Revisiting Hunter and Davisson (1969) and Gregersen et al. (1973): Establishing residual force-Article

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The paper revisits the 1963 Lock and Dam 4 pile tests analyzed by Hunter and Davisson (1969), alongside full-scale tests by Gregersen et al. (1973), to clarify how residual force affects interpretation of instrumented pile load tests.<br /><br />Driving can leave a pile with locked-in axial forces caused by interaction between shaft resistance and toe response. These residual forces distort measured force distributions: analyses that treat the pile as initially unstressed may overestimate shaft resistance and underestimate toe resistance. Hunter and Davisson correctly identified the issue and advocated combining instrumented compression and tension tests, but Fellenius notes that the force remaining after a test cannot simply be assumed to equal the original residual-force distribution. Loading and unloading change pile–soil response through hysteresis.<br /><br />Reanalysis of the historical tests uses effective-stress concepts and considers full load–movement behavior rather than relying on a single “capacity” value. Simulations indicate that residual force can make a pile appear stiffer and can increase capacity estimates based on criteria such as the Davisson offset limit, although it does not change the plunging-failure load. The records also show no significant difference between impact-driven and vibratory-driven piles, while jetting reduced the observed response.<br /><br />Gregersen et al.’s measurements, calibrated before installation, independently confirmed residual force and showed that it can change during successive loading and unloading cycles. The paper concludes that residual force should be measured or explicitly considered when interpreting instrumented tests and designing foundations, particularly where soil subsidence and downdrag are relevant. Compression and tension testing together provide the strongest basis for determining true load transfer; where this is impractical, informed assessment of residual-force effects is essential.

Keywords

residual force

instrumented pile load tests

pile shaft resistance

toe resistance

effective stress

pile driving

load transfer

Davisson offset limit

hysteresis

foundation design