Residual Force. Revisiting Hunter and Davisson (1969)-Paper

Paper

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Bengt H. Fellenius revisits Hunter and Davisson’s pioneering 1969 analysis of instrumented pile tests at the Lock and Dam 4 project. Those tests combined compression (push) and tension (pull) loading and demonstrated that driving can leave piles with residual, or locked-in, axial forces that distort measured load-transfer distributions.<br /><br />Fellenius re-analyzes the original records using effective-stress-based methods and pile movement rather than relying on conventional “capacity” definitions. He finds that ignoring residual force can make interpreted shaft resistance appear too high and toe resistance too low. The original recommendation to conduct both push and pull tests remains technically valuable, though it is seldom followed. However, Fellenius challenges the assumption that the force distribution remaining after unloading a pull test equals the residual distribution that existed beforehand: soil–pile response depends on loading history and hysteresis.<br /><br />The analysis also shows that residual force can stiffen a pile’s load–movement response and increase apparent capacity under some definitions, although it does not change the plunging-failure load. At the test site, vibrated piles performed similarly to impact-driven piles, while the jetted pile showed reduced response.<br /><br />The paper emphasizes that residual forces matter in interpreting instrumented tests and in design, particularly where downdrag or general subsidence is relevant. It offers a framework for estimating their effects when paired push-and-pull testing is unavailable, and notes that bored piles generally lack substantial installation-induced residual force, though residual forces can develop in subsiding soils.

Keywords

Bengt H. Fellenius

Hunter and Davisson

Lock and Dam 4

instrumented pile tests

residual axial force

load-transfer distribution

effective stress method

shaft resistance

toe resistance

push and pull tests