الفهرس 
Objectives of the studyOnly 14 pages are availabe for public view
 |  | from | 304 |  |  |
| | | from | 304 | | |
Abstract
The increased demand for underground systems in urban areas has
led to many tunnels being constructed close to existing structures. An
indispensable prerequisite to successful tunnelling projects is to predict
the deformation in order to avert any potential damage of building or
buried utilities. The effects of tunnelling on pile foundation supporting
these structures are therefore, of great concern. This thesis aimed to
develop a better understanding of the problem and contribute to the
design and analysis of pile foundations. The response of pile foundation
due to tunnel construction is principally a three-dimensional (3-D)
problem whether it is the tunnel advancement or the pile foundation. The
analyses described in this thesis were performed using finite element
program ABAQUS 6.11. This software provides the flexible features to
model the details of tunnel construction in soils. Therefore a threedimensional finite element model to simulate the phase tunnel
advancement including the application of excess face pressure, rate of
shield advancement, over-cutting, and lining erection with activation of
grouting material was developed to understand the pile response. All the
soils, shield, tunnel lining, pile foundation were modelled using 20-noded
continuum solid element. The main elements of the interaction such as;
ground continuum, the piles, the pile caps, the precast lining segments,
the tail skin grouting, the developed gap around TBM due to machine
overcutting, and the TBM shield are modelled using prismatic solid
element C3D20R, which is a three-dimensional 20-node hexahedra
element with 8 integration points (reduced integration). The model
boundary conditions are determined after conducting preliminary
sensitivity analyses concerning its effect on the pile caps vertical
displacements in terms of the tunnel diameter. Soil convergence around the tunnel excavation was modelled
using a non-associated elastic-perfectly plastic Mohr-Coulomb failure
criterion. The shield, tunnel lining elements, piles elements, and pile caps
elements are characterized as elastic elements with different elastic
properties to account for the different stiffnesses of the these elements.
The tail grout used to fill the developed annular ground gap around the
TBM due to tunnelling overcutting is updated simultaneously using solid
elements. Therefore, calibration with measured surface settlement during
shield passage was necessary. The elastic parameters of grouting material
are determined according to the state of the setting of the grout from the
liquid state to the hardening state in accordance to Mindess and Young,
(1981).
The process of tunnel was modelled in two steps; first, the initial
conditions were set up for the model before excavation of the tunnel. It
was achieved by specifying the distribution of effective vertical and
horizontal stress (using coefficient of earth pressure at rest, K0=0.5). The
initial conditions were completed with simulating the pile cap and its
connected piles. After establishing the initial conditions, the analyses
continued with modelling excavation of the tunnel Slurry shield tunnel
boring machine. The 3D finite element modelling of the groundtunnelling-piling interaction is visualized taking into consideration the
details of tunnelling activities and the rate of tunnel advance.
Advancement of TBM was simulated simultaneously as follows; i)
applying the excess face pressure, ii) removal of soil elements and
activation of shield, and iii) activation of lining elements and grouting
elements from the liquid to hardening state.
This numerical model is verified by back analysis of field data
obtained from two cases of studies. The first case considers of the
stability of El-Attabe Garage building due to the execution of the Greater
Cairo Metro Line 3-Phase 1, while the second case considers the stability
of an existing motorway constructed of contiguous pile walls due to the
construction Metro project in Shiraz city Iran crosses below the
underpass.
The valuable field monitoring data of the case histories was only
limited to a specific range of tunnel-pile configurations, and tunnelling
parameters. Further understanding of the tunnel-pile interaction problem
outside the range is therefore required. To bridge the gap of knowledge, a set of parametric studies is implemented using three-dimensional (3-D)
finite element (FE) model. Parametric studies are employing the
calibrated finite element model of Cairo Metro tunnel to evaluate the
effect of i) pile grouping, ii) pile cap rigidity, iii) the location of pile tip
relative to tunnel centreline, iv) offset of pile cap from tunnel centreline,
v) the effect of changing pile diameter, vi) the effect of pre-tunnelling
loading, vii) the tunnel excess face pressure, and vii) the tunnel over-cut.
The building stiffness is investigated using a hypothetical pile foundation
having 100 piles. The followings can be concluded from this study in the
next section. The results of the parametric studies are presented in the
form of charts. Some of these charts illustrate the deformation developed
in the pile in vertical, transvers and longitudinal directions while, the
other curves outlined the bending moment and axial load generated along
pile shaft due to tunnelling. These charts are vast improvement of tunnelsoil-pile interaction. It is to be noted that the following conclusion are
drawn from the studied cases only.