الفهرس 
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Abstract
The main objective of this research is to conduct detailed geophysical
investigations to image the subsurface geology and to characterize the soils and rocks
in terms of their engineering geological properties in view of determining their
suitability for building foundation. The problematic conditions in El-Obour city are
swelling of clay beds, which are found in the subsurface at different depths. The
appearing of soil water to the surface is representing other environmental problem
within some sites in the city.
Geophysical methods help to diagnose the characteristics of the above
problems and are capable of producing better extrapolations of engineering properties
of soils and rocks of the whole area by taking denser spacing measurements than
direct sampling. These conditions motivate to conduct integrated geophysical and
direct geotechnical methods for better understanding of the subsurface properties of
layers as foundation material.
The field survey was executed through two gradual stages; the resistivity
survey in the form of 1D Schlumberger sounding, 2D resistivity imaging and shallow
seismic refraction. These techniques have been selected to compare the results for
assessing the relative merits and demerits of each technique and to provide enhanced
view which is more informative than using single method.
The investigated site is located between latitudes 30.261°-30.224°N and
longitudes 31.437°-31.482°E. The site includes 5 districts; Youth habitation, 800
Super Unit, 1st district, Tarfihia district and services center of the city.
The study indicates that the presence of great thickness of clay layer at the low
topography area near the western side plays an important role in preventing the
infiltration of water and appearance of surface water on the ground surface. The
recognized clay layer in the investigated area, especially these layers which are
encountered at shallow depths must be taken in consideration for engineering
purposes, where it may cause problems during foundation construction.
The low thickness of about 4 to 16 m of the clay is concentrated to the eastern
part, while the higher thickness is concentrated to the western and southern
directions. The greater thickness of clay layer of about 16 to 34 m could be the reason
for the appearance of surface water seepage on the ground surface at western part of
Tarfihia district and parts of services center of the city.
The clays fall in the range of high plasticity index and low shrinkage limit and
expected to have high to very high swelling properties. It has very high expansive
potential. Thus, these expansive clays should be treated before building.
A good matching of 2D resistivity and seismic refraction results was obtained
and correlated with borehole results which show that these techniques are
appropriated to be applied in near surface mapping of bedrock.
Velocity maps were constructed for the clay layer and the bed rock. Also the
geotechnical and mechanical properties have been calculated at the northern part of
the investigated area depending on the resulted velocities. It revealed that the bed
rock at the western part is low to moderately competent material.
According to the resistivity and P-wave velocity distributions, sharp contact
between sand, sandstone and sandy limestone bedrock could be noticed running N-S
along the axis of the surveyed area. This indicates that great care must be taken when
designing the foundation system along the lithologic discontinuity and in the
undeveloped western part.