strength steel that could withstand some deformation before
the slide was halted completely.
The second part of the solution involved the installation of
30 permanent anchors through the existing retaining wall and
connected by a cast-in-place concrete waler.
“Those anchors will pick up the load and tension against
that waler to provide further resistance,” said Kapronczai.
In addition to the micropiles and the anchoring work, a
considerable amount of earthwork was required to establish
an access road from Highway 99 and maintain safe working
platforms for the drilling rigs and other equipment. These
earthworks were completed by a local subcontractor called
GNS Contracting Ltd., which was a big help on the project.
“We were not able to bring in additional earth onto the
slide area because that would have had a detrimental effect
on the actual slide movement,” said Kapronczai. “The challenging
aspect of the earthworks was balancing the load with
a cut and fill to create these platforms so we’ve minimized any
movement.”
Kapronczai says Casagrande C-14 drilling rigs were used for
the drilling aspects of the project. Grouting plants, Atlas Copco
air compressors and a crane for assisting with the installation
of materials were also used on-site, as well as an assortment of
bulldozers, excavators and rock trucks that were required for
the earthworks portion of the project.
Safety top priority
While the risk of a catastrophic slope failure occurring was
considered to be very low, there was always a chance of slope
movement accelerating during construction and causing
greater distress to the existing retaining structure. For this
reason, precautions were taken during every stage to minimize
the load on the worksite and maintain the highest safety standards
and to protect site personnel.
Worker safety was top of mind at all times and, to this end,
there was ongoing slope monitoring throughout the project.
“If there were any red flags, we could react immediately,”
said Kapronczai.
This was accomplished using slope inclinometers and realtime
surficial monitoring using a CYCLOPS integrated survey
network. The monitoring equipment was supplied by SIXENSE.
According to Hazenberg, all of the materials and techniques
utilized during construction were prescribed through
numerous detailed plans for the project.
“There was a quality management plan, a safety management
plan, an environmental management plan and an
engineering plan, of course, that were all instrumental to our
work execution,” he said.
Kapronczai says because it was a remote project, adequate
safety facilities and trained personnel needed to be on site at
all times. The location provided additional challenges, including
where to house the project’s workers (up to two dozen or
so at the peak of construction) but fortunately the Town of
Lillooet wasn’t too far away.
“We tried to work with the local community (Lillooet) as
much as possible in terms of sourcing a lot of our materials
and equipment and for our worker accommodations as well,”
said Kapronczai.
PHOTOS COURTESY OF AGRA FOUNDATIONS LIMITED
PROJECT SPOTLIGHT
adding to a shotcrete and tie-back wall that had been installed
in 2006. According to Hazenberg, neither of these structures
was having any effect on the slide itself, but had acted effectively
as a retaining wall supporting the rail bed.
“A challenging thing about this slide is the depth,” he said.
“The active slide surface is approximately 16 to 18 metres
below ground. These structures…were installed in the upper
portion, so they were basically being carried along intact with
the slide.”
Hazenberg says the project was very unusual from a geotechnical
perspective because they were dealing with what
was essentially a failed condition.
“We had a retaining wall that for all intents and purposes
was showing signs of distress, and we also had an active slide
that was moving at a rate that was considered extremely high,”
he said. “Most solutions that you would install would typically
be for a static situation where you’re trying to improve a condition
or provide an installation that would mitigate future
events. In this case here, the event had already happened and
we were trying to manage it.”
For the track mitigation project, a two-part solution was
employed to first arrest the slide movement and secondly to
improve the global slope stability. That was accomplished by
installing structural elements that went all the way through
the active slide zone and into the underlying surface below the
slip plane.
“We’re satisfied with the result,” said Hazenberg. “The slide
has been monitored ever since the completion of the work and
our works remain effective.”
Two-part solution
The first part of the solution involved the installation of 250
battered and fully grouted micropiles, which were drilled using
a down-hole hammer application.
Phillip Kapronczai, AGRA’s project manager for the site,
says the piles extended down below the slip plane of the slide.
They acted as ductile shear piles and were made of high tensile
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