works on the concept of ultrasonic pulse velocity that is
measured along the pile length. To perform the test, access
tubes should be installed in the steel case ahead of pile construction.
While CSL provides critical information about the
quality of pile material at different depths, it does not provide
information about potential defects outside of the steel case.
Thermal integrity profiling has gained popularity among
engineers over the past few years. The test uses temperature
history, which is collected at different depths, to study the
strength gain across the pile length. The test is easy to implement
and provides information about the entire cross section of
the pile (inside and outside the steel cage). The practice has
been standardized as ASTM D7949 (2014).
Parallel seismic tests have been used for evaluating the
unknown length of existing piles and deep foundations. The
procedure has been described by the ACI 228.2R guideline.
Quality control of deep foundations
New construction
Quality control of new construction is an integral component
for successful construction of deep foundations. Quality
related issues with material and workmanship or defects
that can occur during placement of concrete or installation
of driven shafts can impact the load bearing capacity of the
piles and affect the performance. Non-destructive tests have
long been utilized by engineers for this purpose, mainly
because alternative methods such as removing soil, visual
inspection or extracting cores are relatively expensive, create
delays in construction timelines and might adversely impact
the quality and integrity of the elements.
Existing structures
Existing infrastructure was designed and built in accordance
with older design codes and construction practices and
guidelines. Reusing these foundations is considered a time
and money saving practice. However, this requires obtaining
critical information about these elements. Access to structural
designs and drawings for these elements is usually very difficult,
if not impossible. Engineers need to obtain information about
the load bearing capacity as well as integrity of these elements
before using them as part of new construction.
Non-destructive quality control for new
deep foundations
Different methods have been developed to evaluate the
quality of newly built deep foundations. Apart from general
fresh concrete tests such as a slump test, air content test and
taking concrete cylinder samples, various NDTs have been
developed to evaluate the integrity of piles. These tests help
identify and quantify integrity and quality related issues in
deep foundations. Depending on the type of deep foundation,
and surrounding soil condition, a proper NDT method can be
deployed to obtain critical information about the safety and
reliability of the piles.
Among existing methods, acoustic methods based on
propagation of stress waves have been widely used for
evaluating integrity and consistency of pile materials and
structures. Low strain pile integrity tests (PIT) and CSL are
two widely accepted methods in this category. Over the past
few years, other test methods based on temperature monitoring
(referred to as Thermal Integrity Testing) of piles have gained
popularity. These tests help identify and quantify the location
and extent of defects in deep foundations. Like any other
test, these methods have certain limitations that need to
be considered.
Low strain impact integrity testing
Low strain pile integrity testing, known as PIT, is the most
widely used NDT method for the evaluation of deep foundations.
PIT provides a cost-effective and easy to deploy test for rapid
assessment of integrity in piles and deep foundations. PIT
was developed based on the concept of impact-echo and
is customized for slender structural elements. In this test,
stress waves and compression mode of deformation are used
to obtain information about the location of anomalies and
defects within pile elements. Fig. 1a schematically shows a
pile integrity test on a sound pile and defected pile.
PIT uses stress waves generated by a hand-held hammer
strike over the pile head. A motion transducer placed on the
pile head records echoes (reflections) from the pile toe or
other internal defects and anomalies. The recorded signal
is amplified, digitalized and used for data interpretation
and analysis.
FEATURE
0 5 10 15
a) Pile integrity test setup b) Sample of pile integrity results
Fig. 1. Pile integrity test on sound and defective pile
ILLUSTRATIONS: FPRIMEC
Sound pile Defective pile
38 Q4 2019 www.pilingcanada.ca
/www.pilingcanada.ca
