Use of interaction domains for a displacement-based design of caisson foundations

Abstract

Caisson foundations, typically adopted for both onshore and offshore structures, are usually subject to combined loading acting during working conditions and exceptional events such as earthquakes. Assessment of their performance under general loadings is therefore fundamental, for both serviceability and ultimate limit states. In this study, a simplified displacement-based approach, aimed at preliminary designing caisson foundations subjected to combined loading, is presented. Such an approach requires the definition of both interaction domains (IDs) and generalised pushover curves, together with the assumption of an associative flow rule. The IDs and pushover curves are obtained by interpreting the results of a set of 3D finite element nonlinear static analyses, where the response of massive cylindrical onshore caisson foundations, embedded in a layered soil profile and subjected to both centred vertical (N) and combined loads (N–Q–M), is investigated. Following previous works, the influence of initial loading factor and caisson embedment ratio on both IDs shape and size is investigated. Additionally, the effect of soil drainage conditions on the IDs is discussed. Role of load reference point (LRP) is also assessed, since a suitable choice of LRP may strongly simplify the geometrical representation of the ID. Analytical expressions for dimensionless IDs and pushover curves are presented and used at a preliminary design stage to evaluate the maximum generalised load acting on the caisson for a given threshold generalised displacement, so as not to exceed either serviceability or ultimate limit states.

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

“…15 the ID M -H cross section for V=25MN is reported. Analogously to what observed in ( [34], [51], [52], [53]), the M -H cross-section can be described by an ellipse, with principal axes counterclockwise rotated with respect to the plane axes: when H and M have the same sign (U4), both the yielded spatial domain and the distance of the ID boundary from the origin of the axes are smaller. In contrast when H and M are opposite in sign (U1-U3), the yielded soil volume larger and the distance of the ID boundary from the origin of the axes are significantly larger.…”

“…During the last decades, the behaviour of foundations under general loading conditions have been widely addressed for different typologies, such as shallow footings ( [24], [25], [26], [27], [28], [29]), monopiles ( [30], [31], [32]), caissons ( [33], [34]), skirted foundations ( [35], [36]), spudcans ( [37], [38]). Both numerical and experimental results have been employed to derive the bearing capacity in terms of interaction domains (IDs), employed as rapid and reliable tools for ultimate limit state (ULS) verifications.…”

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

“…6. Analogously to what observed for shallow foundations [8] and for caissons [9], the M y -H x section shape is an ellipse whose principal axes are counter-clockwise rotated from the coordinate axes. The orientation of the ellipse principal axes depends on the plastic mechanism developing in the foundation soil: when H x and M y are opposite (Fig.…”

Numerical Back-Analysis of Dynamic Centrifuge Tests on the Seismic Behaviour of Caisson Foundations Supporting Bridge Piers

“…For simplicity, the deck is assumed to be reproduced by a tip mass of ms = 194.40 Mg. The total mass of the caisson is mc = 1024.78 Mg, while the mass of the pier is mp = 143.64 Mg with a bending stiffness EI = 30.7 GN•m 2 , where E and I are Young modulus and cross-sectional moment of inertia, respectively. The system is subjected to ground motion at the bedrock depth (z = 17 m), here represented as a horizontal acceleration time history.…”