DFI Magazine September/October 2020 - 118

Regardless of the information provided, the
testing consultant is rarely on the design
team and is not in a position to declare a
foundation "defective and requiring
remediation before acceptance." At a
minimum, it is stepping on toes to make
such a statement.
The authors of the paper suspect the
desire for clients to have the testing
consultant declare a foundation acceptable
or to reject it is an unintended consequence
of the terminology used within the industry.
The literature is wrought with examples of

99-025 Drilled Shafts: Construction
Procedures and Design Methods, there is
considerable discussion about CSL, but
suggested rating criteria are not provided.
However, by 2000, several state Departments of Transportation (DOT) were performing CSL with regularity. The CCRC, as
published in the May 2010 FHWA-NHI-10016 (GEC 010, Table 20-2), included signal
distortion/strength along with velocity
reduction and an explanation of the indicated conditions. The CCRC published by
the FHWA (summarized in the table below)

Velocity
Reduction,
VR (%)

Signal
Distortion/Strength

Concrete
Rating

0-10

none/normal
energy reduction = 6dB

Good (G)

10-20

minor/lower
energy reduction
6.1 to 9 dB

Questionable
(Q)

>20

severe/much lower
energy reduction > 9dB

Poor/defect
(P/D)

contamination, intrusion,
and/or poor quality concrete

No signal

None

No Signal
(NS)

Intrusion or severe defect;
could also be caused by tube
debonding

˜ 60

severe/much lower
energy reduction
= 12dB

Water (W)

Water intrusion or water
filled gravel intrusion with
few or no fines

Indicated Conditions
Acceptable quality concrete
Minor contamination,
intrusion, or questionable
quality concrete

Concrete Condition Rating Criteria from 2010 FHWA manual

the terms anomaly, flaw and defect being
used interchangeably. As a matter of policy,
ASTM D6760 avoids interpretation of CSL
results and leaves shaft acceptance to
engineering judgment. Likins et al. (2004)
state that, although CSL testing is straightforward, "there is no general common
consensus (in most parts of the world)
concerning what reduction in amplitude or
delay in first arrival time defines a defect."
Often, projects require CSL, but the
specifications do not outline criteria for the
testing consultant to use. In the absence of
project-specific criteria, many consultants
use the Concrete Condition Rating Criteria
(CCRC), in various forms, as the basis for
interpretation of the data. From the
literature, the origins of the CCRC are
somewhat ambiguous, but it is generally
attributed to Larry Olson, P.E., whose company performs nondestructive evaluations
of structures and infrastructure, around
2000. In the 1999 Federal Highway
Administration Publication No. FHWA-IF-

118 * DEEP FOUNDATIONS * SEPT/OCT 2020

has been modified by several state DOTs
with respect to the range for questionable
concrete. Some state DOTs use velocity
reductions of 10% to 20%, while others use
10% to 25% to indicate questionable
concrete. Others disregard the questionable
rating. Some authorities define poor concrete
as velocity reductions or FAT delays greater
than 30%. Still, others utilize a combination
of FAT delays (or velocity decreases) with
energy reductions.

A New Criteria
The September 2018 FHWA GEC 010
presents a similar CCRC as before, but
acknowledges Amir's Deep Foundations
paper and the alternative criteria. In part,
the recommendations stem from the
understanding that CSL data should be
used as a part of the shaft acceptance
process, and thus needs some form of
classification to delineate acceptable versus
abnormal results. The concrete rating
terminology in the CCRC causes confusion

with respect to shaft acceptance. Therefore,
terms like questionable and poor/defect are
replaced in the DFI paper with the
following categories: Class A (Acceptable
CSL test results); Class B (Conditionally
acceptable CSL test results); and, Class C
(Highly abnormal CSL results).
The more significant change is with the
terminology. The limits (thresholds) corresponding to the new terminology are
presented in the following table; they are
not significantly different from those in the
CCRC. Specifically, CCRC is based on
velocity reduction, while the criteria
within the DFI paper is based on FAT,
which are comparable. For instance, a 30%
increase in FAT is equivalent to a 23%
reduction in velocity.
A more detailed definition of each class
can be found in the paper, which is available
at www.dfi.org/viewpub.asp?tid=WPCSL-2019. In summary, it states that:
* Data within Class A are considered within
normal ranges, and no additional assessment is needed.
* Data in Class B require an assessment
that includes the number of occurrences and their respective locations to
determine the significance of the results
relative to shaft performance.
* Data within Class C typically need
more evaluation, often requiring an
assessment by the Engineer of Record.
A greater likelihood also exists of
requiring more invasive field testing,
and potentially, of shaft remediation.

% FAT
increase

% velocity
decrease

Relationship between FAT and CCRC
velocity results

http://www.dfi.org/viewpub.asp?tid=WP-CSL-2019

DFI Magazine September/October 2020

Table of Contents for the Digital Edition of DFI Magazine September/October 2020