Brittle fractures and ductile shear bands in argillaceous sediments: inferences from Oligocene Boom Clay (Belgium)

Dehandschutter, Boris; Vandycke, Sara; Sintubin, Manuel; Vandenberghe, Noël; Wouters, Laurent

doi:10.1016/j.jsg.2004.08.014

Cited by 71 publications

(57 citation statements)

References 49 publications

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“…Due to the depth at which it has been sampled (223 m) and to the high corresponding in situ vertical effective stress (estimated at 2.45 MPa with an average soil unit mass ρ = 2.1 Mg/m 3 at a depth of 223 m), Boom clay can certainly be considered as a cross anisotropic material. This is also suggested by the scanning electron microscope observations carried out by Dehandschutter et al (2004) in which bedding planes were clearly observed (note also that the Boom clay layer is gently dipping (±1°) towards the North-North-East -see Mertens et al (2004) and Figure 1). …”

Section: Water Retention Curve and Swelling Behavioursupporting

confidence: 60%

Suction effects in deep Boom Clay block samples

et al. 2007

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Extensive investigations have been and are being carried out on a stiff clay from an underground research laboratory located at Mol (Belgium) called Boom clay, in the context of research into deep nuclear waste disposal. Suction effects in deep Boom clay block samples were investigated through the characterisation of the water retention and of the swelling properties of the clay. The data obtained allowed an estimation of the sample initial suction that was reasonably compatible with the in-situ state of stress at a depth of 223 m. The relationship between suction and stress changes during loading and unloading sequences were also examined by running oedometer tests with suction measurements. A rather wide range of the ratio s/σ' v (being s the suction and σ' v the effective vertical stress) was obtained (0.61 -1), different from that proposed by Bishop et al;(1974). Finally, the effect of suction release under an isotropic stress close to the estimated sample suction was investigated. A slight swelling (1.7%) was observed and further compression provided a satisfactory value of the overconsolidation ratio confirming the suggestions of taking some precautions before putting a swelling sample in contact with water as suggested by Graham et al. (1987). The various experimental data gathered in this study finally evidenced a relatively good state of conservation of the block sample used.

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Section: Water Retention Curve and Swelling Behavioursupporting

confidence: 60%

Suction effects in deep Boom Clay block samples

et al. 2007

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“…Contrary to the undeformed OPA, the gouge microstructure contains no fossils and has a much higher fabric intensity and drastically less calcite grains. Many smaller open fractures are present, which we confidently interpret as artifacts from desiccation and/or unloading (see Dehandschutter et al, 2005;Houben, 2013). Figure 11 provides a micrograph comparison of gouge and the undeformed OPA (shaly facies).…”

Section: Microstructurementioning

confidence: 80%

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Laurich

Urai

Vollmer³

et al. 2018

Solid Earth

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Abstract. We studied gouge from an upper-crustal, lowoffset reverse fault in slightly overconsolidated claystone in the Mont Terri rock laboratory (Switzerland). The laboratory is designed to evaluate the suitability of the Opalinus Clay formation (OPA) to host a repository for radioactive waste.The gouge occurs in thin bands and lenses in the fault zone; it is darker in color and less fissile than the surrounding rock. It shows a matrix-based, P-foliated microfabric bordered and truncated by micrometer-thin shear zones consisting of aligned clay grains, as shown with broad-ion-beam scanning electron microscopy (BIB-SEM) and optical microscopy. Selected area electron diffraction based on transmission electron microscopy (TEM) shows evidence for randomly oriented nanometer-sized clay particles in the gouge matrix, surrounding larger elongated phyllosilicates with a strict P foliation. For the first time for the OPA, we report the occurrence of amorphous SiO 2 grains within the gouge. Gouge has lower SEM-visible porosity and almost no calcite grains compared to the undeformed OPA.We present two hypotheses to explain the origin of gouge in the Main Fault: (i) "authigenic generation" consisting of fluid-mediated removal of calcite from the deforming OPA during shearing and (ii) "clay smear" consisting of mechanical smearing of calcite-poor (yet to be identified) source layers into the fault zone. Based on our data we prefer the first or a combination of both, but more work is needed to resolve this.Microstructures indicate a range of deformation mechanisms including solution-precipitation processes and a gouge that is weaker than the OPA because of the lower fraction of hard grains. For gouge, we infer a more ratedependent frictional rheology than suggested from laboratory experiments on the undeformed OPA.

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“…Damage was also studied by means of seismic and acoustic (Lavrov et al, 2002) measurements. Boom clay can exhibit both ductile and brittle behaviours (Dehandschutter et al, 2005). More recent studies using advanced imaging technique provided evidence of cracks in Boom Clay samples (Bésuelle et al, 2013) The transition between the failure modes depends strongly on the confining pressure and is also influenced by the water content (Al-Shayea, 2001) and by the overconsolidation ratio.…”

Section: Summary Of Boom Clay Data From the Literaturementioning

confidence: 99%

“…Experimental evidence show that clayey soils can exhibit either a brittle or a ductile behaviour (Dehandschutter et al, 2005). The transition between both behaviours depends on multiple factors including moisture content (Al-Shayea, 2001).…”

Section: Introductionmentioning

confidence: 99%

A fully coupled damage-plasticity model for unsaturated geomaterials accounting for the ductile–brittle transition in drying clayey soils

Pense

Arson

Pouya

2016

International Journal of Solids and Structures

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To cite this version:Solenn Le Pense, Chloé Arson, Ahmad Pouya.A fully coupled damage-plasticity model for unsaturated geomaterials accounting for the ductile-brittle transition in drying clayey soils.International AbstractThis paper presents a hydro-mechanical constitutive model for clayey soils accounting for damageplasticity couplings. Specific features of unsaturated clays such as confining pressure and suction effects on elastic domain and plastic strains are accounted for. A double effective stress incorporating both the effect of suction and damage is defined based on thermodynamical considerations, which results in a unique stress variable being thermodynamically conjugated to elastic strain.Coupling between damage and plasticity phenomena is achieved by following the principle of strain equivalence and incorporating the double effective stress into plasticity equations. Two distinct criteria are defined for damage and plasticity, which can be activated either independently or simultaneously. Their formulation in terms of effective stress and suction allows them to evolve in the total stress space with suction and damage changes. This leads to a direct coupling between damage and plasticity and allows the model to capture the ductile/brittle behaviour transition occurring when clays are drying. Model predictions are compared with experimental data on Boom Clay, and the flexibility of the model is illustrated by presenting results of simulations in which either damage or plasticity dominates the coupled behaviour.

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Brittle fractures and ductile shear bands in argillaceous sediments: inferences from Oligocene Boom Clay (Belgium)

Cited by 71 publications

References 49 publications

Suction effects in deep Boom Clay block samples

Suction effects in deep Boom Clay block samples

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

A fully coupled damage-plasticity model for unsaturated geomaterials accounting for the ductile–brittle transition in drying clayey soils

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