Shear strength and consolidation characteristics of Obhor Sabkha, Saudi Arabia

The shear strength and consolidation characteristics of the subsoil of Obhor sabkha (north of Jeddah, Saudi Arabia) are critically reviewed. The problems of assessment and the practical implications are discussed. Aging, desiccation, cementation and groundwater table changes appear to have contributed to the observed variation in the properties of the lightly overconsolidated soft grey, sensitive, silty clay covering the landward two-thirds of the sabkha. The overconsolidation of the underlying stiff, brown, sandy silty clay is considered to be due to desiccation and erosion followed by a rise in sea-level during the last transgression of the Red Sea. Field vane tests sometimes show locally high undrained shear strength in the soft clay due to interference by large gypsum crystals or marine shells, both of which also cause difficulty in sampling and specimen preparation. The nature and the thickness of the uppermost soil units, the position of groundwater table and the chemical nature of the environment in the different parts of the sabkha are shown to be an important consideration influencing the selection of appropriate types of foundation and any requirements for soil improvement.