This paper deals with the geotechnical characterization of Sultana soils (Najran region, Saudi Arabia) by in situ and laboratory tests, for a project proposal for the construction of commercial and government buildings. Geotechnical parameters of the subsoil were analyzed with a view to using the soil as an earth construction material and as a foundation for buildings constructed on the grounds tested. The site was investigated by means of boreholes, trial pits, standard penetration tests, plate load tests, Seismological data, particle size analyses, modified Proctor Tests, Oedometer and direct shear tests. The study contains full description to the subsurface soil conditions and provides recommendations for collapse potential, foundation type, foundation depth, allowable net bearing capacity, estimation for the expected settlement. In this paper a review of the principal results of the in situ and laboratory investigations is described. Results of the study revealed that within the maximum depth of 10.0 m of boring, the soil was found to be composed of brown soil mixture of sand and clayey silt with little gravel, classified as (SM) and (SC) according to USCS classification and as (A-2-4) and A-2-6 according to AASHTO classification. The area was found to consist in general of collapsible soils, classified as collapsible alluvial soils. The results show that the collapse potential of the majority of semi-arid soils tested were classified as severe trouble soils and natural moisture content is an important factor influencing the collapse potential of the soil. In addition, the results of this study provide the parameters to evaluate the soil behavior and the geotechnical model for the foundation bearing capacity and soil settlements evaluation.
