Last edited 27 May 2018

Pile integrity test

Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics to support them.

Pile foundations are deep foundations. They are formed by long, slender, columnar elements typically made from steel or reinforced concrete, or sometimes timber. A foundation is described as 'piled' when its depth is more than three times its breadth.

While the integrity of superstructure members can be tested and assessed from visual examinations, dimensions checks and so on, pile foundations, once they are in place, can be more difficult to test. Flaws and defects may develop during construction or subsequent excavation and trimming.

Pile integrity testing is used to discover and assess flaws before further damage occurs. It is a low-strain, non-destructive method and can be used to test any form of concrete or timber pile as well as drilled shafts, as long as they are not excessively slender. It can be used either for forensic examinations on existing piles or for quality assurance for new construction.

Various techniques can be used for interpreting the records of force and velocity taken under the impact of a light hammer blow. The most common technique is known as the transient dynamic response (TDR) method, which is both quick and cost-effective. Based on wave propagation theory, the top of a pile is struck with a hand-held hammer to generate a compression wave. This wave travels at a constant speed down the length of the pile and is measured with an accelerometer or geophone placed on top of the pile.

Any abnormalities or changes in cross-sectional area (e.g. due to the presence of a void) produce wave reflections which can be measured and mapped on a digitally-simulated profile of the pile.

While pile integrity testing can provide an indication as to the soundness of the pile, it does have some limitations. It cannot be used over pile caps and does not provide an indication of the pile’s bearing capacity. In addition, the test is not effective at evaluating the section of a pile below cracks that may cross the entire cross-sectional area of the pile.

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