Page 341 - Rock Mechanics For Underground Mining

PRE-REINFORCEMENT

Figure 11.8 Analysis of conver-
gence and the extent of the plastic
zone in a tunnel in a rock mass having
a Hoek-Brown strength criterion and
subject to an initial hydrostatic stress
field: (a) problem definition and data;
(b) ground reaction curves and nor-
malised extent of the plastic zone at

section SS for three values of GSI.
The crosses are values calculated us-
ing the code FLAC 3D (after Carranza-
Torrens and Fairhurst, 1999).
stopes is illustrated in Figure 11.10. At a given stage of mining (Figure 11.10a),
cables are installed to reinforce the rock mass over three or four lifts of mining. The
cables are installed on approximately 2 m square grids; this spacing may be reduced
or increased depending on the rock mass quality. Cables are installed normal to the
rock surface when they are used for general pre-reinforcement. If shear on a particular
◦
◦
discontinuity is to be resisted, the cables should be installed at an angle of 20 –40 to
the discontinuity. As illustrated in Figure 11.11a, cables installed in cut-and-fill stope
backs may also be used to provide some pre-reinforcement to the hangingwall.
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