Visco-elastic load transfer models for axially loaded piles

Viscoelastic or creep behaviour can have a significant influence on the load transfer (t-z) response at the pile-soil interface, and thus on the pile load settlement relationship. Many experimental and theoretical models for pile load transfer behaviour have been presented. However, none of these has led to a closed-form expression which captures both non-linearity and viscoelastic behaviour of the soil. In this paper, non-linear viscoelastic shaft and base load transfer (t-z) models are presented, based on integration of a generalized viscoelastic stress-strain model for the soil. The resulting shaft model is verified through published field and laboratory test data. With these models, the previous closed-form solutions evolved for a pile in a nonhomogeneous media have been readily extended to account for visco-elastic response. For 1-step loading case, the closed-form predictions have been verified extensively with previous more rigorous numerical analysis, and with the new GASPILE program analysis. Parametric studies on two kinds of commonly encountered loading: step loading, ramp (linear increase followed by sustained) loading have been performed. Two examples of the prediction of the effects of creep on the load settlement relationship by the solutions and the program GASPILE, have been presented. Copyright (C) 2000 John Wiley & Sons, Ltd.