Commentary to: Prediction, Testing, and Analysis of a 50 M Long Pile in Soft Marine Clay-Journal of the Deep Foundations Institute, 13(2) 1-7-Article

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Saye and Stuedlein comment on a 50 m precast concrete pile driven into nearly normally consolidated marine clay in Gothenburg, Sweden. They describe the case as an example of good installation and testing practice that minimized disturbance: the pile was installed in four sections nearly continuously in one day, then allowed to set up for about seven months before load testing so excess pore pressure could dissipate.<br /><br />The original study reported two interpretations of shaft resistance: four pile segments with β-values from 0.42 to 0.19 and a weighted average of about 0.25, or a single β-value of 0.19. The commentators consider the single value consistent with the SHANSEP-based method. Using an average overconsolidation ratio (OCR) of 1.05, they calculate β ≈ 0.20; assuming OCR = 1.0 gives β = 0.194. This agrees well with the test result, and they note that pile-installation damage observed in other cases was not evident here.<br /><br />Although the pile’s 50 m length exceeds that of most piles in the empirical data underlying the SHANSEP relationship, the test does not indicate that a length adjustment is needed. The authors also argue against applying the capacity reduction for long piles proposed by Semple and Rigden, explaining that its underlying β-coefficients relate to particular testing procedures involving pile redriving and incrementally longer piles.

Keywords

precast concrete pile

Gothenburg Sweden

marine clay

shaft resistance

beta value

SHANSEP method

overconsolidation ratio

pile installation

load testing

capacity reduction