High strain testing of contiguous steel piles? 2

[LittleWheels]

I have a pile wall composed of large diameter steel tubes linked by clutches and a very stiff capping beam.

I am concerned that clutch friction might increase the assessed capacity of a pile (tested individually) when in reality all piles in the locality would be loaded simultaneously and there would be no benefit from clutch friction. Probably clutch friction isn't a huge capacity contributor but somebody must already know the answer.

In addition, the soil between the CAPWAPed pile and the adjacent untested piles might be assessed as providing a greater resistance than would actually exist when the piles are simultaneously loaded.

Are there any papers examining the effects of the adjacent piles on the assessed capacity of a pile when it is high strain tested? I have not yet found such research.

 

[SlideRuleEra]

Like PEinc, I didn't expect to find test results on dynamic evaluation of interlocked piles... but something very close showed up:

"Determination of Vertical Resistance for Sheet Pile Abutments", R&D report for the North Carolina DOT.

Here is an excerpt from the executive summary:

 

[LittleWheels]

Thanks SRE, that paper looks very interesting. I have some more homework to do.

 

[PEinc]

Nice find, SRE. However, I had a driven H-Pile project a few years ago where, in our pre-driving discussions, GRL did not recommend using their WEAP or dynamic analysis for capacity of vibrated H-Piles. I assume that their reluctance would be even greater if vibrating sheet piles.

http://www.PeirceEngineering.com

 

[SlideRuleEra]

PEinc - Like you, I was taken aback about a vibratory hammer being used. To my knowledge, there is no dynamic testing that gives satisfactory results with that type hammer. Then, hidden away on page 41 of the report was this one brief sentence that removed the problem:

That made sense and was in line with common practice, set the pile with the vibratory hammer, then switch to the impact hammer for final driving and dynamic testing.

I was not familiar with that model, but sure knew about Mckiernan-Terry brand (MKT) hammers in general (we owned and used a single-acting MKT DE-30 impact diesel hammer, maximum energy of 22,400 ft-lb, for bridge construction).

Looked up the specs for the MKT 9B3 hammer used for this test project (specs attached). It's a double-acting "steam" (compressed air) impact hammer with maximum rated energy of 8750 ft-lb. A modest size hammer but more than capable of driving and dynamic testing PZ-27 sheeting used.

The report's author should have make the info on the hammer used for dynamic testing more prominent.

 

[PEinc]

SRE, GRL told me that, although their WEAP program includes vibratory hammer analyses capability, the process isn't refined enough for use. I am surprised that the paper you found does not discuss problems associated with interlock friction and effects of interlocked, adjacent SSP during capacity testing.

http://www.PeirceEngineering.com

 

[SlideRuleEra]

Yes, I suppose the omission is because of the study's goal is to see if sheet pile can replace HP for bridge end bents.

With the lack of guidance on interlock friction, I would get the relative elevations of marks at a convenient locations of the side of each of two adjacent piles then perform the dynamic testing on the pile between these two. Getting the relative elevations is quick and easy, and:

If adjacent piles have not moved when dynamic test is complete, doesn't say much.

But, if the adjacent piles have moved, seems like a clear sign dynamic test results indicate higher bearing than it really is.

Maybe better than doing nothing.

 

[PEinc]

Good, cheap idea.

http://www.PeirceEngineering.com