الفهرس 
INTRODUCTION AND PREVIOUS WORKOnly 14 pages are availabe for public view
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Abstract
The study area is an elongated strip of land located south of Cairo at distance about 18 km east of the Nile valley. The study area is located between latitudes 29° 48\ 08.6\\ N & 29° 49\ 54.7\\ N and longitudes 31° 23\ 57.1\\ E & 31° 25\ 24.4\\ E and between northing 3297963.95175 & 3301229.709045 and easting 345335.471848 & 347678.691627. It has an uneven topography, comprising several terraces reaching about 350.0 m above the sea level. Existing relative elevation differences within the area are ranged between 10 and 50 m. It covers about 7.7 km2.
The present work introduces geological, geophysical, geotechnical, and geochemical studies to evaluate the geotechnical properties of the Eocene limestone of the study area and emphasis the possibilities of these carbonate rocks for their economic utilization as building material and for chemical industry.
Topography of the east of Helwan area is characterized by heights and wadis. The main topographic heights are El-Qurn height, El-Halawna height, and the Observatory plateau. The main wadis in the study area are Wadi Abu Seeli and Wadi Gibbu. Other minor wadis drain into the main wadis. Wadi Gibbu drain into the Nile valley.
The area is dissected and transacted by four sets of complex normal faults, trending mainly northwest–southeast. Additionally, its subsurface bedrock is affected by several sets of joints, trending mainly east–west to northwest–southeast.
The area’s bedrock geology is mad up, from the top (recent) to bottom (old) of the followings; (1) the surfacial Late Quaternary Wadi deposits, composed mainly of pale yellow/yellowish brown, loose, fine-grained sand and gravel (in granule and pebble sizes) with little/traces of salty/calcareous/gypseous silt and iron oxides. Such thin deposits were developed in very shallow elongated depressions or drainage channels, in the form of small-scale Wadi terraces, fans and fillings, and could be delivered at the short time spans of annual floods and heavy rains from the adjacent eastern mountainous region; (2) the Upper Eocene El-Qurn Formation, composed mainly of yellowish white, medium hard, cavernous, Nummulitic, limestone, marl/marly limestone and chalk/chalky limestone with thin dolomite and gypsum bands. The outcropped thickness is averaged as 65.0 m; and (3) the Middle Eocene Observatory Formation, composed mainly of white/pale yellowish white, fractured, fossiliferous, hard limestone with thin marly limestone and dolomite bands. The outcropped thickness is averaged as 75.0 m, while its total thickness can reach 100.0 m.
A joint multi-spacing electromagnetic–terrain conductivity meter, very low frequency electromagnetic, and DC–resistivity horizontal profiling survey was conducted at the study area. The main objective of the survey was to highlight the applicability, efficiency and reliability of utilizing such non-invasive surface techniques in a field like geologic mapping, and hence to image both the vertical and lateral electrical resistivity structures of the subsurface bedrock. Consequently, a total of reliable 6 multi-spacing electromagnetic–terrain conductivity meter, 6 very low frequency electromagnetic, and 7 DC–resistivity horizontal profiles were carried out. All data sets were transformed–inverted extensively and consistently in terms of two-dimensional (2D) electrical resistivity smoothed-earth models. They could be used effectively and inexpensively to interpret the area’s bedrock geologic sequence using the encountered consecutive electrically resistive and conductive anomalies.
Notably, the encountered subsurface electrical resistivity/conductivity structures below all surveying profiles are correlated well with the mapped geological faults in the field. They even could provide a useful understanding of their faulting fashion. Absolute resistivity values were not necessarily diagnostic, but their vertical and lateral variations could provide more diagnostic information about the layering, lateral extensions and thicknesses, and hence suggested reliable geo-electric earth models. Nevertheless, such earth models should be used in the context of all a-priori information derived from the available drilled boreholes and/or collected stratigraphic sections.
The study demonstrated that a detailed multi-spacing electromagnetic–terrain conductivity meter, very low frequency electromagnetic, and DC–resistivity horizontal profiling survey can be used to reliably image both the vertical and horizontal resistivity structures resulting from the subsurface bedrock geology with a high-resolution. They can even help design an optimal geotechnical investigative program, not only for the whole eastern extensional area of the 15th of May city, but also for the other new urban communities within the Egyptian desert.
Twenty-four fresh carbonate rock samples were collected from the study area representing the Middle Eocene and Upper Eocene rock units. These foundation samples were investigated for the physical and mechanical properties.
Also, these samples were analyzed to measure the compressional and shear wave (P-Wave & S-Wave) velocities using sonic viewer instrument, and hence the geotechnical parameters estimation is applied on the compressional waves and shear waves velocities. That process targeted to calculate the rock mechanical properties. Also, foundation material bearing capacity is calculated due to probability and possibility of liquefaction occurrences and/or shear failure.
The Middle Eocene carbonate rocks show natural moisture content ranging from 0.47 % to 1.76 % with an average of 1.15 %, the bulk density values vary from 1.98 gm/cm3 to 2.55 gm/cm3 with an average of 2.29 gm/cm3, the specific gravity values range from 2.23 to 2.52 with an average of 2.42, and the apparent porosity values vary from 9.79 % to 23.41 % with an average of 17.72 %
Respectively. The Upper Eocene carbonate rocks show natural moisture content ranging from 0.48 % to 2.35 % with an average of 1.10 %, the bulk density values vary from 1.90 gm/cm3 to 2.40 gm/cm3 with an average of 2.19 gm/cm3, the specific gravity values range from 2.37 to 2.80 with an average of 2.53, and the apparent porosity values vary from 7.79 % to 32.98 % with an average of 21.01 %
It is clearly observed that, the Upper Eocene carbonates have high apparent porosity values than the Middle Eocene rocks. This is due to the Upper Eocene carbonates are characterized by high percentages of micro-fractures and porosity than the Middle Eocene.
The dry uniaxial compressive strength values of the Middle Eocene carbonate rocks range between 84.9 Kg/cm2 and 465.45 Kg/cm2 with an average of 252.20 Kg/cm2. According to (Egyptian Code, 2001) classification, the most studied Middle Eocene carbonate rocks are considered as medium hard rocks, however two carbonate rocks are classified as medium weak rock.
The dry uniaxial compressive strength values of the Upper Eocene carbonate rocks range between 95.60 Kg/cm2 and 245.41 Kg/cm2 with an average of 160.65 Kg/cm2. According to (Egyptian Code, 2001) classification, the most studied Upper Eocene carbonate rocks are considered as medium hard rocks, however five carbonate rocks are classified as medium weak rock.
It is observed that the uniaxial compressive strength values of the Eocene rock samples decrease with increasing the water content after soaking for the same tested samples.
The bivariant relationships of the mechanical properties with the physical properties of the studied rocks revealed the following:
(1) The apparent porosity has non-significant negative relation with the rock strength parameter. This relation revealed that when apparent porosity increases, the compressive strength rapidly decreases.
(2) The increase in the bulk density caused the rock strength increase especially when the density was more than 2.30 gm/cm3.
(3) The compressive strength values of rock samples with natural moisture content are higher than those of the water saturated rock samples.
The measured compressional and shear wave velocities values [Vp and Vs] for the Middle Eocene rock samples range between 2220 m/s and 4830 m/s with an average of 3571.25 m/s for P-Wave and between 1250 m/s and 2310 m/s with an average of 1866.25 m/s for S-Wave.
The calculated Poisson’s ratio values for the Middle Eocene rock samples range from 0.24 to 0.35 with an average of 0.28 and for the Upper Eocene rock samples range from 0.22 to 0.34 with an average of 0.30 which indicating fairly to moderately competent rocks.
Based on the measured bulk density and Vp and Vs values, a number of elastic modulus have been calculated for the different rocks as follow:
The calculated Young’s modulus values for the Middle Eocene rocks range between 7.85E+04 and 3.68E+05 with an average of 2.24E+05, and for the Upper Eocene rocks range between 8.14E+04 and 2.11E+05 with an average of 1.47E+05.
The calculated Shear modulus values for the Middle Eocene rocks range between 3.09E+04 and 1.36E+05 with an average of 8.51E+04, and for the Upper Eocene rocks range between 3.21E+04 and 8.21E+04 with an average of 5.73E+04.
The calculated Bulk modulus values for the Middle Eocene rocks range between 5.63E+04 and 4.13E+05 with an average of 2.10E+05, and for the Upper Eocene rocks range between 5.86E+04 and 1.85E+05 with an average of 1.20E+05.
The calculated Lames constant values for the Middle Eocene rocks range between 3.57E+04 and 3.23E+05 with an average of 1.53E+05, and for the Upper Eocene rocks range between 5.86E+04 and 1.85E+05 with an average of 1.20E+05.
The calculated N-Value ‘SPT’ values for the Middle Eocene rocks range between 2.25E+03 and 1.36E+04 with an average of 8.10E+03, and for the Upper Eocene rocks range between 2.53E+03 and 7.11E+03 with an average of 4.78E+03.
The average of the calculated material index values for the Middle Eocene rock is -0.195 and for the Upper Eocene rocks is -0.14.
The average of the calculated concentration index values for the Middle Eocene rock is 4.41 and for the Upper Eocene rocks is 4.59.
The average of the calculated stress ratio values for the Middle Eocene rock is 0.43 and for the Upper Eocene rocks is 0.40.
The average of the calculated density gradient values for the Middle Eocene rock is 1.62 and for the Upper Eocene rocks is 1.68.
The Poisson’s ratio, rigidity modulus, N-value (SPT), concentration index, material index, density gradient, and the stress ratio, suggest fairly to moderately competent rocks, except some zones are competent (samples: Ob-2, Ob-4, Qn-11, Qn-14, Qn-15, and Qn-16) as the scale of soil or rock classification (Abd El Rahman, 1991).
The calculated ultimate bearing pressure values for the Middle Eocene rocks range between 67.41 Kg/cm2 and 408.05 Kg/cm2 with an average of 242.68 Kg/cm2, and the evaluated allowable or working bearing pressure values range between 18.73 Kg/cm2 and 148.27 Kg/cm2 with an average of 82.62 Kg/cm2.
The calculated ultimate bearing pressure values for the Upper Eocene rocks range between 75.63 Kg/cm2 and 212.79 Kg/cm2 with an average of 143.12 Kg/cm2, and the evaluated allowable or working bearing pressure values range between 21.24 Kg/cm2 and 68.20 Kg/cm2 with an average of 43.62 Kg/cm2.
from the obtained results, it is found that there is a good correlation and matching between the ultimate bearing pressure values obtained from the direct measurements using the universal testing machine and values obtained from the calculations. Also, there is a good correlation between measured Vp and Vs values.
Complete chemical analysis was carried out for 238 borehole samples of limestone for the determination of L.O.I, SiO2, Al2O3, Fe2O3, CaO, MgO, K2O, Na2O, TiO2, Mn2O3, P2O5 and Clˉ.
The loss on ignition (LOI) values of the evaluated boreholes range between 38.27 and 43.87 with an average of 42.30, the SiO2 values range between 0.26 and 7.73 with an average of 3.04, the Al2O3 values range between 0.12 and 1.29 with an average of 0.47, the Fe2O3 values range between 0.01 and 0.63 with an average of 0.19, the CaO values range between 45.20 and 55.24 with an average of 51.73, the MgO values range between 0.16 and 6.60 with an average of 1.17, the SO3 values range between 0.00 and 2.54 with an average of 0.22, the alkalies (K2O+Na2O) values range between 0.01 and 1.28 with an average of 0.19, and the Cl- values range between 0.03 and 1.03 with an average of 0.15.
The results of the chemical analysis reveal that the best limestone occurrences are located in the northern and central parts of the study area at which higher percentages of CaO and less occurrences of MgO, SiO2, and Cl- takes place. The content of volatile components and alkalis (K2O, Na2O, and SO3) in this limestone is low in nearly all samples that will not have a meaningful effect on the final quality of the cement produced or on the manufacturing process and make it suitable for all types of cements.