-loading history, material density and particle shape are also found to be influential. In particular, it was found that non-coaxiality is more significant in preloaded specimens. The observations on the strength anisotropy and deformation non-coaxiality were successfully explained based on the Stress-

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“…Direct microstructural studies on Boom Clay, at the scale of pores and grains, were done using scanning electron microscopy (SEM) on broken surfaces of Boom Clay (Baeyens et al, 1985;Al Mukhtar et al, 1996;De Craen et al, 1999;Romero et al, 1999;Hildenbrand & Urai, 2003), but suffered from difficulties in the interpretation of the images, due to the roughness of the surfaces. Recent developments in the field of micro-focus X-ray computed tomography (μ-CT) (Bésuelle et al, 2006;Jin, 2007;Bugani et al, 2009;Sok et al, 2009;Bell et al, 2011;Cnudde et al, 2011) allow describing the 3D fabrics of clay materials and its evolution under load, but the resolutions achieved are not good enough to resolve porosity. The emergence of ion-beam milling tools, like focussed (FIB) and broad-ion-beam (BIB) cross-sectioning (Holzer et al, 2006(Holzer et al, , 2007(Holzer et al, , 2010Loucks et al, 2009;Desbois et al, 2010a, b;2011a, b;Holzer & Cantoni, 2012) led to an important progress in imaging microstructures and porosity in argillaceous materials, down to the nm-scale resolution.…”

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confidence: 99%

Variations in the morphology of porosity in the Boom Clay Formation: insights from 2D high resolution BIB-SEM imaging and Mercury injection Porosimetry

Hemes

Desbois

Urai

et al. 2013

Netherlands Journal of Geosciences

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Boom Clay is considered as one of the potential host rocks for the disposal of high level and/or long lived radioactive waste in a geological formation in Belgium (Mol study site, Mol-1 borehole) and the Netherlands. The direct characterisation of the pore space is essential to help understand the transport properties of radionuclides in argillaceous materials.This contribution aims to characterise and compare the morphology of the pore space in different Boom Clay samples, representing end-members with regard to mineralogy (i.e. clay content) and grain-size distribution of this formation. Broad ion beam (BIB) cross-sectioning is combined with SEM imaging of porosity and Mercury injection Porosimetry (MIP) to characterise the variability of the pore space in Boom Clay at the nm- to μm-scale within representative 2D areas and to relate microstructural observations to fluid flow properties of the bulk sample material. Segmented pores in 2D BIB surfaces are classified according to the mineralogy, generating representative datasets of up to 100,000 pores per cross-section.Results show total SEM-resolved porosities of 10-20% and different characteristic mineral phase internal pore morphologies and intra-phase porosities.Most of the nano-porosity resides in the clay matrix. In addition, in the silt-rich samples, larger inter-aggregate pores contribute to a major part of the resolved porosity. Pore-size distributions within the clay matrix suggest power-law behaviour of pore areas with exponents between 1.56-1.74. Mercury injection Porosimetry, with access to pore-throat diameters down to 3.6 nm, shows total interconnected porosities between 27-35 Vol.-%, and the observed hysteresis in the MIP intrusion vs. extrusion curves suggests relatively high pore-body to pore-throat ratios in Boom Clay. The difference between BIB-SEM visible and MIP measured porosities is explained by the resolution limit of the BIB-SEM method, as well as the limited size of the BIB-polished cross-section areas analysed. Compilation of the results provides a conceptual model of the pore network in fine- and coarse-grained samples of Boom Clay, where different mineral phases show characteristic internal porosities and pore morphologies and the overall pore space can be modelled based on the distribution of these mineral phases, as well as the grain-size distribution of the samples investigated.

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X‐ray Micro CT for Studying Strain Localization in Clay Rocks under Triaxial Compression

Cited by 34 publications

References 25 publications

Study on the Progressive Failure Characteristics of Longmaxi Shale under Uniaxial Compression Conditions by X-ray Micro-Computed Tomography

Study on the Progressive Failure Characteristics of Longmaxi Shale under Uniaxial Compression Conditions by X-ray Micro-Computed Tomography

Experimental investigation on the deformation characteristics of granular materials under drained rotational shear

Variations in the morphology of porosity in the Boom Clay Formation: insights from 2D high resolution BIB-SEM imaging and Mercury injection Porosimetry

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