concept using two probes is applied to identify the extent of
the defects at a specified depth (ASTM D6760, 2016).
The advantages of deploying a CSL test in integrity assessment
of new piles include:
• Ultrasonic crosshole testing is an ideal test for evaluation
of large diameter piles.
• There is no limit on the shaft length.
• Provides precise information about the location and the
extent of defects.
• Soil profile does not impact the test results.
• Easy data interpretation.
The CSL method has some disadvantages:
• This method is expensive and is not fast enough for condition
assessment of piles.
• Boreholes should be installed before placement of
concrete. Boreholes might break or experience damage
during construction that results in inconclusive
test results.
• Stress waves cover areas between emitter and receiver
probes. Therefore, larger diameter piles need a number of
boreholes to achieve conclusive results.
• The test does not provide information about concrete sections
outside the steel cage.
• This test is not commonly used for existing piles and deep
foundations because it usually needs pre-construction
preparation (i.e. boreholes need to be installed before
concrete placement).
Thermal Integrity Profiling
Thermal Integrity Profiling (TIP) uses the temperature variation
of cement paste of concrete for integrity evaluation of piles
and deep foundations. This method covers a wide range of
piles and deep foundations including drilled shafts, bored
piles, micropiles, augured cast-in-place piles, continuous
flight augured piles, drilled displacement piles and more.
The concept behind this technology is to record temperature
changes and history during the curing time of cement.
This temperature can be correlated to the strength gain of
concrete and integrity of piles and deep foundations. Fig. 4
shows a typical temperature history of normal concrete over
the pile depth.
This technology includes a number of temperature
sensors along pile length, connected by wire to a data
acquisition system. The sensor holding the cables is attached
to longitudinal steel rebar of the reinforcing cage. Each sensor
logs the temperature of its surrounding area in a specified
time interval to track and record temperature variations and
the evolution of concrete strength. The temperature at any
location of deep foundations depends on the pile size and
diameter, concrete mix design, concrete cover thickness outside
of the reinforcing cage and other factors.
The temperature history is compared with a reference
graph for integrity evaluation. It is obvious that TIP
measurements colder than the reference graph indicate
a lack of sufficient cement which can be caused by necking,
soil inclusion or poor-quality concrete; while warmer
than normal measurements are indicative of an increase
in cross-sectional dimensions (Mullins and Kranc, 2007).
TIP has several advantages compared to previously
described methods:
• Can be used to evaluate the portion of concrete outside
the steel cage.
• Provides real time data on pile quality, which can shorten
the construction timeline.
• Data interpretation is relatively easy.
TIP measurement has some limitation for integrity testing
of piles and deep foundation including:
• Can only be used for integrity testing of new piles.
• Measurements need a reference graph for comparing
recorded logs for integrity evaluation.
• Wires and sensors may be damaged during installation
and concrete placement.
• Measurement is a comparative method for integrity
evaluation. Change in mix design may result in a huge
difference when compared to the reference graph even
though the concrete pile is sound.
Fig. 4. Thermal integrity profiling
FEATURE
40 Q4 2019 www.pilingcanada.ca
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