Presentation1 integrity problems of concrete piles-emergency

integrity problems of concrete piles-emergency

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INTEGRITY PROBLEMS OF CONCRETE PILES
ENGINEERSTALK
Mohammad Alhusein, PhD
Managing Partner
M:[phone]
E: [email protected]
W: www.superarc.net
INTEGRITY PROBLEMS OF CONCRETE PILES
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2. WEBINAR OUTLINE
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Introduction
Common Defective Construction for Bored Piles
Boring Problems
Improper drilled shaft stabilization method and procedure
Inadequate or poor base cleaning method
Reinforcement cage is not properly fabricated
Poor Concreting Technique
Pile Testing —Anomalies, Flaws and Defects
PIT motivation and advantages

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Introduction

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Ultimate Bearing Capacity -Static
Formula Method (Q
u= Q
p+ Q
s)
Embedded
Length
= D
Q
u= Ultimate Bearing Capacity
Q
s= fA
s
f = Unit Frictional
Resistance
A
S= Shaft Area
q
P= Unit Bearing
Capacity
A
P= Area of Point
Q
P= q
PA
P

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Static Pile Capacity

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Common Defective Construction for Bored Piles
Boring Problems
Improper drilled shaft stabilization method and procedure
Inadequate or poor base cleaning method
Reinforcement cage is not properly fabricated
Poor Concreting Technique

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Soil collapse is common at the
transition between compacted
Soil Layers and the less
compacted Layers.
During a vibration, it is hard to
protect the hole from mud. Because of ground water and the firm fine sand that lie below it, high pressure is needed to
bore the piles, causing vibration and soil collapse.
Boring Problems

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Improper drilled shaft stabilization method and procedure
Shaft Friction: Load / Settlement Curves –After Burland-CIRIA PG3

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CIRIA PG3
Results of element bottom cleaning (including measured
bottom sediment thickness using a Shaft Inspection
Device (SID) prior to reinforcing steel placement and
concreting.
The thickness of sediment shall be measured at four
locations around the perimeter and one at the center of
the pile using a Shaft Inspection Device (SID). The
maximum allowed thickness of debris shall be 50 mm
and the average shall not exceed 25 mm at the time of
concreting.

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Bentonite to comply with ACI 336.1-01
“Specification for the Construction of Drilled Piers”

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CIRIA PG3

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Sieve Zone-I Zone-II Zone-IIIZone-IV
10mm 100 100 100 100
4.75mm 90-100 90-100 90-100 95-100
2.36mm 60-95 75-100 85-100 95-100
1.18mm 30-70 55-90 75-100 90-100
600mic 15-34 35-59 60-79 80-100
300mic 5-20 8-30 12-40 15-50
150mic 0-10 0-10 0-10 0-15
FINE AGGREGATES (FA) (SAND)
FA can be natural sand or crushed sand (produced by crushing rock
pieces), most of which passes 4.75mm and is governed by IS: 383-1970
sieve. It shall satisfy any of the following grading requirements.

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CIRIA PG3

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CIRIA R144-2CIRIA R144-2

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CIRIA R144-2

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CIRIA R144-2
CIRIA PG7

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CIRIA PG7

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CIRIA PG7

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Alabama department of transportation specifications of drilled shaft construction

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506.10 Testing Requirements For Drilled Shafts
Alabama department of transportation specifications of drilled shaft construction

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Reinforcement cage is not properly fabricated
Poor Concreting Technique
Defects Arising from General Construction Problems:
(a)placing concrete by free fall without directing the stream away from reinforcing steel or the
sides of the excavation,
(b)excavating a borehole for a drilled shaft near a shaft that has just been concreted,
(c)placing concrete through water that has accumulated in the borehole,
(d)drilling the shaft out of position,
(e)developing mud waves in surface soil without protecting the newly concreted shaft,
placing lateral loads on the setting or green concrete at the shaft head, which causes
cracks.

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Concrete Flow in Under TremiePlacement
A mixture with the desired workability
will not result in more than a few
inches of difference in height between
the top of the concrete surface near
the tremieand the concrete on the
outside of the reinforcement.
The Contractor shall maintain a continuous
record of the volume of concrete used and
the level of the concrete in the pipe. Any
deviations from the theoretical, or expected,
volume/level relationship shall be
immediately reported to the Engineer.
The volume of concrete : not less than 105% of the
nominal volume of the pile.

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Exposure of Trapped Laitance Attributed to Inadequate Workability

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Restriction of Lateral Flow by Reinforcing Cage

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Effects of Loss of Workability During Concrete Placement

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Major Defects in Concrete Drilled Shafts
1-Major Voids
Similar to cracks, voids can affect the consistency and quality of pile materials. Voids can affect the load bearing
capacity of concrete piles, as they reduce the effective cross-sectional dimension. pile integrity testing does not
provide any useful information about the portion of the pile that locates underneath the major voids or cracks.
2-Soil Inclusion
According toHON-FUNG CYRIL CHAN ( 1987 )Inclusion of foreign material, soil lumps, slurry, etc. within the body of
the pile can negatively impact the integrity of piles and deep foundations. This could happen as a result of borehole
wall slide into the hole which can potentially create gaps over length of pile. Soil inclusion can impact the load
bearing capacity of the pile.Evaluating soil inclusion through acoustic waves can be quite challenging since the
acoustic impedance between the two regions of hardened concrete and soil might not be significant. Methods such
as pile integrity test (sonic-echo) can be used to evaluate the integrity issues.
3-Necking
Necking in concrete piles can happen during casting of pile shaft in soft clay. This rapid change of cross section (as a
results of necking) can be a source of integrity problem. Necking can affect the load bearing capacity of concrete
piles. According to
ZhaoyinZhou, “Poor performance and large water loss of mud causes water swelling of plastic
layer or form lax honeycomb thick mud cake; improper distance between neighboring pile constructions, the stresses in the layers of soil has not been diffused, soft clay creeps in new holes, or the bit size wears excessively are the main causes.”

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4-Bulging
El-Wakil and Kassimcite that bulging is defined as a kind ofpileshape imperfection; bulging increases the pile
cross-section in certain areas along thepile length. Whilebulging may increase the pile ultimate load capacity, it is
still considered as a pile defect and should be investigated. Pile integrity testing can effectively help identify
bulging and necking in concrete piles.

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Pile Testing —Anomalies, Flaws and Defects
Pile integrity means strict adherence to the relevant drawings and specifications.
This includes the pile geometry (e.g., length, diameter or width and verticality) as well as
continuity and material properties.
Since the construction process of piles is practically blind, practitioners realized early on that pile
integrity should not be taken for granted.
Starting in the early 1960s, the discipline of pile integrity testing has made giant steps in both testing
methods and their implementation worldwide.
Presently, the prevalent methods are the low -strain impact method (ASTM D5882, Standard Test
Method for Low Strain Impact Integrity Testing of Deep Foundations) and the crossholeultrasonic
method (ASTM D6760, Standard Test Method for Integrity Testing of Concrete Deep Foundations by
Ultrasonic CrossholeTesting).

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Definitions-ASTM D6760 − 16
(Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing)
Anomaly: Any irregular feature in the results from the nondestructive testing (NDT). An anomaly may be due
to the testing instrument (e.g., noise), the means used (e.g., access tube debonding), the surrounding soil
(e.g., abrupt changes of soil friction) or the pile itself. It is the responsibility of the personnel and/or
agency performing the testing to gather and analyze all relevant data and to try to resolve every anomaly.
Flaw: Any deviation from the planned shape or composition of the pile, which does not necessarily detract
from the performance of the pile.
Defect: A flaw that, because of either size or location, may detract from the resistance , durability and/or
performance of the pile. The geotechnical engineer and the structural engineer are jointly responsible
for deciding whether a specific flaw constitutes a defect.

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EXAMPLES: JoramM. Amir, Ph.D., C.E., D.GE, Piletest.com Ltd.
DEEP FOUNDATIONS • MAY/JUNE 2019 • 93
I -Anomaly That Is Not a Flaw:
An anomaly that is not a flaw, also
known as a false positive, will be
illustrated using two cases: one from
crossholeultrasonic testing of a
barrette and one from low-strain
impact testing on a pile.

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As shown on the graphic “Ultrasonic test results on a
barrette,” (Fig 2) the first arrival time (FAT) is shown in
red and the relative energy (RE) in shown in blue.
Down to a depth of about 22 m (72 ft), both curves
appear rather regular (i.e., relatively straight lines) with
nearly constant values of FAT and RE.
However, below this depth and down to about 29.3 m
(96 ft), the FAT gradually decreases from 330 μsecto
100 μsec, doubtlessly an anomaly.
A quick questioning onsite revealed the reason;
the foundation element was reinforced only in the
upper 21 m (69 ft).
Nevertheless, the engineer required that the access
tubes be extended all the way to the bottom of the
barrette.

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With no rebar cage to keep them aligned, the access
tubes dangled freely and likely moved toward each
other.
This result had certainly nothing to do with the barrette
itself and, accordingly, was not declared a flaw.

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The following reflectogramwas generated from low-
strain impact testing of a driven pile that was 27 m
(88.6 ft) long.
From a review of the output (Fig 3 ), a major anomaly
appears at a depth of about 12.5 m(41 ft).
However, after questioning the client about the pile, it
was discovered that this pile consisted of two
interlocked sections.
What appeared as a discontinuity in the reflectogram
was actually just the joint between the two sections and
was therefore not declared a flaw.

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II -Anomaly That Is a Flaw:
An anomaly that is a flaw includes “soft bottom” conditions, which
occur when the bottom of a drilled shaft constructed using a drilling
support fluid (i.e., slurry) is not cleaned properly.
The only existing method in which the soft bottom condition is
detected and appears as an anomaly is the crossholeultrasonic
logging (CSL) method. With the CSL method, a soft bottom
condition manifests as a large increase in the FAT with a
corresponding decrease of the RE (Fig 4). Understandably, a soft
bottom condition anomaly, should be reported as a flaw.

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III -Flaw That Is Not an Anomaly and
Not a Defect:
A flaw that is not an anomaly and not a
defect includes a minor soil pocket in the
pile which is, by definition, a flaw (Fig 5).
However, due to its small size, the flaw
may be undetectable even by today’s
most sensitive instruments and, therefore,
cannot produce an anomaly. Fortunately,
such a small flaw affects neither the
capacity nor the durability of the
foundation element; thus, the flaw is not a
defect.

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IV -Anomaly That Is a Defect:
An example of when an anomaly is actually a
defect (i.e., true positive) is discussed hereafter.
From the results of CSL testing performed on a
drilled shaft, a major anomaly was discovered at a
depths between 1.8 m and 3 m (6 ftand 10 ft),
where the FAT increased from 190 μsecto
a maximum of about 330 μsec, an increase of
about 74%. The attenuation increased by 16 dB,
which was an 84% decrease in the energy (Fig 6).
Since this feature was quite shallow and the
groundwater level much deeper than the location
of the anomaly, it was decided to excavate around
the pile to expose the anomaly. Upon excavating
around the pile, visual observations confirmed the
test results and suspicions that this anomaly was
indeed a flaw. Due to its size and location, the
flaw was justly classified as a defect (Fig 7 ).

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V –Defect That Is Not an Anomaly:
A defect that is not an anomaly (i.e., a
false negative) represents all the true
defects that go undetected, such as :
Deviation from the vertical, which is
not detected unless tested using a
dedicated system.
“Soft bottom” conditions that were
undetected by either the low strain
impact method or thermal imaging.
Large bulges, which are undetectable
by CSL testing.
However, defects such as the ones
listed above could have been detected
by selecting a proper test method.

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PIT motivation and advantages
What is Pile Integrity ?
In general,Pile Integrityrefers (ASTM D 5882) to certain characteristics of deep
foundations and piles such as:
Physical Dimensions of Pile (Length or Cross-Section);
Continuity of Pile (presence of Voids or Major Cracks); and
Consistency of the Pile Material.
Certainpile construction practicescan lead to defects in drilled shafts. These defects
can be major voids, poor quality concrete, geometric errors, and entrapped slurry or ground water. These defects may negatively impact the load bearing capacity and load
distribution properties.
Piles and deep foundationstransmit top structure loads to strong substrate through
friction and/or standing on bed rock. This load transmission is performed effectively when
there are no major integrity problems in concrete piles; Defects may result in partial settlement to significant damage or collapse of the top structure.

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Pile Construction Methods
Before we begin, let us briefly review the main three methods of pile construction:
•Dry Method:In this procedure, the borehole is excavated, and backfilled directly
with concrete.
•Casing Method:In this procedure,a temporary casing is used to support the
borehole, prevent caving, and prevent intrusion of groundwater before placement of
concrete.
•Direct Slurry Displacement:In this method, drilling fluid is used to stabilize the
borehole during excavation. The liquid is then displaced by placing concrete under the fluid throughtremie
pipe.

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Low Strain Integrity Methods
•PILE INTEGRITY TESTING (PIT)
•Measure Pile Top Motion, Reflections from Defects
•CROSS-HOLE SONIC LOGGING (CSL)
•Determines Concrete Quality Between Tubes in Shaft
•For larger augercastpiles
•SINGLE-HOLE SONIC LOGGING (SSL)
•For smaller augercastpiles
•PARALLEL SEISMIC (PS)
•Hit Pile, Measure Hydrophone in Parallel Tube
•Determines only Pile Length,

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Pile Integrity Testing looks for defects
Small hammer
impact device
Accelerometer
measures response
(defect)
One person operation
Pile Integrity Test # ASTM D5882

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Accelerometers
Non-instrumented hammer Instrumented hammer

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PIT motivation and advantages
•prime function is to locate majordefects
(to evaluate questionable shafts)
Important
•inexpensive, can test many piles
(good for quality assurance)
•no advance selection required
(good for forensic purposes)

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Local Defect: small medium large
Local Bulge: small medium large
PIT -Basic Interpretations

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Normal test (pile
top “free”)
Good Pile
Bad Pile
800 mm drilled shafts
L = 25 m (L/D = 31)

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800 mm drilled shafts
L = 25 m (L/D = 31)
magnification = 40x
P98
Defective
P125
Good Shaft
Top Bottom

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Classifications
(4 categories proposed by GRL)
•A -Good Pile
Clear toe response, no obvious defect; sound shaft
•B -Bad Pile
Clear identification of serious defect; no toe signal
–needs contingency tests or corrective measures
•C -Possible Defect
–re-test, other tests, reduce capacity or replace
•D -Inconclusive data
(poor pile top quality,
or no reflections due to strong soil)
–fix pile top & re-test; might give info for upper pile shaft
which is reason to accept pile.

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•Compare with other observations
•Re-test with PIT (trim pile top to solid concrete)
•Excavate if near top
•Request pile core
•Request a PDA test or a static test
•Replace pile (or repair)
•Other?
•Have a planwhat to do if find a defect
What to do if find a “problem” ?

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–Averaging several blows (reduce random noise)
–Magnification versus time (compensate for losses)
–High pass filtering (or pivoting)
(eliminate low frequencies; keeps data near zero)
–Wavelet filters (or low pass);
(eliminate high frequencies)
–Rayleigh wave correction (experimental)
Conclusions
Important!
•Use similar processingfor similar pilesin similar soils.
Compare results to spot unusual piles.
•Data processing usually includes:

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•Interpretation looks for:
–Good data (consistent & reasonable)
–Similarity or differences for different piles
–Rapidly changing features in data
–Toe signal (tension or compression)
–Shaft uniformity
–Indications of major defects(+/-cycle)
–Comparison with soil profile, installation records
•Integrity testing locates major defects. It is limited to
general interpretations rather than exact detail. Do not
use “heroic effort” to read more than data really tells.
Conclusions

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Ultrasonic CrossholeTestingprovides information about the homogeneity and integrity of concrete.
The method can be used for quality control of concrete piles. This method overcomes the limitation of
low strain impact integrity testing. vertical holes are created using tubes at the time of pile construction
(at least two). The tubes are filled with water.An acoustic wave emitter transducer is lowered to the
bottom of one tube; while another acoustic wave receiving transducer is placed at the bottom of second
tube.Both transducers are pulled upward at the same rate. The signals are analyzed and integrity
profile of the pile is developed. an ultrasonic profile. The test procedure is standardized asASTM D6760
Applications:Cross Hole testing can be used to determine the location of defects, as well as identifying
the extent of the defects. The test can be done on larger diameter piles.
Limitations:Requires installation of tubes during pile construction. Data recording and analysis might
be expensive. Access to the tip of the wall is needed for most applications.
CROSS- HOLE SONIC LOGGING (CSL)

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CROSS- HOLE SONIC LOGGING (CSL)

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CROSS- HOLE SONIC LOGGING (CSL)

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CROSS- HOLE SONIC LOGGING (CSL)
First Arrival Time for
Analysis of CSL Test
Results
In this procedure, the arrival
time of the first peak in the
ultrasonic pulse wave train
is (First Arrival Time, FAT),
and the overall amplitude of
the early part of pulse is
measured. A practical
challenge in the FAT
method is distinguishing
between peaks in the wave
train, and the noise in the
construction site. This is
often performed through
filtering out the noise by
assigning a threshold value.

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CROSS- HOLE SONIC LOGGING (CSL)

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CROSS- HOLE SONIC LOGGING (CSL)
Capabilities of Ultrasonic CorssholeTest
CrossholeSonic Test is a great test for identifying Anomalies in concrete shafts such as soil
inclusion, poor quality concrete (low density, low modulus), and major voids.
In general, the transit time of ultrasonic pulse between every two access tubes is measured using a
high precision data acquisition system.
The resolution of the scan along elevation can be controlled by the rate of the withdrawal of the
transducers in the tube (normally performed form the bottom to top).
The resolution of the scan at each elevation depends on a number of parameters, such as the
selected frequency (pulse wavelength), the number and horizontal spacing of access tubes.
A modern CSL is equipped with transducers that can operate between 25 to 50 kHz, allowing
detection of defects as small as 2.5” to 4” (in each horizon). It is recommended to keep the spacing
of the probes to about 12’ (3.6 m).

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CROSS- HOLE SONIC LOGGING (CSL)
Key Advantages of CrossholeSonic Logging
The interpretation of the test results in CSL test is relatively easy (compared to other tests, such as the low
strain pile integrity test).
In theory, there is no limitations with regards to shaft length or diameter. The test results are not affected by skin
friction, variation in soil stiffness, or damping characteristics.
The test can be further enhanced by implementing a diagonal positioning of the probes (in which the elevation
of transmitting transducer has an offset with the receiving transducer).
This would enable engineers in creating 2D and 3D maps of defects inside shaft.

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CROSS- HOLE SONIC LOGGING (CSL)
Disadvantages and Practical Limitations
The main disadvantage of the test relates to the fact that most access tubes are installed inside the steel
reinforcement cage.
This would limit the amount of information that can be obtained from concrete area that lies beyond the steel
cage (which happens to be the most problematic area in most cases).
CSL test does not provide information about small horizontal defects.
Another practical consideration is the installation of tubes. As the shaft dimeter increases, the minimum
number of access tubes is also increased.
This will increase the number of paths that need CSL measurement (labor intensive and time consuming).
The CSL test offers no indication of the concrete cover or cage alignment but simply that the integrity of the shaft
central core section.

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CROSS- HOLE SONIC LOGGING (CSL)
Practical Considerations
Access Tubes |Steel Access Tubes or PVC Access Tubes?
Proper selection of access tubes is critical in performing CSL test.
Access tubes can either be steel, or PVC. However, experiences from North America have shown that the
PVC tubes are less reliable, and might result in unwanted challenges such as debondingfrom the
concrete. Plastic tends to lose its bond to concrete after a few weeks (following concrete placement).
Since ultrasonic wave cannot pass through air, the debonding issue makes rendering the CSL test
ineffective.
What is the proper size of Access Tubes?
Access tubes are typical 1 to 2 inches in diameter (25 mm –50 mm). Access tubes are filled with water to
provide acoustic coupling, as a result, they should be water tight at the ends to prevent the penetration of
soil, groundwater and debris inside the tube.

83. INTEGRITY PROBLEMS OF CONCRETE PILES
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CROSS- HOLE SONIC LOGGING (CSL)

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