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BHP Western Australia Iron Ore geotechnical open cut slope design system: a simple pragmatic process for slope risk decisions

A transparent, pragmatic geotechnical design system is outlined that presents a selection of risk options with associated risk/reward for decision makers. Risk options termed ‘robust’, ‘balanced’ and ‘aggressive’ have been defined appropriate to ‘critical infrastructure’, ‘typical industry’ and ‘low risk’ mining environments (where the safety risk and the consequences of failure on the budgeted mine plan are acceptably low), respectively. The geotechnical model includes ‘most realistic’ and ‘reasonable lower case’ conditions. A ‘realistic’ design principle requires reporting a Factor of Safety on the realistic case, rather than to reduce design inputs due to uncertainty. Uncertainty is transparently covered by the ‘lower case’ in sensitivity analyses. Indicative probabilities of failure are estimated and a simple empirical tool estimates the consequence of failure in terms of the area of mining floor impacted. These together with indicative value or tonnage estimates are presented to the decision maker (risk owner), with a selection recommendation. Post decisions, designs including any residual hazards are passed to the operational engineers to design risk-based slope monitoring, to ensure operational safety, and reconciliation programs, as required. Adoption of the realistic principle has facilitated risk owners taking decisions based on a more transparent presentation of risk since 2014 and made a material contribution to a step change slope angle increase in the mines of BHP Western Australian Iron Ore.