SLOPE STABILITY
Blink and you ’ ll miss it
Paul Moore looks at some highlights from the Slope Stability 2024 conference in Brazil plus as usual reviews some new approaches and techniques
Two of the stand-out presentations from the International Slope Stability Symposium , held 14-19 April in Minas Gerais , Brazil , looked at new approaches to slope stability monitoring – firstly a paper titled “ Developing a ‘ Mapping-Monitoring-Modeling ' Digital Twin for slope stability hazard response optimisation ” from IDS GeoRadar , its parent company Hexagon Mining , customer Barrick Gold Corporation and specialist geotechnical engineering company Gecko Geotechnics .
The authors , including IDS GeoRadar ’ s Managing Director Niccolo Colí , state that technological improvements including the routine use of aerial photogrammetry , semi-automatic rock mass characterisation , three-dimensional slope stability modelling and ground-based radar monitoring ( ie mapping , modelling and monitoring ) “ can now be applied rapidly to develop a continuously improving digital twin in parallel to an excavation sequence . This is critical for reconciling the effectiveness of geotechnical models for predicting future slope stability ( or instability ).”
The paper presented semi-brittle and brittle slope failure case studies from Barrick Gold ’ s Pueblo Viejo gold mine which were managed using a digital twin approach and multiple layers of monitoring . Monitoring systems used to manage safety risks were developed in response to uncertainties in ground characterisation and limitations in slope stability analysis and design , particularly prior to excavation . The near realtime comparison of the three-dimensional model with observed slope conditions allowed critical structures to be added to the geotechnical model as mining progressed .
Pueblo Viejo gold mine is located approximately 80 km north of Santo Domingo , in the Dominican Republic . The mine is located at an altitude of approximately 300 to 500 m above sea level . The geological setting is structurally complex with several phases of thrust faulting and hydrothermal alteration . Due to the complex ground conditions and tropical setting , several instabilities and geotechnical challenges have occurred and were retrospectively reviewed for incorporation into future designs .
To proactively manage geotechnical risk at Pueblo Viejo , a mapping-modelling-monitoring digital twin was developed and maintained in parallel with mining operations and 24 / 7 remote monitoring of radar data . Its purpose is to develop and routinely update reliable predictions of future pit slope behaviour through the ongoing mapping , monitoring and updating of slope stability models at various time scales , including but not limited to : three month or quarterly plans , successive pushbacks and life-of-mine ( LoM ) plans .
The digital twin produced at Pueblo Viejo mine is developed and updated manually on a routine basis and incorporates mapping , including the acquisition and analysis of structures mapped from in-pit face mapping and aerial photogrammetry as excavations progress ; monitoring , including the acquisition and review of real time , ground-based , interferometric
Pueblo Viejo Gold Mine : monitoring instrumentation including IDS GeoRadar IBIS- ArcSAR radar ( left ) and Leica TM60 robotic total station with Pangea Geosystems telemetry ( right )
synthetic aperture radar ( Gb-InSAR ) with full pit coverage for safety and model validation ; and modelling , including the development and updating of three-dimensional ( 3D ) limit equilibrium ( LE ) slope stability models to predict and reconcile slope performance . Where complex failure mechanisms are encountered or anticipated , 3D finite element ( FE ) models are also developed .
The Moore and Monte Negro pits at Pueblo Viejo gold mine have historically adopted relatively aggressive slope designs ( within accepted industry design standards and guidelines ) using narrow successive pushbacks to reduce slope stand-up time requirements . As a result , a higher fall of ground failure frequency is experienced at the mine .
Pueblo Viejo gold mine has an extensive array of monitoring instrumentation , including sitewide satellite InSAR service with time series data updates on a fortnightly basis for the early detection of hazards and to manage ductile instabilities . It also has seven IDS GeoRadar IBIS- ArcSAR radar systems deployed to monitor all pit walls for the early detection of hazards and to manage brittle to ductile instabilities . Multiple radar systems are used to understand partial vector displacements where datasets overlap . To complement the local ( site ) geotechnical engineering team who operate on day shift , the radar systems are 24 / 7 monitored in real time for new hotspots or change in movement trends by Hexagon ’ s qualified remote monitoring teams . Nine automatic total stations monitoring several hundred survey prisms for understanding true
AUGUST 2024 | International Mining 75