GROUND SUPPORT
The Geobrugg MESHA™ mounted on a jumbo
boom picks up the roll of mesh and makes the
bolts at the same time
unrolling process. No personnel are exposed to
unsupported ground, due to the ability of the
jumbo to pick up the mesh roll cassette with the
manipulator arm.
During a trial at South Deep in South Africa,
the MESHA™ seemed to be more effective than
conventional meshing and there was no damage
noted to the MINAX ® G80/3 mesh after blasting.
Additionally, with the use of high tensile-strength
meshes, the rock face remains visible for inspection.
Geobrugg concludes: “After successful
laboratory testing of high-tensile chain link mesh
under both static and dynamic conditions, it was
shown that this kind of mesh is suitable for
ground support in potential rockburst areas. In
contrast to shotcrete, the rock remains visible for
inspection by the geotechnical personnel. Due to
the use of the MESHA™ installation device, this
light but strong mesh can be installed in a fully
mechanised way. To achieve an increase in
performance overall, it is necessary to improve on
the factors that had a major impact on the lost
time, such as failures associated with the
mechanical and the grouting systems and other
associated factors, such as lack of water, which
are more logistical issues. Improvement of the
factors causing delay will make the automatised
application method of the mesh using the
MESHA™ system, an efficient and safe tool.”
The company adds: “It can be concluded that
both the high-tensile chain link mesh and its fully
mechanised installation can increase the safety
of mining personnel, the quality of the installed
ground support, and the performance, due to a
reduction in personnel and increasing the speed
of mining development.”
serviced from Jennmar’s new
Kalgoorlie facility. Jennmar
states: “The welcome addition
of the Gold Fields business
recognises the hard work and
commitment of our technical
and service personnel and
brings growth and new
opportunity to our Perth
facility.”
In March 2017 Jennmar also
commenced distribution from
its new depot in Kalgoorlie.
“This new facility will
warehouse and supply the
complete range of Jennmar products and will
enable us to meet the requirements of our
important goldfields customers.”
Hand and arm injuries account for the largest
percentage of safety incidences in all industries
nationwide in Australia and the potential for
these injuries has been further engineered out at
Jennmar Australia. In December 2016, Jennmar
commissioned an automated feed system and
packing robot for the 600 t plate press at its
Smeaton Grange manufacturing plant. This new
equipment will remove 100% of the manual
handling associated with the manufacture and
packing of its heavy cable bolt plates.
In December 2016, Jennmar commissioned an
automated feed system and packing robot for
the 600 t plate press at its Smeaton Grange
manufacturing plant
Normet on re-entry
Growth at Jennmar Australia
Jennmar has commenced supply of ground
support solutions to its newest Australian
custo mer, Gold Fields, from March 2017. The Gold
Fields business includes four minesites located in
Western Australia and will be supplied and
64 International Mining | AUGUST 2017
The threshold for re-entry into a shotcreted
heading has reduced over the last 20-30 years to
a generalised 1–2 MPa of compressive strength, a
key performance indicator of shotcrete
toughness. In a paper entitled Shotcrete: early
strength and re-entry revisited – practices and
technology, Mike Rispin, Senior Vice President –
Global Sales and Marketing at Normet Group
states: “The early, past norm for re-entry into a
shotcreted heading was in the 8–18 hr range. The
standard was very conservative, by today’s
measures, and reflective of the immaturity of
understanding of the method’s performance
characteristics. As the parameters of shotcrete
became more wisely understood, the re-entry
time for standard shotcreted headings moved in
many mines to eight hours. That standard moved
lower to four hours and eventually two hours.
This progression came as the result of a
combination of ground support theory and
empirical progressions, and included a
maturation of concrete strength development
measurement methods.”
Ultimately, it is the mine’s ground control
engineer who will determine what compressive
strength is required to provide a safe re-entry
time policy for the mine based on anticipated and
observed ground conditions. “This compressive
strength is a key performance indicator of the
shotcrete’s toughness, and its ability to resist
falls of ground due to various failure
mechanisms. Today, the industry norm for re-
entry under ‘typical’ ground conditions (if such a
thing can exist in such a globally diverse
industry) is the assurance of reaching 1 MPa
compressive strength. This is a standard that was
being strived for some 15 years ago and is in
more widespread application today. Today, this
threshold is typically reached within 30–120 min,
depending on many factors including concrete
raw material selection, mix design (including the
important water/cementitious ratio), spraying
equipment selection and application technique,
and temperature.”
Technology has been a major driver in the
ability of shotcrete to develop that critical early
strength without impinging on its ultimate
strength, or the continuous rate of strength
development. “Correspondingly, achieving the
‘best’ early strength is not a safety or
performance success unless the shotcrete
maintains a steady strength development without
enduring a dormant period, and without
sacrificing final performance which is needed in
the long-term.”
Recent technology advancements have and
continue to contribute to ever earlier, safe re-
entries:
n HCA + dormant secondary accelerator in the
mix giving superior results at very early age.
n Accelerators which can handle the challenges
of blended cements.
n Emergence of alternate fibre materials like
basalt.
n Collecting data automatically from the
sprayed concrete operation.
Future developments for shotcrete such as low