Application of VES and TDEM techniques to investigate sea water intrusion in Sidi Abdel Rahman area, northwestern coast of Egypt

The present study is an approach to detect the sea/freshwater interface in Sidi Abdel Rahman area, northwestern coast of Egypt using both vertical electrical sounding and time domain electromagnetic. The measured vertical electrical soundings are interpreted in 1D and 2D manner. The 1D inversion is carried out using the commercial software (RESIST), whereas 2D resistivity nonlinear iterative inversion scheme based on the finite element technique and regularization method was used. The time domain electromagnetic stations are interpreted using Temixxl-4 software by Interpex Ltd. To have the advantages of the vertical electrical sounding in shallow depths and time domain electromagnetic in deep depths, a joint inversion algorithm is applied for the electric profile and the nearby electromagnetic profile. Very low resistivity values have been observed near the coast as well as a considerable salt/fresh water interface. The tip-top portion of the interface lies approximately 1,000 m from the shore line.     

A Coastal Aquifer Study Using Magnetotelluric and Gravity Methods in Abo Zenema, Egypt

Magnetotelluric (MT) soundings and gravity methods were employed to study the deep freshwater aquifer in the area north of Abo Zenema city on the eastern side of the Gulf of Suez, Egypt. Seven MT sites and 48 gravity stations were surveyed along northeast–southwest profiles as close as possible to a line perpendicular to the coast of the Gulf of Suez. The MT survey was conducted using high and low frequencies to investigate shallow and deep areas, respectively. One-dimensional inversion was conducted using a heuristic inversion scheme of the Bostick algorithm. The MT data were also inverted with a 2-D smooth model inversion routine using the nonlinear conjugate gradient method to infer variation in vertical and lateral resistivity inside the Earth. A 100-Ohm-m homogeneous half-space initial model was used to invert the TE mode data only. Then, the inverted model obtained from the TE mode data was used as an initial model for inversion of the TM mode data. The inverted model thus obtained from the TM mode data inversion was used as an initial model for the inversion of the joint TE and TM responses. Two-dimensional (2-D) forward modeling of the gravity data was conducted using the 2-D polygon method of Talwani’s algorithm for an arbitrarily shaped body and was based on the subsurface information from the MT survey and the available information about the geological structure of the study area. This method enabled us to obtain the basement structure of the coastal aquifer in the study area. The results from the analysis and the interpretation of MT and gravity data were used to detect and delineate the groundwater coastal aquifer in the study area.     

Geotechnical assessment of ground conditions around a tilted building in Cairo, Egypt using geophysical approaches

The flood plain of the Nile River has been a safe dwelling throughout history. Recently with a growing population and vast growing urbanization, some buildings have started to experience structural damages, which are not related to their construction design, but rather to the ground conditions around the buildings' foundations. Variations in properties of the soil supporting the buildings' foundations such as soil-bearing capacity, moisture content, and scouring may eventually lead to the failure of these buildings. This study is attempting to characterize the variations in the soil properties around the City Star shopping mall, in eastern Cairo, where a large building has tilted over the past few years. This tilting may lead to the collapse of the whole building if it continues at the same rate. An integrated geophysical investigation including multi-channel analysis of surface wave (MASW), ground-penetrating radar (GPR), and 2-D electrical resistivity tomography (ERT) was used around the affected building to help detect possible causes of deterioration. The GPR data showed a soil-filled layer overlaying a thick bottom layer of higher moisture content. The MASW data revealed a middle layer of relatively low shear wave velocity sandwiched between two relatively high shear wave velocity layers. The ERT data showed an upper low resistivity layer overlying a high resistivity layer. Integrating the interpretations of the three geophysical methods provides a combined model that reflects lateral and vertical variation in the soil properties. This variation becomes dramatic near the tilted corner of the building.     

The impact of the geologic setting on the Quaternary aquifer,El-Tur area,Southwest Sinai,Egypt

The groundwater extracted from the unconfined Quaternary aquifer is the main source of water supply in El-Tur area. The area is bounded from the east by the elevated basement complex of Southern Sinai and from the west by El-Qabaliyat Ridge. The wadis dissecting these highlands form effective watersheds of the Quaternary aquifer. These wadis form areas of focused recharge. Recharge also occurs directly via the Quaternary sediments covering El-Qaa Plain. Subsurface lateral groundwater flow from the fractured basement contributes significant recharge to the aquifer as well. The aquifer sediment facies affect the type and quality of groundwater. In the eastern part where the aquifer is composed mainly of gravel and coarse sand with fragments of weathered basement, the Na-Cl-SO₄ water dominates. In the west where the facies change is rapid and complex, many water types arise. The base exchange index (BEX) is positive in this part reflecting the role of clay minerals in changing the water types via cation exchange. In the east where clays are insignificant in the aquifer, the BEX is negative. In the western part next to El-Qabaliyat Ridge, the wells discharging from the calcareous sand zone have low groundwater salinities compared to the wells discharging from the alluvium. In general, the groundwater salinity increases in the direction of groundwater flow from the northeast to the southwest which reflects the dissolution of aquifer sediments. The concentration relationships between the major ions on one hand and chloride on the other reflect the dissolution of calcium carbonates, precipitation of K- and Mg-bearing minerals, and cation exchange of Ca for Na on clay minerals. The hydrochemical models support these reactions. In addition, they show that the effect of evaporation on the recharge water in the western catchment is about four times its effect on the eastern recharge water which reflects the rapid recharge through the wadis draining the fractured basement. Moreover, the contribution from the eastern catchment in sample No. 23 is more than four-folds the contribution from the western recharge area. The stable isotopes (²H and ¹⁸O) show that the Quaternary aquifer is recharging from recent rainfall. However, upward leakage of Paleogene groundwater (depleted in ¹⁸O) also occurs. The groundwater level map shows strong overpumping impact especially in the areas close to El-Tur city.     

Visualized liquefaction behavior of sandy soil deposited in water under undrained cyclic shearing

Acta Geotechnica - Water films probably form beneath less-permeable interlayers in liquefiable deposits during an earthquake, further resulting in devastating disasters. However, the development of...