Squeezing Ground Task Force
Squeezing ground conditions pose a serious challenge for a number of underground mines. In the mining context, a practical definition for squeezing ground conditions is when the total displacement of an excavation or, more specifically, the drive closure reaches at least tens of centimetres within the life expectancy of a supported drive. In general, mine drives are designed to be in operation for up to two years. It is also implied that in squeezing ground conditions the resulting loads and displacements will be greater than the capacity of a “stiff” support system. This often results in the significant failure of ground support, and necessitates extensive rehabilitation work.
The Squeezing Ground Task Force was formed in 2007 by the Australian Centre for Geomechanics as a research initiative to facilitate a better understanding of squeezing ground conditions and how different mines manage these issues. The primary ground control aim of the mines dealing with squeezing ground is often to devise a ground support system and strategy that will enable them to complete mining locally, without needing to go through expensive rehabilitation work. Some mines temporarily achieve this goal by a trial-and-error process; at least, until the ground has worsened or until the stress increases. Many other mines operating in squeezing environments resigned themselves to reducing the number of rehabilitation cycles to one or two.
The Squeezing Ground Task Force was a collaboration between the ACG, Professor John Hadjigeorgiou of Laval University, and industry partners BHP Billiton Nickel West, Norilsk Nickel Australia Pty Ltd, Goldfields of Australia, Agnico Eagle and Xstrata Nickel. In May 2008, the task force completed a state-of-the-art review of the squeezing ground problems in selected underground mines owned by the industry partners. Site visits were undertaken in July 2007 in Canada and in October 2007 in Australia. In total, four Western Australian mines (Maggie Hayes, Black Swan Nickel, Waroonga, Perseverance), and one Canadian mine (LaRonde) were visited by the Squeezing Ground Task Force. The Canadian leg of the visit included visits to two Xstrata Nickel mines: Craig and Fraser.
The comparison of the practices between the five mines involved in the Squeezing Ground Task Force allowed the task force to draw some pertinent conclusions. This investigation has also challenged some of the conventional wisdom and helped formulate some interesting questions that could eventually be addressed in future research.
The most obvious observation from the mine visits is the clear dichotomy between Australian and Canadian ground support practices. In terms of surface support, Australian mines are using an excessive amount of fibrecrete, while the Canadian mines rely primarily on weld-mesh, at times supplemented with mesh-straps. On the other hand, reinforcement practices in Australia are strongly driven by the installation technique, which are more mechanised, relying almost entirely on Jumbos. From the Squeezing Ground Task Force observations, a new research proposal to address squeezing ground problems is currently in preparation.