The document reviews low strain impact tests for evaluating pile integrity in deep foundations, highlighting the methods, tools, and practical considerations required for effective testing. It details the theory behind the low strain impact integrity test and outlines the advantages and disadvantages of this testing method. Key aspects include timing, surface preparation, and data analysis techniques necessary for accurate results.

1. A quick review of low strain impact
tests for deep foundations
What is Pile Integrity?

2. In This Video
•What is Pile Integrity
•How To Evaluate Pile Integrity
•Low Strain Impact Integrity Test
•Practical Considerations
•Analysis and Reporting
2

3. “Pile integrity is the qualitative
evaluation of the physical
dimensions, continuity of a pile, and
consistency of the pile material.”
3

4. Why do we need to test?
4

5. Sound pile Major Defect Bulging Necking

6. How to Evaluate Pile Integrity
The theory behind the low strain impact integrity test
6

7. • Low Strain Impact Integrity Test – ASTM D 5882
• High Strain Dynamic Testing – ASTM D 4945
• Crosshole Sonic Logging – ASTM D 6760
• Parallel Seismic Method
• Thermal Integrity Profiling – ASTM D7949
7
Methods for Testing

8. The Sonic-Echo Method
8
Low Strain Impact
Integrity Test

9. The Test in a Nutshell
Evaluate integrity of deep
foundation by “measuring and
analyzing the velocity response of
the pile induced by an impact
device usually applied axially and
perpendicularly to the pile head
surface.”
Motion
transducer
𝑃𝑖𝑙𝑒 𝐻𝑒𝑎𝑑
𝑃𝑖𝑙𝑒 𝑇𝑜𝑒
𝑉𝑜𝑖𝑑
𝐼𝑚𝑝𝑎𝑐𝑡𝑜𝑟
𝐻𝑎𝑛𝑑 ℎ𝑒𝑙𝑑 ℎ𝑎𝑚𝑚𝑒𝑟

10. What tools are needed for testing?
1. Hammer
2. Motion Transducer
• Velocity or acceleration sensor
3. Data Recording Unit
Motion
transducer
Materials Needed

11. -1.5
-1
-0.5
0
0.5
1
1.5
-5 0 5 10 15 20 25 30
Amp
Depth (meter)
How it Works

12. Motion
transducer
𝑃𝑖𝑙𝑒 𝐻𝑒𝑎𝑑
Time
D
𝑑1 =
1
2
𝑉. ∆𝑡1
𝑃𝑖𝑙𝑒 𝑇𝑜𝑒
d1
𝑉𝑜𝑖𝑑
D
d1
𝐷 =
1
2
𝑉. ∆𝑡
𝐼𝑚𝑝𝑎𝑐𝑡𝑜𝑟
𝐻𝑎𝑛𝑑 ℎ𝑒𝑙𝑑 ℎ𝑎𝑚𝑚𝑒𝑟
stress wave
The Theory

13. • Evaluate integrity and consistency of pile material
• Evaluate unknown length of piles or shafts
• Evaluate pile cross-sectional area and length
13
Applications

14. • Pile preparation is relatively easy
• The process of testing and data collection is rapid and
inexpensive
• PIT can identify major defects
14
Advantages

15. • Can not be used to determine the load bearing capacity of
piles
• Interpretation of test results need experience
• Can’t be conducted over the pile cap
• Sensitive length (L) to pile diameter (D) ratio.
• Piles with highly variable cross-section or multiple
discontinuities/anomalies may be difficult to evaluate
15
Disadvantages

16. Practical Considerations
Some things to consider when testing.
16

17. You can test 7 days after casting or
after concrete achieve 75% of its
design strength.
17
Timing

18. Make sure the pile head is:
• Accessible,
• Above water,
• Clean of loose concrete, or soil
18
Surface Preparation

19. You will need bonding material to
attach the motion transducer. Use a
thin layer wax, petroleum jelly, or
putty.
19
Bonding material
Bonding Material

20. 20
Pile Diameter < 500 mm Pile Diameter > 500 mm
Place sensor at
center
Place sensor at 3
different locations
Pile Placement
Location of
impacts

21. 21
300 mm
Impactor Distance

22. 22
90°
Motion Transducer
Position
When testing, ensure that
• The device is perpendicular to the pile
axis
• The impacts are applied parallel to the
motion transducer

23. • If individual impacts are recorded, collect at least 10
impacts per pile;
• Rule of thumb: perform 3 blows and use the average for
each record.
• General: The more hammer blows recorded, the greater
reduction in the effects of random noise. The background
noise can be reduced by a factor of √n, where n is the
number of superimposed signals from the same pile.
23
Number of Records

24. • Light Hammer
• Use for piles less than 1 m
• Less than 1kg
• Heavy Hammer
• Use for larger piles, more than 1m
in diameter
• Should be 1.5 – 6 Kg
Type of Hammer

25. Data Analysis
Some things to consider when testing.
25

26. -1.5
-1
-0.5
0
0.5
1
1.5
-5 0 5 10 15 20 25 30
Amp
Depth (meter)
26
Bottom echo
impulse
Pile Integrity Test Record

27. 27
• Motion Transducers collect acceleration or velocity
induced by arriving echoes from the impact to the pile
head
• If an acceleration transducer is used, measurements
should be integrated and displayed in velocity format
• Given the stress wave speed, the time stamp, or
horizontal axis can be converted to depth
Pile Integrity Test Record

28. • Operators shall monitor the velocity from several impact
events for consistency.
• Do not use the records of impacts that cause the
measurement device to overload (saturated signal with
flat tip).
• Results should be repeatable. If they are not repeatable,
do not use the data. Check sensor placement and
attachment to pile head.
28
Data Quality Check

29. • Stress wave speed
depends on the quality
of pile material.
• Stress wave speed in
concrete is
approximately 3,600
m/s (medium strength)
to 4,400 m/s (high
quality).
• In most cases, 4,000
m/s (13,000 ft/s) is a
good first guess. 29
-1.5
-1
-0.5
0
0.5
1
1.5
-5 0 5 10 15 20 25 30
Amp
Time // or Depth (meter)
Stress Wave Speed

30. • Filtering minimizes noise
caused by:
• High frequency reflections
from boundary
• High frequency noise from
sudden or sharp changes in
cross section
• High frequency noise
induced by careless hammer
blow
• A Low Pass filter can be
used to reduce/remove the
effect of high frequency
noise 30
-1.5
-1
-0.5
0
0.5
1
1.5
-5 0 5 10 15 20 25 30
Amp
Time // or Depth (meter)
Filtering

31.  Amplification is used to
amplify low energy echoes.
 An exponential
amplification function is
applied to amplify the
reflections from pile toe or
defects in deep depths
𝑉𝑎𝑚𝑝 = 𝑉. 𝑒
ln 𝑋.
𝑡
𝑇
 Low Pass filter can be
used to reduce/remove
the effect of high
frequency noise. 31
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
-5 0 5 10 15 20 25 30
Amp
Time // or Depth (meter)
Amplification function
Amplification

32. 𝑉𝑜𝑖𝑑
Sound Pile Pile with Defect

33. -1.5
-1
-0.5
0
0.5
1
1.5
-5 0 5 10 15 20 25 30
Amp
Depth (meter)
33
-1.5
-1
-0.5
0
0.5
1
1.5
-5 0 5 10 15 20 25 30
Amp
Depth (meter)
toe toe
Potential defect
The Good, The Bad, & …

34.  Concrete strength (samples/cores)
 Record pile diameter
 Initial estimation of pile length
 Initial estimation of wave speed in concrete
 Soil profile (soil stratigraphy)
 Construction record, observation
34
Other Information to
Record

35.  Email: support@fprimec.com
 Tel: +1 (647) 933 6633
 For more information: www.fprimec.com/ipile
FPrimeC Solutions Inc.
300 – 2 Simcoe St. S.
Oshawa, ON, L1H 8C1
35
Have Questions ?