3503
Modelling of wave-induced non linear dynamic soil response in vertical breakwaters
foundation
Une modélisation de la réponse dynamique non linéaire du sol de fondation de digues verticales
induite par le mouvement des vagues.
Stickle M. M. & de la Fuente P.
Univ. Politécnica de Madrid, Spain
Oteo C.
Univ. da Coruña, Spain
ABSTRACT: A theoretical and numerical framework to model the soil-water-structure interaction involved in a breakwater structure
subjected to sea wave actions, focused in the special case of impulsive sea wave actions due to breaking waves, is presented. The
model includes i) soil skeleton-pore fluid interaction governed by the
u-p
w
Generalized Biot formulation including dynamic effects, ii)
non-linear elastoplastic soil behaviour described by a Generalized Plasticity sand constitutive model coupled with a conservative
hyperelastic formulation for the dependence of the elastic stiffness on the stress, iii) coupling between caisson an rubble mound
through a non-linear frictional contact constraint model. The Finite element numerical solution of the settled governing equations is
outlined. A large scale model test is numerically reproduced under the scope of the proposed soil-water-structure interaction model.
The wave-induced soil response mechanisms experimentally observed have been numerically reproduced.
RÉSUMÉ : Un cadre théorique et numérique est présenté pour modéliser l’interaction sol-eau-structure dans le cas d’une digue
verticale soumise aux actions des vagues dans le cas particulier d’actions dynamiques dues à des vagues déferlantes. Le modèle
comprend, i) l’interaction squelette du sol- fluide interstitiel, gouvernée par la formulation u-p
w
généralisée de Biot comprenant les
effets dynamiques, ii) le comportement élastoplastique non-linéaire du sol décrit par un modèle constitutif de plasticité généralisée
pour sables couplé avec une formulation conservative hyperélastique pour la dépendance du module élastique avec la contrainte, iii)
couplage entre un caisson et un enrochement à l’aide d’un modèle non-linéaire de contact avec frottement. La solution numérique par
éléments finis des équations correspondantes est décrite. Un essai à grande échelle est modélisé numériquement dans le cadre du
modèle d'interaction sol-eau-structure proposé. Les mécanismes de réponse du sol aux sollicitations par les vagues observés
expérimentalement sont bien reproduits par le modèle numérique.
KEYWORDS: soil-water-structure interaction, breakwater foundation, Generalized Biot, Generalized Plasticity, contact mechanics.
1 INTRODUCTION.
Caisson type breakwaters are one of the most commonly used
marine structures. Unfortunately not enough attention has been
devoted in the last century to geotechnical design aspects, as
this was the case for the hydraulic and structural problems. On
the other hand the damage suffered by many breakwaters has
been related with wave induced foundation response. For
example, under impact and cyclic wave loading, saturated soils
may experience large unacceptable permanent deformations due
to progressively drop of soil strength with a pore pressure build
up (liquefaction).
Most of the developed researches (Yamamoto et al 1978,
Jeng et al 2001) have modelled the seabed soil skeleton-pore
fluid interaction through the pseudostatic Biot Formulation.
This theory, even if it is the base of most of subsequence
developments, does not include dynamic terms. However
several researches (Jeng et al 2003, Ulker et al 2010) have
shown the significant relation of these terms with the wave
induced effective stress development.
Most soil models used in the investigations of sea floor
dynamics have been limited to the poroelastic model. Only a
few contributions (Pastor et al 2006) have incorporated
advanced constitutive relations that are able to represent
properly the features of soil response under cyclic loading. This
is a prominent aspect within any model proposed to analyze the
geomechanical behaviour of a breakwater foundation because is
indispensable to investigate the possible degradation process,
for example liquefaction, leading to a diffuse failure
mechanism.
The caisson-rubble mound interaction phenomenon,
responsible of the principal loads transmitted to the foundation,
has been investigated mostly through elastic Mass-Spring-
Dashpot models (Goda 1994, Oumeraci et al 1994) where the
caisson structure is modelled as a point mass. These models are
not able to analyze the different interface strain-stress states
involved in this contact surface. Few researches have employed
frictional contact mechanics of deformable bodies to represent
this interaction phenomenon not analyzing geomechanical
implication.
In the next chapter the proposed theoretical model for the
soil-water-structure interaction involved in a breakwater
structure subjected to sea wave actions is presented. Afterwards
the Finite Element numerical solution is outlined leading to
some related numerical analyses with reference to precise
boundary value problems of specific physical nature in order to
justify the theoretical model and its numerical approach.
2 SOIL-WATER-STRUCTURE THEORETICAL MODEL
The soil-water-breakwater interaction has been modelled
coupling different physical systems, such that independent
solution of each system being impossible without simultaneous
solution of the others.
The physical systems involved in the soil-water-breakwater
interaction analysis are the caisson, the rubble mound and the
sea bed (Figure 1). The coupling among these three occurs on
domain interface via the boundary conditions. The rubble
mound and the sea bed are already coupled media, where
skeleton-pore fluid interaction exists, and the coupling occurs
through the governing partial differential equations describing
each physical phase.
Sea waves are not modelled as a proper physical system in
it
., de la Fuente P.
