Missouri University of Science and Technology Scholars' Mine International Conference on Case Histories in (2008) - Sixth International Conference on Case Geotechnical Engineering Histories in Geotechnical Engineering 14 Aug 2008, 2:15pm - 4:00pm Testing and Stabilization of Saline Sabkha Soils: A Review Omar Saeed Baghabra Al-Amoudi King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia Follow this and additional works at: https://scholarsmine.mst.edu/icchge Part of the Geotechnical Engineering Commons Recommended Citation Al-Amoudi, Omar Saeed Baghabra, "Testing and Stabilization of Saline Sabkha Soils: A Review" (2008). International Conference on Case Histories in Geotechnical Engineering. 45. https://scholarsmine.mst.edu/icchge/6icchge/session07/45 This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License. This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in International Conference on Case Histories in Geotechnical Engineering by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. TESTING AND STABILIZATION OF SALINE SABKHA SOILS: A REVIEW Omar Saeed Baghabra Al-Amoudi Assistant Dean, Continuing Education programs Professor, Department of Civil Engineering King Fahd University of Petroleum and Minerals Dhahran 31261, Saudi Arabia (Fax: + 966-3-860-4770; e-mail: [email protected]) ABSTRACT Sabkha is one of the many types of evaporate regimes that exist around the globe. In addition to being distributed along the coasts, sabkha soils cover a number of continental depressions, both of which usually form in hot, arid climates and are associated with shallow groundwater tables. Sabkhas are well distributed locally and over the whole world. Sabkhas are characterized as being salt- full and water-sensitive soils. The presence of soluble salts makes the use of distilled water in testing these soils, as recommended by ASTM, etc., inappropriate. Further, sabkha soils possess low strength at their natural condition. Therefore, it would be imperative to stabilize the sabkha soil at the actual moisture content in the field. In this paper, the author reviews the modifications on some ASTM standard test methods in order to properly assess the geotechnical properties of sabkha soils. Moreover, two stabilizing programs of sabkha soil using lime and cement at various dosages are presented. The first program was concerned with stabilizing the sabkha at the optimum moisture content, while the second study was devoted to stabilize the sabkha at high (i.e., natural) moisture contents. The results of these studies indicate that sabkha (as a typical evaporitic soil) can be practically used by the construction industry in many field applications. INTRODUCTION by a sand dune or a hill. Such a confinement increases the closure of sabkha terrains thereby augmenting their salinity. The term “SABKHA” is originally an Arabic expression that Table 1 depicts the chemical analysis of Ras Al-Ghar sabkha has long been in use to denote indefinitely salt-encrusted flats which is part of Ar-Riyyas sabkha, eastern Saudi Arabia, and underlain by sand, silt and/or clay. Scientifically speaking, compares it with the analysis of sea water from a nearby there is no unanimous consensus on a “precise” definition of vicinity (Al-Amoudi, 1999). The data therein indicates that “sabkha”, because these soils have been exposed to multi- the sabkha brine is about three to six times more concentrated disciplinary research by geologists, sedimentologists, than sea water from the same vicinity. hydrologists, environmentalists, chemists, civil engineers, etc. (Al-Amoudi, 1999). The definition of sabkha is further Along the Arabian Gulf coasts, sabkha soils extend complicated by the considerable ramification of names for intermittently with varying inland extensions. The various types of high water-table situations in the Middle East sedimentary features, mineralogical composition and the (Fooks et al., 1986). The best “descriptive” definition for the chemistry of the interstitial brines in such coastal sabkhas vary sabkha system has been reported by Al-Amoudi and Asi greatly in both the horizontal and vertical directions (Al- (1991) as the large (in size or dimension), extremely flat Amoudi, et al., 1992a). Horizontal variations are related to (horizontal terrains with small, imperceptible slopes), saline, proximity from the shoreline, while vertical variations evaporative areas (due to the hot and dry environment), represent successive stages in the development of the sabkha situated either along the coasts (i.e., called coastal sabkhas) or cycle (Al-Amoudi, 1999). Surprisingly, the local people are further inland (i.e., called continental or inland sabkhas) of still unaware of the whole spectrum of its hostile nature, and many arid, semi-tropical countries. Ideally, a typical coastal even engineers and researchers are still calling the sabkha a sabkha terrain will be bordered on the seaward direction by a “special soil” (Stipho, 1989), despite the prevalence of sabkha barrier (beach dune or a salt dome) and on the inland direction soils in the Arabian Peninsula and in the world (Al-Amoudi, et al., 1992b), as shown in Figs. 1 and 2, respectively. grain-size distribution, for example, as recommended by Geotechnically, sabkha soils are considered to be highly international standards (i.e., ASTM, BS, DIN, etc.), variable in terms of grain size and shape, texture, degree of inappropriate because DW tends to dissolve the readily cementation, diagenetic minerals, layering, compaction, etc., soluble salts that are part of the sabkha soil (Al-Amoudi and due to the presence of alternating uncemented and cemented Abduljauwad, 1994b). layers as well as lumps of quartz and/or carbonate sand. However, the principal cementing materials in sabkhas are o o o o aragonite, calcite, gypsum, anhydrite with halite (NaCl) being 40 45 50 55 N always present. IRAN KUWAIT Table 1: Chemical analysis of the sabkha brine and seawater 30o 30o in mg/mL (i.e., parts per thousand) Wadi As-Sirhan Ions Ras Al-Ghar KFUPM Beach o QATAR 25o Brine Seawater 25 Yanbu Riyadh U.A.E. Na+ 78.8 20.7 • Jeddah Mg++ 10.32 2.30 + Al-Lith o K 3.06 0.73 20o R 20 ++ E Ca 1.45 0.76 D OMAN Jizan ++ S Fe Trace Trace E Sr++ 0.029 0.013 A o o − 15 YEMEN Arabian 15 Cl 157.2 36.9 Br− 0.49 0.121 Sea − − (SO4) 5.45 5.12 − 500km (HCO3) 0.087 0.128 o o o o PH 6.9 8.3 40 45 50 55 Conductivity* 208,000 46,200 Fig. 1. Distribution of sabkhas in the Arabian Peninsula *Microsiemens. In addition, naturally existing sabkha soils often possess low The variability of its geotechnical properties and the presence unconfined compression strength of only 20 kPa ( ≅ 3 psi ) of highly concentrated brines make the sabkha a typical “salt- below the salt-encrusted layer and an SPT value of 0 to 10 full” and “water-sensitive” environment, and pose many (Al-Amoudi and Abduljauwad, 1995b). Furthermore, the geotechnical problems to the construction industry in general collapse potential of these loose, low density and unstable and to the geotechnical engineers in particular. Despite these soils presents an unacceptable risk in normal practice and calls hostile attributes, very little has so far, been published on the for the improvement of their mechanical properties before any geotechnical properties of sabkha soils except for their construction takes place (Al-Amoudi, 1994). utilization in highway and sewerage projects, housing construction or for typical subsurface boring logs (Al-Amoudi, This paper presents a critical review of the standard and non- 1999). Recently, several “pilot” studies have been reported by standard “modified” tests that are often used to test sabkha local experts on classical testing and stabilization of sabkha soils. Further, the paper summarizes the research conducted at soils (Owais and Bowman, 1981; Hossain and Sabtan, 1994; King Fahd University of Petroleum and Minerals (KFUPM) Abu Talem and Egeli, 1981; Akili and Torrance, 1981; on chemical stabilization of this “unusual” soil with the Ghazali et al., 1985; Al-Shamrani and Dowian, 1997; Sabtan purpose of using the sabkha as a construction material. et al., 1995; Shehata et al., 1990; Al-Shamrani, 1998) without due consideration to the sabkha as being a “unique” soil. Among the major problems that the geotechnical engineer presently faces is the “appropriate” determination of some of the geotechnical properties of sabkha, which has not as yet been well addressed. For elucidation, the presence of soluble salts makes the use of distilled water (DW) in testing for 180o 135o 90o 45o 0o 45o 90o 135o 180o 90o 90o 45o 45o ATLANTIC PACIFIC OCEAN OCEAN 0o 0o INDIAN OCEAN 45o 45o Active Locations Potential Locations 180o 135o 90o 45o 0o 45o 90o 135o 180o Fig. 2. World map showing active and potential locations of sabkha EXPERIMENTAL PROGRAM water (DW), (2) non-aqueous methylene chloride (MC), and (3) sabkha brine (SB) obtained from the same vicinity where Sabkha Soil the soil samples were collected. Materials passing the finest sieve (No. 200) were collected and prepared for hydrometer Disturbed and undisturbed surficial sabkha soil samples were tests. retrieved from Ras Al-Ghar site, which is located about 15 km southeast of Al-Jubail Industrial City, eastern Saudi Arabia, Though the Ras Al-Ghar sabkha doesn’t possess any plasticity where the largest petrochemical industrial plants are situated. and the soil was classified as non-plastic (Al-Amoudi et al., o Disturbed samples were air-dried in the laboratory (22 ± 3 C) 1992a), the plastic limit (wp), liquid limit (wL) and plasticity and crushed gently using plastic hammers to break apart index (PI) should be determined for plastic sabkha soils in cemented particles to pass an ASTM No.