Finite Element Analyses of Piled Foundations: Interaction Domains Under Undrained Conditions

Abstract

Most of the bridges in Europe countries are now approaching their design life. Therefore, at present crucial is the choice of the most suitable retrofitting solution taking the current design standards into account. From an economic point of view the costs related to the foundations adaptation are not negligible at all, even because design approaches are in general over-conservative. For instance, in case of piled foundations, the presence of the raft is conventionally disregarded in the calculation of the pile group bearing capacity under general loading. In this work a pile group foundation embedded in a silty-clay soil stratum is studied to emphasise how the use of a non-standard approach may allow to make more sustainable the interventions. An extensive 3D pseudo-static finite element numerical analyses campaign, under general loading, accounting for the non-linear soil mechanical behaviour, was performed. The results were interpreted in terms of interaction domains for the piled foundation system (raft + piles).

Numerical study and theoretical interpretation of the role of rafts in piled foundations on cohesive soils

“…In [41] the limit analysis theory, under the simplifying hypotheses of [39], [40], is used for the determination of the pile group ID without uncoupling horizontal and vertical loads. Despite being sound approaches in case of long piles and small raft widths, when the pile length is comparable to the raft width ( [23], [42], [43]), disregarding the joint piles-raft constraint and the soil-raft interaction may lead to a significative underestimation of the foundation bearing capacity. In this paper, the authors (i) put in evidence the role of the pile-raft-soil mechanical interaction and (ii) propose an innovative approach for deriving geotechnical IDs of "large" piled-raft foundation systems in uniform clay layers.…”