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GROUND CONTROL Support in Many Forms Maintaining roof-support integrity is essential in any mine. E&MJ; looks at today's support options from the expert supplier's viewpoint. By Simon Walker, European Editor Rock support, a critical area of mining practice, will gain further importance as mines get deeper with higher rock stresses. Support systems that provided adequate protection in the past will need to be modified and upgraded in order to fulfil their future role, with new combinations of technologies required to satisfy safety demands. As an example, rockbolting practice has developed markedly over time, with current systems giving greater protection while requiring less labor for installation. Similarly, shotcrete support is becoming increasingly mainstream, especially in areas of a mine that are likely to remain in use for a long time—such as crusher chambers—or will be subjected to heavy wear, a case in point being drawpoints in a block-caving operation. Rockbolting concepts have also been extended to include cable bolts, once the exclusive domain of major civil engineering projects such as caverns but now increasingly becoming commonplace as 48 E&MJ; • DECEMBER 2012 an in-depth support method for, say, a weak hangingwall in open stoping or cutand-fill mining. Mesh screen is also much more widely used than before, acting as a catch-all for spalling rock and as reinforcement for shotcrete. However, the major disadvantage here is that mesh is time-consuming, and hence expensive, to install properly, as well as being awkward to handle. One potential answer seems to be thin, sprayed-on membranes which, while still at a relatively early stage along the acceptance path—in hard rock mining, at least—can provide an equivalent capability in terms of spall protection, yet at significantly lower labor input. Rather than looking once again at the various systems that are currently on offer in technical terms, E&MJ; asked some of the world's leading suppliers of rockbolts, shotcreting admixtures and TSL membranes for their views on how these systems have been developed in recent years, where they are heading, and what challenges are on the horizon for ground control in mining. Here are some of their responses. The Major Advances E&MJ; asked what major advances have been achieved in ground-control technology in hard rock mining over the past 10 to 15 years. According to Lars Hage, technical manager for sprayed concrete at the Switzerland-based producer of construction and mining concrete admixtures, BASF, the first and foremost point is that there has been a vast improvement in the attitude and approach to safety in underground environments. The biggest advance in terms of ground control technology, he said, has been the move from dry- to wet-mix sprayed concrete, with developments in the concrete industry meaning that it is now possible to produce wet-mix sprayed concrete with compressive strengths of more than 60 MPa at 28 days. www.e-mj.com