Project-Mining-Endako-Expansion-Escape-Tunnel-Fraser

CASE STUDY
ENDAKO EXPANSION
ESCAPE TUNNEL
The Endako Mine is a Molybdenum mine located near Fraser
Lake, approximately 160km west of Prince George, British
Columbia. Thompson Creek Mining needed to lower the cost of
ore production as well as modernize its 45-year-old mill. In
2008, the mine announced its plans for expansion. The
processing capacity at the Endako Mine would be increased
from 31,000 tons of ore per day to 55,000 tons.
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Owner
Thompson Creek Mining Ltd.
Installer
Sharp Construction Ltd.
Design Consultant
Hatch
Location
Fraser Lake, BC
ENDAKO EXPANSION ESCAPE TUNNEL
The expanded facility was designed to
have a lower production cost and the
easiest way to accomplish this was by
increasing the capacity of the new mill.
The increased capacity at the mill
resulted in a need for larger ore
supplies, higher capacity
transportation methods at a lower cost,
and an ore stockpile that would be
much deeper than typically
encountered by Armtec.
The challenge that Hatch designers
faced was to install a 2,280mm
diameter emergency escape tunnel,
below the ore stockpile, from the
terminating end of a cast-in-place
concrete reclaim tunnel to a safe exit
point. After a geotechnical
investigation was completed, Hatch
discovered that the tunnel would be
situated well into bedrock and that a
large amount of additional drilling and
blasting would be required to make the
original alignment work. Having
reviewed several options, it was
decided that the final layout would
have the tunnel running alongside the
conveyor gallery for 50m, allowing it to
daylight outside of the bedrock zone,
and then the alignment would deflect
45° and travel another 71m
The final alignment provided a major
challenge to Armtec with regards to
the actual design and supply of the
2,280mm diameter Multi-Plate escape
tunnel—the tunnel needed to be
designed for an overburden of 48m
since it traveled almost directly below
the center of the ore stockpile. This
depth of overburden exceeded the
normal maximum allowed for a
structure of this size and resulted in a
safety factor that was less than the
industry standard.
Armtec and Hatch worked together to
determine an acceptable factor of
OUTSIDE VIEW OF TUNNEL DURING BACKFILLING AND COMPACTION
safety for this application. Some of the
criteria considered in determining an
appropriate safety factor included:
• Stockpiles are conical and soil
pressures will decrease moving away
from the peak.
• Average pressure over an area under
the stockpile cone is not representative
of standard design assumption which
is fully flat overburden.
• 6m of permanent fill would be
carefully placed and compacted to
100% Standard Proctor Density,
allowing the use of a soil pressure
reduction factor (k) for the
permanent cover.
• The stockpile material was wellgraded angular and could develop
some shear strength even in an
uncompacted state.
• Extra attention to quality control in
assembly and backfilling to reduce risk.
ENDAKO EXPANSION ESCAPE TUNNEL
Given that Armtec and Hatch were
going to deviate from normal design
procedures, it was decided that utmost
attention to quality control would be
required and Hatch requested that
Armtec provide on-site support during
construction and a final structure
certification upon completion. This is
normal procedure for large span
structures (spans > 6m) and Armtec
had a quality management plan in
place and ready to go. This started
with a preconstruction meeting to
define roles and responsibilities,
included an experienced Armtec site
representative to monitor the
contractor throughout the assembly
and backfilling process, and was
completed with a structure
walkthrough by the Armtec Region
Engineer for final sign-off.
The actual Multi-Plate structure
included several unique features. The
shell design required that the number
of bolts be doubled along the seams of
the Multi-Plate underneath the deepest
overburden sections. In order to
economize the design, the steel
thickness was decreased as the tunnel
progressed further away from the
center of the stockpile. Lastly, Armtec
also supplied three prefabricated
Multi-Plate elbows in order to match
the alignment provided by Hatch.
Armtec has a history of striving for
excellence and was proud to have
partnered with Hatch in providing a
solution that was cost effective and
required ingenuity.
MATERIAL DELIVERED IN COMPACT BUNDLES
LABOURER ASSEMBLES MULTI-PLATE
CONCRETE COLLAR CAST
ESCAPE TUNNEL TO GALLERY CONNECTION,
INSIDE VIEW
ASSEMBLY COMPLETED
PLACING AND COMPACTION OF CRITICAL
BACKFILL ZONE
READY FOR A DOOR TO BE INSTALLED
ESCAPE TUNNEL EXIT
RECLAIM PILE ABOVE ESCAPE TUNNEL
Armtec is a leading Canadian infrastructure and construction materials company combining creative
engineered solutions, relevant advice, dedicated people, proven products and a national presence with
a local focus on exceptional customer service.
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Armtec / Case Study / Endako Expansion Escape Tunnel | 2012–03