Geotechnical and Geochemical Properties of Al-Nekhaila Sabkha, South of Jeddah

Abstract

Sabkhas are widespread along the coastal plains of the Red Sea. The development of sabkha is mostly attributed to the hot climate where evaporation, which is responsible of the development of brines, largely exceeds precipitation. The soil poses several geotechnical problems specially when wet. The high sulfate and chloride content in the groundwater may also cause corrosive action on reinforced concrete. The city of Jeddah is rapidly expanding and new residential and commercial buildings are constructed each year in the area close to the shoreline where sabkhas exist. If the expansion extends southward, it will reach Al-Nekhaila sabkha. Therefore, the geotechnical and geochemical characteristics of this sabkha were considered. The field investigations were performed by three in situ tests, namely Mackintosh probing, vane shear, and sand cone, to a maximum depth of 9 m. Three main soil units have been identified; sand (SM, SC, and SP), silt (ML, and MH) and clay (CL, and CH). The salts are present as cementing material between the soil grains in the top one meter. The sand ranges from loose to medium dense as indicated by the soil probing. The average undrained shear strength for the silt is 84 kN/m2 and for the clay is 90 kN/m2. Some geotechnical problems are expected from the clay layer. The groundwater level is 1 m to 2.5 m deep and is classified as saline to brine.