Page 360 - Rock Mechanics For Underground Mining

ROCK SUPPORT AND REINFORCEMENT

Figure 11.28 Alternative methods
of grouting cables into upholes (after
Hoek et al. 1995).

admixtures such as accelerators or retarders, plasticisers, microsilica and reinforcing
fibres. Gunite, which pre-dates shotcrete in its use in underground construction, is
pneumatically applied mortar. Because it lacks the larger aggregate sizes of up to
25 mm typically used in shotcrete, gunite is not able to develop the same resistance to
deformation and load-carrying capacity as shotcrete. For at least 50 years, shotcrete
has been used with outstanding success in civil engineering underground construction
in a wide variety of ground types. It is so successful because it satisfies most of
the requirements for the provision of satisfactory primary support or reinforcement
discussed in section 11.2. Over the last 20 years, shotcrete has found increasing
use in underground mining practice, initially for the support of the more permanent
excavations but now increasingly for the support of stopes and stope accesses (Brown
1999b, Brummer and Swan, 2001). It may also be used as part of the support and
reinforcement system in mild rock burst conditions (Hoek et al., 1995, Kaiser and
Tannant, 2001). Shotcrete is being used increasingly in conjunction with, or as a
replacement for, mesh to provide primary support of headings. Brummer and Swan
(2001) describe a case of the use of wet mix steel fibre reinforced shotcrete to provide
the total drift support in a sublevel caving operation at the Stobie Mine, Ontario,
Canada. Bolts are used in drifts only at intersections.
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