A new technique for preparing rock spheres

Vickers, B L; Thill, R.E.

doi:10.1088/0022-3735/2/10/422

Cited by 17 publications

(4 citation statements)

References 2 publications

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“…The best way to evaluate the anisotropy of any physical property in the laboratory is to work on rock sarnples with a spherical shape (Vickers & Thill 1969;Hrouda et al 1993), thus avoiding uncertainties due to rock heterogeneity between multiple samples and presenting always the same shape to the measuring apparatus (geometry of contact, constant volume or distance of investigation). However, owing to the difficulty of machining spheres, it is generally easier to work on cylindrical cores.…”

Section: Bedding Foliation and Anisotropy Of Physical Propertiesmentioning

confidence: 99%

Effects of bedding and foliation on mechanical anisotropy, damage evolution and failure mode

Baud

Louis

David

et al. 2005

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In this study we review recent advances in our understanding of anisotropy in rocks, focusing on dilatant and compactant failure in sandstones and in a foliated metamorphic rock. In sandstones, the anisotropy can be associated with bedding, as in the Rothbach sandstone, or it can also be due to shape anisotropy of the grains and/or the pores, as in the Bentheim sandstone. Two scenarios are proposed for the development of anisotropy in these two end members. In a metamorphic rock with strong foliation like the Four-mile gneiss, it has been commonly observed that the brittle strength is minimum at a foliation angle of about 30 ~ ~ A damage mechanics model is proposed that underscores the dominant role of biotite foliation in the development of microcracking. In contrast it is often observed in sandstones with strong bedding that the strength is minimum in the direction parallel to bedding. New results for the Rothbach sandstone showed that compared to parallel-to-bedding samples: (i) in the brittle faulting regime the perpendicular-to-bedding samples have both a higher strength and dilatancy stress; and (ii) in the cataclastic flow regime the compactive yield envelope for the perpendicular-to-bedding samples expands significantly towards higher stress values.Significant anisotropy in mechanical behaviour and failure strength may arise from planar rock fabrics such as bedding in sedimentary rocks, cleavage in slates and preferred orientation, and/or arrangement of minerals and cracks in crystalline igneous and metamorphic rocks.

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Section: Bedding Foliation and Anisotropy Of Physical Propertiesmentioning

confidence: 99%

Effects of bedding and foliation on mechanical anisotropy, damage evolution and failure mode

Baud

Louis

David

et al. 2005

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“…The sphere preparation process is described in detail elsewhere [Vickers and Thill, 1969]. EXPERIMENTAL METI-I OD Ultrasonic pulse method.…”

Section: Selection and Preparation Of Specimensmentioning

confidence: 99%

Correlation of longitudinal velocity variation with rock fabric

Thill¹,

Willard²,

Bur³

1969

J. Geophys. Res.

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Comparisons of longitudinal (compressional) wave velocity with structural subfabrics have been made for Yule marble, Newberry Crater pumice, and Salisbury granite. Velocities were (1) measured omnidirectionally in spherical specimens by an ultrasonic pulse technique and (2) plotted and contoured on equal area nets. These contour patterns show velocity anisotropy that can be interpreted in terms of elastic symmetry. Microstructural subfabrics were determined from oriented thin sections of the specimens. Subfabrics were then displayed on equal area nets for comparison of their symmetries with those of the longitudinal wave velocities. The two structural subfabric elements selected for comparison were crystallographic orientation of constituent anisotropic minerals and shape and orientation of pores or cracks. The longitudinal velocity symmetry in Yule marble appears to be axial, whereas in both Newberry Crater pumice and Salisbury granite the pattern is orthorhombic. The pattern of longitudinal velocity anisotropy is associated with preferred orientation of calcite optic axes in Yule marble, preferred orientation of elongate vesicles in the Newberry Crater pumice, and preferred orientation of microfractures in quartz in the Salisbury granite. A prospectus given suggests that the petrophysical technique described can be used to determine elastic symmetry, orient rock to inherent elastic symmetry axes, indicate sample homogeneity, and supplement conventional petrofabric techniques.

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“…Unfortunately, such an experimental configuration does not allow for the application of a deviatoric (anisotropic) stress on the rock sample, only the effects of confining pressure (isotropic) on elastic anisotropy can be explored. An apparatus dedicated to the measurement of the P-wave ultrasonic traveltimes across a spherical rock sample under confining pressures up to 400 MPa was designed at the Czech Academy of Sciences (Pros & Babuška 1967;Pros & Babuška 1968;Thill et al 1969Thill et al , 1973Vickers & Thill 1969;Pros & Podroužková 1974). One of the earliest works on such data to compute the elasticity tensor from only P-wave ultrasonic measurements was by Jech (1991), who suggested a non-linear iterative least-square optimization procedure to solve Christoffel's equation for the triclinic symmetry class involving 21 unknown elasticity parameters (Slawinski 2007).…”

Section: Introductionmentioning

confidence: 99%

Estimation of the anisotropy parameters of transversely isotropic shales with a tilted symmetry axis

Nadri¹,

Sarout²,

Bóna

et al. 2012

Geophysical Journal International

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SUMMARY This paper reports a new approach for the estimation of Thomsen anisotropy parameters and symmetry axis orientation from ultrasonic P‐wave traveltime measurements on transversely isotropic shale samples of arbitrary geometry. This approach can be used for core samples cut in any direction with respect to the bedding plane, because no a priori assumption regarding the symmetry axis orientation is made. This orientation is rather part of the solution of the inverse problem together with the anisotropy parameters themselves. Very fast simulated reannealing is used to search for the best possible estimate of the model parameters. The methodology is applied to spherical and cylindrical anisotropic shale samples.

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A new technique for preparing rock spheres

Cited by 17 publications

References 2 publications

Effects of bedding and foliation on mechanical anisotropy, damage evolution and failure mode

Effects of bedding and foliation on mechanical anisotropy, damage evolution and failure mode

Correlation of longitudinal velocity variation with rock fabric

Estimation of the anisotropy parameters of transversely isotropic shales with a tilted symmetry axis

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