Integrated Geotechnical, Sedimentological and Shallow Seismic Studies for Construction Purposes in New Cities: A Case Study from Egypt

Geotechnical and geophysical studies for construction sites in new cities are critically needed to investigate and select the most appropriate sites and characterize their properties. So, this research involves geotechnical, sedimentological, and shallow seismic studies for investigating the Social Housing area in Badr City in Egypt as a case study. This city has a strategic future where it is planned as one of the most promising industrial cities in Egypt along the Cairo-Suez road. To study the physical, chemical, and geotechnical properties of the ground, a total of 105 sedimentary samples have been taken from 66 boreholes (48 very fine friable sand/silt, 27 sandstone/siltstones, and limestone, and 30 claystone/siltstone samples) at a depth range of 0.5-10 m. The investigation results revealed that the studied samples are characterized by average natural moisture = 21.8%, Liquid Limit (LL ) = 86%, Plastic Limit (PL ) = 33.8%, and Plasticity Index (PI) = 54.7%. These high values are attributed to the presence of high clay content (65-85%) of the studied samples which are considered silty clays with high plasticity. The results of the X-ray diffraction curves indicated the dominance of smectite, kaolinite, and illite minerals. Besides, compression strength ranges from 55 to 265 kg/cm2 with an average of 160 kg/cm2, and low densities values (av. = 2.12 g/cm3), so they need to be stabilized or reinforced when starting to construct big establishments. In addition, the average swelling pressure and free swelling of the claystone are 4.57 kg/cm2 and 215% respectively. These geotechnical values indicate medium to weak sediments with high plasticity. The chemical analysis of these sediments reveals high percentages of calcium carbonate will lower the sediment index properties, which causes aggregation of the grains in the sediments. The high sulfates and chloride content increases the corrosion chance of the concrete foundations. The total dissolved solids (TDS) were 3024 mg/L including sulfate 4.04 mg/L and chloride 2712.5 mg/L which indicate moderate to high aggressive nature. On the other side, the electric conductivity (E.C) = 1771 mmhos/cm, and the pH equals 7.4 which indicates a moderate to non-aggressive nature. Petrographically, the sandstone samples are composed of quartz arenite rich in quartz grains (approx. 90%) with subordinate feldspars and lithic fragments with traces of heavy minerals. The quartz grains are described as mono to polycrystalline. Considering the geophysical investigations, the shallow seismic refraction technique was also applied to evaluate the foundation rock properties in the area by recording the time arrival of the refracted seismic waves and their interpretation in terms of subsurface geoseismic layers and their diagnostic physical and dynamic properties. The ultimate bearing capacity values of the bedrock (second layer) vary between 0.239 g/cm2, and 7.40 g/cm2, the allowable bearing capacity is between 0.0795 to 2.4676 g/cm2 and hence the factor of safety is equal to 3. The study indicates that this kind of sediments should be reinforced by traditional means such as piles, micro piles, and/or other new technical methods and improved by engineering treatments before any construction. However, the southern parts of the region are characterized by good material quality, thereby these parts are suitable for civil and construction purposes.