3D modelling of bored pile installation effects and long term monitoring of a propped retaining wall

Abstract

In the last few decades much effort has been spent to investigate the installation effects of diaphragm wall panels in an overconsolidated deposit. Conversely, in the literature there is relatively little focus on the effects of bored pile construction. In this thesis a number of three dimensional finite difference analyses using FLAC3D have been carried out to investigate the stress changes and consequent movements due to bored pile and diaphragm wall installation in stiff clay. The three-dimensional numerical models developed to carry out these analyses were used to analyse, interpret and explain the instrumented data of ground stress changes during bored pile wall installation in an overconsolidated clay deposit in connection with the Channel Tunnel Rail Link (CTRL; now HS1) at Ashford. Two different soil models were implemented in the three dimensional finite difference analyses, having linear and non-linear stress strain characteristic. It was found that both analyses could capture the observed pattern of changes in stresses. Furthermore, it was found that the difference in stress changes and ground movements after a single pile or panel installation were primarily a consequence of the different geometry between pile and panel. In the literature, only limited research has been carried out to quantify the three dimensional effects of diaphragm wall installation. For this thesis a number of three dimensional finite difference analyses, using FLAC3D, were carried out, to investigate the installation effects of a group of panels in an overconsolidated clay deposit. One of the key uncertainties associated with the design of in situ embedded retaining walls in an overconsolidated deposit concerns the long-term horizontal stress acting on the wall. There is some concern that the high in situ horizontal stresses in an overconsolidated deposit may become re-established in the long-term, despite the reductions that occur during retaining wall installation and subsequent excavation in front of the wall. This thesis also presents long term case record from an embedded retaining wall that forms part of the Channel Tunnel Rail Link at Ashford, Kent, and a retaining wall at Coventry are also presented. Approximately 13 years of lateral stress monitoring around the embedded retaining wall at Ashford are presented and discussed. The long term field data shows that the in situ total horizontal stresses in the ground close to a retaining wall in an overconsolidated clay deposit did not re-establish in the long term

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ORCID for W. Powrie: orcid.org/0000-0002-2271-0826

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