Low Strain Integrity Test query?

[LittleWheels]

I have a project with 1500mm and 1800mm cast in situ piles. Long sacrificial liners driven through the seabed (soft silt), pulling up in weak rock, socket cut into hard rock. Some piles are being CAPWAPed (high strain dynamic test), more are being low strain integrity tested. It is the low strain integrity test that prompts this question.

There doesn't seem to be much consistency between national standards and guidance regarding maximum applicable pile diameters and lengths for the low strain test method. ASTM D5887 vs. ICE's Manual of Geotechnical Engineering vs. AS 2159 vs. IS 14893. Some limit pile lengths (these may vary depending on soil type) and some limit pile diameter for low strain integrity testing. I understand that excessively wide piles may not restrict wave direction to 1D (along the pile) but there doesn't seem to be much agreement as to what excessively wide actually is.

What is the current consensus regarding low strain integrity tests for cast in place piles and when alternative integrity methods should be adopted?

 

[LittleWheels]

Should I have posted this query in another sub-forum?

 

[geotechguy1]

It's a pretty specialized topic even by Geotech standards. You could try reaching out to one of the suppliers like GRL / PDI

 

[LittleWheels]

PDI have suggested thermal integrity testing as better for large diameter piles but otherwise to test at multiple locations across the pile. No guidance regarding what diameter is too big for low strain testing.

https://www.fprimec.com/how-to-perform-low-strain-pile-integrity-test/

seems to be the most concise practical guidance that I found.

 

[geotechguy1]

https://www.pile.com/resources/faqs...o for,ratio may exceed 30 — even reaching 60.

https://www.pile.com/resources/faqs/faq-maximum-size-foundation-can-tested-pit/

Not sure if they referred you to these which does seem to partially answer the question and an explanation of the older L/D ratio. Codes change like molasses and are often conservative (sometimes in a manner that is unconservative or wrong and they just don't realise it).

 

[LittleWheels]

Those webpages are fine as far as they go but the big question in my mind is more related to large diameter piles, rather than long piles. Some advice and codes regarding low strain tests are specifically limited to 1500mm dia. piles or even smaller while some of our piles are 1800mm.

There are some vague suggestions to use bigger hammers on large diameter piles to alter the frequencies created and to encourage 1D wave motion. Is there something codified about that or regarding how many test locations should be done across the pile's top surface, to better examine upper sections of a large pile?

I understand that codes usually lag the consensus on any subject. What are the PIT community's thoughts about whether low strain integrity tests are meaningful on such large diameter piles?

If PIT is only able to detect upper-level defects on large piles, it may not be worth even doing PIT on large diameter marine piles that have a liner for the first 15-20m or more. It would be very uncommon to have detectable defects within the liner.

 

[LittleWheels]

Does anybody here want to poke their head above the parapet and give their thoughts on what might be a reasonable or practical maximum pile diameter for low strain integrity testing?