Visco-elastic load transfer models for axially loaded piles

Abstract

SUMMARYViscoelastic or creep behaviour can have a signi"cant in#uence 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 veri"ed through published "eld 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 veri"ed 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 e!ects of creep on the load settlement relationship by the solutions and the program GASPILE, have been presented.

Analysis of creep settlement of pile groups in linear viscoelastic soil

“…The general equation governing the viscoelastic behavior of soil can be derived from the compatibility conditions between the mechanical components as proposed by Guo and can be generalized as Equation : The soil in contact with the pile experiences a constant stress throughout the service life of the structure and is thus known to undergo creep over a period of time. On integrating the differential equation for viscoelastic behavior for the case of creep, ie, a constant stress σ acting on the system, the time‐dependent strain function for step‐loading as proposed by Guo can be obtained as The time dependent strain response of the soil under constant stress is depicted through Figure , in which the strain is a time‐dependent function governed by Equation . The initial and final strains at time t = 0 and time t = ∞ are evaluated from Equation and used as boundary conditions.…”

“…Several analytical, numerical, and experimental studies have been made on the immediate settlement of single piles and pile groups that are capable of predicting immediate settlements with good accuracy. However, studies on time‐dependent settlements have been limited owing to its complexity and the assumption that it accounts for only an insignificant proportion of the total settlement. It is however essential to investigate the long‐term settlement for structures such as railway and highway bridges, nuclear power plants, and other important structures because excessive settlements may create severe safety issues.…”

“…Bartolomey et al developed a mathematical model to predict time‐dependent settlement of piles by treating soil as a viscoelastic‐plastic material. Guo proposed closed‐form solutions in nonlinear viscoelastic soil to analyze the creep‐behavior of piles. Danno and Kimura evaluated the long‐term displacement of pile foundations in soft clay using coupled FEM and centrifuge model tests.…”

Load transfer approach for laterally loaded piles

“…The sacri"ce of using an approximate stress "eld often leads to exact closed-form solutions for piles, which generally compare well with more rigorous numerical approaches, e.g. for vertical loading piles [5,16,17]. In contrast, complicated expressions for piles may result from using assumed displacement expressions only (e.g.…”