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Pile integrity and low strain dynamic testing

There have been many major breakthroughs in integrity and low strain dynamic testing in the 20 years since the first Stress Wave conference in Stockholm, Sweden.

The conference was set up in 1980 by a few pioneers in stress wave theory and its application to piled foundations. Since then, the number of participants has been on the increase, as has the volume and content of papers submitted to each conference, even from the so-called 'peripheral'countries.

This undoubtedly reflects the interest of engineers worldwide in determining what happens to deep foundations once they are installed, irrespective of the installation procedure used.

As a result, sonic integrity tests have been standardised in most industrialised countries and are beginning to be applied in several others. Furthermore, quality control through non-destructive testing has begun to be included in the technical specifications for piled foundation construction in most civil engineering works by private companies or by government agencies in countries that have adopted the technology.

Availability of this technology has resulted in early detection of defects likely to jeopardise the stability of deep foundations and the superstructure above, and has reduced the occurrence of accidents likely to lead to the loss of both lives and assets.

Safety of foundation works has been longstanding concern in the construction community, particularly works associated with excavations and piles.

This concern arose from the very nature of these structures, the imperfect knowledge of the soil profile, the wide range of building methods and customs, a general lack of effective quality control methods, lack of tests and measurements on the behaviour of the soil-structure interaction and a certain blend of pseudo-confidence and fatalistic resignation (or hope? ) that '. . . pile contractors surely know what they are doing . . .'

Results obtained from quality control carried out since the technology began to be applied in Argentina and in the rest of the world has allowed industry to establish without doubt that sonic integrity tests are an essential tool in finding out the condition of piles both old and new.

As in every indirect investigation technique, where diagnosis is obtained through analysing measurements with sensitive instruments or image analysis of signals corresponding to physical and mechanical phenomenon, the unavoidable requirements are:

Availability of appropriate equipment, with proved and reliable hardware and software.

Skilled operators.

Periodic calibration of sensors.

An exhaustive and reliable soil investigation.

An adequate control of the execution of the foundations.

Full knowledge of the foundation engineering, geotechnical engineering and foundation dynamics by the engineer in charge of the integrity tests.

Independent criteria and ethical integrity on its behalf.

The session will be followed by the Confidence of pile integrity testing workshop which will provide another opportunity for delegates to exchange ideas about ways to achieve professional good practice.

Juan Goldemberg, Geotecnica Cientec, Buenos Aires, Argentina

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