Would appreciate information on available non-destructive test methods (and likely accuracies) for deteremining insitu pile lengths. This testing is required as part of an initial investigation for dispute resolution between client and contractor. The second option will most likely involve actual excavation beside suspect piles. Availability of methods in Australia would be appreciated and I thank all those in advance for their assistance.
I was checking for replies to some of my questions when I saw your post. By happy coincidence I have just recently forwarded acouple of replies on this to another group. Hope this helps you.
In this case, the piles were under an exisiting structure, it sounds, in your case, as though the pile cap may not yet be in place and you could strike the pile. If the latter is the case, and you know the pile cross sectional properties and wave velocity, you should be able to get the time of a wave return from the toe after impact. Half of this value would represent the length of the pile. Pile integrity testing equipment should be available to test this. Alternateively, if you can at least expose some of the top of the side of the pile, the following references will provide some guidance.
This State of Georgia DOT research project might also be of interest to you, although it sounds like interpretation was problematic. This project was 5 years ago, so it might be worthwhile to see if there has been any follow up.
Nondestructive Assessment of Pile Tip Elevations (RP 9406)
The objective of this research project is to develop a nondestructive test procedure to assess pile tip elevations in the foundations of GDOT bridges. For many of the 14,500 bridges on the state route system, pile tip elevations are unknown because design and construction records no longer exist. Thus the capacity of these piles cannot be easily determined, particularly in the presence of scour. Although soil boring and other intrusive tests are capable of determining pile tip elevations, Performing these intrusive tests on a large number of bridges is extremely time consuming and expensive. Nondestructive testing is an effective alternative for assessing pile tip elevations. In nondestructive tests, stress waves are generated by impacting on a pile on an exposed surface. These stress waves then propagate downward along the pile and are reflected at the tip. The arrival of the reflected wave is monitored by sensors attached to the pile tip. Several interpretation methods are available which determine the pile length from these measurements. The study was completed at the end of 1995, and a draft final report has been completed. The analysis of the data collected from piles with known lengths was more complicated than expected, and practical analysis procedures have not been developed at present. For further information, contact David Jared, (404) 363-7586 or FAX (404) 363-7684.
I recommend you get a copy of : GT-16 (0.7 M) - "Determination of Unknown Subsurface Bridge Foundations," (NCHRP 21-5 Interim Report Summary) at http://www.fhwa.dot.gov/bridge/geonote.htm for a start. This is a pdf document you can get for free.
Pile Dynamics makes several devices for electronic measurments. See more information at www.pile.com
Pile Driving Analyzer needs you to impact the pile with a large weight (pile driving hammer, or large drop weight). If you can move the pile, you will probably see a toe reflection. If it is a steel pile so you know the wavespeed (constant 5123 m/s) then you can calculate length. For concrete where wavespeed is variable, you can estimate length within about ten percent.
Pile Integrity Tester uses a small hand held hammer to hit free pile. Pile must be concrete, and there are other restrictions.
You might contact Dr Julian Seidel at Monash University in Melbourne, Victoria as he knows methods and can advise on applications and refer you to various test agencies with the necessary equipment.