الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Egypt has many large underground construction projects which primarily depend on cut-off
walls and retaining systems. However, there are many constraints that limit the ability to use
these systems optimally. Some of the most important constraints are high costs, lack of
national design standards, and the adverse effects of underground constructions on the
surrounding environment. Most excavation pits at recent days mainly depend on diaphragm
walls that are subjected to highly variable loads during its service lives. These variable
loads, in addition to the variability in site conditions, increasing the uncertainties that need to
be considered for safe, yet economic design. Uncertainties in diaphragm walls can be divided
into two main categories: geotechnical and model uncertainty. Assessment and quantification
of these uncertainties are required for efficient and sustainable design.
Current geotechnical uncertainty values have shortcomings that warrant the need for further
research. The lack of information on the in-site conditions during the implementation of
diaphragm walls can lead to huge risks for the quality of construction, stability, and safety of
working staff and surrounding buildings. Different kinds of uncertainties have been
enumerated at different construction stages of diaphragm walls such as verticality of the
panels, trench stability, installation of steel cages and casting structure concrete. A case study
with the monitoring tool CSL (cross-hole sonic logging) was driven to explore the defects
during implementation.
Failure in the joints of diaphragm walls and their exposure to ground water pressure may
have far reaching effects ranging from water leakage to the risk of calamitous loss of stability
for the retaining wall. Impacts of deficient joints in diaphragm walls have led to the
development of a study to monitor the joint integrity of diaphragm walls during
construction. By applying an analytical study on milled joints of hydraulic drilling machines,
it is now possible to record the surface area of exposed water leakage during the construction
of panels. This allows for implementation of corrective action during the construction process
if joint quality does not indicate a watertight connection to the adjacent panel. This analytical
study, used for different types of geometrical imperfections, especially off-verticality,
attempts to study their effect on the water seepage between joints at different construction
stages of diaphragm walls.
A case study on the underground structure of pump station projects was
explained. Diaphragm walls were used as the retaining system during construction,
a dewatering system was used to decrease the water table from -2:00m to plug level, showing the different kinds of risks during construction due to inappropriate soil properties used in the
design model, and unexpected leakage from joints between panels during the excavation
stage inside the station, and the remedial works used to complete the project
During this research, the effect of geometrical imperfection (off-verticality) was integrated
into (PLAXIS® 2D) code to help other engineers to apply it into their specific project as well
as to spread the method among the cut-off walls design industry in order to get more
feedback from experienced geotechnical engineers.
The effect of inclination on the overall factor of safety was discussed by using a numerical
model of (PLAXIS® 2D) with a 40 m depth of braced diaphragm wall, groundwater table at
(-2.00m) and excavation level (-12.00m), with change in the verticality of the diaphragm wall
units to an allowable quantity according to the Egyptian building code (1/100), the use
of dewatering to lower water level to excavation level. This study shows the variance in the
measure of different forces’ effects on the diaphragm wall using the same geometrical
parameters of the diaphragm wall unit section.
More importantly a case study on the CSL test observed on an individual diaphragm wall
panel with depth of 44m shows the absence of homogenous concrete sections around the end
of the barrette (38.00m from the top of the barrette). Based on the data from that case study, a
two-dimensional finite element software (PLAXIS® 2D) is applied in this study to establish
a comparison between models of excavation pits of diaphragm wall retaining systems to
detect the effect of the results of CSL testing on the overall factor of safety.