8
amenable to minimal shoulder support and narrower top
cuts can be utilized to service wider stopes.
This is more often the case for mines where the rock is
of Good rock quality (RMR 60 Q 10).
APPLICATIONS AND LIMITATIONS
Good data collection is essential in order to generate DFN
models. For projects which are in early investigation phases,
joint set orientations and spacings can be measured via
oriented core methods. In the cases where underground
exposures exist, cell mapping is the preferred method of
data collection. Both data collection methods should focus
on joint fabrics across the deposit area. Discrete features
such as major faults and geological contacts are generally
not considered in the DFN model. Having a robust struc-
tural geology understanding of the project may allow for
engineering decision making relating to mining directions
(strike of stopes) and stope dimensions.
Further to the joint statistics and fracture intensity, sta-
bility is also dependent on rock density. Should areas be
encountered where rock density is greater than what has
been assumed, the support may no longer meet the design
criterion, particularly for the back. Furthermore, all sup-
port configurations must be installed per the designed spac-
ings using the proper installation technique and QA/QC to
manufacturer specifications.
Optimization of the ground support recommenda-
tions can be investigated using instrumentation (MPBXs
Figure 18. DFN Example case with minimal rib bolting
and TDR) to measure the depth and magnitude of
displacements.
Rule of Thumb
When there is little, or no data available to predict joint
orientations, lengths, or spacings of the joint fabric and a
DFN model cannot be generated, most stope shoulders
can be stabilized with ordinary pattern bolting (without
secondary support) if the TC width is nominally 2/3 of
the stope span (S) as presented in Figure 19. This rule-of-
thumb can be used in early stages of mine design and plan-
ning, particularly in projects of Poor (1 Q 4) or Fair (4
Q 10) rock using Barton’s NGI Q system of rock mass
classification (1974).
CONCLUSIONS
The method presented in this paper provides a framework
for considering how a stope top cut dimension will affect
stope stability and deciding if secondary support is neces-
sary in stope shoulders. In general, wider stopes are only
necessary in rock of poor or fair classification. In these
cases, when the stope shoulders are in tension, they may
fail if the fracture networks are well connected and allow for
progressive ravelling. When determining support require-
ments and TC width dimensions, the following should be
considered for fair or poor quality rock masses:
Figure 19. General Stope TC Guidance in Fair or Poor Rock
amenable to minimal shoulder support and narrower top
cuts can be utilized to service wider stopes.
This is more often the case for mines where the rock is
of Good rock quality (RMR 60 Q 10).
APPLICATIONS AND LIMITATIONS
Good data collection is essential in order to generate DFN
models. For projects which are in early investigation phases,
joint set orientations and spacings can be measured via
oriented core methods. In the cases where underground
exposures exist, cell mapping is the preferred method of
data collection. Both data collection methods should focus
on joint fabrics across the deposit area. Discrete features
such as major faults and geological contacts are generally
not considered in the DFN model. Having a robust struc-
tural geology understanding of the project may allow for
engineering decision making relating to mining directions
(strike of stopes) and stope dimensions.
Further to the joint statistics and fracture intensity, sta-
bility is also dependent on rock density. Should areas be
encountered where rock density is greater than what has
been assumed, the support may no longer meet the design
criterion, particularly for the back. Furthermore, all sup-
port configurations must be installed per the designed spac-
ings using the proper installation technique and QA/QC to
manufacturer specifications.
Optimization of the ground support recommenda-
tions can be investigated using instrumentation (MPBXs
Figure 18. DFN Example case with minimal rib bolting
and TDR) to measure the depth and magnitude of
displacements.
Rule of Thumb
When there is little, or no data available to predict joint
orientations, lengths, or spacings of the joint fabric and a
DFN model cannot be generated, most stope shoulders
can be stabilized with ordinary pattern bolting (without
secondary support) if the TC width is nominally 2/3 of
the stope span (S) as presented in Figure 19. This rule-of-
thumb can be used in early stages of mine design and plan-
ning, particularly in projects of Poor (1 Q 4) or Fair (4
Q 10) rock using Barton’s NGI Q system of rock mass
classification (1974).
CONCLUSIONS
The method presented in this paper provides a framework
for considering how a stope top cut dimension will affect
stope stability and deciding if secondary support is neces-
sary in stope shoulders. In general, wider stopes are only
necessary in rock of poor or fair classification. In these
cases, when the stope shoulders are in tension, they may
fail if the fracture networks are well connected and allow for
progressive ravelling. When determining support require-
ments and TC width dimensions, the following should be
considered for fair or poor quality rock masses:
Figure 19. General Stope TC Guidance in Fair or Poor Rock