Spotlight Feature Articles Ansul Modern Open Pits February 16 | Page 3

MODERN OPEN PITS_proof 21/10/2015 10:05 Page 2 MODERN OPEN PITS mining operations were to be conducted in close proximity to the walls. In November of 2014, the ring net mesh system was successfully installed and operations resumed. This plan makes it possible to mine the remaining 175 ft of ore safely, below a 2,000 ft tall highwall. The project was completed safely and with no incidents. Mastering rockfall protection IM also spoke with Roland Bucher, General Manager of Geobrugg Australia Pty Ltd. Swiss parent company Geobrugg is well known as a global leader in the supply of high-tensile steel wire mesh; while its rockfall protection systems provide effective protection for people, infrastructure, equipment, access roads, tunnel portals, and buildings. Its slope stabilisation systems provide highly sustainable solutions for securing unstable slopes or for reinforcing existing retaining structures of any kind as well as shotcrete walls. On demand for these types of solutions at minesites, he states: “It is not a straightforward answer, it all depends on the individual pit, especially the geology, and both the strategic and safety approach of each mining company. The orientation and steepness (dip) of the orebody and therefore the rock mass in the pit slopes – both the footwall and hanging wall – in terms of structures and orientation, as well as possible blast damage on the pit slope, are factors to consider.” In terms of the differences between the approach to rockfall protection and slope stabilisation installations between mining and a road cutting for example, “mining projects tend to be considered temporary, with a requirement for a shorter design life, but with the likelihood of higher rockfall frequency. Along a road or a railway corridor the likelihood of a rockfall or an impact is generally lower but the exposure is much longer, such as a design life of 50-100 years.” Some Geobrugg mining applications are customised designs to fit the site’s specific requirements. Most of the time, standard systems, which are 1:1 field tested can be used. On the use of radar monitoring in conjunction with its technology, Bucher states: “Radar is used as a monitoring system, whereas what Geobrugg offers are mitigation systems. These are often used side by side, or one is chosen over the other based on the specific issue and strategy on site.” Companies like Geobrugg are often contacted after a rockfall event has happened, to keep a certain work area in the pit safe from rockfalls and to continue with the mining process in that area thereafter. In recent times, some of the mining companies have been reviewing their slope design/angle and try to steepen certain pit slopes to either access more ore or reduce the waste movement (improve the strip ratio). Mitigation systems like rockfall barriers (catch zone one zone two Safe, flexible survey and monitoring solution Proactively manage geotechnical risk and help maintain site safety with Maptek Sentry. • • • • • Survey and monitor with a single system Track surface movements and analyse trends Map highwall structures from detailed 3D laser scan imagery Use rockfall data to maintain geotechnical databases Act quickly and decisively on safety measures [email protected] | www.maptek.com fences), mesh drapes or slope stabilisation are considered in certain areas to achieve the steeper pit slope design and maintain the same risk level. An example of recent project work is at Grange Resources (see Hutchison B.J., Macqueen G.K., Dolting S.L., Morrison A-T. 2013. Drape mesh protection at Savage River Mine, Tasmania. Slope Stability 2013, Brisbane, Australia, pp 1,345-1,359), which in 2010 experienced two large wall failures at their Savage River mine in Tasmania, Australia. These rockslides buried a significant portion of the magnetite ore scheduled to be mined in the following two years. To ensure long term ore supply, a major cutback was required to get back down onto the orebody. Several different approaches and mine plans were considered before deciding on a cast blast and drape mesh option to speed up the bench advance. Various mesh design schemes were assessed, before selecting a Geobrugg drape mesh system to cover the 60 to 80 m high, steeply dipping, haematite coated shear. The intent was to allow rapid mining bench advances during the cutback and rockslide removal process. By adopting this approach considerable time was saved by eliminating extensive pre-splitting, trim blast and rock support requirements associated with Grange’s normal mining procedures. Two large cast blasts were taken to remove rock material in front of the back scarp. The cast