This
type of work had never been tried in Thailand using
HDD. However, other solutions were considered too expensive,
and Strega convinced BCKT that HDD would work. In addition
to not having been done before, the project ran the
risk of wrecking very expensive equipment. The Vermeer
D80 x 100 had to be painstakingly lowered into the 20
meter-deep station box using an 80-ton crane, and set
up behind the front wall. Once the rig was lowered and
set up, Strega's crew drilled nine holes, allowing the
drill head to pass through the wall and into the clay.
The bores were then drilled to a depth of 54 meters.
At such depths, guidance of the drill head required
a special cable transmitter that could take readings
as accurate as -/+ o.1%. Strega used DCI's Mach III
sensitive pitch cable transmitter for the job. After
drilling the holes, the columns were pushed in by hand
and a pump was used to insert the grout. The PVC casing
for the inclinometer was lightly grouted around the
outside so that it would remain flexible enough to react
to any movements.
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