The Pile Integrity Tester confirms the absence of major cracks and voids on any type of concrete foundations prior to construction of the superstructure. It may also test piles integral in the structure, such as those supporting existing bridges or towers, and determine their length.
The Low Strain Dynamic Testing method employed by the PIT is fast enough to permit testing of every pile on site.
PIT performs the wave equation-based non-destructive test known as Pulse or Sonic Echo Test, or Low Strain Dynamic Test. The test consists of attaching one or two accelerometers to the foundation, and using a small hand-held hammer to impact it. The accelerometer data reveals any significant changes in cross section that may exist along the shaft. The PIT-W software post processes the data and generates report.
Method of Testing
There are Indian Standards for the pile integrity test & the most commonly used worldwide is Pile Integrity Test as per ASTM – D 5882 – 07, “Standard Test Method for Low Strain Integrity Testing of Piles”. Relevant clause from the said ASTM standard is reproduced below: Clause no. 5.2.3 : Placement of Transducers – The motion sensor should be placed at or near the pile head using a suitable, or temporary, bonding material (that is wax, vaseline etc.) so that it is assured that it correctly measures the axial pile motion. The motion sensor is placed generally near the center of pile. Additional locations should be considered for piles with diameters greater than 500 mm. The low strain impact should be applied to the pile head within a distance of 300 mm from the motion sensor.
To check the integrity of pile.
Piles with necking are selected for dynamic tests.
In the sonic test, the top of the pile is hit with a plastic hammer and the reflected waves are recorded by a suitable computerized equipment. From the resulting signal, or reflectogram, one can determine both length and continuity of the pile. Although a powerful tool, the sonic method also has limitations, such as: the test produces no information regarding the pile capacity, and gives only limited information about the concrete quality. The sonic system, can only discover material impedance changes. It cannot tell anything whether these impedance changes are due to poor concrete or due to reduced cross section. Even then this test is a fast & economical tool for determining discontinuities in the pile shaft. If pile records are available, then the results can be fine tuned for greater & more reliable information.
Limitations Of The Test
The accuracy of the length determination depends on the assumed wave velocity. This factor, which depends on the grade and age of the concrete, varies from pile to pile and may cause an error of the order of 10 percent.
Site Preparation Guide
For the test to be effective, the top of the pile should consist of clean concrete and free of debris, laitance and bentonite. Testing a pile with a head which was not properly prepared may yield misleading results.