Offshore installation and testing in Alaska
team can see a 360-degree plan view of the shaft, which
allows them to create a 3D model of the walls. With real-time
display results, the sonar caliper is an efficient technology
used to spot sidewall irregularities and estimate hole volume
before concreting.
Frequently used to determine the length of existing piles
and foundations, low-strain pile integrity testing, also known
as a pile integrity test (PIT), entails striking the pile top with
a hand-held hammer as an accelerometer records the pile’s
subsequent small movements. The time record of the pile
movement can be interpreted for changes in the pile’s crosssection
and stiffness with depth.
Thermal Integrity Profiling (TIP) is used as an integrity
test for drilled concrete deep foundations. The test evaluates
the pile down the length of the cage using the heat generated
by the curing cement to assess quality of the concrete in
the drilled shaft and the shape of the cross-section. For TIP,
sensors passively record the temperature of the hydrating
concrete, capturing the temperature changes at determined
time intervals, typically every 15 minutes. An analyst looks
for zones that are cooler than expected to identify potential
integrity issues.
Crosshole sonic logging (CSL) tests the integrity of the
concrete using sound transmission. During a CSL test, transmitters
and receivers are lowered into pre-installed tubes or
coreholes. The arrival time of the sound wave data is interpreted
for the speed of transmission, which indicates the
concrete stiffness and integrity with depth.
The bi-directional test method, developed by Jorj O.
Osterberg, PhD, is performed using a high-capacity loading
device built into a driven or drilled pile. As pressure is
applied, the device works by loading in two directions –
upward against upper skin friction and downward against
base resistance. The pile provides the entire test load and no
overhead reaction frame is required, a distinct advantage in a
marine environment. It is possible to test every pile using the
bi-directional test method, but the decision must be made
ahead of time so the cell can be installed.
An alternative during the foundation construction phase,
the RIM-cell is a more current technology that provides bidirectional
loading for confirmation of pile capacity and
integrity for drilled piles. The RIM-cell has a donut shape
to permit normal concreting procedures and uses grout to
restore the integrity of the pile after applying the proof load.
Although testing has come a long way and contractors can
proceed with confidence on marine projects when the test
results are favourable, there is still room for improvement.
“Geophysics will be the next big thing that will change
the way we build on land and in marine environments,”
said Bullock. “It’s not the challenges that we find that cause
COVER FEATURE
PHOTO COURTESY OF PILE DYNAMICS INC. CONTINUED ON PAGE 38
36 Q2 2020 www.pilingcanada.ca
/www.pilingcanada.ca
