DFI Magazine September/October 2020 - 117

transmitter and receiver by the FAT value
yields the approximate concrete wave
speed, which also is a relative indicator of
concrete quality. During the data analysis,
the testing consultant looks for increases in
FAT (or conversely, decreases in velocity)
and signal strength, and determines if
trends exist in location and extents.

Changing Interpretations
These increases in FAT and decreases in
velocity and energy are often referred to as
anomalies, which might illicit a negative
response in the reader of a CSL report if that
is based on Merriam-Webster's dictionary
definition of "something different,
a b n o r m a l , p e c u l i a r, o r n o t e a s i l y
classified." However, it should come as no
surprise to designers that cast-in-place
foundations are not completely homogeneous. There are variations within each
concrete truck and, given the number of
trucks required to construct cast-in-place
foundations, variations throughout the
foundation length based on placement
techniques and how each load mixes with
the others. In fact, some of the design
elements themselves contribute to nonuniformity, such as variations in hoop
reinforcement spacing with depth and
overlapping column and foundation
reinforcing in the upper portion of a
foundation element, partial depth permanent casing, and diameter reductions in
rock sockets. Aggregate flow through two
rebar cages with tightly spaced hoops at the
top will be different, for example, from that
of a single cage with a wider spacing closer
to the bottom.
One must get their head out of the sand
(pun intended) and accept that cast-inplace foundations are not homogenous. In
fact, it should invoke confidence in the
resolution of CSL when the data shows
some minor anomalies. The difficulty, as is
the case with many nondestructive test
methods, is determining when an anomaly
is significant enough to compromise the
intended foundation's performance.
Anomalous CSL data identified with
delayed arrival times and/or reduced signal
strength may suggest structural nonuniformities, or flaws, such as contaminated,
segregated or low-strength concrete,
honeycombing or large-bleed water relics.

Congestion of overlapping steel for shaft and column, which can produce
anomalous CSL data

Depending on the location, extent and
severity of the flaw, it may affect the
performance of the foundation. If so, then
this defect would require remediation or
replacement of the foundation element.
In a May/June 2019 Deep Foundations
magazine article titled "Pile Testing -
Anomalies, Flaws and Defects," task force
member Amir elaborated on this concept.
The white paper similarly distinguishes
between the three terms, as summarized at
right and in the diagram:

Anomalies can differ from flaws, a
subset of which may cause defects
requiring a response. (credit: Joram Amir)

Anomaly: Abnormal CSL data that
deviates from expectations.
Flaw: Any imperfection in the planned
shape or material of the foundation that
may not necessarily affect its performance.
Defect: Any flaw that, because of size,
location and inferred concrete properties,
will have a significant adverse effect on the
performance of the foundation.
The testing consultant can summarize
the extents of anomalous CSL data in their
report. But, making a claim that the
anomalies are flaws requires judgment.
Ideally, the testing consultant should be
provided with design and construction
records to determine, at the very least, if the
test was performed to the bottom of the
foundation. In general, human nature is to
provide a more conservative conclusion
about the testing results when no design or
construction information is provided.

DEEP FOUNDATIONS * SEPT/OCT 2020 * 117
DFI Magazine September/October 2020

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