To achieve the study objectives, structural, geomorphological, seismic refraction and vertical electrical sounding (VES) investigations are carried out and integrated in the proposed site aiming at imaging shallow subsurface layers, determine the geotechnical characteristics and competency of the subsoil as foundation materials and evaluate their suitability for civil engineering constructions. Set of professional software programs were used such as SEISVIEW, IPI2Win. 6, Surfer and Geosoft Oasis Montag.
Geological setting and structural analysis of Wadi Habib area
Wadi Habib drainage trunk channel runs in a general east-west direction on the limestone plateau east of Assiut town. Its entrance is a triangular flat area which is bounded from two sides (northeastern and southwestern) by the Eocene limestone plateau where it opens from its northwestern side to Wadi El-Assiuti main channel.
The exposed sedimentary sequence in the studied area is mainly represented by the Eocene carbonate rocks (Serai, Drunka and Minia formations), which is unconformably overlain, in some areas; by the Oligocene elongate mounds of gravels. Together with the Pliocene chocolate brown marlstone and mudstone deposits which are recorded only in the subdued ground in the lower reaches of the western parts of the studied area and the Pleistocene (Issawia and Qena formations) and the recent fine clastic deposits (Fig. 1).
Surface structural analysis of the studied area shows that the capping Eocene formations are essentially composed of nearly horizontal limestone beds except at the vicinity of faults, which represent the main structural features affecting the area. They are mostly of high angle normal faults with various extensions and relatively small throw amounts. Folding is represented by very dense fold system superimposed on the fault system (Gigot et al., 1986 and Bakheit, 1989). The surface faults which have been affected the study area was traced from the geological map of the Gebel El-Urf Quadrangle prepared by the Egyptian Geological survey (1983). Faults are grouped into NNW- SSE, NW – SE (Gulf of Suez – Red Sea trend), WNW – ESE and ENE – WSW categories arranged in decreasing order of abundance. The subsurface faults affecting the basement complex in the study area are delineated from the magnetic data by Bakheit (1989) showing an upward extension in the overlying sedimentary cover. However, relatively younger faults affecting the sedimentary cover are recorded (Fig. 1). The contrast between the Azimuth frequency diagram of the surface structural pattern (A and B) and that interpreted from magnetic data (C) shows that the NW tectonic trend represents the best pronounced direction among surface fractures. It is very rare among fracture trends interpreted from magnetic data.
Geomorphometrical Analysis
The quantitative interpretation of the drainage net of Wadi Habib was carried out to determine the morphometric properties of this basin and their effect to the flash flood hazards and groundwater replenishment. The analysis includes; stream order, stream numbers, stream lengths, bifurcation ratio, drainage density, drainage frequency, valley index, texture ratio and basin shape (elongation and circularity ratios).
Accordingly, the drainage net of Wadi Habib basin is well developed, integrated, dense, and controlled by fractures (faults and joints). The hydrological assessment of morphometric parameters and their consequent surface runoff variables emphasize that, huge quantities of surface runoff water would be yielded and their overland flows towards the outlets have considerably highly–peaked discharges. The basin is underlain by highly resistance and impermeable exposed rocks of rough surface and great possibility to collect surface runoff during flash flood periods. Nevertheless, Wadi Habib area can infiltrate a considerable amount of surface water, which increases the ground water potentiality (Fig.2&3).
The calculated bifurcation ratios and basin bifurcation ratio for the studied Wadi Habib basin is about 5.1403 Table (1). This indicates that Wadi Habib basin is mountainous, hilly and dangerous floods (Mucullagh, 1978). The analyzed morphometric properties of the drainage net of Wadi Habib area has been shown in Table (2). The relief ratio of Wadi Habib basin is relatively small value 0.0044) indicates that the surface of Wadi Habib basin characterized by low relief and presence of isolated hills (Inselbergs).
Seismic Refraction Survey:
A total of 32 short discontinuous doubled forward and reverse seismic profiles (120 m length with 10 m geophone spacing) were conducted in line spreads in two directions N 35° W and N 55° E to detect the geoseismic layers, thicknesses and corresponding compressional and shear velocities (Vp and Vs) using ES-1225 seismograph (EG&G GEOMETRICS), 12 volt battery set, 110/220 volt batterycharger, Geophone spread cable (240 m length), 12 Geophones, Sledge hammer (8 kg weight), Hammer switch and Striker plate (Fig. 4 A, B & C , Table 3). Three geoseismic layers of different lithological and elastic properties are achieved. The geotechnical parameters are estimated, mapped and compared to indicate the characteristics of the foundation layer for civil engineering constructions in the investigated site. (Figs 5-6, Table 4).
Geotechnical Parameters Estimation:
Computation of geotechnical parameters for subsurface material in a construction site is very important before foundation design. These parameters involving kinetic elastic moduli (e.g.shear modulus, Young's modulus and Poisson's ratio), soil material competence parameters (concentration index, material index, standard penetration testing, density-gradient and stress ratio) and the bearing capacity (ultimate and allowable) are estimated (Table 4). The estimated parameters names and symbols, equations used, references as well as the minimum, maximum and mean values for the surface layer are given in Table 4. Hence, their indications to the characteristics of the foundation layers for civil engineering constructions in the investigated site could be concluded. All the estimated seismic and geotechnical parameters of the foundation layer (the first seismic layer) in Wadi Habib site are mapped (Fig 6 a,b,c,d,e,f,g,h,i,j,k and l), compared , interpreted and discussed based on the referenced classification data (Tables 4, 5, 6, 7, 8 and 9).
Vertical Electrical Sounding (VES) Survey:
A total of 30 VES’es are also implemented, processed, inverted and interpreted to realize the geological and hydrogeological conditions. Using Terrameter SAS 300, Terrameter SAS 2000 Booster, Ni – Cd batteries, Battery charger, Stainless-steel electrodes, Wire reel for current line and potential lines. (Fig. 7, Table 10). The final interpreted results were used for the preparation of geoelectrical sections, and maps. Subsurface geoelectrical layers are delineated and verified from the correlation with bore logs. (Table 10, Figs 8-9). All estimated resistivity parameters of Foundation Layer in Wadi Habib site are mapped and compared (Figs 9 a, b, c and d).