ABSTRACT
The Perseverance Mine is a nickel mine consisting primarily of a sublevel cave. The ground support regime required to maintain access has evolved over the years due to very poor ground conditions, and until recently comprised an initial layer of steel fibre reinforced shotcrete, then weld-mesh over the whole profile, split set bolts and 3m long grouted and partly-debonded GEWI (rebars) installed in the sidewalls and backs, and a second 50 mm thick layer of steel fibre reinforced shotcrete sprayed over the mesh. This intensive support regime undergoes significant deformation in the order of 100-400mm, a process which begins before the level development is complete.
An investigation was undertaken to establish whether the post-crack performance of the shotcrete could be improved. In particular, it was decided to investigate the new range of synthetic fibres to see if their performance was beneficial when tested over large deformations. Tests showed that synthetic fibres can outperform high quality steel fibres over large deflections. This enabled the mine to redesign their ground support to use a single layer of high toughness shotcrete. The mine is now spraying a single 75 mm thick shotcrete layer reinforced with 12kg/m3 of Barchip Xtreme synthetic fibre. Large cost savings have been realised without compromising post-crack performance. The thinner layer also altered the way the shotcrete performed with a larger number of small cracks being the most evident change compared to past behaviour.
