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

The geology of the United Arab Emirates (UAE), and the Arabian Gulf Area, has been substantially influenced by the deposition of marine sediments associated with numerous sea level changes during relatively recent geological time. With the exception of mountainous regions shared with Oman in the north-east, the country is relatively low-lying, with near-surface geology dominated by deposits of Quaternary to late Pleistocene age, including mobile aeolian dune sands, sabkha/evaporite deposits and marine sands. Dubai is situated towards the eastern extremity of the geologically stable Arabian Plate and is separated from the unstable Iranian Fold Belt to the north by the Arabian Gulf. It is believed that a tilting of the entire Arabian Plate occurred during the early Permian period, resulting in uplift in southern Yemen and depression to the north-east. Tectonic movements peripheral to folding of the Iranian Zagros Range during the Plio-Pleistocene epoch probably contributed to the formation of both the Arabian Gulf depression and the mountainous regions in the north-east of the UAE and Oman.

The main stratigraphic units encountered in Dubai are described briefly below, and a typical geotechnical profile is illustrated in Fig. 4.

The groundwater table is typically 1–3 m below ground surface.

Alrifai [8] presents some data on unconfined compressive strength (UCS) for relatively shallow strata, and the UCS values are low, generally between 1 and 3 MPa, with a considerable scatter in the data.

There is relatively little published information on foundation design parameters for buildings in Dubai. Poulos and Davids [28] have presented some information on pile design parameters employed for the design of the Emirates Towers. Alrifai [8] presents some data from a series of five load tests on bored piles with diameters ranging between 0.6 and 1.0 m, and length between about 12 and 18 m. There were 4 tests in compression and one in tension, and on the basis of these tests, Alrifai offered the following recommendations:

Kuwait is part of the north-eastern Arabian Peninsula which rises gradually from the shores of the Arabian Gulf with gentle undulations towards the mountainous regions of the western Najd and the Hijaz. The mainland slopes generally towards the sea at an average gradient of 1 in 500, the highest elevation being 270 m in the south-west corner. In the north, an extensive plain is strewn with a thin layer of gravel, while the south-eastern quarter is low lying, flat and sandy. Behind the Az Zawr escarpment, there is a highly calcareous crust on the ground surface, creating hard areas devoid of sand.

The upper sedimentary rocks of Kuwait were deposited in shallow seas or were laid by streams, with the position of the shoreline changing frequently. Underneath the recent deposits, rocks ranging from Miocene to Pleistocene occur to a maximum thickness of 1000 m. In north Kuwait, beneath the recent superficial deposits, lies the Dibdibba sequence, which ranges in thickness from 80 to 100 m from east to west across the country and from 100 m to almost zero thickness between the northern boundary and the Al Zawr escarpment. This formation consists of sands and gravel underlain by consolidated sandstones, conglomerates and siltstones. Below the Dibdibba formation are the lower Fars conglomeratic sandstones, variegated shale and thin fossiliferous limestones having a thickness of 60–120 m, and then the Ghar formation, which is about 170 m thick and consists of partly cemented coarse pebbly sandstones, with minor beds of shale near the base.

In south Kuwait, the strata above the Eocene are known as the Kuwait group. This is a thick bed of sandstones, sands and some shale, with a thickness that varies between about 5 and 200 m. The upper part of the Eocene sequence, the Dammam limestone, consists of about 200 m of soft chalky limestone and hard dolomitic limestone, with a chert cap that may be up to 10 m thick in some areas.

Abdullah and Kamal [1] have reported the occurrence of sinkholes arising from the presence of karstic limestone underlying 35–40 m of overburden at an urbanized site in Kuwait. They present an analysis of the causes of these sinkholes and discuss the consequences for future developments. Their investigations have identified similar conditions in other parts of the eastern coastline of the Arabian Peninsula, which had experienced similar problems with sinkholes.

Saleh et al. [30] give a more detailed description of the geological origin of the coastal “sabkha” deposits in northern Kuwait. Sabkhas are coastal flat areas that extend above the high tide level and consist of evaporate-rich sediments. These salt-bearing soils can be leached, resulting in a reduction in strength, penetration resistance and bearing capacity, and an increase in permeability, void ratio and compressibility [21].

Saleh et al. [30] provide a generalized stratigraphic profile which is reproduced in Fig. 5.

Saleh et al. [30] identify the following lithologic units within the coastal areas of Kuwait:

Ismael et al. [19] present shallow borehole details along a section 35 km long, running from Andalus in the west to Salmiya in the east, and these are reproduced in Fig. 6. The first two strata listed above can be identified. Average SPT values increase with depth from the surface to a depth of about 7 m.

Ismael [16, 17] has presented geotechnical data on near-surface cemented sand deposits Within the upper 3.5 m, the effective stress strength parameters were within the following ranges: c′ = 31–190 kPa, ϕ′ = 34.2°–38.7°. The compression index ranged between 0.06 and 0.10, while the range of the recompression index was 0.013–0.028.

Limited published information exists on foundation performance in Kuwait. Al-Sanad et al. [7] summarize data on Young’s modulus obtained from pressuremeter tests (PMT), and plate load tests for a site in Kuwait City, and this data is reproduced in Fig. 7. The modulus values for first loading of the plate were reasonably consistent with the PMT test data, but significantly higher values were found from reloading and cyclic loading tests on the plate.

The results of some pile load tests carried out in Kuwait have been presented by Ismael and Al-Sanad [20] and Ismael [13, 17‐18]. Typically, the skin friction values for relatively short bored piles in cemented sands are between 80 and 107 kPa, and are larger than those for driven piles (about 60 kPa), a characteristic that is not uncommon in soils with a relatively high carbonate content. For the short piles tested, there seems to be little difference between the values for compression and uplift, although for longer more compressible piles, it would be expected that the skin friction in uplift would be less than the value for compression. It was also found that, for small groups of bored piles at relatively close spacings, the group efficiency factor was greater than 1, and for a 4-pile group at 3-diameter spacing, an efficiency factor exceeding 1.9 was observed.

Ismael [15] presented the results of lateral loading tests on single pile sand small pile groups. The piles were relatively short (up to about 5 m) and located in cemented silty sands. Parabolic p–y curves were obtained and it was found that ignoring the cohesion of the cemented sand resulted in an over-conservative prediction of load–deflection characteristics. However, for short piles, extensive wetting and disturbance caused softening and partial loss of cementation of the near-surface soils, and it was recommended that a reduction of 30–40% in the cohesion be allowed for to reflect this effect.

The Qatar peninsula is geologically a part of the Arabian Gulf basin, between the stable Arabian Shield of western Saudi Arabia and the mobile south-western Iranian belt. The structure of Qatar consists of an anticlinal arch with a north–south axis running through the centre of the country. The geological succession consists of a sequence of shallow water marine limestones and dolomites with interbedded clays, marls and shales of Tertiary age. These are overlain by Quaternary and Recent deposits, which are typically less than 10 m thick and consist of gravelly sands, weakly cemented, with local patches containing secondary gypsum.

A summary of the Tertiary geological strata of Qatar is presented in Table 2. The Simsima Limestone of the Upper Damman forms the surface of almost all of Qatar and comprises chalky limestone with varying thicknesses of dolomitic limestone. This deposit is generally surface-hardened over most of its outcrop, but may also contain irregular pockets of clay in the Doha area.

The Lower Damman deposits generally comprise chalky limestone with a shale layer (Midra Shale) present in the southern two-thirds of Qatar. A reduction in calcium carbonate and an increase in magnesium carbonate are apparent in the transition between the Lower Damman and the underlying Rus Formation.

The Rus Formation can be divided into two provinces at the centre of Qatar, a carbonate facies and a sulphate facies. In the latter (in which Doha is situated), the typical depositional cycle (about 5 m thick) is typically as follows:

The sulphate facies of the Rus Formation was deposited in a subsiding area of relatively rapid and turbid evaporitic sedimentation. Typically, the core recovery during drilling may reduce from about 80% in the Damman Formation to less than 50% in the gypsum-bearing Rus Formation. In the northern region of Qatar, the Rus Formation may be about 30 m thick, but increases to the order of 100 m thick towards the west and south-east.

The underlying Umm Er Radhuma Formation contains limestone and dolomite.

There is little or no published information on geotechnical profiles and properties for sites in Qatar. A typical geotechnical profile in Doha at the site of a high-rise building is shown in Fig. 8. Below the Simsima Limestone and the Midra Shale, the uniaxial compressive strength of the various strata is low to very low, even at depths in excess of 100 m.

Poulos [27] has described the design process for a tall building in Doha, Qatar. This high-rise tower is still under construction and will be in excess of 400 m tall, with 74 storeys and three basement levels. It is founded on a pile-supported raft, with piles extending 40–50 m below the base of the raft. A low-rise podium area is to be located adjacent to the tower.

A total of 23 boreholes were drilled at the site, to depths of up to 120 m. The in situ testing consisted of the following:

An extensive program of laboratory testing was undertaken, both conventional and specialized. The conventional tests included particle size distribution, unconfined compressive strength, point load strength, and carbonate content tests. The specialized tests included the following:

A program of pile load testing was also undertaken, consisting of four compression tests on piles of various length (3 with 1.5 m diameter and one with 0.9 m diameter) and two tension tests on piles about 26 m long, one 0.9 m in diameter and the other 0.75 m diameter. On the basis of the above information, a geotechnical model was progressively developed for the site. The site was quite uniform laterally, and so only a single model was necessary. Table 3 summarizes the final model adopted by the author for the foundation design verification process. The modulus and skin friction parameters were influenced heavily by the results of the pile load tests. It will be noted that the strata generally become weaker with increasing depth, and no reliable end bearing stratum was found within an acceptable depth. For the raft, an ultimate bearing pressure of 2.1 MPa was assessed.

Descriptions of the geology of Saudi Arabia are given by Evans [10], Oweis and Bowman [25] and Al-Refeai and Al-Ghamdy [6], among others. As illustrated in Fig. 2, Saudi Arabia is divided into two basic geological zones:

Many areas in the Kingdom of Saudi Arabia are associated with problematic soils and complex subsoil conditions. Typical problems include expansive soils, collapsing soils, sabkha deposits (salt-bearing soils), loose Aeolian deposits, and shifting sand dunes [6]. Sabkha deposits pose a particular problem in foundation design, as their salt content can adversely affect the durability of structures and foundations that are in contact with the soil. 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. In the central region, a thick stratum of highly weathered limestone with calcite crystals can contain solution cavities and solution collapse breccia. The city of Riyadh has particular problems with limestone cavities.

Oweis and Bowman [25] have presented typical geotechnical profiles for four zones:

Robertson et al. [29] and Pollastro [26] present a detailed account of the geology and tectonics of the Oman region. Oman is located on the south-eastern margin of the Arabian plate and is close to the boundaries of the Iranian, Indian, and African plates. Consequently, plate movements have resulted in complex structural, sedimentation, and burial histories. Oman is tectonically bounded on the south by the Gulf of Aden spreading zone, to the east by the Masirah Transform Fault and the Owen Fracture Zone Trough, and to the north by the complex Zagros–Makran convergent plate margin, compression along which produced the Oman Mountains [24].

Precambrian metamorphic and igneous basement rocks are known from a limited number of wells and from exposures of bedrock along the Huqf–Haushi Uplift on Oman’s eastern margin (see Fig. 16). The Ghaba Salt Basin, South Oman Salt Basin, and to a lesser extent, the Fahud Salt Basin, are part of a series of subsiding rift basins stretching from India and Pakistan across the Arabian Shield to central Iran that formed during the Infracambrian and lower Cambrian (about 600–540 Ma). These rift basins were formed by extension from strike-slip movement of the Najd transform fault system which ultimately dislocated the Arabian plate some 300 km to the east. A typical generalized cross section across the Ghaba and Fahud Salt Basins is shown in Fig. 17.

The sedimentary section in the hydrocarbon producing provinces of Oman is made up of rocks ranging from Proterozoic to Recent. Clastic rocks comprise most of the lower Paleozoic part of the section, whereas, the Permian through Tertiary part of the section are predominantly carbonate rocks and reflect climatic variations due to Omanís changing paleolatitude through geologic time.

The Huqf Supergroup contains several clastic and carbonate source rocks which form the basis of the primary petroleum systems for hydrocarbons produced throughout Oman. The Cambrian Ara Formation is a carbonate/evaporite sequence with thick salt deposits (up to 1000 m). The thick Ara evaporites were deposited in geographically-restricted basins during periods of low relative sea level where stratified, anoxic conditions periodically prevailed and organicrich sediments and salt were deposited. The lower Paleozoic section along the southern rim of the Arabian platform is comprised of mainly continental clastics, with some marine intercalations, which form important hydrocarbon reservoirs in the Ghaba and Fahud Salt Basins. A thick sequence of rift fill terrigenous and shallow-marine siliciclastics of the Haima Supergroup overlies the Ara Formation.

In the Ghaba Salt Basin, sediments of the Haima Supergroup fill and cover the margins of the basin reaching thicknesses up to 6 km along the central axis [9]. Pre-existing, highly variable topography caused major variations in sediment infill. Numerous unconformities are present throughout the Paleozoic in Oman. Two major and very broad uplift and erosional events in eastern Oman removed most of the Silurian and Lower Devonian sediments and the interval between mid-Devonian and Upper Carboniferous; these erosional events are recognized in deep wells from the main producing fields in the Ghaba and Fahud Salt Basins. Late Carboniferous time is marked in Oman by glaciation and subsequent deposition of glacial clastics of the Gharif Formation.

The Tertiary deposits comprise the Umm Er Radhuma, Rus and Damman formations, and these are underlain by the Aydim, Zalumah and Ashawq formations of late Eocene and Oligocene age.

The Quaternary deposits are heterogeneous in nature and of different origins. They comprise alluvial deposits, colluvial deposits, Aeolian deposits and travertine and littoral marine deposits.

There appears to be relatively little published information on the near-surface stratigraphy in Oman. Al-Rawas and Qarnaruddin [5] identified expansive soils at different sites in northern Oman, between 35 and 45 km west of Muscat. They found that smectite is the major clay mineral, but that the expansive soils were influenced by the composition of the parent rocks. The expansive soils and rocks are generally variable with changes in colour, structure and lithology. A typical shallow profile containing expansive clay is shown in Fig. 18 [5].

Aeolian and reworked calcareous sediments known as “desert fill” can be present in low-lying topographic depressions, and this desert fill occurs as a light greenish-brown poorly sorted sand comprising carbonate and ophiolitic material of the conglomerates.

For the expansive clays found in northern Oman, Al-Rawas and Qarnaruddin [5] reported the following plasticity characteristics from 12 samples:

Liquid limit: 47–82;

Plastic limit: 14–44;

Plasticity Index: 15–67;

Natural water content: 10–25%;

Free swell: 45–95% (from 4 samples).

No information on strength or compressibility characteristics were provided.

Tarawneh et al. [31] have presented the results of in situ testing at a site near the Arabian Sea in Muscat. CPT and pressuremeter testing were carried out to provide data for the prediction of shallow foundation settlements and comparisons with measured settlements from load tests. The site consisted of a profile of gravelly sand, clean sand and silty sand, which had been subjected to dynamic compaction to improve its engineering properties. The water table was between 0.75 and 1.2 m below ground level.

Figures 19 and 20 show the CPT test results on the treated ground for two locations, and significant variability can be observed between the two locations. The results of pressuremeter tests for pressuremeter modulus and limit pressure are shown in Figs. 21 and 22.

Loading tests were carried out on square steel plates 2.5 m × 2.5 m, and the load test results showed very different settlement behavior, with the test at Location 1 being much stiffer (approximately 8 times) than at Location 2. While the CPT tests indicated somewhat lower values at Location 2, neither these tests nor the pressuremeter tests showed such a large divergence in the soil stiffness. Backfigured average values of soil Young’s modulus were about 32 MPa for Location 1 and 4 MPa for Location 2. Unfortunately, there appears to be no other published information that might assist in understanding the reasons for the divergence in stiffness at the sites, and also, the relatively low values of Young’s modulus for the treated sands.