DFI Magazine September/October 2020 - 116

Integrity Testing with Crosshole
Sonic Logging
Ideally, a cast-in-place foundation project
consists of a sound design, an appropriate
set of plans and project-specific specifications, reasonable submittals and review,
and thoughtful observation and detailed
documentation of construction by a qualified contractor. Quality assurance/control
should take place at various stages of
construction, such as during drilling and
clean out, insertion of reinforcement,
grouting or concrete placement, and
finishing. If these steps are properly
implemented and reported, the design
team should be able to make an informed
decision on whether an as-built foundation
element meets the intent of design.
However, integrity testing may also be
performed as the final step of constructing
a cast-in-place foundation. If performed,
the integrity testing report is often seen as
the bow that wraps up construction of the
foundation element, which may be a reason
it often seems to carry a disproportionate
amount of influence. Integrity testing
should work in tandem with previous
design, construction and quality measures
- not supersede them. If a tremie was
CSL test schematic with moveable
source and reception probes (below),
and anomalous FAT and relative energy
data (right) obtained by CSL for a South
Carolina bridge

116 * DEEP FOUNDATIONS * SEPT/OCT 2020

accidently removed from the concrete
during a pour, it should be documented,
and the log provided to the testing
consultant. Their test may corroborate any
existing concern or indicate the tremie
appeared to be reinserted properly, without
creating segregation.
The integrity testing consultant was
likely not on site observing the foundation
construction, but if so, rarely as part of the
design team as well. Given their scope may
only be integrity testing, they are not in a
position to unconditionally "accept or
reject" a foundation, even if construction
documentation is provided. Experience
suggests that specification language and
criteria terminology exacerbate the
"between-a-rock-and-a-hard-place"
situation the testing consultant may
experience, so the authors set out to clarify.
Although there are several methods to
assess the integrity of cast-in-place
foundations, the focus of the paper was CSL
(ASTM 6760 - Standard Test Method for

Integrity Testing of Concrete Deep Foundations
by Ultrasonic Crosshole Testing). Over the last
two decades, due to its relatively simple data
collection procedures and subsequent data
analysis, CSL has been used extensively as a
quality assurance tool. The test is typically
performed between two parallel access
tubes, where the source probe within one
tube emits an ultrasonic pulse that travels
through the concrete and is received by
another probe in another tube. The time is
recorded between pulse generation and
signal reception (first arrival time, or FAT),
as is the strength of the received signal.
To assess the full depth of the cast-inplace element, the source and receiver
probes are pulled simultaneously within
the tubes and hundreds of tests are
performed. The FAT from each individual
test is stacked vertically, and, if the tubes
are parallel and the cast-in-place
foundation is homogenous, the FAT and
signal strength should be consistent as
well. Dividing the distance between
DFI Magazine September/October 2020

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