Monitoring of a Large Wall Failure at Tom Price Iron Orre Mine

Abstract

Towards the end of 2006, routine Electronic Distance Measurement (EDM) prism monitoring highlighted rapid acceleration of one prism. At this stage, there were no visible signs of failure close to the prism and all other monitoring points in the vicinity could no longer be read. The prism itself was situated on a berm that was no longer accessible. A week later the prism was still accelerating with the only evidence of wall movements being two sets of cracks, one 30 m below the prism near the pit floor and the other about 50 m above the prism, suggesting the possibility of a large scale wall failure. A GroundProbe Slope Stability Radar was available for a few days and was deployed to scan a large section of wall. After a day of radar monitoring it was apparent that movement was occurring over an area approximately 265 m wide and nearly 100 m high. Movement rates were up to 30 mm per day and accelerating rapidly. The eastern half of the pit below the affected area was closed off and failure commenced two days later. The radar remained at the site for the initial part of the failure allowing correlation of movement rates and magnitudes with those recorded by prism monitoring.It appears that the failure mechanism is a combination of sliding on a fault plane, sliding on the contact between the Footwall Zone and the Mount McRae Shale and rock mass failure through the Dales Gorge Member to produce significant floor heave at the base of the failure.

Development of an early-warning time-of-failure analysis methodology for open-pit mine slopes utilizing ground-based slope stability radar monitoring data

“…The addition of ground-based radar to conventional geodetic prism monitoring programs in open-pit mines has enhanced active monitoring of unstable slopes. Published examples of successful implementation include the Leinster Nickel Mine (Cahill and Lee 2006), Potgietersrust Platinum Mine (Little 2006), Tom Price Mine (Day and Seery 2007), Barrick Goldstrike Mine (Armstrong and Rose 2009), Bingham Canyon Mine (Doyle and Reese 2011), Kemess South Mine (Yang et al 2011), Grasberg Open Pit (Ginting et al 2011), Wallaby Mine (Jones et al 2011), and Savage River Mine (Macqueen et al 2013). Ground-based radar provides three main advantages over traditional geodetic point monitoring: (i) broad slope coverage area, (ii) near real-time slope deformation data, and (iii) remote measurements without the need to install prism reflectors, reducing worker exposure to rock-fall hazards.…”

“…This allows the geotechnical engineer to see the distribution of slope surface deformation behaviour within the scan area and its progression over time. However, when an accelerating slope deformation trend is detected, common practice involves arbitrarily selecting a single or small cluster of pixels for analysis rather than systematically utilizing the full spatial coverage provided by the radar (e.g., Cahill and Lee 2006;Little 2006;Day and Seery 2007;Harries and Roberts 2007).…”

An extensional mechanism of instability and failure in the walls of open pit mines

“…A number of published papers contribute to an understanding of the mechanics of open pit walls, including, from amongst many others: Brenda Mine (Calder and Blackwell, 1980;Blackwell and Calder, 1982), Tripp Mine (Miller, 1982), Highmont Mine (Newcomen and Martin, 1988), Muja Mine (Joass, 1993), Telfer Mine (Thompson and Cierlitza, 1993), Aznalcollar Mine (Hencher et al, 1996), Betze-Post Mine (Rose and Sharon, 2000;Sharon, 2001;Rose and Hungr, 2007), Highland Valley Lornex Mine (Newcomen and Shwydiuk, 2003), Chuquicamata (Calderon et al, 2003), Nchanga Mine (Naismith and Wessels, 2005;Wessels, 2009), Tom Price Iron Ore Mine (Day and Seery, 2007), Yallourn Mine (Victorian Government, 2008).…”

Open pit numerical model calibration using a pseudo three-dimensional radar monitoring technique

“…The IBIS-M system is suited for safety critical monitoring, being capable of performing real-time, near-continuous (5 minute interval), line-of-sight (1D) monitoring of large areas, day or night and in all weather conditions (Farina et al, 2012). Such capabilities are helping to establish radar as a key tool for managing unstable pit slopes, quickly identifying the size, extent and temporal behaviour of a developing failure (Day and Seery, 2007;Harries et al, 2006;Harries and Roberts, 2007). Rödelsperger et al (2010) describe the advantages and disadvantages of the IBIS-M unit as compared to other forms of monitoring.…”