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Geotechnical aspects of sabkha at Jubail, Saudi Arabia

Abstract A large industrial complex was planned to be sited at Jubail on the Gulf Coast of Saudi Arabia. The sabkha here is essentially a near sea level, fiat area of fine grained soils, partially cemented by salt (sodium chloride) and calcium sulphate. Very little carbonate was found. The rest of the site was covered by sand dunes which, further inland, reached a height of 30 m. The presence of artesian water, detected and measured at widespread locations, probably conducted through fissures in the underlying Hadrukh bedrock, was a particularly note-worthy feature of the area, having an important influence on the design of foundations and submerged structures of which examples are given. The artesian condition has been reported by a few observers for other sabkha areas. Jubail sabkha does not appear to conform in other ways with conditions at other sabkhas; for example, no traces were found of algal filaments, nor does it fit currently accepted ideas of formation or classification. At Jubail, numerous site investigation boreholes were sunk to assist the design of installations. Measurements in many of these boreholes showed artesian heads, some up to 6 m or more above ground level in sabkha areas and up to 15 m above sabkha level in dune areas. Analyses have been developed in the paper to give rates of upward flow and limits of rise of artesian water in sabkha areas. For construction reasons, sabkha was covered with 1.5 m to 3 m of compacted dune sandfill; further evidence for the underlying artesian condition was the discovery (predicted by the authors) of the rise of groundwater above the original ground surface and into sandfill. Calculations gave average rates of rise between 0.2mm/day and 1 mm/day. These artesian conditions are believed to receive a significant contribution from the sand dunes where high water tables have been recorded. Ideas have been put forward which could form a basis for a revised theory of the origin and continued existence of sabkhas at Jubail and at other similar locations. The influence of artesian water on the design of installations at the industrial complex is discussed.