Abstract
Problematic soils are those that make the construction of structures extremely difficult. They include collapsible soils which are widely distributed in North America, Europe, Russia and Asia. They show low dry density and moisture content in all testing schedule due to presence of cementation bonds or loess structure especially at unsaturated state in arid or semi-arid regions. Therefore, conditions in arid and semi-arid climates favor the formation of the most problematic collapsible soils. Arid and semi-arid soils are mainly found in the Middle east (Arabian desert). The basic objectives of this study are to describe the properties and characteristics of semi-arid soils of Najran (Saudi Arabia), it also investigates the collapsibility characteristics and behavior of the materials with particular reference to their response to wetting under different stress levels. Undisturbed soil samples from Najran area situated in the south of Saudi Arabia have been collected and studied by using both single and double Oedometer tests. The results show that the highest value of collapse potential (CP=12.76%) of Najran soil is given by double Oedometer tests for a depth of 1.5m which represents a very severe trouble.