The revised edition of AS 2159, issued in November 2009, will have significant effects on the design of piles and on the costs of installation. The effects will be felt by structural engineers, geotechnical engineers, piling contractors and developers.
This paper will discuss the effects of the most significant changes, such as :
· Assessment of the geotechnical strength reduction factor, ?g, is now more rigorous than previously.
· ?gb, the basic geotechnical strength reduction factor, is assessed from rating the risk of 3 geotechnical, 4 design and 2 installation factors.
· ?g is the product of ?gb and a testing benefit factor, which provides an increase in design strength when the ultimate geotechnical strength is verified by a test loading programme.
· Where an ultimate load testing programme is not carried out, proof load testing to verify pile performance shall be carried out, or the value of ?g is to be reduced to a minimal value.
· Unless a minimal value of ?g is adopted, integrity testing of 5% to 25% of installed piles is to be carried out.
· The design structural strength of concrete piles now contains a factor which reflects the method of concrete placement in the pile.
· The acceptance criteria, or settlement, for most common sizes of piles are lower than the previous version of the standard.
Emphasis will be made on the advantages of higher standards of geotechnical investigations. Geotechnical engineers will need to ensure that the scope of investigation and testing is adequate to allow structural engineers and developers to take advantage of higher design strength of piles.
The cost implications of the revisions will be discussed.