FEATURE
Work underway in an active landslide area
COURTESY OF DOUBLESTAR DRILLING
highway or building an alternate highway outside the landslide
area weren’t viable options.
Instead, Alberta Transportation moved quickly to provide
a temporary fix so at least one lane could be reopened to traffic.
Geotechnical engineers determined the landslide failure
plane and remediation plan. Within two weeks, emergency
grading work was performed and a steel pipe was installed to
divert highway surface water runoff past the landslide area.
As a long-term solution, tied-back tangent pile walls were
selected as the best remediation method to stabilize the landslide
mass and anchor the remaining strata. Two tied-back
walls were constructed about 300 metres apart from each
other just below the damaged sections of highway. Both walls
were installed by Doublestar Drilling using Soilmec SM-14,
SM-20 and SR-30 rigs. Once the walls were complete, three
layers of expanded polystyrene geofoam blocks were used as
backfill to reconstruct the highway embankment and reduce
the soil pressure on the walls.
Challenges and solutions
Performing stabilization work on a sloping hillside within an
active slide area and with limited access was extremely challenging.
The landslide had the potential to continue to move
downslope. Furthermore, this demanding work occurred
during an abnormally cold Alberta winter at temperatures
as low as -30 degrees Celsius (-22 degrees Fahrenheit). Safety
was a great concern for the people and equipment.
Subsurface conditions at the site consisted of up to four
metres of firm clay fill underlain by a hard, high-plasticity
clay interbedded with silt and sand layers to depths of about
20 metres, which was underlain by very hard clay till. The
landslide failure plane was primarily located in the upper
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