Sabkha Soil CE 498 Abdulwahab Mubarki Report 1

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King Saud University

College Of Engineering

Civil Engineering Department

Improvement of Jizan Sabkha Soil by Using Lime

By

Abdulwahab Mohammed Mubarki

Advisor: Prof. Hosain Alawaji

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CONTENT

LIST OF TABLES

LIST OF TABLES

ABSTRACT

CHAPTER 1 : INTRODUCTION

1. l Introduction

1.2 Sabkha Soil and its Distribution

1.3 Objective of Study

CHAPTER 2 : LITERATURE REVIEW

2.1 Introduction

2.2 Potential Engineering Problems of Sabkha

2.2.1 Problems due to periodic changes in moisture content

2.2.2 Problems due to excessive differential settlement

2.2.3 Problems due to the proximity of groundwater table

2.2.4 Problems due to presence of highly corrosive salts and brines

CHAPTER 3 : EXPERIMENTAL WORK

3.1 Introduction

3.2 Tested Materials

3.2.l Soils

3.2.2 Hydrated lime

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3.3 Properties of Jizan Sabkha Soil

3.3.1 Sieve Analysis

3.3.2 Specific Gravity

3.3.3 Compaction Tests

3.4 Consolidation Test

CHAPTER 4 : CONCLUION

REFERENCES

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LIST OF TBLES

Tables No.

1.1 Distribution of sabkhas in the Arabian Peninsula

3.1 Summary of physical properties for Jizan sabkha soil

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LIST OF FIGURES

Figure No.

1.1 Distribution of sabkhas in the Arabian Peninsula

2.1 Profile characteristic in sabkha sediment

2.2 Consistency Limits of sabkha sediment from Jizan

2.3 Typical plate load test on sabkha in Jizan

3.1 Grain size distribution curve for Jizan Sabkha soil

3.2 Compaction test results for Jizan Sabkha soil

3.3 Effect of lime on the compressibility characteristics

3.4 e - log p curve for Jizan untreated soil

3.5 e - log p curve for Jizan soil (treated with 3% lime)




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ABSTRACT

This project is concern with Jizan sabkha soil which brought from Jizan area. The

study is directed to investigate the level of improvement achieved by lime addition on

compressibility characteristics and bearing capacity.

First, an overview of physical properties of tested soil are presented from these tests

this soil is classified as SM (Silty Sand), according to USCS and A-2-4, according to

AASHTO. Secondly a laboratory testing program was designed to investigate the effect of

lime addition on the compressibility characteristics and bearing capacity.

The results show decreas in settlement with increasing lime content.

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CHAPTER 1

INTRODUCTION

1.1 Introduction

Sabkha is soil that have high concentrations of salts. These soils originate due to

capillary suction and intense evaporation in the coastal and inland flat plains of Saudi

Arabia. Sometimes the salinity of the pore fluid reaches as high or higher than sea

water. The high salt content has great impact on the strength properties of soils and

also on structures in contact with the soil. Salt-bearing soils are extensively found on

the eastern coastal plains and at locations on the western coastal plains of the

Kingdom.

Sabkha deposits are usually very soft, problematic, susceptible to salt leaching,

and not suitable for foundation support . Sabkha with the following undesirable

characteristics:

a. Very soft, not good for foundation support.

b. Loses strength upon wetting.

c. Aggression toward concrete and steel.

d. Salt leaching affect soil properties.

e. Subject to volume change.

need to be stabilized.

Many procedures have been studied to improve the sabkha soils. The most

widely applied methods involve the use cementing agents, which rely for their

effectiveness on the formation of cementing bonds between the soil particles. The

two most common agents are Portland cement and hydrated lime . In the application

of each of these additives, the soil components and the stabilizing agent are both

involved in the chemical changes responsible for the soil alternation.

In this project sabkha soil from Jizan will be treated with hydrated lime and

the oedometer tests and the bearing capacity test will be studied.

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1.2 Sabkha Soil and its Distribution

Sabkhas are characterized as being large, flat, salt-encrusted, evaporative terrains

situated either along the coasts (coastal sabkhas) or farther inland (continental or

inland sabkhas) .

A large number of sabkhas, both coastal and continental, occur in Saudi Arabia,

especially in the well-populated cities along the Arabian Gulf and Red Sea coasts[ 4].

The prevalence of sabkhas along the southern and southwestern shores of the

Arabian Gulf, particularly in the United Arab Emirates and Qatar, is well-

documented in the literature, Figure 1.1 shows the distribution of sabkha soils in the

Arabian Peninsula .

Fig. 1.1 Distribution of sabkhas in the Arabian Peninsula [4].

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1.3 Objective of Study

Is to improve the physical and compressibility of sabkha soil by using lime in

different percentages.

The Oedometer tests and Bearing capacity tests will be studied.

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Salt-bearing plains in Saudi Arabia are generally categorized by layered

sediments of fine silty clay covered with few meters of fine dune sand [1]. The

geotechnical properties of sabkha sediments in Jizan region are summarized in

(Figure 2.1) Plasticity characteristics of sabkhas from Jizan region are shown in

(Figure 2.2) which demonstrate the range of variation in consistency limits which

reflect the heterogeneity of the sabkha profiles.

This heterogeneity is the distinctive feature of sabkhas that gives rise to

uncertainties in evaluating their engineering behaviour [3]. Typical load-

displacement relations obtained from plate load tests in Jizan are shown in (Figure

2.3). It can be seen that these sabkha deposits are also affected by soaking, with a

significant increase in settlement when tested in an inundated condition.

Fig. 2.1 Profile characteristic in sabkha sediment [3]

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Fig. 2.2 Consistency Limits of sabkha sediment from Jizan [3]

Fig. 2.3 Typical plate load test on sabkha in Jizan [3]

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2.2 Potential Engineering Problems of Sabkha

Sabkha soils present a series of engineering problems that result from their

variable nature, poor mechanical problems, high evaporate and organic contents. The

general potential problems associated with building on sabkha deposits can be

summarized as follows: [1]

(1) The susceptibility of sabkhas soil to flooding due to low elevation and the

difficulty of excavation below the water table and associated dewatering problems.

(2) The extreme variation in cementation of sandy sabkhas attributed to unequal

precipitation of soluble and relatively insoluble salts within the sabkhas sediments.

Soluble salts in the upper part of the sabkha sediments can be washed away by floods

tides or merely due to absorption of water from atmosphere, so that sabkhas strength

will be decreased.

(3) Variation of compressibility characteristics of sabkha sediments, particularly in

the uncemented layers could lead to excessive. differential settlement. Sabkha

deposits could vary from a very loose state to a dense state. The extreme variation in

layer thickness contributes to the problems of settlement. In addition, sabkha soils

invariably contain an appreciable amount of organic matters. They are therefore

characterized by being highly compressible with a significant part of the settlement

taking place as secondary compression. Thus, serious foundation instability problems

are to be expected if the sabkha plains are used for urban development.

(4) The potential adverse reactions and chemical changes that may influence

sediment properties and structures embedded in sabkhas. These chemical potentials

could be explained by the potential instability of gypsum and the associated volume

change resulting from alternate hydration and dehydration, under hot and humid

conditions. The high concentrations of chlorides and sulphates in sabkha sediments

and ground water is very corrosive to both concrete and steel. Measure must be taken

to protect the construction materials from the highly corrosive effect of the salts

present in sabkhas.

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(5) The accessibility of large sabkha sites for parts of the year become impassable

upon saturation. Thus, provision of temporary roads adds to the cost of developments

in sabkha flats.

(6) The distinct feature of sabkha sediments is their high variable composition

laterally and vertically. Variations have been noted in terms of layering, grain size,

segmentation, organic matter content and digenetic minerals. Lateral variation

appears to depend on proximity with respect to the shoreline, while vertical variation

arises from the development sequence of sabkha sediments, prevailing depositional

environment and subsequent diagnosis [1]. Analysis of the sabkha behavior is

complicated by the complex and heterogeneous nature of sabkha profile with respect

to soil composition and stratification.

(7) Evaporative pumping processes in a desert environment are responsible for the

accumulation of evaporate minerals, particularly at shallow depth in the Aeolian

mantle. The collapse potential of the Aeolian mantle is attributed to the week

cementation of the soil grains by the evaporates, and to be considered as a major

geotechnical problem in new construction sites.

(8) The inability to assess by conventional probes the degree of cementation of

sabkha sands particularly in the lightly to moderately cemented range.

(9) Potential carbonate leaching in high carbonate content soils and potential volume

changes that may occur in gypsum dominated layers.

In general the geotechnical problems associated with sabkha soils could be

grouped into four main categories[4]:

2.2.1 Problems due to periodic changes in moisture content

The periodic changes in the high moisture content of sabkhas, particularly in

the capillary zones, will certainly lead to large changes in density, consistency, and

strength, as well as to significant effects on the volume change characteristics of the

soil. Such changes can result in periodic swelling and shrinkage in the soil that can

cause serious damage to foundations as well as to the structures above them,

especially to lightweight structures. In these cases, particularly if the sabkha contains

large proportions of fine-grained particles, swelling pressures may lead to excessive

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foundation movements which can cause damage in the form of wide cracks which

tend to increase in size from the foundation right up to the full height of the building.

2.2.2 Problems due to excessive differential settlement

Excessive differential settlement can take place in structures built on top of a

sabkha soil by virtue of the in homogeneity of its profile, the looseness of certain

layers within the profile and the highly variable compressibility of its various

components. The physical composition of sabkhas can vary in classification from

sand to clay within the same site and layers in the sabkha soil, with their relatively

high void ratios and intercalating clay and/or salt lenses or pockets (frequently of

high compressibility), can cause severe differential settlements, thereby leading to

serious cracks and tilting in constructions on such soils.

2.2.3 Problems due to the proximity of groundwater table

The groundwater table usually lies within a short distance from the sabkha

surface, and fluctuations in its level, although infrequent in the short-term, is thought

to have been rising during the last 25 years in many areas in eastern Saudi Arabia as

well as in the other Arabian Gulf states. The rise in groundwater level in the older

suburbs of Kuwait city, has been estimated to vary from one to two meters in the past

thirty years Similar rates have also been estimated in the case of sabkha terrains in

Jubail. For both locations, the rise in groundwater has principally been attributed to

the overdose in water consumption for irrigation and domestic needs. These rises in

groundwater levels will certainly have serious geotechnical consequences on

foundations and other substructures built on or in sabkha deposits. Al-Sanad and

Shaqour [8] have recently reported many geotechnical impacts associated with rising

subsurface water tables; these impacts are summarized as follows:

(1) Flooding of improperly water proofed basements, which will cause significant

disturbances, both functional and, in the long-term, structural;

(2) Development of uplift pressure, which must be resisted by the weight of the

structure;

(3) Increased cost of technical and constructional requirements needed for

dewatering the construction site and for water-proofing;

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(4) Reduction in effective stresses as a consequence of increased pore water pressure,

which results in the reduction in shear strength of the sabkha soils;

(5) The soil bearing capacity (qult) depends on the shear strength parameters (φ' and

c'), the width of foundation (B), effective unit weight of the soil (γ') the depth of

embedment (Df) and the position of groundwater level relative to the base of the

foundation. Thus, qult will accordingly reduce following a rise in the groundwater

table;

(6) Increase in lateral pressure on basement walls owing to increased hydrostatic

pressures; and

(7) Settlement of buildings becomes imminent due to the wetting of sabkha or due to

the compressibility of dewatered, loose, sandy soils.

2.2.4 Problems due to presence of highly corrosive salts and brines

observed in Jubail, eastern Saudi Arabia, whereby recent fills of good quality

were almost totally contaminated with various salts. The high concentrations of

chloride and sulfate salts in sabkha brine are known to be highly corrosive to both

concrete and steel reinforcement. Moreover, the conjoint prevalence of these salts

poses several unresolved questions regarding their concomitant, and sometimes

cumulative, interaction with reinforced concrete foundations. The problem is

significantly intensified by the co-existence of intermittent, but regularly occurring,

moisture with this high salt content that is liable to produce the worst conditions and

the most severe deterioration. Further, the crystallization of these salts in the concrete

pores often leads to its slow disintegration due to pressures caused by the

crystallization power of salts. This form of crystallization-induced disintegration in

the concrete foundation usually occurs above the water table, where crystallization is

enhanced by evaporation. The various forms of brine attack present severe conditions

for ordinary "Portland cement" and warrants strict precautionary measures[2].

These problems are in addition to the susceptibility of sabkha terrains to

flooding because of the low elevation of the sabkha surface, and to the difficulties of

excavation below the water table. Furthermore, sabkha flats can not be reclaimed for

agricultural or other community projects.

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CHAPTER 3

EXPERIMENTAL WORK

3.1 Introduction

In this chapter the physical properties of tested soil are first presented. These

tests include: sieve analysis, specific gravity and standard compaction test . Secondly

the effect of lime addition on the compressibility characteristics of tested soils.

3.2 Tested Materials

3.2.1 Soils

The soil sampls were obtained from a site in Jizan city.

3.2.2 Hydrated lime

Hydrated lime which is available in the local market was used in this study.

3.3 Properties of Jizan Sabkha Soil

To determine the soil properties, routine tests were conducted. These tests

include:

3.3.1 Sieve Analysis

Sieve analysis tests were performed using US Bureau Standard sieve (USCS)

for the determination of the grain size distribution. Figure 3.1 shows the grain size

distribution curve for Jizan sabkha soil.

3.3.2 Specific Gravity

This test deals with the determination of the specific gravity, Gs of soil solid

particles with diameters smaller than the opening of the NO.4 sieve (4.75 mm) by

means of a pyconmeter. The Gs is one of the basic characteristics of the soil. It is

very important in calculation of test data in other tests. The Gs test was performed

according to ASTM D854- 58. Table 3.1 shows the properties of Jizan sabkha

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soil.

Fig. 3.1 Grain size distribution curve for Jizan Sabkha soil

Soil Properties Results

Liquid Limit , LL , %

Plastic Limit , PL , %

Plasticity Index , PI , % Non-plastic Specific Gravity , Gs 2.66

Gravel , % 0 Sand , % 57.1 Silt , % 26.9 Clay , % 16

% Passing # 200 42.9 Soil classification : SM

Unified system Silty Sand

AASHTO A-2-4 Table 3.1 Summary of physical properties for Jizan sabkha soil

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3.3.3 Copmaction Test

To determine the compaction characteristics of tested soils, standard

compaction tests were performed according to (ASTM) D698-70 . Standard

compaction test were conducted on Jizan sabkha soil to determine its compaction

characteristics (maximum dry density and optimum water content ) . The compaction

test result is shown in Figure 3.2.

Fig. 3.2 Compaction test results for Jizan Sabkha soil

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3.4 Consolidation Test

To determine the compressibility characteristics of tested soils, standard

consolidation tests were performed on Jizan sabkha soil. To study the effect of lime

addition on the compressibility characteristics of tested soils, the lime were added

using 3 , 6 , 9 , 12 % lime by weight of dry Sabkha. The samples compacted at 91%

of the maximum dry density.

The Pressure versus Settlement results for untreated and lime treated sabkha

are presented in figure 3.3. Which show decreas in settlement with increasing lime

content. The e - log p curves for untreated and lime treated sabkha are shown in

figures 3.4 , 3.5 , 3.6 , 3.7 , 3.8.

Fig. 3.3 Effect of lime on the compressibility characteristics

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CHAPTER 4

CONCLUION

This project is concern with Jizan sabkha soil which brought from Jizan area.

Physical properties of tested soil are presented from these tests this soil is classified

as SM (Silty Sand), according to USCS and A-2-4, according to AASHTO. A

laboratory study was under taken to evaluate the ability of lime addition to improve

the physical and compressibility of Jizan sabkha soil.

The experimental work has shown that the settlement decreas with the

increase in lime content.

Next Semester program

- Bearing capacity determination by performing a series of footing loading

tests.

- To determain the shear strength parameter (φ' and c'), traxial test or direct

shear test are performed on the soil.

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REFERENCES

[1] Akili, W., "On Sabkha Sands of Eastern Saudi Arabia", Proceedings, .

Symposium on Geotechnical Problems in Saudi Arabia, King Saud University,

Riyadh, 1981, vol. II, pp. 775-791.

[2] Al-Amoudi, O. S. B., "Studies on Soil-Foundation Interaction in the Sabkha

Environment of the Eastern Province of Saudi Arabia"Ph.D.Dissertation,Department

of Civil Engineering, King Fahd University of Petroleum and Minerals, Dhahran,

1992, vols. I and II.

[3] Erol, A.O., "Engineering Geological Considerations in a Salt Dome Region

Surrounded by Sabkha Sediments, Saudi Arabia", Engineering Geology, 26 (1989),

pp.215-232.

[4] Al-Amoudi, O.S.B., El-Naggar Z.R., and Asi, 1.M., "The Sabkha Soil in the

Kingdom of Saudi Arabia and Its Engineering Problems", Al-Muhandis (The

Engineer), 6(2) (1992), pp. 56-62 (in Arabic).

Sabkha Soil CE 498 Abdulwahab Mubarki Report 1

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