APPLICATION OF GEOELECTRIC AND GROUND PENETRATING RADAR TECHNIQUES TO ESTIMATE SHALLOW SUBSURFACE FEATURES AT EL BANAFSEG DISTRICT, NEW CAIRO CITY, EGYPT

Document Type : Original Article

Authors

1 Geology Department, Al-Azhar University, Cairo, Egypt

2 Ministry of Education, Saudi Arabia

Abstract

A site located at El Banafseg District, northern part of New Cairo City, Egypt, has been suffered under complicated and different aspects of hazards and risks following constructions. These complications are connected with the problem of limestone fracturing and clay layers, which cause clay swelling. A surface geoelectric resistivity consists of 14 vertical electrical resistivity soundings (VES) are conducted with the aim of identifying the prevailed subsurface conditions at the study area.
The interpretation of the collected resistivity data reveals a common subsurface earth succession, that consists of following resistivity layers: 1) Surface layer; which is the surface cover around the area composed of sand and often a mixture of sand with gravels, sandstone, shaly sands, and sandy limestone in some places with wide range of resistivity values (from 50 to180 Ohm.m) . 2) First geoelectric layer that has resistivity values ranging from 10 to 100 Ω.m, and thickness varying from 2 to 66 m, consisting of shaly sand with shale or clay intercalations. This type of facies is relatively suitable for direct foundation above them. It also has allowable bearing capacity between 1.5 and 3 kg/cm2. 3) Second geoelectric layer has resistivity value ranging from 0.5 to 10 Ω.m, and thickness varying from 4 m to 65 m. This layer is composed of shale bed. This shale type may cause some engineering troubles. 4) Third geoelectric layer that has a resistivity value ranging from 100 to 730 Ω.m. This layer is composed of sandy limestone facies.
Ground Penetration Radar survey was carried out in which twenty profiles are conducted. Interpretation of the ground penetrating radar sections has been done in the light of the in-situ calibration and utilizing previously published GPR works on similar areas. The surface observed fractures, joints and shale bed are detected by ground penetrating radar method. These sections revealed anomalous zones characterized by different types of reflections and zones, where the radar signals are highly attenuated with the presence of very weak reflection surfaces. Processing the digitally acquired radar data was achieved via system software. A comparative study of the resolution of the applied geophysical techniques may detect shale layers, surface joints, fractures, and help in reducing the cost and saving the time and money.

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