Authors: Fietze, C; Creighton, A; Castro, LM; Hammah, R

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DOI https://doi.org/10.36487/ACG_rep/1308_01_Fietze

Cite As:
Fietze, C, Creighton, A, Castro, LM & Hammah, R 2013, 'Pit slope design in phyllites for the Simandou large open pit project', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 115-125, https://doi.org/10.36487/ACG_rep/1308_01_Fietze

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Abstract:
At the Simandou iron ore project site in Guinea, phyllites with varying degrees of strength and alteration are prevalent. Their presence makes it difficult to adequately characterise, classify and estimate the strengths of the rock masses. The foliation in the phyllite has low strength, and thus induces anisotropic behaviour. This paper will present information on how these difficult-to-classify rock mass units were treated in the design of the Simandou open pit. In order to geomechanically characterise the Simandou rock masses, significant attention was paid to the weathering and alteration processes of the phyllite. The strength of the rock masses closely correlated to the degree of alteration and weathering; the most weathered phyllites had the weakest strength. The strength of the more altered rock mass used for the pit slope design was estimated from a combination of laboratory rock testing and back-analysis. The back-analysis was based on slope instabilities that had occurred on natural slopes in the Simandou area. The geotechnical risks, most likely to arise, were identified and taken into account in the pit slope design. Since toppling was the most serious of these risks, the paper discusses it in greater detail. Parametric numerical analyses of toppling were performed to evaluate the importance of the variation in the strength and stiffness of the materials and the likely mode of failure, where toppling or shear (rotational-type failure) could develop.

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