Authors: Maldonado, A; Dight, PM; Mercer, K

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DOI https://doi.org/10.36487/ACG_repo/2025_44

Cite As:
Maldonado, A, Dight, PM & Mercer, K 2020, 'The intact rock strength of anisotropic rocks in the Pilbara: the use of field estimations, practical limitations of calibrations and statistical bias', in PM Dight (ed.), Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 691-702, https://doi.org/10.36487/ACG_repo/2025_44

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Abstract:
The uniaxial compressive strength (UCS) is an essential input parameter of the Hoek & Brown failure criterion to represent the shear strength of rock masses, which is frequently used for slope stability analysis in the mining industry. This paper presents the use of the field estimated strength (FES) as a way to estimate the UCS, which is not a new idea but rather a regular practice applied by consultants and internal engineers within BHP Iron Ore for the last 20 years. However, the paper puts emphasis on the practical limitations related to the FES calibration by spot sampling, the bias effects caused by ‘length-weighted’ calculations due to the skewness distribution on FES and presents a logarithmic transformation on FES as a manner to test similarity of typical values. The paper concludes presenting typical values as defined by statistical similarity ‘hypothesis testing’ on FES data of the same stratigraphical rock units across different locations in the Pilbara.

Keywords: UCS, field estimated strength, length-weighted, skewness, hypothesis testing

References:
Hoek 2000, Practical Rock Engineering, Short course notes, Vancouver, Canada.
International Society for Rock Mechanics 1978, ‘Suggested methods for the quantitative description of the discontinuities in rock masses’, Journal of Rock Mechanics and Mining and Geomechanics, vol. 15, pp. 319–368.
Levine, D 2013, Statistics for managers, Pearson Publication, Melbourne.
Maldonado, A & Haile, A 2015, ‘Application of ANOVA and Tuckey-Cramer, statistical analysis to determine similarity of rock mass strength properties across Banded Iron Formations of the Pilbara region in Western Australia’, Proceedings of the 2015 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, The Southern African Institute of Mining and Metallurgy, Johannesburg.
Manewell 2008, The Hydrogeology and Hydrochemistry of the Mt. Tom Price Mine, Pilbara, Western Australia – A Groundwater Flow Model, Thesis, Engineering Geology University of Canterbury.
McKillup, S & Darby Dyar, M 2010, Geostatistics Explained: An Introductory Guide for Earth Scientists, Cambridge University Press.




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