Cofferdam construction
Because most of the new facilities have been moved under-ground
and built in basalt bedrock, the only aspect of the
project involving deep foundation work was a cofferdam
erected in John Hart Reservoir, the man-made lake that feeds
the John Hart powerhouse, but is also the City of Campbell
River’s main water supply.
The steel cofferdam was built by FRPD in 2015 to support
excavation work for the new water intake. It was installed
beside a 24-metre-deep, double silt curtain that enabled
FRPD to drill piles without fear of impacting water quality for
both fish and area residents.
“There was a fair amount of turbidity or cloudiness within
the water captured in the work area, but nothing went in to
the wider reservoir,” Watson said. “Turbidity within the reser-voir
was a significant project risk but we did not have one
water quality issue.”
According to Sarah Clark, president and CEO of FRDP, the
company utilized 75 interlocking 914-millimetre pipe piles for
the cofferdam, which was 58 metres long and created a work
area of 420 square metres between it and the John Hart dam.
Clark notes the cofferdam was constructed from land
utilizing Manitowoc 3900W and 4100W crawler cranes
equipped with reverse circulation, rotary percussion drill
heads and semi-fixed lead systems.
“The interlocking pipe piles…were drilled into five metres
of basalt with rotary percussion technology that utilized a
custom frame for alignment,” Clark said.
FRPD returned in 2017 to remove the cofferdam and also
to support blasting operations necessary for construction of
the new water intake for the John Hart Generating Station.
According to Clark, a Liebherr 883 crawler crane and an
American Piledriving Equipment 200 vibratory hammer
were used to remove the cofferdam. FRPD also utilized the
Liebherr 883 during this time to clamshell dredge the blast
rock from the intake structure, says Clark.
FRPD supplied most of the equipment for its work on the
project and utilized numerous suppliers, including many
local businesses. Among the notable suppliers, Clark says,
were Pinnacle Drilling Products, which provided ring bits
and specialized drill tooling, and Wadit, which supplied the
piling interlock sealant for the cofferdam.
Clark says her company was grateful for the opportunity
to work with on a “legacy project” such as this.
“The John Hart project was a great opportunity for FRPD
to show how adaptable and conscientious our team is.
Taking care of the city’s reservoir was a top priority and the
crew delivered a great end result while taking care each step
of the way,” said Clark.
Reasons for the project
According to Watson, the driving forces behind the John Hart
project were:
1. Reducing seismic risk
2. Increasing reliability
3. Protecting the downstream fish habitat
Because the existing facility and pipelines are unlikely to
withstand even a moderate earthquake, the new generating
station has been built to modern-day seismic standards.
“With this new facility being underground in bedrock, it’s
seismically much more robust and stronger,” Watson said.
The old generating station equipment is also in poor con-dition,
with a less-than-optimal electrical output that’s been
declining for years. The new facility will be more efficient and
more reliable.
According to Watson, the new generating station will gen-erate
132 megawatts, enough to power roughly 80,000 homes
compared to about 74,000 homes with the old system.
“Overall, we’re getting nearly a 10 per cent increase in
power output using the same amount of water flow,” Watson
said. “It’s just more modern equipment.”
The project also features a number of long-term environ-mental
benefits. If the new generating station stops working
for any reason, the new water bypass facility will allow water
to continue to flow, preserving the downstream habitat for
fish. According to Watson, that’s particularly important in
an area like Campbell River, which is widely regarded as “the
salmon capital of the world.”
PROJECT SPOTLIGHT
“With this new facility being underground in bedrock,
it’s seismically much more robust and stronger.”
– Stephen Watson, BC Hydro
The steel piles are shown in place, allowing the contractor to then
remove about 20 metres of vertical rock and then tunnel under the dam
44 Q2 2018 www.pilingcanada.ca
