10
Table 5. Corrosion mitigation optimization and action
items for future research
Corrosion
Identified Factors
for Optimization
Action Items for Future Study and
Action Research
Minimize Oxygen
exposure
Thin spray on liner (TSL)for entire drift
exposure to rust or sealing shotcrete.
Spray-on liners for small spaces
with modest and portable spraying
equipment.
Minimize Blast
Damage
Blast study for overbreak optimization:
Low density explosives proper drill
hole spacing, perimeter blasting. Bring
in consultants to optimize mechanized
excavation: minimize affected zone.
Most likely using contractors: monitor
initial blasting.
Hydrology
(source of water)
Seal off water by grouting around long-
term openings especially 9 and 10 shaft
of high pH and identified wet zones.
Potential to test around #9 shaft on 68L
Potential use on 58L 10 shaft excavation
if needed.
Overcoring of bolts
for testing of over
coring drills
“New bolts” not previously tested need
to be placed for future over-coreing
and his includes sending to the lab for
metallurgy and tensile testing. Need
to find bolter or vendor specializing in
overcoring entire 8–10 depth for bolts.
Cost studies trade-
offs
Main concern is availability and
increased cost of corrosion resistant
coatings for ground support elements.
Rehab based on
corrosion and
damage
Develop standards for rehab:
Use coated bolts, mesh, fibercrete
SUMMARY AND CONCLUSIONS
The recipe for corrosion on underground support(bolts)
and other support elements (mesh, hangers) is the oxida-
tion of sulfides (dominantly pyrite) in an aqueous solution
(water) or high-humidity environment that produces high
pH acids and paste particulates that attack the exposed
metal (usually iron and steel components). Areas of high
pyrite are potentially more susceptible, but without water,
the processes is halted. Corrosion is considered a very rapid
process once the rock is exposed to oxygen when the drift is
excavated. The depth of saturation is thought to be accen-
tuated by blasting for the first 1–2 meters, which is also in
the zone of the primary support for bolts. The surface of
the drifts are covered with a thin shotcrete shell that helps
to neutralize the acids, but may deteriorate the shotcrete in
the process. A potential partial solution is the application
of a thin spray on layer (TSL) and/or shotcrete the entire
drift to the floor.
Practical mitigation strategies are to isolate the steel
components from the corrosive acids or electrolysis flu-
ids by fully encapsulating or limiting the steel exposure or
dewatering with drilling. Bolts may still corrode, as move-
ment and cracks form between the bolt and rock by ground
movement or by gaps in final installation process. Other
alternatives include adding protective plastic or other coat-
ings to the bolts, but this is usually expensive, and may be
limited to availability or cost. Pumpable resin is the pre-
ferred system to replace manual cartridge system to insure
QA/QC in addition to full encapsulation. Another way is
to seal off the areas of known high pyrite and water such
as around the #9 and #10 shaft. Bolt pull testing is the
preferred proof of support capability, but limited overcor-
ing may be needed to explain results. Extra bolts should be
earmarked for testing based on corrosion hazard mapping
in conjunction with water pH, conductivity and salinity
measurements. This should be a part of damage mapping
system to insure ground support capability.
REFERENCES
Bieniawski, Z.T., 1989, Engineering rock mass classifica-
tions: a complete manual for engineers and geologists
in mining, civil, and petroleum engineering: New
York, Wiley, xii, 251 p.
Clarke, S.J., and Sieders, G., 2014, Comparison of Glass-
fibre Reinforced Polymer Rock Bolts with Double
Corrosion Protection Steel Rock Bolts for Use in Tunnel
Applications, 15th Australian Tunnelling Conference
2014 Sydney, NSW, 17–19 September 2014.
Corrosion Testing Laboratories, Inc., 2019, Metallurgical
Comparison of Resin Bolts TPL2 Pumping Station
Versus New Bolts, September 2019, Internal Report
CTL Report 36195 to Resolution Copper.
Grimstad, E., and Barton, N., 1993, Updating the Q-
system for NMT, in Kompen, Opsahll, and Berg,
eds., International Symposium on Sprayed Concrete-
Modern use of wet mix sprayed concrete for under-
ground support, Norwegian Concrete Association,
Oslo.
Hadjigeorgiou, J., and Dorian, J.F., 2013, Corrosion con-
siderations in the design and operation of rock support
systems, 2013 Australian Centre for Geomechanics,
Perth, ISBN 978-0-9806154-7-0, Ground Support
2013 — Y. Potvin and B. Brady (eds).
Hassell, R.C., Villaescusa, E. and Thompson, A.G., 2006,
Testing and evaluation of corrosion on cable bolt
Table 5. Corrosion mitigation optimization and action
items for future research
Corrosion
Identified Factors
for Optimization
Action Items for Future Study and
Action Research
Minimize Oxygen
exposure
Thin spray on liner (TSL)for entire drift
exposure to rust or sealing shotcrete.
Spray-on liners for small spaces
with modest and portable spraying
equipment.
Minimize Blast
Damage
Blast study for overbreak optimization:
Low density explosives proper drill
hole spacing, perimeter blasting. Bring
in consultants to optimize mechanized
excavation: minimize affected zone.
Most likely using contractors: monitor
initial blasting.
Hydrology
(source of water)
Seal off water by grouting around long-
term openings especially 9 and 10 shaft
of high pH and identified wet zones.
Potential to test around #9 shaft on 68L
Potential use on 58L 10 shaft excavation
if needed.
Overcoring of bolts
for testing of over
coring drills
“New bolts” not previously tested need
to be placed for future over-coreing
and his includes sending to the lab for
metallurgy and tensile testing. Need
to find bolter or vendor specializing in
overcoring entire 8–10 depth for bolts.
Cost studies trade-
offs
Main concern is availability and
increased cost of corrosion resistant
coatings for ground support elements.
Rehab based on
corrosion and
damage
Develop standards for rehab:
Use coated bolts, mesh, fibercrete
SUMMARY AND CONCLUSIONS
The recipe for corrosion on underground support(bolts)
and other support elements (mesh, hangers) is the oxida-
tion of sulfides (dominantly pyrite) in an aqueous solution
(water) or high-humidity environment that produces high
pH acids and paste particulates that attack the exposed
metal (usually iron and steel components). Areas of high
pyrite are potentially more susceptible, but without water,
the processes is halted. Corrosion is considered a very rapid
process once the rock is exposed to oxygen when the drift is
excavated. The depth of saturation is thought to be accen-
tuated by blasting for the first 1–2 meters, which is also in
the zone of the primary support for bolts. The surface of
the drifts are covered with a thin shotcrete shell that helps
to neutralize the acids, but may deteriorate the shotcrete in
the process. A potential partial solution is the application
of a thin spray on layer (TSL) and/or shotcrete the entire
drift to the floor.
Practical mitigation strategies are to isolate the steel
components from the corrosive acids or electrolysis flu-
ids by fully encapsulating or limiting the steel exposure or
dewatering with drilling. Bolts may still corrode, as move-
ment and cracks form between the bolt and rock by ground
movement or by gaps in final installation process. Other
alternatives include adding protective plastic or other coat-
ings to the bolts, but this is usually expensive, and may be
limited to availability or cost. Pumpable resin is the pre-
ferred system to replace manual cartridge system to insure
QA/QC in addition to full encapsulation. Another way is
to seal off the areas of known high pyrite and water such
as around the #9 and #10 shaft. Bolt pull testing is the
preferred proof of support capability, but limited overcor-
ing may be needed to explain results. Extra bolts should be
earmarked for testing based on corrosion hazard mapping
in conjunction with water pH, conductivity and salinity
measurements. This should be a part of damage mapping
system to insure ground support capability.
REFERENCES
Bieniawski, Z.T., 1989, Engineering rock mass classifica-
tions: a complete manual for engineers and geologists
in mining, civil, and petroleum engineering: New
York, Wiley, xii, 251 p.
Clarke, S.J., and Sieders, G., 2014, Comparison of Glass-
fibre Reinforced Polymer Rock Bolts with Double
Corrosion Protection Steel Rock Bolts for Use in Tunnel
Applications, 15th Australian Tunnelling Conference
2014 Sydney, NSW, 17–19 September 2014.
Corrosion Testing Laboratories, Inc., 2019, Metallurgical
Comparison of Resin Bolts TPL2 Pumping Station
Versus New Bolts, September 2019, Internal Report
CTL Report 36195 to Resolution Copper.
Grimstad, E., and Barton, N., 1993, Updating the Q-
system for NMT, in Kompen, Opsahll, and Berg,
eds., International Symposium on Sprayed Concrete-
Modern use of wet mix sprayed concrete for under-
ground support, Norwegian Concrete Association,
Oslo.
Hadjigeorgiou, J., and Dorian, J.F., 2013, Corrosion con-
siderations in the design and operation of rock support
systems, 2013 Australian Centre for Geomechanics,
Perth, ISBN 978-0-9806154-7-0, Ground Support
2013 — Y. Potvin and B. Brady (eds).
Hassell, R.C., Villaescusa, E. and Thompson, A.G., 2006,
Testing and evaluation of corrosion on cable bolt