Dead Sea Water
as a
Soil Improvement Agent

 

Bassam Z. Mahasneh

Department of Civil Engineering, Mu’tah University, Jordan

 

ABSTRACT

The study reported in this paper is concerned with using water from Dead Sea as a soil stabilization agent. Three materials, a clay soil, a white fine aggregate, and the base course material have been studied. Each material has been mixed with both tap water and Dead Sea water separately and the resulting soil properties have been measured for comparison. The plasticity index has decreased from 13 using tap water to 6 using Dead Sea water for the clay soil, from 10 using tap water to 3 using Dead Sea water for white fine aggregate, and from 6 using tap water to 1.0 using Dead Sea water for base course. The maximum dry unit weight and the optimum moisture content obtained from the standard and the modified Proctor tests for clay soil was found to decrease by the addition of Dead Sea water, to the extent that the maximum dry unit weight decreased from 20.8 kN/m3 to 17.3 kN/m3 and the optimum moisture content decreased from 22% to 11%. The maximum dry unit weight for white fine aggregate increased from 19.1 kN/m3 to 22.5 kN/m3 and the optimum moisture content decreased from 12% to 7%. For the base course, the maximum dry unit weight increased from 21 kN/m3 to 22.5 kN/m3 and the optimum moisture content decreased from 10% to 7%. The unconfined compressive strength for the three materials using Dead Sea water was noticed and the important improvement was clear in the base course and the white fine aggregate where the unconfined compressive strength increased from 93 kN/m2 to 130 kN/m2 and 47 kN/m2 to 63 kN/m2, respectively, while for the clay soil, the unconfined compressive strength increased from 35 kN/m2 to 57 kN/m2 in comparison with that for tap water.

Keywords: Dead Sea, Soil Improvement, Base course, Clay soil, White fine aggregate, Unconfined Compressive Strength.

 

INTRODUCTION

Soil stabilization has been used in nearly every type of soil engineering problem; its most common application is in the strengthening of soil components of highway and airfield pavements. A completely consistent classification of soil stabilization techniques is not available. Chen (1981). Classifications are based on the method of treatment being used e.g. dewatering, compaction, thermal or electrical treatment, or the use of additives as asphalt or cement.

A difficult problem in civil engineering work exists when the sub-grade is found to be clay. Soils having high clay content have a tendency to swell when their moisture contents is allowed to increase, Chen (1981). This increase in moisture content may come from rains, floods, leaking sewer lines, or from the reduction of surface evaporation when an area is covered by a building or pavement. Frequently, these clayey soils cause the cracking and breaking up of pavements, railways, highway embankments, roadways, foundations and channel or reservoir linings, Erdal Cokca (1999).

Several studies have been made on soil stabilization using different stabilizing agents. Pyne (1955) showed the effectiveness of addition of calcium chloride to soil treatment. Lopez and Castano (2001) used Calcium oxide as a stabilization technique on clay soils in order to inhibit its expansion-contraction properties. Ghafoori and Cai (1997), and Ghafoori (2000), used coal combustion by-products in roller compacted concrete, roadway and parking lots. Muntohar and Gendut Hantoro (2000), and Muntohar (1999), investigated the effect of fly ash and pozzolanic material on soil improvement. Moreover, recent research showed that pozzolanic material coupled with rice husk ash was a potential material for soil improvement, Muntohar (1999).

Form the previously mentioned studies, it is expected that metal oxides, hydroxides, or halides additives can enhance soil stabilization. However, none of these studies investigates the use of a mixture of these compounds as a soil stabilization agent.

The Dead Sea is one of the most prominent geomorphologic features in Jordan and its water contains 330gm salt per liter of water. In this paper, The idea of using Dead Sea water as soil properties improvement agent comes as a result of understanding what the others did regard using calcium chloride, metal oxides, etc, and the idea comes to investigate the ability of using the Dead Sea water because it contains many kinds of salts (Sodium chloride, Potassium, etc.), as soil improvement agent comes to reveal the benefit of using Dead Sea water in soil stabilization, pavement design, and foundation construction.

 

METHODOLOGY AND EXPERIMENTS

About Dead Sea

The Dead Sea is about 400 m below sea level and is the lowest area in the world. It consists of two sub-areas; Northern and Southern sub-areas. The Lisan Peninsula separates them. Dead Sea Water is characterized by its high concentration of salts (as high as 330 gm/liter), HRH prince Faisal Dead Sea Research Center.

The Dead Sea area climate is dry and hot. The temperature in Summer may reach as high as 40°C or more, and in Winter may decrease about 10°C, and the average annual temperature is about 23.5°C. Furthermore, the average annual rainfall is about 100 mm, and the maximum relative humidity is about 55% in Winter and 27% in Summer. The economical importance of the Dead Sea evolves from its location and water chemical composition and can be summarized as:

Dissolved minerals: Salt Concentration, as mentioned above, reaches up to 330 gm/liter, and the available salts are: potassium chloride, sodium chloride, magnesium chloride, magnesium bromide, and calcium chloride. The ionic concentration of Dead Sea water for the three sub-layers forming the water body (upper, transitional, and lower) is summarized in (Table 1). Other trace elements such as iodine, uranium, nickel, lead, iron, and lithium also exist in the Dead Sea water.

 

Table 1. Ionic Concentration of Dead Sea water (gm/liter).

Layer Depth (m) Ca++ Mg++ Na+ K+ Cl- Br- SO4- - HCO3 total
Upper 0-40 16.38 36.15 38.51 6.5 196.94 4.6 0.58 0.23 299.89
Transitional 40-100 16.6 40.57 38.47 7.15 210.67 5.15 0.49 0.22 319.22
Lower 100-400 17.18 42.43 39.70 7.59 219.25 5.27 0.42 0.22 332.06
Average 330 16.86 40.65 39.15 7.26 212.40 5.12 0.47 0.22 322.13

 

Experimental Study

Three types of soils were investigated in this study; (clayey soil, white fine aggregate, and base course). Each weights of 10 kg from each type where brought from a construction site in the southern part of Jordan, while the salty water was brought from the Dead Sea of Jordan. The three samples were dried at 100 °C and sieved to different particle sizes to fulfill the standard requirements (ASTM D421 and ASTM D422). Then, the samples were saved in a dry place for further procedures while the salty water was saved in closed containers at room temperature. Figure 1 (a, b, and c) represent the grain size distribution curves for the studied three materials; clay soil, white fine aggregate, and base course respectively, showing the percentage of clay, silt, sand, and gravel in each type of material.

 



(a) Clay soil



(b) White fine aggregate



(c) Base course

Figure 1. The grain size distribution curves for clay soil,
white fine aggregate, and base course.

Compaction test

Standard Proctor compaction test

Samples of 3kg of soil that passed No. 4 Sieve were mixed with both tap and salty water separately, and compacted into 944 cm3 mold. The moisture content versus the dry unit weight curves defines the maximum dry unit weight and the optimum moisture content, (ASTM D698-78) of the compacted soils (see Figures, 2, 3, and 4).

 



Figure 2. Dry unit weight versus moisture content
using tap water and Dead Sea water - For clay soil.

Modified Proctor compaction test

Samples of 3kg of soil that passed (3/8 inch sieve) retained on (No. 4 Sieve) were mixed with both tap and salty water separately, and compacted into 944cm3 mold. The moisture content versus the dry unit weight curves defines the maximum dry unit weight and the optimum moisture content, (ASTM and AASHTO T 180-90) of the compacted soils, (see Figures, 2, 3, and 4).

 



Figure 3. Unit weight versus moisture content
using tap water and Dead Sea water for fine aggregate

 



Figure 4. Unit weight versus moisture content
using tap water and Dead Sea water for the base course

Liquid and Plastic Limit (Atterberg’s Limits).

Sample of about 100 g of moist soil was mixed with both tap and salty water separately, to form a uniform paste, (ASTM D 4318). This was made to see the effect of using Dead Sea water on the liquid and plastic limit in compare with that for the tap water. The results shows a clear change in the liquid and plastic limit after using Dead Sea water in mixing the soils, and all materials shows tendency to stiffen and a drop in the liquid and plastic limit while using the Dead Sea water in mixing the soils (see Tables 3, 4, and 5).

 

Table 2. The specific gravity, porosity and moisture content for the tested materials.

Soil type Specific gravity Optimum Moisture content % Porosity %
Clay soil 2.78 13% - 27% 35 – 60
Fine aggregate 2.65 12% - 14% 20 – 35
Base course 2.52 10% - 14% 25 - 50

 

Table 3. Atterberg’s limits for clay soil with tap water and Dead Sea water.

Water type Liquid limit Plastic limit Plasticity index
tap water 38 25 13
Dead Sea water 28 23 6

 

Table 4. Atterberg’s limits for fine aggregate with tap water and Dead Sea water.

Water type Liquid limit Plastic limit Plasticity index
tap water 24 14 10
Dead Sea water 19 15 3

 

Table 5. Atterberg’s limits for base course with tap water and Dead Sea water.

Water type Liquid limit Plastic limit Plasticity index
tap water 23 17 6
Dead Sea water 18 17 1

 

Unconfined Compression Test

Saturated soil samples with the same density and moisture content have been taken (trimmed) from the compacted soil samples; molded in cylindrical shape (of dimensions 4.5 inch height by 2 inch diameter) and placed in the unconfined compression machine where a constant rate of strain is applied till failure (ASTM D 2166-85) (see Figures 5, 6, and 7).

 

 



Figure 5. Stress strain relation for clay soil with tap water and Dead Sea water,
Unconfined compression test.

 



Figure 6. Stress strain relation for White fine aggregate with tap water and Dead Sea Water,
Unconfined compression test.

 

 



Figure 7. Stress-strain relation for base course with tap water and Dead Sea water,
Unconfined undrained test.

RESULTS AND DISCUSSION

The soil samples were tested to examine their physical properties. Table 2 illustrates the specific gravity, porosity and the optimum moisture content for clay, fine aggregate and base course. The highest specific gravity and porosity was for clay soil of 2.78 and 35%-45% respectively. The lowest specific gravity was for the base course with value 2.52. The moisture content was ranged from 13% to 27% for clay soil, 12% to 14% for fine aggregate, and 10% to 14% for base course. The porosity was ranged from 35 5to 45% for clay soil, 20% to 35% for fine aggregate, and 25% to 50% for base course.

The Atterberg’s limits, maximum dry unit weight, optimum moisture content, and the unconfined compressive strength were obtained for the three types of soils. Tables 3, 4, and 5 show the Atterberg’s limits using tap and Dead Sea water for clay, fine aggregate and base course, respectively. When mixing with tap water, the results show that the highest liquid limit was for clay, while the lowest liquid limit was for the base course, the highest plastic limit was for clay soil and the lowest was for the base course. The calculated Plasticity index was 13.4% for clay soil. When using salty water this value decreases to 5.5% for clay soil and 1.0% for base course. This decrease may be attributed to substitution of water molecules by salts that decrease the double layer system, which decreases the water content in the studied samples to become more stiff material, (Lopez and Castano 2001).

Figure 1 (a, b, and c) present the grain size distribution for the three materials; clay soil, white fine aggregate, and the base course, respectively. The sieve and hydrometer analyses showed that, the grain size distribution for the clay soil was 39% clay, 39% silt, 22% sand and 0.14% gravel which represent a clay loam soil. The grain size distribution for the fine aggregate was 13% clay, 21% silt, 48% sand, and 18% gravel which represent a sandy clay loam. The grain size distribution for the base course was 2% silt, 15%sand, and 83% gravel that represent a granular material.

Figures 2, 3, and 4 represent the compaction test for the studied soil samples when using both tap and salty water. In the case of tap water, the maximum dry unit weight for clay and base course were in the range of 21 and 22.5 kN/m3 respectively. For the fine aggregate the maximum dry unit weight was 19.1 kN/m3. When comparing these results with those obtained using salty water, the maximum dry unit weight decreased from 20.8 kN/m3 to 17.3 kN/m3. However, the maximum dry unit weight increases from 19.1 kN/m3 to 20.4 kN/m3 for fine aggregate soil, and little increases from 22.8 kN/m3 to 23.1 kN/m3 for base course. The decrease in the maximum dry density could be explained by the existence of repulsive force between the salts molecules and the clay intermolecular structure causing an increase in the intermolecular distances and an increase in the void ratio, (Emil and William (1990) and Emil (1962)). In addition, some of the salt ions have attracted some of the clay particles, which lead to forming coagulation phenomena that affects the fragility of the clay compaction test, (Lopez et al 1999). On the other hand, the observed increase in the dry unit weight for the base course soil can be interpreted as a result of a chemical reaction between the salt molecules and soil particles, which partially contain lime. A chemical reaction takes place between sodium, potassium and magnesium chlorides from salt with calcium oxides and hydroxide from soil to form calcium chloride. This calcium chloride has an effect of enhancing the hardening of the soil and as a result increasing the dry unit weight, (Lopez et al 2001, Emil and William 1990 and Emil 1962). Figures 5 and 6 and 7 show the relation between the unconfined shear strength and strain for the three materials, clay, fine aggregate and base course soils using tap and salty water, respectively. It is evident from Figure 5 that clay soil has a higher unconfined compressive strength using Dead Sea water than that of using tap water. The addition of salty water increased the unconfined compressive strength of the clay soil. Figure 6. Present the effect of Dead Sea water on the white fine aggregate, and it is clear that the Dead Sea water enhances the unconfined compressive strength. In all cases, clay soil has multilayers of gibbsite and silica sheets with hydrogen bonding linking these sheets, (I.S. Dunn et al, 1980). Upon axial compression, these sheets become closer to each other and the tendency of these sheets to resist compression is high, which leads to higher shear strength. On the other hand, the structure of base course has a compacted calcium oxide molecule, which fail more rapidly than clay. Figure 7. Shows that when salty water is added to the base course, the shear strength is enhanced. This is due to the change of calcium oxides and hydroxide into calcium chloride, which has more resistance to shear, (Lopez et al (2001)).

CONCLUSION

Three different types of materials (clay, fine aggregate, and base course) were tested for their liquid and plastic limits, dry unit weight and shear strength in the presence of tap and salty water from Dead Sea. The addition of salty water to all the soil samples has enhanced the liquid and plastic limits for all soils, dry unit weight for both fine aggregate and base course, and the resistance to stresses for base course, white fine aggregate, and clay soil respectively. This could help improving soil strength and the other physical properties.

ACKNOWLEDGEMENTS

 

The author would like to acknowledge Dr. Mohammed Al-zoubi, Dr. Reyad Shawabkeh, Dr. Onf Ziadat, and Dr. Abdul Aziz Khlaifat for their reviewing this manuscript, and for the technicians of soil mechanics lab. Eng. Wafa Sihaimat, Hussien Al-saraireh and Ahmad Alhabashneh and my students (Ruba, Lina and Alia) for their help in the experimental part.

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