A pile integrity assessment can only be as good as the quality of the test data. Precast piles may be checked for mechanical damaged cracks. Only limited information may be obtained for secant type piling because of binding between adjacent piles. These tests can be usefully implemented on all types of individual cast in-situ piles. Pile integrity testing is carried out by Geosure (Pty) Ltd using the Diagnostic Pile Analyser supplied by NDT Technology and, which provides a rapid and relatively inexpensive means of screening groups of piles for anomalies, which might affect pile performance. The adjacent plates show the severity of some of the anomalies identified. These piles were exposed to the depths where acoustic anomalies were identified. 25% of the piles tested showed severe necking in the pile’s shaft. On an upmarket development in Durban, Geosure were appointed to carry out integrity tests on all piles cast. Recently Geosure using the DIAGNOSTIC PILE ANALYSER identified acoustic anomalies in several piles. Where practical the pile is exposed at the approximate depth of the anomaly to confirm the findings of the integrity test.
Once an anomaly is identified in the interpretation of the results, further appropriate testing may be carried out. Prior to carrying out pile tapping the piles will require the following minimum preparation: The results are then downloaded and computed in the office, and changes in impedance are related to physical features of the pile, taking into account piling methods, material properties and subsoil conditions. These tests have a depth limitation, typically 30 to 35 times pile diameter that are usually dependant on soil conditions. 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. When the signal is processed in the time domain the test is called the Sonic Echo Test, and the Frequency Response Test in the frequency domain. The tests are based on locating impedance along the pile shaft by using vibration waves at the top of the pile formed by striking the pile top with an impulse hammer (refer to Figure 1) whilst simultaneously measuring its vibratory response. The tests can be implemented on all types of individual cast insitu piles of 250mm diameter and upwards and is a non-intrusive test.
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