Modelling the effects of structure degradation in geotechnical problems

Abstract

Bond degradation is an irreversible phenomenon that, experimentally, appears to be controlled by plastic strain accumulation. Conventional constitutive soil models do not capture the effects of small strain non‐linearity, recent stress history as well as material structure and its consequent reduction due to bond degradation. The aim of this thesis is to investigate the behaviour of a constitutive model that describes the initial structure, on various geotechnical problems. The kinematic hardening structured constitutive model (Rouainia and Muir Wood, 2000) ,formulated within a framework of kinematic hardening and bounding surface plasticity, was implemented into the PLAXIS Finite Element Analysis software package and was used to simulate a variety of boundary value problems. The implementation of the model was validated through a number of single finite element analyses of laboratory tests on natural clay from the Vallericca valley in Italy. The model was further adopted in the finite element analyses of geotechnical problems. The first of these simulated the Self Boring Pressuremeter test in London Clay, with the main focus being the characterisation of the degree of initial structure of London clay, as well as identifying the effect of structure related parameters. The premise that the SBPM is installed without damage was also investigated. The second boundary value problem involved the 2D and 3Danalysis of an embankment situated on soft structured clay in Saint Alban, Canada. The numerical predictions of pore‐water pressures and settlements are also compared with field measurements. The model developed in this work was then adopted in the study of the behaviour of a deep excavation located in Boston, Massachusetts, USA. The numerical simulations were aimed to demonstrate that the added features of the model implemented in this work such as small strain stiffness, structure and anisotropy are vital components to give a good prediction. Comparison of the predicted wall profiles, time dependent dissipation of excess pore water pressures and associated ground heave with field data are provided.