Maldonado, A & Dight, PM 2020, 'The shear strength of bedding partings in shales of the Pilbara: the similarity
of non-dilatational angles, mineralogy relationships, and nominal roughness', in PM Dight (ed.), Slope Stability 2020: Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering
, Australian Centre for Geomechanics, Perth, pp. 551-564, https://doi.org/10.36487/ACG_repo/2025_33
Laboratory direct shear test results for natural bedding and sawcut defects have been statistically analysed in shales and banded iron formation materials across BHP Western Australian Iron Ore deposits (BHP WAIO) to prove the hypothesis of similarity of shear strength of defects.
The following paper provides typical Hencher corrected friction angles based on statistical methods to group data sharing similar characteristics. This paper justifies the existence of similar populations of shear strength of defects based on rigorous statistical analysis of valid direct shear test samples collected from multiple projects of the Pilbara. Spatial distribution bias effects and normality tests have been checked. Surface ‘geotechnical’ weathering grades do not explain the reduction of the shear strength of defects in shales. The use of base of completed oxidation and spectral signatures have provided a better explanation for the variability observed on the shear strength of defects. Where weathered shale samples from the Brockman column have greater frictional strength than fresh samples, a paradoxical phenomenon that can be attributed to chemical alteration generating additional textural roughness.
Keywords: shear strength, shale, bedding partings
Barton, N 1973, ‘Review of a new shear strength criterion for rock joints’, Engineering Geology, vol. 7, pp. 287–332.
Barton, N 1976, ‘The shear strength of rock and rock joints’, International Journal of Rock Mechanics & Mining Sciences, vol.13, pp. 255–279.
Barton, N 1995, ‘The influence of joint properties in modelling jointed rock masses’, Proceedings of the 8th International Society for Rock Mechanics Congress, International Society of Rock Mechanics, Salzburg, pp. 1023–1032.
Barton, N & Bandis, SC 1990, ‘Review of predictive capabilities of JRC-JCS model in engineering practice’, in N Barton & O Stephansson (eds), Proceedings of the International Symposium on Rock Joints, Balkema, Rotterdam, pp. 603–610.
Barton, N & Choubey, V 1977, ‘The shear strength of rock and rock joints in theory and practice’, Journal of Rock Mechanics and Rock Engineering, vol. 10, pp. 1–54.
Gill, DE, Ro, T & Leite, MH 2005a, ‘Determining the minimal number of specimens for laboratory testing of rock properties’, Engineering Geology, vol. 78, vol. 1–2, pp. 29–51.
Gill, DE, Corthesy, R & Leite, MH 2005b, ‘A statistical approach for determining practical rock strength and deformability values from laboratory tests’, Engineering Geology, vol. 78, issue 1–2, pp. 53–67.
Hencher, S 2012, Practical Engineering Geology, CRC Press, Boca Raton.
Hencher, S & Richards, LR 2015, ‘Assessing the shear strength of rock discontinuities at laboratory and field scales’, Rock Mechanics & Rock Engineering, vol. 48, issue 3, pp. 883–905.
Hoek, E 2004 Rock Engineering, Course notes, Canada, 313 p.
International Society for Rock Mechanics 1978, ‘Suggested methods for the quantitative description of the discontinuities in rock masses’, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, vol. 15, issue 6,
Kepert, DA 2001, The mapped stratigraphy and structure of the mining Area C region, an eclectic synthesis of geological mapping by BHPBIO exploration 1994-2001, internal report.
Levine, DM, Stephan, DF & Szabat, KA 2013, Statistics for Managers, Pearson Higher Ed USA, USA.
Mc Killup, S & Dyar, MD 2010, Geostatistics Examined, An Introductory Guide for Earth Scientists, Cambridge University Press, Cambridge.
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’, in TR Stacey (ed.), 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.
Mercer, K 2013, ‘Linear Anisotropic Model History of development Part 1’, Australian Centre for Geomechanics Newsletter,