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Pile integrity test (PIT) is defined as a qualitative evaluation of the integrity of piles. As per ASTM D5882, pile integrity comprises the material’s physical dimension, continuity, and consistency. The physical dimension includes the length and the cross-section of the pile, while the continuity of the pile refers to voids or significant cracks.

This article explains the important features of the pile integrity test and its methods.

Purpose of Pile Integrity Test

Pile foundation efficiently transfers the loads acting on the massive superstructure to the lower layers of the soil. Despite their relatively high cost, they are highly demanded for bridges, high-rise buildings, etc. 

But the unique geometry of the piles brings in specific challenges during their construction. The most common challenges involve issues pertaining to concrete placement, steel cage installation, pile formation, casing management, drilling, slurry management, etc.

All these issues can result in discontinuity, and bring about changes in the cross-section that may affect the overall pile integrity.

Once the pile elements are buried underground, there is no option to conduct quality control and assurance. In most cases, the pile head is the only accessible portion to undergo inspection and testing.

Hence, several reliable and cost-effective methods were developed to evaluate the quality and integrity of pile elements, one such method is the pile integrity test. There are several methods to conduct the pile integrity test. The selection of test depends on the pile dimension, type of pile, and the soil condition.

Types of Pile Integrity Test 

The most common non-destructive test (NDT) methods used for the evaluation of pile integrity are:

  1. Low-strain pile integrity test
  2. Crosshole sonic logging
  3. Thermal integrity test

1. Low-Strain Pile Integrity Test

The low-strain impact integrity test on deep foundation or pile integrity test is the most commonly used non-destructive method of testing for evaluating the integrity of pile elements.

Low Strain Integrity Testing (PIT); Image Courtesy: GRL Engineers. inc
Figure-1: Low-Strain Integrity Testing (PIT)
Image Courtesy: GRL Engineers

In this method, the pile head’s response against an externally applied impact is recorded using a high precision transducer. The transducer is mounted on the pile head during the test procedure. The transducer used can either be a velocity sensor or an accelerator. 

The test method can use the pulse-echo method (PEM)/sonic-echo (SE) method and impulse-response (IR)/transient response procedures to determine the acceleration and the source information.

The low-strain pile integrity test determines the:

  • Discontinuity in piles like voids and cracks
  • Changes in pile cross-section like necking or bulging
  • Depth of the pile
  • Consistency of the pile materials

The method does not provide the bearing capacity of the pile and cannot be performed over pile caps. Also, the test is not effective when conducted on piles having variable cross-sections.

2. Crosshole Sonic Logging

This test provides information on the homogeneity and integrity of the concrete. Vertical holes are created using tubes during the construction of piles (minimum of two piles are made). The tubes are filled with water during the test. An acoustic wave emitter transducer is placed in tube-1 at its bottom, and an acoustic wave receiving transducer is placed at the bottom of tube-2. Both the transducers are lifted at the same rate.

The test analyses the signal and develops the integrity of the profile, called as the ultrasonic profile. The test is followed as per ASTM D6760.

Crosshole Sonic Logging; Image Courtesy: GRL Engineers. inc
Figure-2: Crosshole Sonic Logging
Image Courtesy: GRL Engineers

The method determines the location and the extent of defects. It can be performed on large diameter piles. The installation of tubes during pile construction is a challenging process. Also, the recording and analysis of the data is expensive.

3. Thermal Integrity Profiling

Thermal integrity profiling (TIP) determines the piles’ integrity by evaluating the temperature variation of the cement paste of the concrete. The test can be performed on a wide range of pile foundations like micro piles, bored piles, drilled shafts, augured cast-in-place piles, etc.

The thermal integrity profiling test records the temperature changes and their history during the curing period of concrete. The temperature recorded is correlated with the strength gain and integrity of foundations.

Thermal Integrity Profiling; Image Courtesy: GRL Engineers. inc
Figure-3: Thermal Integrity Profiling
Image Courtesy: GRL Engineers

TIP possesses the following advantages over other methods:

  • The thermal integrity profiling method evaluates the portion of concrete present outside the steel cage
  • It generates real-time data on the quality of the pile, which helps to reduce the construction timeline
  • The interpretation of data is very easy

Thermal integrity profiling method has some limitations:

  • The technique can only be used on new piles
  • It requires a reference graph to compare the recorded logs
  • The TIP wires and sensors may get damaged during installation and the concrete placement.

FAQs

What is the pile integrity test?

Pile integrity test is defined as a qualitative evaluation of the integrity of piles. As per ASTM D5882, pile integrity comprises the material’s physical dimension, continuity, and consistency.

What are the types of pile integrity test methods?

The most common non-destructive test (NDT) methods used for the evaluation of pile integrity are:
1. Low-strain pile integrity test
2. Crosshole sonic logging
3. Thermal integrity test

What does a low strain pile integrity test provide?

The low strain pile integrity test determines the:
1. Discontinuity in piles like voids and cracks
2. Changes in pile cross-section like necking or bulging
3. Depth of the pile
4. Consistency of the pile materials

Read More

Integrity Testing of Concrete Piles for Proper Functioning

Non-destructive Tests on RC Structures: Basic Methods, and Purposes

DESIGN ISSUES IN PILE FOUNDATIONS

Neenu Arjun

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