Comparing Analytical Models with Slipping and Non-Slipping Interface in Axially Loaded Tension Piles-Paper

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The paper compares analytical models for axially loaded tension piles that either allow or prohibit pile–soil slipping before failure. In the slipping model, shaft resistance depends on relative movement between the pile and surrounding soil; in the non-slipping model, it depends on pile displacement, effectively assuming a perfectly bonded interface. The authors represent slipping using an interface with a virtual thickness and develop both formulations within concentric cylindrical theory.<br /><br />The slipping formulation was verified against axisymmetric PLAXIS 2D analyses. Its load-transfer factors agreed with established theoretical estimates, and its predicted load–displacement curves closely matched numerical results across more than 80 cases.<br /><br />Both analytical models were then compared with measurements from a full-scale pile pullout test. They produced different load–displacement responses. With identical stiffness inputs, the non-slipping model predicted a stiffer response and higher load at a given displacement. This occurs because soil moves upward during loading, making pile displacement greater than the relative pile–soil slip that mobilizes shaft resistance.<br /><br />The authors recommend calibrating stiffness parameters separately for each model rather than using the same values. Pile load tests or empirical load–displacement curves can inform non-slipping models, while interface shear tests can help calibrate slipping models. The slipping formulation may offer a fast tool for preliminary estimates or checks; the authors report it was at least 20 times faster than finite-element analysis in their automated procedure. Further work is needed to account for initial stress and changes in shaft normal stiffness.

Keywords

tension piles

axially loaded

pile-soil slipping

non-slipping model

shaft resistance

load-displacement response

PLAXIS 2D

pullout test

interface shear

concentric cylindrical theory