Engineering Geological Mapping of Al Jubail City
Gabel Z. Al-Barakati, Abdulkhaleg S. Al-Doban, Marwan M. Al Saikhan, Khalid S. Al Wagdani,
Ashraf S. Sijeni, and Abdullah A. Sabtan
Urban development and the expansion in the industrial areas are long faced with many geologic constrains. The engineering geological mapping help in recognizing the importance of the geological conditions in founding and growth stages of cities. Al Jubail is the site of one of the most important petrochemical industries in the world. The city is expanding rapidly and subjected to a number of geotechnical problems arising in part, from the lack of the proper mapping. Huge construction works are still going on since the 80's, which require an extra effort to match the weak nature of the soil that may requires foundation modification and/or soil improvement. The present investigation program starts with mapping the geological units in the area, followed by extensive in-situ testing and surface soil sampling that covers the industrial city and the old city of Al Jubail. The samples were tested for their engineering properties and the engineering geological zones were identified and characterized. The field and laboratory works were based on the system set by the American Association for Engineering Geologists (AAEG) to map the geology of the major cities of the world. A multi-purpose surface comprehensive engineering geological map was prepared at a scale of 1:50. The map shows surface modifications in the soil type, and the new boundary between the various geological units. In addition, a database was constructed from obtained information in this research, and from related information from numerous geotechnical reports that were collected and analyzed. It was found that Al Jubail area is composed of sand dunes and sand sheet, and low-lying sabkhas that pose a number of significant challenges for the planners and designers. The upper one to two meters is mainly loose poorly graded sand (SP) with low relative density and sandy or clayey week sabkhas. As a result, large-scale raising of the ground level and rectifying the soil was carried out by using either sand dune or dredged soil from the sea. The compiled knowledge from previous investigations was used to prepare several cross sectional profiles along the important lines to describe the types and thicknesses of soil laterally and vertically to a depth of 20 meters. Based on that, an increase in the percentage of silt was observed in the deep sand, and the soil is classified as poorly graded sand with silt (SP SM). The soils become stronger downward and lenses of other soils exist at various levels. The detail in the constructed engineering geological map is proportional to its scale since it covers a large area (more than 500 km2). The identified geological hazards include drifting sand and migrating dunes, the weak and corrosive sabkhas, and the geotechnical problems of the fill materials in the form of settlement or vertical water percolation. The engineering map and the cross sections will provide a general picture of the material type and their engineering properties in Al Jubail. It is important to serve the developers, construction companies, consulting engineers, and the city residents to avoid problematic grounds or hazardous environments.
Al-Barakati, G.Z., Al-Doban, A.S.,.Al Saikhan M.M., Al Wagdani, K.S., Sijeni, A.S. and Sabtan, A.A., 2009, Engineering geological mapping of Al Jubail City: Saudi Geological Survey SGS-TR-2008-3, 35 p, 9 tables, 36 figures, 3 apps, 2 plates.