Drape mesh protection at the Savage River Mine, Tasmania

Abstract

In June and August of 2010 Grange Resources 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 blasts were each 40 m in height and cast 30–35% of the blasted rock off the face from in front of the haematite coated shear, which formed the back scarps of the two rock failures. The drape mesh system was installed between April and October of 2011. The system was very successful in protecting personnel and equipment from rockfalls on the backscarp during the subsequent mining phase. This paper describes the various processes associated with mine planning, cast blasting, drape mesh design, drape mesh tendering and selection, and installation; as well as the costs. The performance of the mesh in retaining potential and actual rockfalls is also described; along with issues associated with radar monitoring.