Revisiting Meyerhof et al. (1981) and McGammon and Golder (1970) - Analysis of tests on piles in want of instrumentation-Article

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Bengt H. Fellenius reanalyzes two historical static pile-loading studies to examine how shaft and toe resistance can be inferred from pile-head load–movement measurements when piles lack adequate instrumentation.<br /><br />For Meyerhof et al. (1981), a 13 m precast concrete pile in clay till had a reported capacity of 1,780 kN. The original authors estimated toe resistance theoretically from screw-plate tests and calculated shaft resistance using soil-strength and effective-stress methods. Fellenius digitized the records and used modern load-transfer software to show that multiple plausible combinations of shaft and toe response can reproduce the measured pile-head curve. The original interpretation may be reasonable, but an alternative analysis yields substantially different resistance shares; neither can be confirmed without measurements of axial force near the pile toe.<br /><br />For McGammon and Golder (1970), pipe piles in sand and clay were tested with the pile toe first open and then restored by grouting and additional driving. The original approach treated the difference between test capacities as toe resistance. Fellenius questions this comparison because the tests reached peak resistance at different movements, and shaft resistance can soften with movement. Changes in installation history, waiting time, and pore pressures also affect results. Reanalysis identifies evidence of time-dependent setup and strain-softening, while showing that the tests do not uniquely establish shaft and toe contributions.<br /><br />The central conclusion is that a pile-head load–movement curve alone cannot reliably separate shaft from toe resistance: plausible models can fit the same curve using different assumptions. Meaningful back-analysis requires instrumenting piles to measure axial-force distribution, especially near the toe. Without such data, loading tests may establish overall capacity but provide limited evidence about how that capacity is mobilized.

Keywords

pile-loading studies

shaft resistance

toe resistance

pile-head load-movement

back-analysis

instrumented piles

load-transfer software

clay till

soil-strength methods

time-dependent setup