To topple or not to topple: managing failures at a case study site

Authors: Weir, FM; Gazi, J; Duran, A Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2535_19

Cite As:
Weir, FM, Gazi, J & Duran, A 2025, 'To topple or not to topple: managing failures at a case study site', 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_19



Abstract:
This paper presents a case study of managing toppling failures at a short-life open pit lithium mine in Australia, where adverse slope performance was encountered early in operations. The geological setting comprises a steeply dipping pegmatite orebody hosted within regionally foliated phyllite. The dominant failure mechanism was flexural toppling along sub-vertical foliation planes, with additional complex toppling and minor wedge failures observed. Slope instability was exacerbated by high pore pressures, poor understanding of rock mass conditions, and limited initial slope monitoring. A revised geotechnical model was developed based on updated structural mapping, back-analysis of failures, and field observations. Stability analyses indicated that even at shallow slope angles, deep-seated toppling could occur in weak, foliated materials under elevated pore pressures. Slope design modifications included flattening inter-ramp slope angles and implementing a practical depressurisation strategy using horizontal drain holes. A significant uplift in slope monitoring – including prisms, radar, drone surveys and extensometers – improved risk management. The case study demonstrates that in structurally complex geological settings, especially those with pervasive foliation, a robust and evolving geotechnical model is essential. The findings underscore the sensitivity of flexural toppling mechanisms to groundwater conditions and highlight the importance of adaptive design and operational controls in short-life mining environments.

Keywords: flexural toppling, slope stability, geotechnical model, depressurisation, pegmatite

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