The inter-scale behaviour of two natural scaly clays

Nardelli, Vincenzo; Coop, M. R.; Vitone, Claudia; Chen, Songying

doi:10.1680/jgele.16.00060

Cited by 20 publications

(5 citation statements)

References 15 publications

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“…Similar behaviour was also observed in several undrained and drained triaxial tests performed on London clay where, besides a decrease of the overall shear strength, the samples tended to fail along the pre-existing fissures (Ward et al, 1965;Webb, 1966;Skempton et al, 1969;Marsland, 1971;Sandroni, 1977;Gasparre et al 2007). A number of experimental investigations have also been carried out on the behaviour of other stiff fissured clays, such as those from southern Italy (Comegna & Picarelli, 2008;Vitone & Cotecchia, 2011;Nardelli et al;. These clays are intensely fissured, with samples containing many closely spaced fissures.…”

Section: Introductionsupporting

confidence: 69%

“…As it is difficult to measure the stiffness of a fissure in practice it is difficult to determine a realistic value. Some experimental results are given in Nardelli et al (2016), in which an inter-particle loading apparatus was employed to study the contact behaviour of clay scales. Interpreting these results gives a fissure stiffness of 𝑘 𝑠 = 𝑘 𝑛 = 2 × 10 5 kN/m 3 .…”

Section: Shear Stiffnessmentioning

confidence: 99%

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Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays

Potts

Pedro

et al. 2021

Géotechnique

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Conventional laboratory triaxial tests apply axisymmetric boundary conditions to a cylindrical sample which has an axisymmetric geometry. For a homogeneous sample this implies that the deformed shape of the sample should maintain an axisymmetric geometry during the test. Consequently, the sample should deform in a barrelling mode and if slip planes develop they should define a cup and cone-like failure surface. However, in many triaxial tests such behaviour is not observed, especially as failure is approached when a planar slip surface develops. Such a deformation mode is not axisymmetric. One reason for this behaviour is that a fissure pre-exists in the sample. Employing hydro-mechanically coupled three-dimensional finite-element analyses, this paper investigates the influence of a single fissure in a triaxial sample of stiff clay on its behaviour throughout the test, focusing on the fissure position, orientation, strength and stiffness, in conjunction with the sample's end-restraints (rough or smooth). The effects are quantified in terms of the sample's overall stiffness and strength, indicating that the presence of a fissure can affect the very small strain stiffness, and that it has a significant effect on the strength of the sample, demonstrating that the conventional methods used to interpret laboratory tests may give unconservative results. The results also show a significant effect of the conditions at the top and bottom surfaces of the sample, where in particular the lateral restraint and rough ends introduce ‘bending’ in the sample.

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Section: Introductionsupporting

confidence: 69%

Section: Shear Stiffnessmentioning

confidence: 99%

Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays

Potts

Pedro

et al. 2021

Géotechnique

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“…The contact tests between pairs of particles have been carried out by means of the Inter-Particle Loading Apparatus, which is a custom-made device designed and built at the City University of Hong Kong [25]. The device has been recently upgraded and its current configuration is capable of applying combinations of either forces or displacement along three orthogonal directions [26]. Other important upgrades include the improvement of the accuracy of the displacement measurements and the increase of the apparatus' stiffness, which also improves the accuracy and reliability of the measured displacements.…”

Section: Experimental Equipmentmentioning

confidence: 99%

An experimental investigation of the micromechanics of Eglin sand

et al. 2017

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The mechanical behaviour of Eglin sand at the micro-scale was studied in this work. Laboratory experiments using unconventional apparatuses were carried out in order to study the contact behaviour of pairs of particles in both compression (normal loading) and shearing (tangential loading) and the strength of grains. Particle fractions were identified according to their colour by visual observation and both their chemical composition and surface morphologies were obtained. The tangential stiffnesses and inter-particle coefficients of frictions for the different fractions found in the sand sample were determined under the range of normal loadings applied (1-9N). The results show some discrepancies between the theoretical models commonly found in literature to describe either the normal or the tangential loading response, which are able to predict the trend of the force-displacement curves but using elastic moduli that are lower than those found in literature, especially in the case of tangential loading. Also, the results of particle crushing tests show quite consistent results (excluding one particle group), probably related to the similar mineralogy of all fractions, which are mainly constituted by silica.

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“…In particular, the fissures are organized into a peculiar intense network that splits the clay into millimetre lens-shaped elements (known as scales -which is the origin of their being referred to as scaly clays in the literature). This paper reports a further step of a long lasting experimental research, which entails the experimental investigation of the geomechanical properties of several differently fissured clays, aiming at their modelling as a single class of geomaterials [8][9][10][11][12][13]. During previous laboratory studies, the SCM scaly clay [9][10][11] were tested in plane strain compression tests at zero confining pressure in the plane of deformation.…”

Section: Introductionmentioning

confidence: 99%

Influence of fissure inclination and confining pressure on the local behaviour of natural clays

et al. 2019

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In this experimental study the influence of fissuring orientation and confinement pressure on the mechanical behaviour of natural clays is investigated. The tested material, the scaly clay from Santa Croce di Magliano (south of Italy), is characterised by an intense network of pre-existing fissures of single orientation. Several plane strain compression tests have been conducted, under different confinement pressures (i.e., from 50 to 600 kPa), on specimens having fissures with vertical, medium and horizontal inclination. Digital Image Correlation has been used to follow the deformation processes of the specimens throughout the tests by measuring incremental shear and volumetric strain maps. The results showed a strong coupling between the total confinement and the fissure inclination, that is controlling both the onset and the development of the patterns of the localisation processes. The new results have been compared with previous ones carried out on the same material without confinement. The comparison shed light on the role of total confinement that becomes particularly relevant from certain levels of pressures and fissuring inclination.

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The inter-scale behaviour of two natural scaly clays

Cited by 20 publications

References 15 publications

Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays

Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays

An experimental investigation of the micromechanics of Eglin sand

Influence of fissure inclination and confining pressure on the local behaviour of natural clays

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