Site Information Required For the Tests

1. Location of the site;
2. Pile types including size, material, and reinforcement;
3. The layout of piles;
4. Details of pile installation (including construction & driving sequence and rest periods );
5. Number of piles to be tested;
6. Subsurface profile/driving details of the piles (more if variations are noted);
7. Depth of water table and soil investigation report, if any;
8. The density of concrete;
9. Strength of concrete;
10. Abnormal conditions were noted while driving/boring or concreting piles. The normal daily report produced by the piling site should contain this information. In addition, any other information concerning planning and conducting the tests including relevant past experiences covering similar test(s) in the area; and 
11. Details of test piles(s), if any.

Different Types of Tests Integrity Test

The commonly used sonic methods, vibration methods, sonic logging techniques, etc, have been tried within the last 15-20 years in different parts of the world. However, the methods based on the One Dimensional Stress Wave approach known as Sonic Integrity Testing, Low Strain Integrity testing or Sonic Echo Testing have been used successfully in various parts of the world. The method is simple and quick enabling dozens of piles to be examined in a single working day without much interference in site activities.

The work carried out on sonic integrity testing of piles in the country has shown its efficiency.

Low Strain Integrity Testing, Sonic Integrity OR Sonic Echo Test

This is a system of assessing the integrity of piles by the use of low-stress waves imparted to the pile shaft and is also known as Sonic Integrity or Sonic Echo Test.

A small metal/hard rubber hammer is used to produce a light tap on top of the pile. The shock travelling down the length of the pile is reflected back from the toe of the pile and recorded through a suitable transducer /accelerometer (also held on top of the pile close to the point of impact ) in a computer disk or diskette for subsequent analysis.

The primary shock wave which travels down the length of the shaft is reflected from the toe by the change in density between the concrete and sub-strata. However, if the pile has any imperfections or discontinuities within its length these will set up secondary reflections which will be added to the return signal.

By a careful analysis of the captured signal and knowledge of the conditions of the ground, age of concrete, etc, a picture of the locations of such problems can be built up. The reflected stress wave can be monitored using either processing technique, the observed signals are amplified and converted into the digital display as velocity versus length or frequency versus mobility records, providing information on the structural integrity of piles.

The stress wave velocity and approximate pile lengths are provided as input for the integrity testing. The stress wave velocity is dependent on Young’s Modulus and the Mass density of pile concrete. This value generally lies between 3000-4000 metres per second depending on the grade of concrete used (M15-M25).

Normally more than one recording of signals is done until repeatability of signals is achieved. If necessary, averaging of signals is also done to achieve more informative signals. In a suspected pile the test should be repeated at more than one location on top of the pile.

In the case of large-diameter piles, the tests shall be conducted at 5-6 places to cover the entire section of the pile.

The tests shall be conducted on piles whose length is correctly recorded or on test piles where available, to determine the value of stress wave velocity and characteristic or reference signal for comparing the signals for testing subsequent piles.

The method of testing involves high skill and the use of computerized equipment. Therefore, the tests should be performed and interpreted by trained and experienced personnel.

FAQ