Page 447 - Rock Mechanics For Underground Mining

REINFORCEMENT OF OPEN STOPE WALLS

Figure 14.13 (a) Stope design for 14.13b–eareprovidedinFigure14.13f.Fortheunreinforcedhangingwall,theanalysis
wall reinforcement study; (b) plas- showed that the wall rock was de-stressed. The related displacement distribution
tic domain around unreinforced stope; indicates wall failure, and the uneven shape of the wall deflection curve reflects the
(c–e) three cases for assessment of re-
five-stage extraction sequence used for the stope. The distributions of wall deflection
inforcement; (f) hangingwall deflec-
tions for various reinforcement pat- for the radial reinforcement pattern and the longitudinal reinforcement pattern are
terns. similar. Both have achieved substantial control of hangingwall displacement, but
instability is inferred near stope mid-height. This is consistent with the observed field
performance of the stope. The wall deflection plot for the uniform distribution of
reinforcement (Figure 14.13e) indicates that this pattern is ineffective in controlling
hangingwall displacements.
Three conclusions are proposed from these analyses. First, the density of rein-
forcement is quite low in these mining applications, compared with what would be
applied around civil excavations subject to boundary instability. Second, the rela-
tively uniform distribution of sparse reinforcement is ineffective in achieving stope
wall control. Finally, where reinforcement is necessarily sparse on average, concen-
tration into appropriately located zones may enhance its ground control potential.
It is notable that the third conclusion was proposed independently by Lappalainen
and Antikainen (1987) from their field observations of reinforcement performance
at the Pyhasalmi Mine, providing a measure of confirmation of the reliability of the
analysis.

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