Evaluating Geomechanical Uncertainty and Slope Reliability Analysis in Open Pit Mine Planning and Optimization

Document Type

Article

Publication Date

1-1-2025

Abstract

Open pit mine Queryplanning involves numerous uncertainties, with geomechanical uncertainty being one of the most critical factors for ensuring safe operations. Slope stability analysis plays a pivotal role in pit optimization, as slope angles directly influence both safety and profitability. However, determining a stable slope angle with certainty is challenging due to limited geomechanical data. This study integrates geomechanical uncertainty into pit optimization through a reliability-based slope stability analysis. Using stochastic modeling, this research evaluates various slope angles for an open pit gold deposit in Alaska, utilizing Rock Quality Designation (RQD) as the primary geomechanical input. The uncertainty of RQD was quantified by developing theoretical probability density function (PDF) of four rock types of the study mine and used to estimate cohesion, internal friction angle, and rock unit weights. Slope stability was assessed using Monte Carlo simulations within the limit equilibrium method, accounting for parameter variability. For slope angles up to 48°, the probability of failure was 0%, ensuring 100% reliability, and generating a cash flow of $2.684 billion. Beyond 48°, increasing the slope steepness raised the probability of failure, with the highest economic value of $2.935 billion at 56°, but a failure probability of 23% and reduced reliability to 77%. This demonstrates a clear trade-off between maximizing cash flow and managing slope stability risk. For a conservative design, a 48° slope is recommended, balancing safety and profitability. However, risk-tolerant operations may consider steeper slopes, accepting increased failure probability for higher profits, with a 1° slope increase adding $26 million but raising the failure risk by 12%.

Publication Title

Mining, Metallurgy and Exploration

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