The recent introduction of ground-based slope stability radar in open-pit mines to complement conventional geodetic monitoring programs provides near real-time deformation measurements over a broad coverage area; this allows geotechnical engineers to observe the spatial distribution of pit wall movements and their progression over time. This paper presents a newly proposed early warning time-of-failure (TOF) analysis procedure for use in real-time with ground-based radar measurements designed to be integrated in an open-pit mine’s trigger action response plan (TARP). The inverse-velocity and slope gradient (SLO) TOF analysis methods are applied to radar displacement measurements using a new systematic multi-pixel selection technique termed the “percent deformation method.” The utilization of the percent deformation method in the proposed real-time TOF analysis methodology gives more-reliable results than current practice by providing recommendations for pixel selections, data filtering, where and how to undertake TOF analyses, and presenting TOF results in real time. The addition of a more rigorous, methodical treatment of radar monitoring data when faced with critical slope instability will reduce uncertainty and increase confidence in any trigger action response decisions, helping to ensure a safer work environment.

Effective management and mitigation of pit slope instability in open pit mines begins with a comprehensive slope monitoring programme. The ability to differentiate between non-critical pit wall movements due to rebound or relaxation of the excavated slopes and movements that may be indicative of slope failure is important for maintaining a safe working environment and maximizing production. Slope failure prediction methods using velocity, acceleration, and strain criteria have been introduced and put into practice over the past few decades. Forty-eight slope failures with surface monitoring data are presented and assessed using the strain-based failure prediction approach, with consideration of the quality of the rock mass and the potential failure mechanism. The results indicate that the strain-based approach can be used to provide general guidance regarding strain thresholds for pit walls for a variety of failure modes in diverse geological environments. The advantages and potential drawbacks of the strain-based and other slope failure prediction methods are discussed. The importance of implementing a pit slope monitoring and performance evaluation system early in mine development is also emphasized. open pit slopes, slope monitoring, failure prediction, pit wall strain, strain criteria, strain thresholds.

Slope monitoring in open pit mines is an essential component of day-to-day operations and plays a key role in assisting geotechnical engineers and mine operators in maintaining mine safety and production schedules. Pit slope monitoring techniques have advanced significantly within the past decade, most notably in ground-based radar technology. Ground-based radar allows real-time monitoring of slope deformation across a broad coverage area, alerting mine staff to wall movements exceeding established thresholds. Lineof-sight measurements derived from the radar can be presented as 3D point clouds for the scan area, allowing mine staff to view the distribution of slope movements across the pit wall with each progressive scan.This paper presents a new methodology for spatial and temporal analysis of deformation point clouds captured by ground-based radar. The methodology builds on two existing early warning methods, the Fukuzono inverse-velocity method and the SLOpe gradient (SLO) method, which are based on the analysis of point measurement data derived from traditional geodetic prism monitoring. However, similar methodologies that fully utilise the spatial and temporal characteristics of ground-based radar data are yet to be developed.Radar data from historical slope failures captured by GroundProbe Slope Stability Radar (SSR) at a number of hard rock mines was utilised in the development of the new spatial and temporal analysis methodology. A slope failure that occurred at an open pit copper mine is presented throughout as a case example. The spatial analysis component of the methodology uses a benchmark point (or pixel), based on an alarm threshold specific to each failure case, and averaged deformation increments based on a percentage of the deformation measured by the benchmark pixel at the time of alarm. The temporal analysis component of the methodology examines deformation and velocity trends for all spatial analysis cases. The results of the spatial and temporal analysis were then used to evaluate the inverse-velocity and SLO time of failure prediction methods. Overall, the proposed methodology will improve, and provide a more systematic means of interpreting spatial and temporal ground-based radar data, aiding geotechnical engineers in managing slope movement alarms and alarm responses to provide a safer working environment for mine employees.The use of ground-based radar for monitoring pit slope wall instabilities has become the state of practice in many of today's open pit mine operations. Ground-based radar systems allow real-time monitoring of active slope instabilities, providing 3D slope deformation point clouds derived from line-of-sight measurements. These 3D point clouds allow mine staff to view the distribution of slope movements across the pit wall with each progressive scan.

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