A precise modelling of the soil behaviour requires accurately taking into account the internal state of the material and its changes during a complex loading. The aim of this work is to design a constitutive model that can reproduce the soil response under a cyclic loading in drained and undrained conditions with a unique set of parameters. Specifically, the Cambou, Jafari and Sidoroff (CJS) model - an elastoplatic model compounded with two plastic mechanisms, isotropic for the first one and deviatoric for the second one - has been improved to include the internal state of the soil better by means of a volumetric state variable and a variable related to the anisotropy of normals at contacts between grains.

1. Introduction

The complex nature of loading of pile foundations in offshore applications (oil production), as well as in in-shore applications (aeolian), requires equally complex constitutive models for soils and pile-soil interfaces. In such systems, the internal state of the material (volume element of soil or interface pilesoil) is bound to evolve greatly throughout the cyclic loading. This change can be observed through two internal variables: the void ratio in relation with non-oriented phenomena, the anisotropy for oriented phenomena. Although void ratio changes are easy to assess throughout experiments, simple access to information related to anisotropy is more difficult to obtain. Thus constitutive models for soils and interface pile soils generally take into account the changes of the material properties by considering the mere influence of density change. In this work, an existing constitutive model for soils called the Cambou, Jafari and Sidoroff (CJS) model, which was previously developed and named after that research team (Cambou et al., 1989), has been modified to take into account better the internal state changes throughout cyclic loadings.

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