Time Domain signal processing is referred to as the Sonic Echo Test , while Frequency Domain processing is called Frequency Response Test . The Frequency Response graph provides the most comprehensive integrity information whilst the sonic echo tests are only used to complement the information obtained from the frequency response tests on selected piles.

The depth limit of the test is typically 20 to 30 times the pile diameter and is usually dependent on the surrounding soil conditions. Once the data has been gathered, the results are downloaded back in our offices with subsequent computing and analysis. Changes in impedance are related to physical features of the pile, taking into account piling methods, material properties and subsoil conditions and these results are then reported to the client with recommendations if necessary.

Prior to carrying out pile tapping the piles will require the following minimum preparation:

•  Piles to be trimmed to sound concrete or grout, with a relatively flat    surface perpendicular to the pile axis. Tests can be carried out when    piles are being trimmed to final trim level.
•  All loose debris and surface water to be cleaned off.
•  Pile head to be accessible (tests may not be possible if steel is    protruding above the pile head)

Once an anomaly is identified in the interpretation of the results, further appropriate testing may be carried out. If this is practical the pile may be exposed at the approximate depth of the anomaly to confirm the findings of the integrity test. Where acoustic anomalies are identified in test results, further investigation of the piles in question may be required.

Pile integrity testing is carried out by Geosure (Pty) Ltd using the Diagnostic Pile Analyser supplied by NDT Technology, which provides a rapid and relatively inexpensive means of screening groups of piles for anomalies, which might affect pile performance. These tests can be usefully implemented on all types of individual cast in situ piles. Only limited information may be obtained for secant type piling because of binding between adjacent piles. Precast piles may be checked for mechanical damaged cracks. A pile integrity assessment can only be as good as the quality of the test data.

The Diagnostic Pile Analyser is a purpose built system which makes extensive use of the latest digital signal acquisition and data processing techniques to ensure the integrity and quality of the test data. The Analyser has provision to carry out both Frequency and Sonic Echo test methods on each pile. The combination of these methods aids the interpretation of complex results and enables difficult assessments to be made with greater confidence and reliability.