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.), 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. 691-702, https://doi.org/10.36487/ACG_repo/2025_44
(https://papers.acg.uwa.edu.au/p/2025_44_Maldonado/)
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