Ahenkorah, I, Hinks, S & Cooper, A 2025, '3D block stability analysis of rock slope in Pilbara iron ore operations', in JJ Potter & J Wesseloo (eds), SSIM 2025: Fourth International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2535_34
(https://papers.acg.uwa.edu.au/p/2535_34_Ahenkorah/)
Abstract: The lithostratigraphic conditions in the Pilbara region of Western Australia are characterised by complex structural features resulting from multiple deformation events leading to significant folding, faulting, jointing/discontinuities, and unfavourable bedding orientations. These complexities present challenges in open pit iron ore mining as they can trigger slope instabilities with considerable safety and economic implications. Improved confidence in stability assessments of large rock slopes can be achieved through a better understanding of the persistence, distribution, and location of unstable blocks within the slope, utilising true 3D geometry. This paper examines the 3D block stability of a planar sliding failure in an open pit iron ore mine using Rocscience RocSlope3. Joints measured via an unmanned aerial vehicle photogrammetry mapping campaign (verified with in-field mapping data) were modelled as planar surfaces, incorporating their orientation, location, and properties (shear strength, persistence and waviness). The limit equilibrium method was applied to assess the stability of each block, predict potential failure locations and magnitudes, and generate heat maps indicating areas with the lowest Factors of Safety, largest failure volumes, and greatest depths. The results demonstrated that valid unstable blocks were formed by intersecting discontinuities, with failure initiated by daylighting and the detachment of blocks. The predicted location and volume of failed blocks, with a Factor of Safety below 1.0, aligned with bench crest failures observed in the field. Overall, the 3D block stability analysis method using Rocscience RocSlope3 offers a promising approach for identifying potential bench crest failures, multi-bench failures, and conducting global slope risk assessments in open pit rock slopes.

Keywords: open pit, slope instability, block stability, kinematic analysis