Authors: Kuijpers, JS; Watson, BP; Henry, G

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Kuijpers, JS, Watson, BP & Henry, G 2008, 'Nonlinear Elastic Behaviour of Bushveld Rock', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium, Australian Centre for Geomechanics, Perth, pp. 475-485.

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Abstract:
In the laboratory, core obtained from certain platinum mines in the Bushveld Complex in South Africa showed a strong nonlinear relationship between applied load and induced deformation. This nonlinear behaviour invalidates assumptions that are typically used for numerical modelling and stress measurements. Consequently, the results from such numerical models and stress measurements may be unrealistic. It was found that specimens that exhibited this nonlinear behaviour often had a relatively low compressive strength. Petrographic study of thin sections showed no connection between mineral composition and this nonlinear behaviour. Also, no correlation was found between the density of micro-fracturing and this nonlinearity. Under the scanning electron microscope (SEM), however, a specimen exhibiting this nonlinear behaviour was found to contain open micro-cracks; no such cracks were observed in a similar specimen, which exhibited a more conventional linear stress–strain relationship. Upon further investigation, it was found that mainly samples from depths in excess of about 1000 m demonstrate nonlinear behaviour. Preliminary results also suggest that this behaviour is affected not only by the in situ stress, but also by the direction of drilling. In these samples, complete crack closure appears to occur only under applied stresses far in excess of the in situ virgin stresses. In addition, it was found that crack sliding also contributes to the observed nonlinear behaviour. This paper analyses and quantifies the nonlinear behaviour and discusses practical implications of such nonlinear behaviour.

References:
Barr, S.P. and Hunt, D.P. (1999) Anelastic strain recovery and the Kaiser effect retention span in the Carnmenellis Granite, U.K. Rock Mech. Rock Engng, 32 (3), pp. 169–193.
Bristow, J.R. (1960) Microcracks and the static and dynamic elastic constants of annealed and heavily cold-worked metals. British J. Appl. J. Phys., 11, pp. 81–85.
Carvalho, F.C.S., Chen, C. and Labuz, J.F. (1997) Measurements of effective elastic modulus and microcrack density, Int. J. Rock Mech. & Min. Sci., Vol. 34, No. 3–4, Paper No. 043.
Cawthorn, R.G. and Webb, S.J. (2001) Connectivity between the western and eastern limbs of the Bushveld Complex. Tectonophysics, 330, pp. 195–209.
Cawthorn, R.G., Eales, H.V., Walraven, F., Uken, R. and Watkeys, M.K. (2006) The Bushveld Complex. The Geology of South Africa. M.R. Johnson, C.R. Anhaeusser and R.J. Thomas, (editors), Geological Society of South Africa, Johannesburg, and Council for Geoscience, Pretoria, pp. 261–281.
Eales, H.V., Botha, W.J., Hattingh, P.J., de Klerk, W.J., Maier, W.D. and Odgers, A.T.R. (1993) The mafic rocks of the Bushveld Complex: a review of emplacement and crystallization history, and mineralization in the light of recent data, Journal of African Earth Sciences, 16, pp. 121–142.
Goodman, R.E., Taylor, R.L. and Brekke, T.L. (1968) A model for the mechanics of joint rock. Journal of the Soil Mechanics and Foundations Division, ASCE.
Henry, G. and Palmer, C. (2007) Petrographic and geochemical report on a suite of Bushveld complex rocks from the Impala platinum mine 10 shaft, Union mine and Amandelbult mine. Internal report YMP0038, CSIR, South Africa.
Holt, R.M., Brignoli, M. and Kenter, C.J. (2000) Core quality: quantification of core-induced rock alteration, Int. J. Rock Mech. & Min. Sci., Vol. 37, pp. 889–907.
Kachanov, M. (1992) Effective elastic properties of cracked solids: critical review of some basic concepts, Appl. Mech. Rev., Vol. 45, pp. 304–335.
Lin, W., Kwasniewski, M. Imamura, T. and Matsuki, K. (2006) Determination of three-dimensional in situ stresses from anelastic strain recovery measurement of cores at great depth, Tectonophysics, 426, pp. 221–238.
Matsuki, K. (1991) Three-dimensional in-situ stress measurement with anelastic strain recovery of a rock core, 7th Int. Congress on Rock Mechanics, Aachen, pp. 557–560.
Perritt, S. and Roberts, M. (2007) Flexural-slip structures in the Bushveld Complex, South African Journal of Structural Geology, 29, pp. 1422–1429.
Sakaguchi, K., Iino, W. and Matsuki, K. (2002) Damage in a rock core caused by induced tensile stresses and its relation to differential strain curve analysis, Int. J. Rock Mech. Min. Sc., 39, pp. 367–380.
Teufel, L.W. (1983) Determination of in-situ stress from anelastic strain recovery measurements of oriented cores, SPE/DOE 11649, Denver, U.S.A, pp. 421–430.
Teufel, L.W. (1989) A mechanism for anaelastic strain recovery of cores from deep boreholes: time-dependent micro cracking, Eos, Trans. Am. Geophys. Union, 70:476.
Walsh, J.B. (1965) The effect of cracks on the uniaxial elastic compression of rocks, J. Geophys. Res., 70, pp. 399–411.
Wang, D.F., Davies, P.J., Yassir, N. and Enever, J. (1997) Laboratory investigations of controls of stresss history on ASR response, Rock Stress, Balkema, Rotterdam, pp. 181–186.
Wolter, K.E. and Berckhemer, H. (1989) Time dependent strain recovery of cores from the KTB deep drill hole, Rock Mech. and Rock Engng., 22, pp. 273–287.




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