SLOPE STABILITY
( 3D ) vector displacements and managing semiductile to ductile instabilities . It also has 15 inclinometers on critical mine infrastructure for the early detection of deep-seated instabilities ; > 200 vibrating wire piezometers ( VWPs ) to monitor pore pressures and ensure slope depressurisation is effective ; plus three Doppler radars ( IDS GeoRadar RockSpot ) which are deployed to track rock fall trajectories and to understand bench performance reliability .
The response aspect of this control measure at Pueblo Viejo is divided into two concurrently utilised components . First 24 / 7 GbSAR monitoring analysis and response to identify threats , which have different responses related to the size of a potential failure . And second , hazard specific TARP ( trigger-action-responseplan ) whereby an audio-visual alarm is triggered in Mine Dispatch .
The digital twin was designed to include mapping of structural and rock mass conditions using aerial photogrammetry , and supplemented by face mapping where safely accessible for every 20 m of vertical advance . 3D LE model updates as local geomechanical conditions were mapped and projected . Targeted monitoring uses ground-based radar systems . Two overlapping IDS GeoRadar IBIS-ArcSAR systems were deployed , in conjunction with a 24 / 7 monitoring and response protocol to facilitate the evacuation of personnel and equipment prior to any collapse .
Photogrammetric 3D models from drone imagery are generally acquired on a monthly basis at Pueblo Viejo mine . Face mapping is completed where safely accessible for every 20 m of vertical advance . The site geotechnical engineers map and reconcile structural features using 3GSM ’ s ShapeMetrix UAV software . All mapped structures are then saved in a central database ( acQuire ). Data from photogrammetric models can also used to generate displacement maps to understand the magnitude and direction of displacements .
Full pit radar monitoring is available at Pueblo Viejo where radars are set up to monitor all operating areas . All measurements of movement area processed and displayed into a single map view ( FPM360 ). Pseudo 3D displacement vector are calculated on overlapping areas by combining interferometric displacements measured from different positions in space .
The paper states : “ The use of mappingmodelling-monitoring utilises and integrates the latest 3D technology to form a digital twin that when routinely updated , can better predict mine slope hazards and facilitate an improved response , not only in terms of safety , but also short- and long-term economics .”
In a case study presented , the ability to manage ground failure safety combined with a digital twin approach has improved mine design reliability and productivity by reducing operational delays . By communicating potential hazards , in 3D and ahead of time , the digital twin approach has also facilitated effective communication between geotechnical engineers , mine planning , mine operations and senior management on hazards and emerging threats in order to effectively manage them with ‘ less surprises .’
In its current form the digital twin process remains a relatively manual process , but will be continued to be implemented by Pueblo Viejo based on the value identified in this case study . It is envisaged with ongoing improvements in technology and software integration , the digital twin process for geotechnical risk identification and reconciliation will be automated by 2030 .
Allowing for vegetation movements in long term tailings dam monitoring
Another presentation from the event was also led by IDS GeoRadar and Hexagon Mining , this time with iron ore mining customer Vale , and was titled “ Long term deformation analysis of vegetated slopes with GBSAR .” Instead of hard rock open pit mining it focuses on tailings dam monitoring , a critical activity that is becoming more and more important . “ In particular , longterm monitoring can be useful to detect slow movements that are indicators of possible future instabilities . To this end , over the last few years GBSARs have proved to be very useful tools for monitoring slow movements of open pit slopes . However , tailings dam slopes are often covered by low vegetation , whose random movements act as an annoying decorrelation source within the radar data , Says Alberto Michelini . Data Scientist Manager at IDS GeoRadar .”
For this reason , on tailings dams achieving standard GBSAR performance is a challenging goal for data processing , especially in the case of long-term monitoring . Over the last two years IDS GeoRadar in collaboration with Vale has developed a new processing algorithm for IBIS radars , named Guardian SMV , with the purpose to measure extremely slow movements (< 10 mm / month ) on low vegetated scenarios . The paper provides a theoretical description of the new algorithm , highlighting the underlying assumptions and the constraints to be considered for its application . The effectiveness of the new algorithm is validated on a case study related to vegetated slopes , through the comparison of the GBSAR displacement with geodetic prism measurements over period of several months .
The continuous monitoring of very slow movements with a reliable detection of displacements in the order of few mm per month , effectively supports advanced pit design and slope optimisation . For this type of monitoring ,
tailings dams are a challenging scenario , especially for interferometric radar systems .
The tailings dam considered for the case study was monitored by a RTS , measuring every minute the position of 38 prisms , and an IBIS-FM GBSAR performing an acquisition every two minutes and providing the displacement measurement of about 80 thousand radar points . The comparison was performed comparing , on a time interval of six months , the displacement measurement of 21 of the available 38 prisms with the displacement obtained by processing with Guardian SMV the IBIS-FM radar data .
RTS provides a 3D pointwise displacement information for each prism , whereas GBSAR gives the displacement measures along the radar LoS of several thousand points covering most of the tailing dam slope . The comparison of the RTS interpolated velocity map with the Guardian-SMV velocity map shows a very good spatial correlation . In particular , both technologies show two main moving areas : a top strip with ~ 0.9-1.5 mm / month LoS deformation rate ; and a central area with ~ 0.3-0.5 mm / month LoS deformation rate .
In the Guardian-SMV map , it is also possible to observe in the central area more localised movement of ~ 1 mm / month . The minor discrepancies between the velocity maps can be related to the intrinsic differences of the two measurement techniques . A further assessment was performed by comparing the displacement time series of the prisms with the Guardian SMV data extracted in correspondence of the prism locations . Such comparison shows a high temporal correlation between Guardian SMV time series and prism measurements .
The paper states : “ The time series highlights the excellent performance of the new Guardian SMV algorithm that , over the analysed six months time interval , was able to measure a total displacement of about 8- 6 mm in the top part ( prisms P1 , P2 ) and about 2 mm in the central part ( prism P3 ), extending the low-end velocity sensitivity range of GBSAR on vegetated slope below 1 mm / month .”
The authors conclude : “ The new Guardian SMV is a new processing algorithm for IBIS radars specifically developed for deformation monitoring of low vegetated slopes , such as tailings dams . The Guardian SMV results were validated by comparing them with those coming from classic RTS monitoring . Thanks to the specific averages introduced in the new SMV algorithm , the random contribution due to vegetation movements is greatly reduced , guaranteeing the slow movement detection in low vegetated environments , with a low-end velocity sensitivity range that becomes comparable to other existing technologies such as RTS or satellite InSAR . This new velocity range
76 International Mining | AUGUST 2024