THESIS
1999
1 v. (various pagings) : ill. ; 30 cm
Abstract
The use of diaphragm walls has been increased substantially over the past two decades and most of them are constructed in congested urban areas. The construction has been observed to cause significant changes of the stress regime and ground deformations around the wall. However, current understanding of the installation effects is still fairly limited. The aims of this research are to investigate the installation effects of the wall on stress changes and deformations; and to study factors that govern the ground responses. A series of three-dimensional numerical analyses has been carried out. Computed results are compared with field measurements, centrifuge model tests as well as theoretical solutions....[
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The use of diaphragm walls has been increased substantially over the past two decades and most of them are constructed in congested urban areas. The construction has been observed to cause significant changes of the stress regime and ground deformations around the wall. However, current understanding of the installation effects is still fairly limited. The aims of this research are to investigate the installation effects of the wall on stress changes and deformations; and to study factors that govern the ground responses. A series of three-dimensional numerical analyses has been carried out. Computed results are compared with field measurements, centrifuge model tests as well as theoretical solutions.
Construction of a diaphragm wall in stiff Gault Clay has been selected and modelled three-dimensionally. The size of the panel is 0.6m wide (W), 8m long (L) and 16m deep (D). After the first panel is installed, substantial reduction in lateral total stress is found behind the centre and above the toe level of the panel. However, an increase of lateral total stress occurs (greater than the initial k[
[white circle]] pressure) at the edges of the panel after the construction. Beneath the toe of the panel, horizontal total stress which is larger than the initial condition is computed. It is concluded that stresses in the ground are transferred simultaneously in both horizontal (by horizontal arching mechanism) and vertical (by downward load transfer mechanism) directions during the construction. Substantial amounts of shear stresses are developed at the edges as well as at the toe of the panel. A settlement bowl occurs at about 0.2D behind the panel after concreting. The computed soil movements (both vertical and horizontal) are not significant at a distance of about 1.5D away from the panel.
Two additional panels adjacent to the first one are modelled and the results of these three panels are used to interpret the installation effects of a diaphragm wall constructed in the stiff Gault Clay. At the end of the construction, a very non-uniform horizontal total stress distribution is calculated behind the wall. Earth pressure behind the centre of panels at the end of the wall installation is smaller than the initial K[
[white circle]] condition. However, stress concentration occurs at the edges of panels where the lateral pressure increases well above the initial conditions before the wall construction. Yielding of soil may occur behind the edges of panels. The ground deformation pattern is very non-uniform behind the wall and the both vertical settlement horizontal movements are insignificant at a distance of 1.5D behind the wall. Further construction of the fourth and fifth panels does not affect the stress regime and ground deformation noticeably behind the first panel
Effects of different initial stresses in the ground and panel lengths on ground responses during a single panel installation are also studied. It is found that both of them have strong influences on the ground responses. For diaphragm wall panel with a longer panel length or installed in ground with a higher initial stress, larger ground movements are computed. The zone of influence on stress regime around the panel is 1/3D beneath the panel, 2D behind it and 0.2D adjacent to it. Normalization charts are provided to estimate three-dimensional ground movements during the installation by means of a conventional two-dimensional analysis.
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