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Abstract

This dissertation investigates the role of transient pore pressures in the progressive failure of large open pit mine slopes. Conventional slope stability analyses often assume constant rock mass strength and rely on predefined failure surfaces and discrete triggering events. However, empirical evidence from over 360 detailed case studies of failures suggests that many mid-slope, multi-bench failures occur without a clear trigger, long after excavation. These patterns point to an alternative failure mechanism driven by the accumulation of damage under cyclic, recharge-induced changes in pore pressure. To evaluate this hypothesis, the research integrates four lines of investigation. First, an empirical analysis of 364 large open pit failures was conducted, classifying cases by hydrogeological conditions and failure timing. Second, a site-specific case study involving a 2011 pit failure in British Columbia was developed using detailed displacement, piezometric, and structural data. Third, calibrated continuum and discontinuum numerical models were constructed to simulate the hydromechanical response of slopes subjected to seasonal recharge. A one-way coupled approach was used to impose transient pore pressures from analogue groundwater models into mechanical simulations. Finally, a risk framework was developed to support the practical assessment of transient pore pressure effects in operational and post-closure settings. The results show that transient pore pressure increases can significantly reduce effective stresses, promoting localized slip and strain weakening, and accelerating failure even in slopes with no persistent structural predisposition. Key mechanisms include distance–dilatancy lag, stress-path–dependent degradation, and step-path rupture propagation. The classification framework based on the Modified Stability Number (N*) and RMR76 offers forecasting capability for identifying potential failure regimes. Post-mine closure scenarios are shown to carry residual risk due to groundwater rebound and pre-damaged slopes. This research advances a mechanism-based understanding of slope failure and provides practical tools for prediction, monitoring, and risk management across the mine life cycle.