CANADIAN TECHNOLOGY
grouting operation. This type of grout is designed
to be pumped overhead in a borehole from an
entry port installed at the collar. The collar of the
borehole acts as the seal to contain the fresh
fluid grout; there is only an entry port for the
grout and an air escape port where a breather
tube is connected. While the grout is filling the
borehole, the captured air escapes through the
Figure 1: A typical automatic cable bolter
breather tube method, or at a thicker consistency
for the grout and insert method.”
These new concepts increase the level of
complexity of the grout formulation as it has to
be sufficiently fluid for a certain period of time to
allow placement but must set quickly to generate
enough heat in order to avoid freezing, which
would permanently damage the grout, Reny
explained. Although the first cementitious grouts
for permafrost applications were originally
developed for structural piles used in
foundations for infrastructure in northern
climates, it was possible to adapt this technology
to the cable bolting practices currently used in
Canadian mines, he said.
This new grouting technology for cable bolting
offers a neat permafrost grout, according to Reny,
who explained that it was developed and tested
with two different consistencies.
A typical fluid consistency grout was
developed for regular manual mixing and
small breather tube pre-inserted in the borehole
from the collar all the way to the extremity of the
hole, parallel to the cable. When the grout fully
fills the borehole, the grout starts to escape
through the breather tube.
“This ensures full encapsulation of the cable
in the borehole,” Reny said. “Then the breather
tube and the entry port are sealed. This grout is
fluid enough to flow through the breather tube
and to fully fill the borehole.”
Additionally, a thick consistency grout was
engineered for use in the field with a cable
bolter, with the plasticity of the grout adapted to
be used with this new automated equipment.
Reny explained: “When a cable bolter is used
to install cable bolts underground, a grout tube
is first inserted all the way to the toe of the
borehole. As the borehole is grouted, the grout
tube is progressively retracted until it reaches
the collar of the borehole. This method is
consistent with the ‘grout and insert’ method as
the borehole is grouted prior to the insertion of
the cable bolt. Once the borehole is grouted, the
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Figure 2: Plasticity and cohesiveness of thick
consistency permafrost grout required for ‘grout
and insert’ method
cable bolt is installed by the cable bolter.”
Unlike other installation methods, such as the
‘breather tube’ method, the collar is not sealed
and therefore the plasticity and cohesiveness of
the grout prove critical to ensuring the grout
stays in place during pumping, after pumping
and when the cable bolt is inserted. A visual
example of the plasticity and cohesiveness of the
thick consistency permafrost grout is shown in
Figure 2.
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52 International Mining | APRIL 2020
I
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