Bored and driven piles are the major substructures that need to be cast properly as defects after construction may seriously affect their designed performance. Thus, it is necessary to determine whether piles has defects or not.
The most common failures of in-situ piles improper tip formation due to contamination of soil with the concrete, intermittent concrete pouring or cold joints and any other improper construction methodology. Precast piles may be cracked due to mishandling during operation.
Sonic echo testing is basically used using noise or sonic echo released into the concrete. There is a device attached that records wavelength with corresponding interpretations.
Pile integrity testing is by far the commonly used pile testing. Persons conducting the test are should be experienced and is capable of interpreting actual results. He should be able to accurately read the repeatedly almost similar wavelength based on the result. Before the actual testing, certain measures need to be followed like top of the pile should be perpendicularly cut free from laitance. The surrounding of the pile should be free from any liquid and piles should be 14 days of age after casting.
As this test can be conducted as early as 2 weeks, advantages may be obtained. This method is economical and early defects may be discovered so rectification will be done immediately. This method is conducted quickly and results may be taken right away.
During the test, light tapping on top of the pile is done using a rubber hammer,
Wavelengths of shock waves are transmitted back from the toe of the pile. The top of the pile is tapped to transducer or accelerator that records the wavelength transmitted.
The first shock wave that travels down the pile length is transmitted because of the change in density between the concrete and the bottom soil stratum. One will know if the pile is intermittent or has discontinuity because cracks have secondary waves that interpretation of the captured signal, it is possible to determine the locations of problems in the pile using this device. Tapping of the hammer is done repeatedly until considerably uniform or repeating signals are achieved.
Although this test is widely accepted and practiced, it has certain limitations.
1. This is only applicable to in-situ casted driven piles. Thus, precast piles are not applicable to the test.
2. Major defects may be known but some small soil intrusion may remain undiscovered.
3. This test does not determine whether the bored piles are vertically aligned properly.
4. This is not applicable for piles surrounded by water as it may catch wavelengths from the liquid.
5. This does not determine if the base or toe of the pile are properly cast.
6. Applicable up to 1500mm diameter piles only.
The test has a complimentary test that may be conducted to determine the soundness of the concrete pile. Ultrasonic pulse velocity test, penetration test, density testing of the cast cubes.