72 reinforced concrete piles with a pile diameter of 1.2 metres
and depth of 18.3 metres.
Tieback anchors
Ground anchors were also required to supplement the shear
resistance provided by the piles. The anchors were bonded
deep into the ground behind the failure plane, beyond where
any future landslide activity was expected to originate.
Doublestar Drilling used two Soilmec SM-14 microdrilling
rigs and one Soilmec SM-20 anchoring rig to meet the geotechnical
design requirements.
FEATURE
For each tangent pile wall, two or three rows of tieback
anchors were installed. Using a special coring bit to drill
through the reinforcing cages, full-length holes were drilled
through the soil and into the bond zone. A combination
of augured, cased and hollow-stem drilling methods were
required to deal with the sloughing conditions. For instance,
casings were required for some holes due to groundwater
seepage and sand pockets. The bond zone was limited to 12
metres in length and 0.2 metres in diameter.
Double-corrosion protected, 32-mm threaded bars were
inserted into the holes above and through the tangent walls,
and then the holes were filled with high-strength grout.
Multiple stages of post grouting were required for this anchor
installation to eliminate voids. The lengths of threaded bar
above the bond zone were also covered by bond breakers to
eliminate load transfer above the board zone.
Three layers of expanded polystyrene geofoam blocks
were used as backfill to reconstruct the highway
embankment and reduce the soil pressure on the walls
COURTESY OF ALBERTA TRANSPORTATION
CONTINUED ON PAGE 39
PILING CANADA 35
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