6
The stope shoulder mass defined by the merged DFN
and stress model must achieve a 1.2 safety factor when
resisted by the bolting in shear. A 1.2 safety factor was the
design criterion and is generally considered acceptable for
temporary excavations such as a stope TC (Ouchi, 2002)
which are promptly mined through.
Figure 15 presents the results of the bolting analysis
for the skarn rock type, which is the most dense rock at the
property. A minimum of 2ft embedment beyond the stope
shoulder was assumed when specifying the length require-
ment. The horizontal spacing was assumed to be 5ft × 5ft,
which would include 6 bolts per rib per row (i.e., 3 bolts in
section for each shoulder),
The results of the bolting analysis plotted by top cut
width and safety factor are presented in Figure 16. No bolt-
ing configuration adequately supports the shoulder at the
16- and 18-foot TC width. The narrowest TC which meets
the design criteria is 20 feet when supported with Twin
Strand Cable Bolts.
Case Study – Conclusions
The designed 16ft wide TC is not suitable for the 35ft
wide stopes at the project site. The minimum TC width
for the 35ft stope is 20ft assuming the following support
configuration:
Figure 14. Ravel Stage 5, final configuration Figure 13. Ravel Stage 4
Table 2. Bolt strength properties
Bolt Type
Tensile
Strength
(tons)
Shear
Reduction
Shear
Strength
(tons)
Standard Swellex (PM12) 12 0.5 6.0
Super Swellex (PM24) 24 0.5 12.0
Cable Bolt (Single Strand) 25 0.6 15.0
Cable Bolt (Twin Strand) 50 0.6 30.0
Rebar (Threaded #7) 15 0.7 10.5
Rebar (Threaded #8) 20 0.7 14.0
Rebar (Forged Head #7) 27 0.7 18.9
Rebar (Forged Head #8) 35 0.7 24.5
Dywidag (#7) 30 0.7 21.0
Dywidag (#8) 39 0.7 27.3
Option No: Option 1 Option 2 Option 3 Option 4 Option 5 Option 6
TC Width (ft): 16 18 20 22 24 25
Stope Width (ft): 35 35 35 35 35 35
Min. Bolt Length (ft): 12 11 10 9 8 7
Bolt Type
Shear
FoS
Shear
FoS
Shear
FoS
Shear
FoS
Shear
FoS
Shear
FoS
Std Swellex (PM12) 0.20 0.22 0.25 0.29 0.34 0.38
Super Swellex (PM24) 0.39 0.44 0.50 0.58 1.02 1.13
Cable Bolt (Single Strand) 0.49 0.55 0.63 0.72 1.19 1.31
Cable Bolt (Twin Strand) 0.99 1.10 1.25 1.44 2.05 2.25
Rebar (Threaded#7) 0.35 0.39 0.44 0.50 0.94 1.03
Rebar (Threaded#8) 0.46 0.51 0.58 0.67 1.14 1.25
Rebar (FH#7) 0.62 0.69 0.79 0.91 1.41 1.56
Rebar (FH#8) 0.81 0.90 1.02 1.18 1.73 1.91
Dywidag (#7) 0.69 0.77 0.88 1.01 1.53 1.69
Dywidag (#8) 0.90 1.00 1.14 1.31 1.89 2.08
Figure 15. Bolting analysis tabulated results
The stope shoulder mass defined by the merged DFN
and stress model must achieve a 1.2 safety factor when
resisted by the bolting in shear. A 1.2 safety factor was the
design criterion and is generally considered acceptable for
temporary excavations such as a stope TC (Ouchi, 2002)
which are promptly mined through.
Figure 15 presents the results of the bolting analysis
for the skarn rock type, which is the most dense rock at the
property. A minimum of 2ft embedment beyond the stope
shoulder was assumed when specifying the length require-
ment. The horizontal spacing was assumed to be 5ft × 5ft,
which would include 6 bolts per rib per row (i.e., 3 bolts in
section for each shoulder),
The results of the bolting analysis plotted by top cut
width and safety factor are presented in Figure 16. No bolt-
ing configuration adequately supports the shoulder at the
16- and 18-foot TC width. The narrowest TC which meets
the design criteria is 20 feet when supported with Twin
Strand Cable Bolts.
Case Study – Conclusions
The designed 16ft wide TC is not suitable for the 35ft
wide stopes at the project site. The minimum TC width
for the 35ft stope is 20ft assuming the following support
configuration:
Figure 14. Ravel Stage 5, final configuration Figure 13. Ravel Stage 4
Table 2. Bolt strength properties
Bolt Type
Tensile
Strength
(tons)
Shear
Reduction
Shear
Strength
(tons)
Standard Swellex (PM12) 12 0.5 6.0
Super Swellex (PM24) 24 0.5 12.0
Cable Bolt (Single Strand) 25 0.6 15.0
Cable Bolt (Twin Strand) 50 0.6 30.0
Rebar (Threaded #7) 15 0.7 10.5
Rebar (Threaded #8) 20 0.7 14.0
Rebar (Forged Head #7) 27 0.7 18.9
Rebar (Forged Head #8) 35 0.7 24.5
Dywidag (#7) 30 0.7 21.0
Dywidag (#8) 39 0.7 27.3
Option No: Option 1 Option 2 Option 3 Option 4 Option 5 Option 6
TC Width (ft): 16 18 20 22 24 25
Stope Width (ft): 35 35 35 35 35 35
Min. Bolt Length (ft): 12 11 10 9 8 7
Bolt Type
Shear
FoS
Shear
FoS
Shear
FoS
Shear
FoS
Shear
FoS
Shear
FoS
Std Swellex (PM12) 0.20 0.22 0.25 0.29 0.34 0.38
Super Swellex (PM24) 0.39 0.44 0.50 0.58 1.02 1.13
Cable Bolt (Single Strand) 0.49 0.55 0.63 0.72 1.19 1.31
Cable Bolt (Twin Strand) 0.99 1.10 1.25 1.44 2.05 2.25
Rebar (Threaded#7) 0.35 0.39 0.44 0.50 0.94 1.03
Rebar (Threaded#8) 0.46 0.51 0.58 0.67 1.14 1.25
Rebar (FH#7) 0.62 0.69 0.79 0.91 1.41 1.56
Rebar (FH#8) 0.81 0.90 1.02 1.18 1.73 1.91
Dywidag (#7) 0.69 0.77 0.88 1.01 1.53 1.69
Dywidag (#8) 0.90 1.00 1.14 1.31 1.89 2.08
Figure 15. Bolting analysis tabulated results