HIGH PROFILE
Full-face raiseboring was used by Cementation
at the Young-Davidson shaft sinking project
Full-face flexibility
Cementation’s shaft sinking work at Young-Davidson
flexed the contractor’s innovation muscles, with large
diameter raiseboring in a three-leg (two phases)
approach helping deliver the lower mine expansion.
IM got to the bottom of this recently-completed project
Project: Young-Davidson gold mine, Ontario,
Canada
Client: Alamos Gold
Scope: Cementation has been involved in the
Young-Davidson shaft project near
Matachewan, in northern Ontario, for
over 10 years. During that time it has
provided studies, engineering,
optimisation, construction and
commissioning. The scope has
encompassed deepening of the existing
MCM rectangular shaft, a new Northgate
production shaft, plus waste and ore
handling infrastructure.
Timeline: Work started in 2009 and the Northgate
shaft was successfully commissioned
earlier this year.
IM: What innovations has the company employed
to ensure it sticks to the budget and timeline set
out by the client?
Cementation: Early contractor involvement in a
project allows the most impactful input to affect
change for project estimates and schedules, as
well as determining realistic and viable
parameters with team buy-in throughout. This is
especially true when, as in the case of
Cementation, the contractor also fields a full
disciplinary engineering group that can work with
the operations team to provide robust solutions
that work.
In 2009, Cementation was invited to participate
in a shaft trade-off analysis for the Young-
Davidson project that would focus on two main
shaft options for the new production shaft; the
base case being a concrete lined shaft from
surface as per the prefeasibility study and an
alternative case of deepening the existing MCM
shaft on the property, supplemented with a
ventilation raise to support ongoing mining
activities. The objective was to identify the
optimum shaft option that would be incorporated
into the feasibility study.
The trade-off considered a raisebore or alimak
pilots and slash or benching for the new 5.5 m
diameter shaft excavation to 700 m depth, with
provision for later deepening to the final 1,503 m
planned shaft bottom. All three methods had the
potential to achieve the final result, but the fullface
raisebore and the Alimak pilot and bench had
shorter schedules than the Alimak pilot and slash
option. In addition, the full-face raisebore was
substantially cheaper than the similar duration
benching option, plus, when evaluated for the
entire shaft length, the raisebore option required
less lateral development than the mechanised
raising methods. In September 2009, the decision
was made to use the full-face raisebore option in
two legs with upgrades to the existing MCM shaft
for the feasibility study.
In February 2010, Cementation was awarded
the engineering, procurement and construction
contract for the MCM shaft upgrades and the new
Northgate shaft, together with headframe and
hoisting plants. This approach allowed an
integrated team familiar with the project to move
through all of the project phases and, with
Cementation’s in-house engineering capabilities
and contractor knowledge for constructability and
safety reviews, the designs were able to be
continuously optimised. As the project moved into
the detailed engineering phase, the team elected
to proceed with a koepe hoist and a concrete
rather than steel headframe, largely to reduce
project capital costs.
Friction hoists typically require less room and
power than an equivalent drum hoist. In this
instance, it was decided to tower mount the hoist
within the headframe. Friction hoists are not ideal
for traditional shaft sinking, but since the choice
here was for a bored full-face shaft there was no
requirement for a sinking excavation setup.
Hoisting systems within a bored shaft require it
to be bored to considerable accuracy to avoid
time and capital costly re-work or modifications to
fabricated designs to accommodate. To mitigate
this risk, Cementation used the MICON selfsteering
Rotary Vertical Drilling System (RVDS).
After the pilot hole broke through for the first 460
m deep leg, the maximum deviation for the hole
was 180 mm to the east, with a total deviation at
the bottom of the hole of 40 mm northeast, well
within the 300 mm acceptable deviation design
parameters, so the estimate and schedule were
protected.
Typically concrete headframes are constructed
by slipforming the concrete shell, then equipping
the internal structure. The headframe contractor
selected for the project by Cementation – Tesc out
of Sudbury, Ontario – proposed a jump forming
system that allowed the steel interior to be
installed as the concrete exterior was being
raised. Tesc and the Cementation engineering
team worked to approve the approach. Beyond
these immediate advantages, the new approach
also allowed for a pause in the headframe
construction to install the ground support in the
first leg of the shaft below as we could not start
piloting and reaming the second leg until this task
was carried out. Slipforming the headframe would
not have allowed for such a pause in headframe
construction.
During construction, the decision was made to
temporarily shorten the depth of the production
shaft and utilise a mid-shaft loading pocket for
interim production hoisting. This allowed for
earlier production and the third leg of the
production shaft to 1,500 m was excavated under
a pentice with eventual changeover to the shaft
bottom loading pocket. Cementation’s approach
allowed this option to be pursued without
detrimental effects to the project economics, for
production and capital purposes. Although this
78 International Mining | SEPTEMBER 2020