PIT Interpretation - Use only PIT-W EN.ppt

PIT(Pile Integrity Test)
Application and Data
Interpretation
Nepali Technocrats|2023

Pile Integrity Testing looks for defects
Small hammer
impact device
Accelerometer
measures response
(defect)
One person operation
Nepali
Technocrats|2023

PIT-FV/VV PIT-X
PIT-X
• Wireless and Small
• Fixed Sampling Freq.
• Able to adjust senility
• Input of gage SN

Accelerometers
Non-instrumented hammer Instrumented hammer

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

Real data is not perfect
• Imperfect piles
– pile top contact surface not smooth
– inhomogeneous material
(modulus versus length)
– inhomogeneous material (particle sizes)
– Pile shape non-uniform versus length
– pile material damping
– soil resistance

Real data is not perfect
• Imperfect impacts
– spherical point contact versus plane wave
(pile not one dimensional)
– protruding reinforcement “rings”
– Rayleigh waves (surface waves)
– “long” inputs versus “short” defects

Grinding top surface to make flat spot
Pile top preparation is key to good data
which is the key to best interpretation.
Shortcuts cause questionable data.

Minimum Pile Preparation
•locate pile
•clean pile top
•smooth surface
•attach accelerometer
can select any pile to test after installation
(no pre-construction access tubes required)
Nepali
Technocrats|2023

Real data is not perfect, so...
“data enhancements” play an
important part in evaluating
low strain integrity tests
• Collect multiple blows:
averaging reduces “random” effects
• Use best possible equipment
low noise, high A/D resolution
signal processing options

Collect Several Blows of Data
No clear toe signal, need more data processing
Same trigger time Nepali Technocrats|2023

Apply “Magnification factor”

Now can clearly see toe
Can also spot defect

Raw data (nothing to base evaluation on)
Select & enter “MAgnification” MA = 40
Drift?

Add “HI”
HiPass Filter

Altered shape
Too small

HI pass filters:
• Removes slow drifts; straightens curve
• Use low values without reducing details
• Avoid very low values that remove detail
(use a value of “HI” that is
at least 10 x the input pulse width)

-0.56
-0.28
0.00
0.28
0.56
4: # 101
cm/s
V 0.360 cm/s (0.375)
43
CAISSON
600MM
07/17/2007 06:49:02 AM
Hi 200.0 m 9.7 Hz
2W 1.00 m 1934 Hz
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 m
x 15 L/D=16 (D=91.41 cm)
14.90 m (3868 m/s)
Example of Improper Application of Hi Pass Filter (HI)
-0.56
-0.28
0.00
0.28
0.56
4: # 101
cm/s
V 0.360 cm/s (0.375)
43
CAISSON
600MM
07/17/2007 06:49:02 AM
2W 1.00 m 1934 Hz
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 m
x 15 L/D=16 (D=91.41 cm)
14.90 m (3868 m/s)
-0.56
-0.28
0.00
0.28
0.56
4: # 101
cm/s
V 0.360 cm/s (0.375)
43
CAISSON
600MM
07/17/2007 06:49:02 AM
Hi 50.0 m 38.7 Hz
2W 1.00 m 1934 Hz
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 m
x 15 L/D=16 (D=91.41 cm)
14.90 m (3868 m/s)

-0.56
-0.28
0.00
0.28
0.56
4: # 101
cm/s
V 0.360 cm/s (0.375)
43
CAISSON
600MM
07/17/2007 06:49:02 AM
Hi 25.0 m 77.4 Hz
2W 1.00 m 1934 Hz
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 m
x 15 L/D=16 (D=91.41 cm)
14.90 m (3868 m/s)
-0.56
-0.28
0.00
0.28
0.56
4: # 101
cm/s
V 0.360 cm/s (0.375)
43
CAISSON
600MM
07/17/2007 06:49:02 AM
Hi 15.0 m 128.9 Hz
2W 1.00 m 1934 Hz
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 m
x 15 L/D=16 (D=91.41 cm)
14.90 m (3868 m/s)
Example of Improper Application of Hi Pass Filter (HI)

Example of Improper Application of Hi Pass
Filter (HI)
-0.47
-0.24
0.00
0.24
0.47
4: # 101+1%
cm/s
V 0.360 cm/s (0.375)
Reference
43
CAISSON
600MM
High Pass:1000.0 m 1.9 Hz
Wavelet 1.00 m 1934 Hz
Pivot 1 %
Relative Vol.:
Construct. Vol.:
Construct. Area:
Max Profile:
Min Profile:
1.19
1.00
1.00
1.75 at 9.07 m
0.99 at 5.62 m
0 2 4 6 8 10 12 14 16 18 20 22 m
14.90 m (3868 m/s)
0 5 10 15 20 25 30 35 diam
x 15
Magn
Use of reference line instead of HI

Show MA magnification function.
Do not use high MD delay.
?

High frequency noise: “noise” or “ringing” complicates
evaluation ( where does noise come from? )
“smoothing” the curve with LoPass filter (“LO”) helps
simplify evaluation

Wavelet (WL) might be more
effective than LO to remove high
frequency noise and smoothen
the curve
Is there an easier and better way
to smooth the curve?

Use wavelet (WL)

Investigate the cause of “ringing” in this record.
18” augercast pile (38’ long) with 22’ cage #8 bars and 18” stickup. #11
center bar full length – initial 7’ stickup
6#
3#

Investigate the cause of “ringing” in this record.
#11 center bar full length – initial 7’ stickup (trimmed to 3’)
3#
6#

24” augercast piles
Pile 4
12 ft protruding
rebar
Pile 6
50.5 ft
Pile 7
114.5 ft
(L/D = 57)
( Pile installation was monitored with a PIR-A )

Improperly data processing could lead
to wrong conclusions:
• Magnification（MA and MD）：avoid
high MD
• LO Pass or Wavelet filtering (LO or WL)
：avoid high value
• HI Pass（HI）：avoid low value

A
F
A
F
A
F
A F
Nepali
Technocrats|2023

Lesson 1: Location of accelerometer and
force impact make a difference.
Lesson 2: Test at multiple locations at
top of larger diameter shafts.
Lesson 3: Can recommend excavation to
inspect / repair near top defects

Good pile with local bulge
at about 25 ft and clear toe
Major defect
near top
Excavation reveals neck

1 lb. Hammer
6 lb. Hammer “Pulse width” affects evaluation.
For wide pulse, defect reflection
superimposes on input to make
what looks like extra wide input.
No Defect Pile with Defect near top

If only measure velocity and if pile test
has unusually wide input pulse,
Then pile may have defect near top.

1 lb hammer 18 lb hammer (92 ft, 72” shaft)
center
north
west
east
south
Larger hammers sometimes makes
inspection of large shafts easier.
Try different hammers on same pile.

Testing same pile with different
hammer sizes is often helpful,
especially for larger, longer piles.
Small hammer to find defects near top
Larger hammer for defects at depth

PIT detected bored pile defect at 4.1 m depth;
confirmed by core

Pile 028
Pile 072
Pile 027
Other piles from
same site:
good pile
pile with bulge
severe defect
near pile top

“We excavated and found some caves.
I could stick my hand all the way to
the middle of the pile and pull out
hand-fulls of soil.”

– Averaging several blows (reduce random noise)
– Magnification versus time (compensate for losses)
– High pass filtering (or pivoting) to remove soil effects
(eliminates very low frequencies; keep data near zero)
– Wavelet filters (or low pass); (use one OR other)
(eliminates very high frequencies from “ringing”)
Conclusions
Important!
• Use similar processing for similar piles in similar soils.
Compare results to spot unusual piles.
• Data processing usually includes:

• 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

• Some studies suggest a 30 L/D limit.
Actually this is only a “rule of thumb” and
useable length depends on:
– soil strength,
– pile uniformity,
– actual diameter and length,
– and equipment noise, filters and resolution.
• We often see much farther ( even to 60 L/D )
PIT Limitations
• Highly non-uniform piles difficult to interpret
• Cracks or mechanical joints block waves
• Small defects or short length hard to find
• Not always applicable: pile type, walls, in structure
• Says little to nothing about pile capacity

• 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 plan what to do if find a defect
What to do if find a “problem” ?

• Integrity testing is not applicable to ALL situations. Do
not promise results and even try to discourage use in
obviously difficult conditions, or at least inform client of
low possibility of success.
• Impossible to predict load capacity by low strain PIT.
At best, gives relative stiffness from mobility analysis,
or identify soft toes from high toe response.
Conclusions

PIT Interpretation - Use only PIT-W EN.ppt

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