core composed of a fine filter dynamically compacted. The
construction of a cement-bentonite secant pile wall in the
middle of the berm transformed it from a berm to a dam wall.
The outer parts of the berm were built from a larger aggregate
that protected the inner core.
Phase II began in the middle of August. HFDI crews
constructed workshops and laydown areas. Next, equipment
was assembled and tested. “All the innovative ideas that
had seemed so bulletproof in the warmth of the office in
Vancouver met the reality of the Canadian North,” said Henry.
“Things didn’t always go as we thought they would.”
Even though the HFDI crew brought significant expertise
in secant pile construction to the project, every pile required
a one metre rock socket, which translated into nearly 10 per
cent of the 10,000 linear metres that were drilled being rock.
The schedule did not afford the team sufficient time for the
rock sockets to be cored using traditional drilling tools.
The crew realized that to complete the required 1,000
piles before the Christmas Day 2018 deadline, they needed
to come up with another strategy. “Centre Rock provided two
cluster drills and considerable know-how, which combined
with Don Henry’s fertile imagination, lead to the creation of
a hybrid system in which the drills could as easily pick up the
rock hammers as an auger,” said Langton.
An air hard line was built that could be broken down and
moved as the construction progressed. The hard line enabled
the drills to stay connected to the bank of compressors that
powered the rock hammers.
Environmental precautions
From the outset of the project, environmental concerns
were addressed concomitantly with operational planning.
To protect the pristine water, two rows of silt curtains were
PROJECT SPOTLIGHT
installed in the lake, both upstream and downstream, of the
construction area. All fish were removed in the areas between
the silt curtains and the construction area; potential adverse
impacts of vibrations created by construction activities on
the fish were carefully monitored.
During the project, all refueling was undertaken with the
utmost care and hydraulic oils in the drills were swapped
for environmentally friendly equivalents. Refuelling always
occurred off the dike.
To assess the risk of permafrost thawing, extensive
geotechnical analyses, including thermal analysis, were conducted
over multiple years with the objective of determining
the effect of the construction of the dike on the thermal
regime in the foundation. The engineering team concluded
that most of the core of the dike should stay frozen during the
lifetime of the structure.
“There were no spills or incidents throughout the project,”
said Henry. “All equipment and supplies were safely removed
when the project was complete.”
Innovative solutions to overcome obstacles
Throughout the project, the crew innovated and adapted to
overcome obstacles. For instance, a grout plant needed to be
built that could produce sufficient volumes of the specialized
design of cement and bentonite required to build the cutoff
wall. It was not an easy feat with the time constraints and
crews still doing final assembly as the containers were being
loaded, but the plant’s production capacity allowed the team
to stay on schedule.
The crew was thrown another curveball when the production
of the grout-bentonite mixture clogged up pumps and
lines. “On the ground, mechanical and software changes
were implemented as everybody got on board to help resolve
Getting the crew
to the worksite
also required
several modes of
transportation for
the two-day trip.
PILING CANADA 47