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Rock Mechanics.pdf - Mining and Blasting

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Figure 11.28 Alternative methods<br />

of grouting cables into upholes (after<br />

Hoek et al. 1995).<br />

ROCK SUPPORT AND REINFORCEMENT<br />

admixtures such as accelerators or retarders, plasticisers, microsilica <strong>and</strong> reinforcing<br />

fibres. Gunite, which pre-dates shotcrete in its use in underground construction, is<br />

pneumatically applied mortar. Because it lacks the larger aggregate sizes of up to<br />

25 mm typically used in shotcrete, gunite is not able to develop the same resistance to<br />

deformation <strong>and</strong> load-carrying capacity as shotcrete. For at least 50 years, shotcrete<br />

has been used with outst<strong>and</strong>ing success in civil engineering underground construction<br />

in a wide variety of ground types. It is so successful because it satisfies most of<br />

the requirements for the provision of satisfactory primary support or reinforcement<br />

discussed in section 11.2. Over the last 20 years, shotcrete has found increasing<br />

use in underground mining practice, initially for the support of the more permanent<br />

excavations but now increasingly for the support of stopes <strong>and</strong> stope accesses (Brown<br />

1999b, Brummer <strong>and</strong> Swan, 2001). It may also be used as part of the support <strong>and</strong><br />

reinforcement system in mild rock burst conditions (Hoek et al., 1995, Kaiser <strong>and</strong><br />

Tannant, 2001). Shotcrete is being used increasingly in conjunction with, or as a<br />

replacement for, mesh to provide primary support of headings. Brummer <strong>and</strong> Swan<br />

(2001) describe a case of the use of wet mix steel fibre reinforced shotcrete to provide<br />

the total drift support in a sublevel caving operation at the Stobie Mine, Ontario,<br />

Canada. Bolts are used in drifts only at intersections.<br />

342

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