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 noteworthy 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.

A review of geological and geotechnical features of some Middle Eastern countries

“…They are highly heterogeneous and exhibit behaviour ranging from non-plastic to highly plastic, with liquid limits as high as 80% or more. More detailed information on sabkha soils is provided by James and Little [22], Hossain and Ali [13], Akili [3] and Akili and Torrance [4]. In coastal areas, coral limestone formations, which, in their natural condition, are soft, non-homogeneous and porous, and can be challenging for foundation designers.…”

Performance of a steel structure on Ar-Rayyas Sabkha soils

“…These bonds can be lost upon wetting with water and, hence, the strength can be significantly decreased (Al-Amoudi et al, 1997;Shehata and Lotfi, 1993). These evaporites form a hard crust when dry, however, a person got sunk to his knee when the crust was wetted (Akili and Ahmad, 1983;Al Amoudi, 1995;James and Little, 1994;Sabtan and Shehata, 2002;Shehata et al, 1989;Shehata et al, 1990).…”

Stabilization of an arid, saline sabkha soil using additives

“…They usually form in hot, arid climates and are associated with shallow groundwater tables (A1-Amoudi & Asi 1991). Artesian conditions, although of marginal significance, have been reported to exist in some of the eastern Saudi sabkha terrains (James & Little 1994;A1-Guwaizani 1994).…”

“…The collapse potential presents an unacceptable risk in normal practice and calls for the improvement of their mechanical properties prior to any construction. A1-Amoudi (1993) reported that for many large-scale construction projects, elaborate techniques such as dynamic compaction, densification piles, stone columns, extensive underdrainage and geotextiles have been employed (Juillie & Sherwood 1983;James & Little 1994). For small-scale structural projects (e.g.…”