FEATURE
Doublestar Drilling constructed two
continuous tangent walls, with piles
penetrating into the hard clay till, in
order to guard against the possibility
of a deeper slip surface developing
at some time in the future.
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high-plasticity clay layer about 12 metres below the ground
surface where the highway traverses the hill. The groundwater
table was about nine to 10 metres below ground surface,
and above the failure plane. These soil conditions, typical of
slide areas, resulted in challenging drilling conditions.
The proper selection of equipment and methods was
important to the success of the project. A Soilmec SR-30
drilling rig was used to install both tangent pile walls, and
Soilmec SM-14 and SM-20 drilling rigs were used to install
all tiebacks. These rigs were selected to overcome the working
space restrictions due to the sloping hillside and active
landslide area.
Cranes were also deployed to help lift and move the tieback
anchor bars. And temperature-controlled, enclosed
grout units were crucial for ensuring continuous operations
throughout the frigid winter.
Tangent pile walls
Doublestar Drilling constructed two continuous tangent
walls, with piles penetrating into the hard clay till, in order
to guard against the possibility of a deeper slip surface developing
at some time in the future. Both walls were installed
parallel to the curving highway on the downhill side.
Continuous tangent pile walls were comprised of a series
of reinforced concrete piles in which adjacent piles touched
without a gap or overlap. These cast-in-place, reinforced,
straight-shaft concrete piles were constructed, and then secondary
piles were constructed in between once the primary
piles reached sufficient strength.
The first continuous tangent pile wall was constructed
using 108 reinforced concrete piles with a diameter of 1.1
metres and depth of 18.3 metres each. In the original geotechnical
design report, this was the only tangent pile wall
proposed.
However, there was subsequent concern about the
groundwater displaced by the first tangent pile wall, so it was
decided that additional support from a second tangent pile
wall was necessary. The second continuous tangent wall was
constructed 300 metres south of the first wall. It consisted of
11014A-FMR_ice-climber-Piling_CAN_3.5x4.75.indd 1 2015-10-21 11:12 AM
Composite aerial photo of the landslide area
COURTESY OF QUEEN’S UNIVERSITY
Two rows of tiebacks installed at 25 and 30 degrees to horizontal
COURTESY OF DOUBLESTAR DRILLING
PILING CANADA 33
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