PIT can be used for cast-in-place concrete piles, driven
piles, steel tube filled concrete piles, augured piles, drilled
shafts, structural columns and timber piles. PIT is not
recommended for integrity testing of steel sheet piles,
H-piles or unfilled steel tube piles because the dominant
mode of vibration changes from compression to bending. The
main features of the PIT can be described as:
• Pile preparation is relatively easy.
• The process of testing and data collection is rapid
and inexpensive.
• PIT can identify major defects (location of defects
and severity).
Some of the main disadvantages of the test can be
summarized as:
• Interpretation of test results requires experience.
• PIT cannot be conducted over the pile cap.
• PIT is sensitive to pile length (L) to pile diameter (D) ratio.
The test results might be unreliable for piles with an L/D
ratio over 30. Surrounding soil friction and change of
dominant mode of vibration from compression to bending
affects the PIT results (Massoudi et al, 2004).
• Piles with highly variable cross sections or multiple
discontinuities/anomalies may be difficult to evaluate
using PIT.
Ultrasonic crosshole testing
Ultrasonic Crosshole Testing (or CSL) is the most common
test for integrity evaluation of large diameter cast-in-place
shafts. This test is an extended form of the ultrasonic pulse
velocity test and provides information about homogeneity
and integrity of concrete material over the pile profile. Fig. 2
schematically shows a general setup for CSL. This method
includes two ultrasonic transducers (i.e. one emitter transducer;
one receiver transducer).
Fig. 2. General setup for crosshole sonic
logging test in deep foundations
FEATURE
The concept behind this method is supported by the
ultrasonic pulse velocity (UPV) concept. UPV measures
the transmission time of stress waves between emitter and
receiver transducers. This travel time can be converted to
wave velocity if the stress wave trajectory between emitter
and receiver probes is known. The wave velocity is directly
correlated with the quality of material. Poor and/or damaged
concrete has a lower wave velocity when compared to sound
concrete. Table 1 shows the relationship between wave velocity
and quality of concrete (Saint-Pierre et al, 2016).
Table 1 – Correlation between quality of
concrete and ultrasonic pulse velocity
Quality of Concrete Pulse Velocity (m/s)
Excellent Greater Than 4,500
Good 3,500 – 4,500
Mediocre/Fair 3,000 – 3,500
Poor 2,000 – 3,000
Very Poor Less Than 2,000
To perform a CSL test, a number of vertical boreholes
(tubes) are made during concrete placement using parallel
metal or plastic (PVC) tubes. The recommended number and
configuration of boreholes depends on pile diameter. Fig. 3
schematically shows the configuration of boreholes for piles
with different diameters. This figure has been adapted by
ASTM standard as ASTM D6760 (2016).
Fig. 3. Configuration of holes in CSL test
(adapted from ASTM D 6760)
The boreholes should be filled with water to ensure there
is constant contact between the device probes and surrounding
area. Both transducers (probes) are pulled upward
at the same rate and the transmission time between the two
probes is measured at each level. If a significant change in
transmission time (or wave velocity) is observed, it might be
correlated to internal anomalies of defects. The tomography
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