الفهرس 
GEOLOGICAL AND STRUCTURAL SITTING OF THE STUDY AREA AND ITS VICINITIESOnly 14 pages are availabe for public view
 |  | from | 150 |  |  |
| | | from | 150 | | |
Abstract
The population in Cairo governorate is increasing rapidly. With the high population growth in Cairo and the high demand for housing, the government is set to announce the construction of a brand new capital city. Located east of Cairo towards Suez, the new capital city, to which the government will relocate, is meant to encompass 70,000 acres, or one-hundred and nine square miles and is forecast to take about twelve years to build.
The new city is being constructed to reduce the population intensity in the original city of Cairo and to create better economic conditions in an appropriate living environment. According to the plans, city would become the new administrative and financial capital of Egypt, housing the main government departments and ministries, as well as foreign embassies.
The study area is located in the eastern part of Cairo; it is about 60 km southeast Cairo on the Cairo-Sukhna Highway, between latitudes 30° 02’ 40.81” N & 29° 57’ 58.28” N and longitudes 31° 39’ 52.04” E & 31° 46’ 04.15” E. Previous, excavations and engineering works in different locations of this plateau reveal the presence of shale and marl intercalation, faults, fracture zones and frequent karstic features such as cavities, voids and sinkholes.
The present work shows the results of applying different geophysical techniques at the study area for engineering purposes. The site represents different geophysical problems, planes for solutions based on the geophysical principals, data acquiring, results, and conclusion with recommendations.
The application of various geophysical techniques had proven to be the most useful way in confronting and overcoming these challenges; the basic applied techniques include the earth observation radar satellite (space-borne (SAR) sensors), geoelectrical resistivity tomography (ERT), ground penetration radar (GPR), and very low frequency (VLF). Further geophysical techniques have been applied according to the local requirements at the site, and help us in locating cavities, and dissolution features in carbonate rocks, and determining the stiffness properties of the ground.
Geologically, Miocene rocks form the most prominent stratigraphic units exposed in region east of the New Cairo City between the Suez-Cairo district and the Ain Sukhna- Qattamayia district, it is underlain by Late Oligocene- Early Miocene basaltic flow and the Oligocene basalt rests above the Early Oligocene red sandstone of Al Gabal Ahmer Formation. The basaltic flow in the study area represents the distal extension of the main basaltic source that developed very near to faults.
In Gebel Ahmar Formation: Basaltic rocks are underlain by non-marine fluvial sediments of Oligocene time, it is composed of varicolored sandstone and gravel with silicified wood trunks.
The East Cairo region is characterized by series of elongated and widely- spaced North-West and East-West trending topographic highs and lows, which are mainly structurally controlled. It is affected by numerous NW, WNW and ENE faults, most are geologically old and were active during Oligocene rifting of Red Sea and Gulf of Suez. NW oriented faults are clearly observed south of Qattamia Road and some of them extends to cut across the New Capital. Many fold structures are recognized in East Cairo region. They have NW to WNW orientation e.g. Gabal Anqabia at the NW corner of the new Administrative Capital.
According to the boreholes studies in district no. 7, we summarized the nature of geology and structure features in study area:
• The study area is affected by two WNW oriented dip-slip normal faults F1 and F2.
• F1 has surface expression and cut the whole stratigraphic succession. However, F2 has not surface expression.
• Accumulated displacement on top basalt for F1 is 19 m with rate of movement ≈ 0.00086 mm/year. However, at top silty sandstone unit (Upper Miocene) it achieved 4.5 m displacement with movement rate ≈0.00036 mm/year
• Accumulated displacement on top basalt for F2 is 10 m with rate of movement ≈ 0.000454mm/year. However, at top silty sandstone unit (Upper Miocene) it achieved 2.5 m displacement with movement rate ≈0.00021mm/year
• Both Faults F1 and F2 do not cut Quaternary sediments. Actually there are no any geomorphological evidences supporting its recent activity. But that does not negate their recent activities.
The earth observation radar satellite (space-borne (SAR) sensors) applied on the study area. The processed SAR images showed linear structures, which were reported in the official geologic map, and appears in the optical Landsat image. According to these images, seven feature zones have been designated, that were investigated in the field using the different geophysical techniques (ERT, GPR, VLF).
Sixteen electrical resistivity tomography profiles have been conducted at the district no. 7 applying three multi-nodes boxes to measure an ERT profile with 48 electrodes, 235 meters’ length, 5 meters between each two successive electrodes to give a penetrating depth reaches to about 45 meters beneath the ground surface using the Syscal R2 system.
The geoelectrical profiling field data, in the form of resistivity imaging, are processed with RES2DINV computer program, which is automatically designed to construct two-dimensional resistivity models of the subsurface.
Four geoelectric layers with different resistivity values (> 300 Ω.m), if this layer is at the surface, it will be interpreted as sand and conglomerate. If it is below the surface, it will be basalt. (100 – 300 Ω.m) it will be interpreted as sandstone layer. (15 – 100 Ω.m) it will be interpreted as sandstone layer. (1 – 15 Ω.m) if this is at the surface, it could be interpreted as shale. If it is down the surface, it will be interpreted as fractured basalt.
The abrupt changes in resistivity values horizontally in the ERT profiles reflects the probability of presence of subsurface structures (fractures (F1 and F2)). These results were confirmed with the boreholes studies that taken in the area.
Fourteen GPR profiles with different lengths had been conducted in the study area using frequency antenna (200 MHz), by SIR4000 Control unit from GSSI.
The data was processed by using Radanwin program for the processing and interpretation of reflected and transmissed data, which operates under windows environment.
Interpreting the present data set oriented to assess the geotechnical factors of the soil at the New Cairo City. Depend on the results of the SAR’s data, we applied GPR technique on 7 districts and The Geo-GPR cross sections along profiles number, reflects the presence of subsurface structures (fractures).
These sections composed of the two main layers include structures and fissures and dissolution soil, some of them extent to penetrate from the first layer into the lower one. The third layer was not found in some sections.
Twelve VLF profiles with different lengths had been carried out, using the T-VLF (IRIS-Instrument). The operating frequencies are normally ranged between 15.0 and 30.0 kHz at measuring azimuths 0o to 180o N.
Data was processed by using the Fraser filter and the Karous-Hjelt filter (also known as the K-H filter). These filters are among the most well-known transformation techniques. To improve the horizontal resolution of local VLF–EM anomalies and make them more easily identifiable, a discrete one-dimensional linear filter-operator was designed using the Fraser filter.
Interpreting the present data set oriented to assess the geotechnical factors of the soil at the New Cairo City. Depend on the results of the SAR’s data, we divided the study area to seven districts upon to the features that showed in the same areas of the GPR surveys.
Along the K-H cross sections, information on the size, shape, and depth of both shallow and sufficiently deep subterranean conductors may be distinguished. A few subsurface anomalies of abnormally high conductivity impact horizontally both the shallow and deep cross sections. These abnormalities indicate fracture zones that influence underlying strata.
Finally, according to what has been studied from various methods on the study area, which has been confirmed by the geological structure of the study area, we have confirmed the possibility of the presence of subsurface structures / fractures, which may need some engineering solutions to build a safe residential city.