Hafez Clay Minerals - 2011 Hafez

7/30/2019 Hafez Clay Minerals - 2011 Hafez

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Clay Minerals and SoilStabilization

Dr. [email protected]
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Details of Lecturer

Course Lecturer: Dr. Mohd Hafez

Room Number: T1-A13-A11Tower1.0, Faculty of Civil Engineering

Email: [email protected]

Tel. No. : 55 43 64 15

office Hours: 8.30 a.m. to 5.0 p.m(Monday to Friday)


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Course outcomes:At the end of the course, the student should be able to:-

a.Understand the objectives of ground improvement

b.Propose types of ground improvement for different ground condition

c.Design ground improvement techniques for a given site condition

d.Propose a suitable method and economical stabilization techniques

e. Understanding the concept of ground contamination from the geotechnical point ofview.

f. Acquire methods of identification, classification and interpretation of ground

contamination types.

g. Propose suitable and economical remediation for different type of groundcontamination materials.

h. Describe the contamination process cycle and acquire the methods of testing of thelevel of ground contamination.


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1.0 Introduction to Ground Improvement Techniques1.1 Ground modification methods

1.2 Choice of method and suitability to ground condition1.3 limitations, advantages and disadvantages

2.0 Mechanical Methods - design and analysis2.1 Static and dynamic compaction

2.2 Vibro-compaction and vibro- repJacement

2.3 Blasting2.4 Dynamic Consolidation

2.5 Stone columns

2.4 Dynamic Consolidation

2.5 Stone columns

SYLLABUS CONTENT


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3.0 Hydraulic Methods - design and analysis3.1 Ground water control3.2 Preloading

3.3 Vertical Drains3.4 Dewatering3.5 Electro~osmosis

4.0 Chemical and Physical Methods - design and analysis

4.1 Lime stabilization - surface and deep mixing4.2 Lime-slurry injection4.3 Application of lime piles

4.4 Grouting and its engineering application..


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5.0 Soil Reinforcement Method - design and analysis5.1 Types of soil reinforcement

5.2 Soil nailing designa and application

5.3 Lightweight material and its application

6.0

7.0

Geotextile as Soil Improvement Material- design and analysis6.1Application as a reinforcement, separator, filter and drainage

material

6.2 Application for embankment, slope stability and retainingstructure

6.3 Application for highway construction

Prediction of Subsidence

7.1 Method of predicting subsidence

7.2 Soil subsidence due to tunneling, excavation, groundwater andliquefaction

7.3 Sinkhole due to underground cavities


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8.0 Geoenvironmental Problems and Regulations8.1 Geoenvironmental and contaminated land8.2 Soil contamination

8.3 The problem and its investigation8.4 Geoenvironmental and contamination problems in Malaysia8.5 Risk assessment and management8.6 Remediation standards and regulation

9.0 Environmental Geology9.1 Brief review of geological fundamentals9.2 Rock and soil classification in engineering geology and geotechnics9.3 Mapping, site investigation and logging9.4 Environmental geohazards9.5 Environmental geochemistry

10.0 Groundwater Flow and Contaminant Transport10.1 Introduction10.2 Groundwater motion10.3 Groundwater flow modeling10.4 Groundwater quality


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11.0Waste Containment Systems and Development of Landfill Sites11.1 Characterization of urban wastes and its engineering properties11.2 Review on engineering properties of soil

11.3 Soil-waste interactions11.4 Waste containment systems (sanitary landfills)11.5 Engineering problems associated with landfill

12.0 Remediation of Contaminated Land

12.1 Introduction12.2 Site characterization12.3 Geostatistics


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ASSESSMENT

-Assignment (3)

- Tests (2)

45%55%

Total : 100 %

RECOMMENDED TEXTBOOK

1- Hansbo, S. (2003). 'Ground Improvement', GEO Forum Nil


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REFERENCES

1.Bell, F.G. (1 993),'Engineering Treatment of Soils', E & F N Span.2.British Standard Institution (1995), 'Code of Practice for StrengthenedfReinforced

Soil and Other Fills', BS 8006, HMSO.3.Koerner, RM. (1985), 'Construction and Geotechnical Methods in FoundationENGINEERING', McGraw Hill.4.Miura, N. and Bergado, DT (1998), 'Improvement of Soft Ground:Design, Analysis and Current Researchers', Asian Center for Soil Improvement andGeosynthetics, Asian Institute of Technology, Bangkok, Thailand.1.National Coal Board (1975), ' Subsidence Engineers Handbook', MiningDepartment'2.U.S. Department of Transportation, 'Geotextile Engineering Manual'.Manfred, R.H. (1998), 'Engineering Principles of Ground Modification, McGrawHill.

1.Journal of Ground Engineering.2. International Conf. On Ground Improvement TechniquesGeosynthethics International Journal9.0 Daniel, D.E. Geotechnical practice for waste disposal , Chapman and Hall,London .


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Objectives1- Increase strength, reduce erodibility2-Reduce distortion

3-Reduce compressibility4-Control shrinkage/ swelling5-Control permeability6-Reduce liquifaction

Application1-Improve sub grade or sub base reduce pavement thickness2-Improve traffic ability on construction sites3-Prepare ground for shallow foundations4-Stabilize slopes5-Reduce erosioninternal seepage6-Construct embankments7-Form load bearing column (in situ) (grouted auger piles)8-Reduce traffic dust9-Contain hazardous wastes

10-Rehabilitate polluted ground


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Chapter 1.0Chemical ground improvement techniques

BACKGROUND


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BACKGROUND

More than 70% of the 5000 km of Malaysia coastal line is made of a

layer of soft soil, with thickness ranged between 20 to 40 meters.The WEAK nature of the soft clay has been a deterrent towardseconomic and tourism development. Resorting to deep concrete pile system in order to build a medium

size structure ( 2-3 stories) is considered a very expensive alternative.Where the foundation costs much more than superstructure. Newly sand reclamation on the soft soil generates negative skinfriction, which almost doubles the length of the concrete pile as well ascosts.

S h il t b i d i d t t k th l d f b ildi


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Such soil must be improved in order to take the loads from building,roads and other objects. Deep Mixing Method ( DMM) includes the Dry Jet Mixing ( DJM)and Wet method (slurry) is quite new techniques, first time was reported

in1957

The main processes were developed in 1970s simultaneously inSweden and Japan

DMM is technique where soil is mixed with one or two stabilizingagents often cement or lime.The two main ways of transporting the stabilizer down to the depth to

be treated can be identified as Wet or Dry.


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Purpose of deep stabilizationReduction of settlement Increase of stability

Increase of bearing capacity Prevention of sliding failure Protection of structures close to excavation Reduction of vibration

Liquefaction mitigation Remediation of contamination ground


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APPLICATION Of Lime- Cementcolumns


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Outline

1. Clay Minerals - Background2. Identification of Clay Minerals3. Specific Surface (Ss)4. Interaction of Water and Clay Minerals

5. Interaction of Clay Particles6. Soil Structure and Fabric7. Soil Fabric-Natural Soil8. Soil Fabric-Clay Soils

9. Soil Fabrics-Granular Soils10. Loess11. Suggested Homework12. References


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BackgroundThe term clay refers to a number of earthy materials that are composedof minerals rich in alumina, silica and water. Clay is not a single mineral,

but a number of minerals. When most clays are wet, they become

"plastic" meaning they can be formed and molded into shapes. Whenthey are "fired" (exposed to very high temperatures), the water is drivenoff and they become as hard as stone. Clay is easily found all over theworld. As a result, nearly all civilizations have used some form of clay

for everything from bricks to pottery to tablets for recording businesstransactions. The minerals that make up clay are so fine that until theinvention of X-ray diffraction ( XRD) analysis, these minerals were notspecifically known. Under extremely high magnification, one can seethat clay minerals can be shaped like flakes, fibers, and even hollowtubes. Clays can also contain other materials such as iron oxide (rust),silica, and rock fragments. These impurities can change thecharacteristics of the clay. For example, iron oxide colors clay red. The

presence of silica increases the plasticity of the clay (that is, makes it

easier to mold and form into shapes).


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ClayThe term clay is used in 3 different ways: to designate a diverse groupof fine-grained minerals, as a rock or sediment term, and as a particle-

size term. Clay is generally defined as any very fine grained, natural,earthy material, which is generally plastic at appropriate water contentsand hardens when dried or fired. Despite the lack of a standarddefinition for clay among geologists, agronomists, engineers, and soilscientists, the term clay is generally understood by all who use it. As

industrial minerals, clays are a complex group, encompassing diversemineral commodities, each having somewhat different mineralogy,geologic occurrence, manufacturing technology, and uses.


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18 APRIL 2007 LIME STABILIZE CLAY 21

Flakyshape

Plate likestructure


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Elements of Earth

12500 km dia

8-35 km crust % by weight in crust

O = 49.2

Si = 25.7Al = 7.5Fe = 4.7Ca = 3.4

Na = 2.6K = 2.4Mg = 1.9other = 2.6

82.4%


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Soil Formation

Parent Rock

Residual soil Transported soil

~ in situ weathering (by

physical & chemical

agents) of parent rock

~ weathered andtransported far away

by wind, water and ice.


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Parent Rock

~ formed by one of these three different processes

igneous sedimentary metamorphic

formed by cooling of

molten magma (lava)

formed by gradual

deposition, and in layers

formed by alteration

of igneous &sedimentary rocks by

pressure/temperaturee.g., limestone, shale

e.g., marble

e.g., granite


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Residual Soils

Formed by in situ weathering of parent rock


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Transported Soils

Transported by: Special name:

wind Aeolian

sea (salt water) Marine

lake (fresh water) Lacustrine

river Alluvial

ice Glacial


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Basic Structural Units

0.26 nm

oxygen

silicon

0.29 nm

aluminium or

magnesium

hydroxyl or

oxygen

Clay minerals are made of two distinct structural units.

Silicon tetrahedron Aluminium Octahedron


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Tetrahedral Sheet

Several tetrahedrons joined together form atetrahedral sheet.

tetrahedron

hexagonal

hole


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Tetrahedral & Octahedral Sheets

For simplicity, lets represent silica tetrahedral sheet by:

Si

and alumina octahedral sheet by:

Al


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Kaolinite

Si

Al

SiAl

Si

Al

Si

Al

joined by strong H-bond

no easy separation

0.72 nm

Typically70-100layers

joined by oxyge

sharing


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Montmorillonite

Si

Al

Si

Si

Al

Si

Si

Al

Si

0.96 nm

joined by weak

van der Waals bond

easily separatedby water

also called smectite; expands on contact with water


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Montmorillonite

A highly reactive (expansive) clay

montmorillonite familyused as drilling mud, in slurry trench walls,

stopping leaks

(OH)4Al4Si8O20.nH2O

high affinity to waterBentonite

swells on contact with water


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Illite

Si

Al

Si

Si

Al

Si

Si

Al

Si

0.96 nm

joined by K+ions

fit into the hexagonal

holes in Si-sheet


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Summary - Montmorillonite

Montmorillonites have very high specific surface,cation exchange capacity, and affinity to water.

They form reactive clays.

Bentonite (a form of Montmorillonite) is frequently used asdrilling mud.

Montmorillonites have very high liquid limit (100+),plasticity index and activity (1-7).


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A Clay Particle

Plate-like or Flaky Shap


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Soil Structure and

Fabric


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Clay Fabric

Flocculated Dispersed

edge-to-face contactface-to-face contact


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Clay Fabric

Electrochemical environment (i.e., pH, acidity, temperature,cations present in the water) during the time ofsedimentation influence clay fabric significantly.

Clay particles tend to align perpendicular to the load applied on them.


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Specific Surface

surface area per unit mass (m2/g)

smaller the grain, higher the specific surface

e.g., soil grain with specific gravity of 2.7

10 mm cube1 mm cube

spec. surface = 222.2 mm2/g spec. surface = 2222.2 mm2/g


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forcelGravationa

forcerelatedSurface

mass/surfacesurfaceSpecificvolume/surfacesurfaceSpecific

g/m3.2cm/g65.2m1

m16S

cm/g65.2,cubem111

g/m103.2cm/g65.2cm1

cm16S

cm/g65.2,cubecm111

2

33

2

s

3

24

33

2

s

3

Example:

Surface related forces: van derWaals forces, capillary forces, etc.

Ss is inversely

proportional tothe particle size

Preferred


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Typical Values

Montmorillonite

Illite

Kaolinite

50-120 m2/gm (external surface)

700-840 m2/gm (including the interlayer surface)

65-100 m2

/gm

10-20 m2/gm

Interlayer surface


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Iso-morphous Substitution

substitution of Si4+ and Al3+ by other lower valence(e.g., Mg2+) cations

results in charge imbalance (net negative)

+

++

+ +

+

+

__ __

_

_

_

___

_

_

_

_

_

_

_

_

_

__

__

positively charged edges

negatively charged faces

Clay Particle with Net negative Charge


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Cation Exchange Capacity (c.e.c)

capacity to attract cations from the water (i.e., measure of

the net negative charge of the clay particle)

measured in meq/100g (net negative charge per 100 g of clay)

milliequivalents

known as exchangeable cations

The replacement power is greater for higher valence andlarger cations.

Al3+ > Ca2+ > Mg2+ >> NH4+ > K+ > H+ > Na+ > Li+


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Adsorbed Water

- -

- -

- -- -

- -

- -

- -

A thin layer of water tightly held to particle; like a skin

1-4 molecules of water (1 nm) thick

more viscous than free water

adsorbed water


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Clay Particle in Water

- -

- -

- -

- -- -

- -

- -

free water

double layer

water

adsorbed water

50 nm

1nm


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2.Identification

of ClayMinerals

Scanning Electron


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Scanning ElectronMicroscope

common technique to see clay particles

plate-likestructure

qualitative


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2.1 X-ray diffraction

The distance of atomic planes d can be determined based on the Braggs

equation.

BC+CD = n, n = 2dsin, d = n/2 sinwhere n is an integer and is the wavelength.

Different clays minerals have various basal spacing (atomic planes). Forexample, the basing spacing of kaolinite is 7.2 .

Mitchell, 1993

2 2 Differential Thermal Analysis


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2.2 Differential Thermal Analysis(DTA)

Forexample:

Quartz changes from the to form at 573 C

and an endothermic peak can be observed.

Differential thermal analysis

(DTA) consists of simultaneouslyheating a test sample and athermally inert substance atconstant rate (usually about 10C/min) to over 1000 C andcontinuously measuring differences

in temperature and the inertmaterial T.

Endothermic (take up heat) orexothermic (liberate heat) reactionscan take place at different heating

temperatures. The mineral typescan be characterized based on thosesignatures shown in the left figure.

(from Mitchell, 1993)T

Temperature (100 C)


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Casagrandes PI-LL Chart

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Liquid Limit

PlasticityIndex

A-line

U-line

montmorillonite illite

kaolinite

chlorite

halloysite


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2.3 Other Methods

1. Electron microscopy2. Specific surface (Ss)

3. Cation exchange capacity (cec)

4. Plasticity chart


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4. Interactionof Water andClay Minerals


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Adsorbed layers

3monolayers

4.5 Clay-Water Interaction

1. Hydrogen bondKaolinite

Oxygen HydroxylClaySurfaces

Free water

Bulk water

The water molecule locked in the adsorbedlayers has different properties compared tothat of the bulk water due to the strongattraction from the surface.

O OH

HO

HO

H

O H

H


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4.5 Clay-Water Interaction (Cont.)

The water moleculeswedge into the interlayer

after adding water

2. Ion hydration

Dry condition

(Interlayer)

Claylayers

cation

The cations are fully hydrated,which results in repulsive forcesand expanding clay layers(hydration energy).

Na+ crystal radius: 0.095 nm

radius of hydrated ion: 0.358 nm


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The concentration of cations is higher in the interlayers (A) compared with thatin the solution (B) due to negatively charged surfaces. Because of thisconcentration difference, water molecules tend to diffuse toward the interlayer

in an attempt to equalize concentration.

3. Osmotic pressure

From Oxtoby etal., 1994

AB


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Relative sizes of adsorbed water layers on sodium montmorillonite andsodium kaolinite

Holtz and Kovacs, 1981


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5.8 Swelling PotentialPractically speaking, the three ingredients generally necessary for

potentially damaging swelling to occur are (1) presence ofmontmorillonite in the soil, (2) the natural water content must be aroundthe PL, and (3) there must be a source of water for the potentiallyswelling clay (Gromko, 1974, from Holtz and Kovacs, 1981)

Holtz and Kovacs, 1981

U.S. Bureau ofReclamation

Lime Stabilization


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Outline:

1- Chemical Method2-Lime3- Lime Stabilization4- Mechanism of Lime Stabilization5- Hydration6- Ion Exchange and Flocculation7- Pozzolanic Reaction8- Carbonation9-Effect of Lime on The Physical Properties of The Soil

[email protected]

Lime Stabilization
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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The Dry Mix Methods or Deep Stabilization has beenemployed for the following specific purposes:Reduction settlementsIncrease of stability

Increase of bearing capacityPrevention of sliding failureProtection of structures close to excavation sitesReduction of vibration

Liquefaction mitigationRemediation of contaminated ground

Methods of Mixing


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Types of auger used in mixing tools


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Differences between concrete pile and lime or cement clay

columns in term of load transferring

Chemical Stabilization


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The main objective of chemical soil stabilization is to favorably change the soil-waterinteractions. Chemical soil stabilization is intended to modify the interaction betweenwater and soil by surface reactions in such manner as to make the behavior of the

soil with respect to water effects most favorable for the given purpose. There aremany types of chemical soil stabilization such as cement stabilization, bitumenstabilization, sodium silicate stabilization and calcium acryl ate stabilization.

The transitional nature of chemically modified clay is both physical and chemical.

Physically, the modified clay is transitional between natural saturated soft clay andcomposite material, and therefore exhibit properties of both the chemical additivesand natural soft clay. In the chemically modified clay, it is the physicochemicalphenomena that influence its engineering properties. The interatomic andintermolecular bonding forces hold matter together and the unbalanced forces existat phase boundaries. The nature and magnitude of all these forces influence theengineering properties of chemically modified clay. Longterm particle interactiondue to physicochemical changes in the modified clay specimen generates many typesof bonds within the specimen

When lime added to clay, reacts with wet soil, it alters the nature of the absorbed


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layer by base exchange. Calcium ions replace the sodium or hydrogen ions. Thedouble layer is usually depressed due to an increasing in the cation concentration .However, sometimes the double layer may expand due to high pH value of lime.

Lime reacts chemically with available silica and alumina in the clay. A naturalcement composed of calcium alumino silicate complex is formed which causes acementing action. The reaction depends upon the effective concentration of thereactants.

LIME Stabilization

Lime in the form of quicklime (calcium oxide - CaO), hydrated lime (calciumhydroxide Ca [OH]2, or lime slurry can be used to treat soils. Quicklime ismanufactured by chemically transforming calcium carbonate (limestone - CaC03)into calcium oxide. Hydrated lime is created when quicklime chemically reactswith water. It is hydrated lime that reacts with clay particles and permanently

transforms them into a strong cementitious matrix. Most lime used for soiltreatment is "high calcium" lime, which contains no more than 5 percentmagnesium oxide or hydroxide. On some occasions, however, "dolomitic" lime isused. Dolomitic lime contains 35 to 46 percent magnesium oxide or hydroxide.Dolomitic lime can perform well in soil stabilization, although the magnesium

fraction reacts more slowly than the calcium fraction.

Soil stabilization by lime means the admixture of this material in the form ofcalcium oxide (CaO) or calcium hydroxide (Ca(OHh) to the soil and the


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calcium oxide (CaO) or calcium hydroxide (Ca(OHh) to the soil, and thecompaction of the mixture at the optimum water content. Lime treatment iscommonly resorted to in order to improve the strength and stiffness properties ofroad foundations, reduce the swell-shrink potential of expansive soils andimprove soft clay properties by surface mixing of lime and soil. Deep mixingtechniques may also be used such as creation of lime columns and lime piles orin situ stabilization of soil by lime slurry injection. More recently lime has alsobeen used to treat chemically contaminated soils. Lime-clay reactions occur viatwo distinct processes:

(i) Rapid ion exchange reactions known as soil improvement or modificationand(ii) slower soil-lime pozzolanic reactions known as stabilisationl-solidification.

Lime modification reactions occur from replacement of exchangeable ions of thesoil with calcium ions released by lime. The increased exchangeable calcium ion

concentration increases the flocculation of clay particles and transforms theplastic soil to a granular and less plastic material. Lime stabilizationsolidification occurs at lime additions in excess of the Lime ModificationOptimum or Initial Consumption of Lime value. According to BS 1924 (1990)

the Initial Consumption of Lime gives an indication of the minimum


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quantity of lime that must be added to a material to achieve asignificant change in properties. During lime stabilisationl-solidification reactions the highly alkaline soil pH (soil pH =12.4)

promotes dissolution of siliceous and aluminous compounds from theclay mineral lattice. The compounds dissolved from the clay minerallattice react with calcium ions in pore water to form calcium silicatehydrate and calcium aluminates hydrate gels, which coat the soil

particles and subsequently crystallize to bond them.

Mechanism of Lime Stabilization

The major strength gain of lime treated clay is mainly derived fromthree reactions; dehydration of soil, ion exchange and pozzolanicreaction. Short-term reactions include hydration (for quicklime) andflocculation (ion exchange). Longerterm reactions are cementationand carbonation.

Hydration


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A large amount of heat is released when quicklime (CaO) is mixedwith clay. This is due to hydration of quicklime with the pore

water of the soil. An immediate reduction of water contents occurswhen quicklime is mixed with cohesive soil, as water is consumedin the hydration process. If a reduction of the natural water contentin a cohesive is desirable, quicklime instead of calcium hydroxide

is used. It is important that the water content of the base clay mustbe sufficient for the complete slackening of the quicklime.

CaO + H20 Ca(OH)2 + HEAT (280 Cal /gm of CaO)

The calcium hydroxide from the hydration of quicklime or when

using calcium hydroxide as a stabilizer, dissociates in the water,increasing the electrolytic concentration and the pH of the porewater, and dissolving the Si02 and AlO3 from the clay particles.This process will result in ion exchange, flocculation, and

pozzolanic reactionsCa(OH)2 Ca ++ + 2(OH)

Ion Exchange and FlocculationWh li i i d i h l di d h i d b d


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When lime is mixed with clay, sodium and other cations adsorbed tothe clay mineral surfaces are exchanged with calcium. This change incation complex affects the structural components of the clay mineral.

Within a period of a couple of minutes up to some hours after mixing,the calcium hydroxide is transformed again due to the presence ofcarbonic acid in the soil. The presence of carbonic acid in the soil isdue to the reaction of carbon dioxide of the air in the soil and the free

water. The reaction results in the dissociation of the lime into Ca++(or Mg++) and (OH)- which modifies the electrical surfaces forces ofthe clay minerals. A transformation of the soil structure begins, i.eflocculation and coagulation of soil particles into larger sizesaggregates and an associated increase in plastic limit. Lime causes theclay to coagulate, aggregate or flocculate. These reactions tend todecrease the liquid limit, increase the plastic limit, decrease the

plasticity index, increase the shrinkage limit, increase the workability,and improve the strength and deformation properties of a soil.


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Plate 2.4 the cation exchange processbetween minerals and additives

Plate 2.5 shows the effect of ion exchange

Plate 2.6 The mechanism of loadTransformation in the stabilized soil


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Lime Reacts Chemically with Clays

to Alter Molecular Interactions

Untreated clays have amolecular structure similar to

some polymers, and give plastic

properties. The structure cantrap water between its molecular

layers, causing volume anddensity changes.

In treated clays Calcium atoms (fromLime) have replaced Sodium and

Hydrogen atoms producing a soil withvery friable characteristics

On-going reaction with available Silicaand Alumina in the soil forms complexcementatious materials (thePOZZALONIC effect.

Flocculation/Agglomeration

Unstabilized Clay Particles

Flocculation/Agglomeration

Clay after flocculation / Agglomeration


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Lime Reacts Chemically with Flyash

to provide Cementatious Result

Reactions between lime and

the Silica and Alumina inflyash form complex

cementitious materials

Lime and Flyash provide afiller for larger particles ofsand or gravel based soils

Essential to the treatment of non-clay soils and aggregates

Pozzolanic Reaction

Calcium Hydroxide

From lime or cement

Cementitious

Material from

pozzolonic reactions

[CSH and CAH]

Clay Particle

Ca (OH )2

Ca (OH )2

Ca (OH )2

Ca (OH )2

Mi i Vi


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Microscopic View


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18 APRIL 2007 LIME STABILIZE CLAY 87

Pozzolonic Reaction The formation of cementing materials

Calcium Silicate Hydrate & CalciumAluminates Hydrate (C-S-H and C-A-H) to

strengthen the soil.

Ca(OH)2 + SiO2

C-S-H Ca(OH)2 + Al2O3 C-A-H

Hydrated gelfrom soilfrom lime


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Plate 2.7 the forming of CSH matrix gel

In order to have additional bonding forces produced in the cement-clay mixture,the silicates and aluminates in the material must be soluble. That will be associatedwith dropping of pH during pozzolanic reaction and a drop in the pH tends topromote the hydrolysis of C3S2Hx, to form CSH. The cement hydration and thepozzolanic reaction can last for months, or even years, after the mixing, and so the

strength of cement treated clay is expected to increase with time.

The gel of calcium silicate cements the soil particles in a

i il t th ff t d d b th h d ti f


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manner similar to the effect produced by the hydration of

Portland cement, but the lime cementing is a much slower

reaction, which requires considerably longer time than the

hydration of cement. The solubility of the pozzolans and

thus their inclination to react with lime is depends on the

pH of the soil water. The rate of reaction also increases

with increased soil temperature.

Carbonation

Lime reacts with carbon dioxide in the atmosphere or in the soil toform relatively weak cementing agent, such as calcium carbonateor magnesium carbonate. The strength of calcium carbonate, which

is formed by this process, can be discounted. The carbonation isprobably a deleterious rather than helpful phenomenon in the soilstabilization.

3- Effect of Lime on The Physical Properties of The Soil

Considering the process described above, one can conclude that lime addition affects


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g p ,all physical properties of the soil. Owing to the coagulation, the grain-size distributioncurve will obviously change and, a number of other characteristics will undergosimilar changes due mainly to this cause. Changes in the grain-size distribution curve

however, are rather difficult to determine, as the usual hydrometric method does notrender a true picture, so these changes should be expressed numerically on the basis ofanother characteristic property. Figures below illustrates the time dependent process ofplasticity index (PI) reduction, which incidentally is also characteristic of thedevelopment rate exhibited by the process described in the section above. Generally,

quick lime will bring about a faster reaction. The effect of calcium treatment on thevolume change of the various soils is similarly significant, as swelling will be almostcompletely eliminated, and the volume change greatly reduced. It shows a typicalreduction in liquid limit as a result of lime treated. As more lime was added to thenatural clay the liquid limit (LL) decreased while the plastic limit (PL)

increased. This can also be seen as a reduction in the plasticity index (PI). When thePI of the soil is at a minimum the soil is said to be fully modified. This trendcontinued from L6 to L18% , while adding more lime above 18%. The trend reversedbetween 18 to 24% . the reverse trend can be as result of excessive lime in themixture, the extra lime works as inoperative element stimulates the de-bondingphenomena in the mixture.

Effect of lime on Atterberg limits80

90


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91

0

10

20

30

40

50

60

70

80

0 6 12 18 24 30

Lime %

Wc%

LL PL PI

The effect of Mixture of lime on Atterberg limits

The effect of Additive on MDD and OMC


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92

OMC and MDD of Lime group

OMC

OMC

OMC

OMC O

MC

M

DD

MDD

MDD

MDD

MDD

23

23.5

24

24.5

25

25.5

26

26.5

27

27.5

28

0 6 12 18 24 30

Lime Content %

OM

C%

13

13.2

13.4

13.6

13.8

14

14.2

14.4

14.6

14.8

15

MDD

(KN)

The relation between OMC & MDD for Lime group

Optimum Moisture Content was increased with increasing lime


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93

Optimum Moisture Content was increased with increasing limecontents from 0.0 to 12% and reached to its peak around 14%. Than thetrend was reversed after 14% to 24% indicating that most of water

content in the mixture have been utilized fully in creating bondsbetween lime and clay particles. While, the extra lime particles in themixture were not used in any modification process. And it might act asinoperative element in the modification process. However, it can be

suggested here to look to the Proctor standard compaction test resultsas primary method to determine the optimum lime content for eachtype of clay soil. In this analysis, the 14% lime is considered theoptimum lime content for this type of clay. However, The value of themaximum dry density was falling greatly once lime was added, the

more lime added to the clay the less MDD could obtained. This isresult of replacing clay by lime particles which is slightly larger andlighter than clay particles.

Predominant Factors That Control Hardning Characterstices of Lime Modifed Clay


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Type of Lime

The efficiency of lime stabilization depends in part on the type

of lime material used. Quicklime is generally more effectivethan hydrated lime (Kezdi, 1979), but generally it needs care

in handling for soils with high moisture contents. Unslaked

lime or quicklime is more effective since water will be

absorbed from the soil and more importantly, the hydration willcause an increase in temperature which is favorable to

strength gain (Brams, 1984).

TEST RESULTS


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Part A: Clay soil with no blending of Lime-Rice Husk Ash (LRHA)

Physical Properties

Natural moisture content, wN

Moisture content (disturbed)

Specific Gravity, Gs

Liquid Limit, LL

Plastic Limit, PL

Shrinkage Limit, SL

Plasticity Index, PI

Maximum Dry Density, gdOptimum Moisture Content

Grain size distribution:

- Coarse particles

- Fine particles

- Clay

- Silt

71.38

18.32

2.60

83.59

37.34

15.82

55.25

1.32 gr/cm3

34

9.24

5.00

30.50

80.76

70.50

Chen (1975) classified

soil with PI > 35%,

having very high swellpotential

roper es me emen

Finesses ( cm2/g ) 2975.00

Specific gravity 3.12


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Chemical Properties

Silica (SiO2) 1.25% 20.44

Alumina ( AlO3 ) 5.50

MgO 1.59

Iron Oxide ( Fe2O3)

Calcium Oxide ( CaO) 73.7 64.86

3CaO.SiO2 66.48

2Ca.SiO2 10.12

3CaO.Al2O3 8.06

4CaO.Al2O3.FeO3 9.43

Potassium Oxide (K2O)

Magnesium Oxide ( MgO) 1.59

Sodium Oxide (Na2O)

pH 12.06SO3 1.96

Loss on Ignition 23.15

Physical Properties

Colour White

Density 3.345

Hardness 3.5-Copper Penny

Composition of RHA

minerals (Wen-Hwei, 1986)

Mineral Composition (%)

SiO2 86.90 - 97.30

K2O 0.58 - 2.50

Na2O 0.00 - 1.75

CaO 0.20 - 1.50

MgO 0.12 - 1.96

Fe2O3 ~ 0.54

P2O5 0.2 2.85

SO3 0.1 1.13

Cl ~ 0.42

Lime ContentThe strength of lime soil mixtures provided they are properly cured


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97

The strength of lime soil mixtures, provided they are properly cured,increases as the lime content is increased. There appears to be nooptimum lime content which produces a maximum strength in a lime

stabilized soil under all conditions. However, it can be stated that fora particular condition of curing time and soil type, there is acorresponding optimum lime content which causes the maximumstrength increase (Herrin and Mitchell, 1961).

Lime Fixation PointThe lime fixation point is defined as the point at which the percentage oflime is such that additional increments of lime produce no appreciableincrease in the plastic limit. Handy et a!. (1965) referred to this point as the

"lime retention point". Based on extensive investigations at Iowa StateUniversity, the concept of the lime fixation point was suggested. Limecontents equal to the lime fixation point for a soil will generally contribute tothe improvement in soil workability, but may not result in sufficient strengthincreases (Hilt and Davidson, 1960),

* Optimum Lime ContentMethods of determining the optimum lime requirement for lime


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98

stabilization have been proposed. Eades and Grim (1966) suggested thatthe amount of lime consumed by a soil after one hour affords a quick

method of determining the percentage of lime required for stabilization,i.e., the lowest percentage of lime required to maintain a pH of 12.6 isthe percentage required to stabilize the soil. However, a strength test isstill necessary to show the percentage of strength increase. McDowell(1959) pointed out that short-time or quick tests probably will notidentify optimum lime contents, but are essential in checking against theuse of non-reactive soils for treatment of lime. On the other hand, whilelong-term tests would do a better job of identifying optimum limecontents, they may be impractical from the standpoint of time, and may

even suggest the use of insufficient amounts of lime due to the idealconditions under which they are run. Hilt and Davidson (1960) gave acorrelation which showed that the amount of lime fixation is in

proportion to the type and amount of clay present and is independent of

the absorbed cation present in the clays. The relationship is given as:=

* Curing Time


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99

gBroms (1984) reported that the shear strength of stabilized clays will normallybe higher than that of untreated clay after mixing. Figure 6.4 shows a typicalplot of the increase of shear strength with time for various types of soils. Theshear strength of clay stabilized with lime will normally be higher than that ofundisturbed clay about one to two hours after mixing even when the sensitivityof the clay is relatively high (Broms, 1984). The undrained final shear strengthof stabilized clay can be, under favorable conditions, as high as 10 to 50 timesthe initial shear strength (Assarson et al. 1974). The shear strength of the

stabilized soil gradually increases with time through pozzolanic reactions whenthe lime reacts with the silicates and aluminatesAn the soil (Broms, 1984). Therate of increase is generally rapid at the early stage of curing time; thereafter,the rate of increase in strength decreases with time. Lime has an initial reactionwith soil taking place during the first 48-72 hours after mixing, and a secondary

reaction which starts after this period and continues indefinitely (Taylor andArman, 1960). Several attempts have been made to express the strength of limestabilized soils as a function of curing time.

12


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100

Lime 12% - 100 mm

0

2

4

6

8

10

0 1 2 3 4 5 6

Strain %

CompressiveStrengthKg/cm

L12-1d L12-7d L12-14d L12-28d L12-56d Clay-O-100mm

the strength development over curing time - 12% lime

Broms (1984) found that the shear strength of stabilized soils as determined byunconfined compression tests increased linearly with time when plotted in loglogscale (log Cu. log t). Brandl (1981) and Okamura and Terashi (1975), however.found that the time- dependent increase in shear strength was approximately

linear with the logarithm of time.

Type of Soil ( Clay Content )


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101

Type of Soil ( Clay Content )For lime treatment to be successful, the clay content of the soil shouldnot be less than 20% and the sum of the silt and clay fractions should

preferably exceed 35%, which is normally the case when the plasticityindex of the soil is larger than 10 (Brams, 1984). The shear strengthincrease of the stabilized soil is highly dependent on pozzolanicreactions, i.e., the reactions of lime with the silicates and aluminates in

the soil.

The following graph shows the relationship between clay

content of soils and 28-day unconfined compressive

strength of soils treated with 5% portland cement or 5%

lime, and (( compacted immediately.)) Adapted from

Christensen, 1969


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102


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103


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104

Relationship between clay content of soils and 28-day

unconfined compressive strength of soils treated with 5%

portland cement or 5% lime, and (( compacted after a 24-

hour delay.)) Adapted from Christensen, 1969.


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105

Linear relationship between cation exchange capacity and claycontent of untreated soil. The deviation of soil No. 10 with 75% claycontent was attributed to the presence of calcite and quartz.Adapted from Christensen, 1969.


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106

Linear relationship between plasticity index and clay content ofuntreated soil. Adapted from Christensen, 1969.

Laboratory testing


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pH test

Standard Proctor Test

Curing SpecimenUnconfined Compressive Strength Test

Grain Size Distribution


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109

The increase in strength with time is in general highest fornormally consolidated silty clays, with low plasticity index and a

low water content. The strength increase in lime treated organicsoils is often very low; even a relatively small amount of organicmaterial can have a large effect on the strength increase (Brams,1984). Gypsum has often been used together with unslaked lime

to stabilize organic soils when lime alone is not effective (Bromsand Anttikoski, 1983). Generally, the effect of lime decreases withincreasing water content (Holm et al. 1983; Miura et al. 1987).

The particle size and shape also influence the properties of soils.As the ion exchange in illite and kaolinite takes place primarily atthe interface and edges, the cation exchange capacity of soils intheir presence may be different as particle size and shape arechanged.

* Clay MineralsEades and Grim (1966) reported that the quantity of lime needed


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110

ades a d G ( 966) epo ted t at t e qua t ty o e eededto effectively treat a clay is dependent on the type of clay mineral

present. Eades and Grim (1966) observed that although

kaolinites, illites~ montmorillonites and other mixed-layeredclays all react with lime to give greater strength "; the quantity

of lime needed to treat a clay is dependent on the type of mineralpresent. Hilt and Davidson (1960) found that from the unconfined

compression test results, kaolinitic and montmorillonitic clayeysoils are effectively stabilized with lime alone. Whereas illiticclays require addition of fly-ash to obtain a significant strengthgain. Lee et at. (1982) found that in terms of strength increase,lime treatment has a greater effect in montmorillonites thankaolinitic soils.

* Soil pHLime addition will increase the pH of the water content in the soil,


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111

p ,and give rise to increased solubility. The base exchange is low whenthe pH-value is less than 7. The long-term chemical reactions in

lime stabilized soils are favored by a high pH-value (PH> 12) sincethe reactions are accelerated due to the increased solubility of thesilicates and aluminates (pozwlans) present in the clays (Broms.1984), Davidson et al. (1965) suggested that a minimum pH of

approximately to.5 is necessary for pozzolanic reaction to takeplace, while Eades and Grim (1966) suggested that the lowestpercentage of lime required to maintain a pH of 12.40 is thepercentage required to stabilize a soil. Broms (1984) pointed outthat the pH of the treated soil will normally exceed 12 even whenonly a few percent of lime has been added to the soil.


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112

pH vs Lime Content


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From the graph, it shows the optimum lime content to change

the pH value of soil is 6%.

pH vs Lime Content


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114

Solubility of Ca(OH)2 in water at 25C and the resulting pH of

the solution. Adapted from Boynton, 1980.

Curing Temperature


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115

The chemical reactions in the soil are favored by a high temperature(Broms, 1984). For lime-soil mixture at the same age, the effect of

increasing the curing temperature is to increase strength (Ruff and Ho,1966). The curing temperature has been found to affect the long termreactions between lime and clay. Broms (1984) attributed the favorableeffects of high curing temperature to the increased solubility of thesilicates and aluminates (pozzolans) in the clay at high temperatures. Forlime stabilized clays, Metcalf (1964) found that the curves (UC strengthversus temperature) were different for different clays, and that there wasan abrupt change in the slope in the vicinity of 45C. Ruff and Ho (1966)extended the work of Metcalf (1964), and suggested that different reactionproducts are formed at different curing temperatures and that the cut-offtemperature is from 23C to 40C. Furthermore, it was found that there

was increase of strength with time at all temperatures, with greater rate ofincrease at the higher temperature. Chaudry (1966) reported that thecompacted lime stabilized Bangkok clay cured at lOOF had higherstrength values than those cured at 70F.

FACTORS AFFECTING THE STABILIZED PROPERTIES

Only limited information is available regarding how various


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116

Only limited information is available regarding how variousfactors influence the engineering properties of a stabilized soil.While the contributory parameters are many (Felt, 1955), someof the more important ones are listed below.1. Stabilizer dosage2. Mixing conditions3. Compaction method and effort

4. Gradation and pulverization5. Curing period and conditions6. Delayed compaction7. Climatic conditions

Stabilization additive


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Stabilization additive

The selection additive is depending on;The type of soil to be stabilized.

The purposed which the stabilized layer will be used.

The type of soil improvement desired.The required strength and durability of the stabilized

layer.

Cost and Environmental Condition.

Stabilizer Dosage


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118

g

The amount of stabilizer determines the supply of calcium, themost necessary component for clay soil stabilization, and calcium

may be supplied from various sources. The presence ofa stabilizer may not only supply calcium to the system, but itsother characteristics may also contribute to the overall propertiesof a stabilized soil. This is true particularly in the case of Portland

cement or lime stabilization of clayey soils.In the case of time-dependent effects, some of the improvement

may occur too late to be of interest or to be applied in designconsiderations. In addition to the supply potential, there is also alower limit of the stabilizer dosage below which the necessarymixing uniformity cannot be achieved in normal constructionoperations in the field as opposed to the laboratory.

Procedures for Designing Soil-Lime Mixes.

In order to determine the necessary lime dosage, a number of mixture


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119

In order to determine the necessary lime dosage, a number of mixturedesign procedures are available for lime. These procedures, listed in theState of the Art Report on Lime Stabilization (State of Art Report, 1976,1987), are given below with the properties these tests are based upon.California Procedure: Optimum moisture content and unconfinedcompressive strength of lime-soil mixes with various lime content.1- Eades and Grim Procedure:

This measures pH to determine the design lime dosage. The amount oflime necessary to achieve a pH of 12.4, the saturation pH of Ca(OH)2, isconsidered to be adequate.2- Illinois Procedure:

This procedure is designed for two stabilization objectives: base or subbase stabilization, and sub grade modification. The criterion used for theformer is based upon the unconfined compressive strength and that forthe latter is based upon the reduction in Plasticity Index (PI).

3- Oklahoma Procedure:

This is based upon the Eades and Grim procedure However a PI


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120

This is based upon the Eades and Grim procedure. However, a PIreduction criterion is also used as an alternative.

4- South Dakota Procedure:Initial lime requirements are determined using the pH procedure ofEades and Grim. Supplemental strength data are generated throughCalifornia Bearing Ratio (CBR) and unconfined strengthmeasurements.5- Texas Procedure:

Unconfined compressive strength is used as the criterion (AASHTO T-220).6- Thompson Procedure:

This procedure is more elaborate than the others and separate criteriaare used for subgrade modification and for base and subbase materials.It combines a number of properties, such as maximum dry density,unconfined compressive strength, PI reduction, etc.

7- Virginia Procedure:This is based upon the compressive strength measurements of curedmixtures of soil and various dosages of lime It will be noted that


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121

mixtures of soil and various dosages of lime. It will be noted thatstrength is usually a secondary criterion, and that durability criteria

are notably absent. Where CBR is used as a strength criterion, clearlythe advantage of stabilized clay soils resides in their lesser loss ofbearing strength after saturation, as the CBR in "dry conditions can

be extremely high for clays but is almost entirely lost upon soaking.

The pH limitations:The pH method suffers from a few limitations. It takes no account ofany interaction between lime and soil that may result in a strength


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122

any interaction between lime and soil that may result in a strengthincrease. In fact, recognizing this limitation, Eades and Grim (1996)

stated explicitly: "The 1 hr pH or 'Quick Test' can be used only todetermine the lime requirements of a soil for stabilization. Sincestrength gains are related to the formation of C-S-H, and as theirformation varies with the mineralogical components of the soil, astrength test is necessary to show the percentage of strength increase.

Another limitation is that the stabilizer amount determined in thismethod is only applicable to lime, and it may lead to a wrong estimateif the stabilizer (such as Portland cement) contains compounds such asalkali sulfates or chlorides that are highly soluble in water. the pH of a

fresh cement paste reaches values of 12 to 13 within a few minutes andbefore the system becomes saturated with respect to calcium hydroxide.Thus, when used to determine the amount of Portland cement requiredfor soil stabilization, the Eades and Grim method can be misleading.

While the above procedures help to identify the lime content thatwill provide the greatest strength many factors influence the strength


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123

will provide the greatest strength, many factors influence the strengthof soil-lime mixtures. The variability of these factors makes it

practically impossible to pinpoint the strength that may be achievedfor lime stabilization of a particular soil. Therefore, strengths of soil-lime mixtures must be verified through strength tests such as CBR,unconfined compressive strength, or resilient modulus.Lime contents between 2 to 10 percent are typically capable of

producing significant strength gains (Little, 1995). While there is nouniversal definition of significant strength gain, most design

procedures implement a requirement for a compressive strengthincrease of 50 psi for lime stabilization to be a viable option (Chou,

1987).

Cement Stabilization

Stabilization Mechanism


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124

Stabilization MechanismStrength gain in soils using cement stabilization occurs through the

same type of pozzolanic reactions found using lime stabilization.Both lime and cement contain the calcium required forthe pozzolanic reactions to occur; however, the origin of the silicarequired for the pozzolanic reactions to occur differs. With limestabilization, the silica is provided when the clay particle is

broken down. With cement stabilization, the cement alreadycontains the silica without needing to break down the clay mineral.Thus, unlike lime stabilization, cement stabilization is fairlyindependent of the soil properties; the only requirement is that the

soil contains some water for the hydration process to begin.


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125

Similar to lime stabilization, carbonation can also occur when usingcement stabilization. When cement is exposed to air, the cement will

react with carbon dioxide from the atmosphere to produce arelatively insoluble calcium carbonate. Thus, similar to lime, properhandling methods and expedited construction procedures should beemployed to avoid premature carbonation of cement throughexposure to air.

Cement Stabilization mechanismThe formation of calcium-silicate-hydrate (C-S-H), upon hydration of


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126

The formation of calcium silicate hydrate (C S H), upon hydration ofPortland cement, is attributed to the development of its strength.

Therefore, the formation of C-S-H may further strengthen a soil that isstabilized with the Ca(OH)2 produced as the by-product of cementhydration. The formation of C-S-H upon hydration is an inherentcharacteristic of Portland cement, but not of lime. Additional C-S-Hcan form in both the Portland cement-soil and lime soil systems due to

the reaction between Ca(OH)2 supplied by either cement or lime andthe silica supplied by soil. This process is known as a pozzolanicreaction. Calcium may also react with alumina and produce C-A-H thatis cementitious in nature.

The reactions are as follows:Ca(OH)2 + SiO2> C-S-HCa(OH)2 + Al2O3> C-A-H

Soil Type Cement Usage UCS Permeability

240 400 k / 3 70 350 kP


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127

Sludge240 to 400 kg/m3(400 to 700 lbs/cy)

70-350 kPa(10-50 psi)

1x10-6 cm/sec

Organic silts andclays

150 to 260 kg/m3(260 to 450 lbs/cy)

350-1400 kPa(50-200 psi)

5x10-7 cm/sec

Cohesive silts & clay

120 to 240 kg/m3

(200 to 400 lbs/cy)

700-2100 kPa

(100-300 psi) 5x10-7

cm/sec

Silty sands and sands120 to 240 kg/m3(200 to 400 lbs/cy)

1400-3500 kPa(200-500 psi)

5x10-6 cm/sec

Sands and gravels120 to 240 kg/m3(200 to 400 lbs/cy)

3000-7000 kPa(400-1000 psi)

1x10-5 cm/sec

Typical strength and permeability characteristics of treated soils.

The Relation between Unconfined Compressive Strength, Modified Compaction Energy,kPa


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128

UnconfinedCompressive Strength,

Standard CompactionEnergy, kPa

Unconfined Compressive Strength, ModifiedCompaction Energy, kPa

ClayTypes Optimum

OMC1% AboveOptimum

OptimumMoisture

Content

1% BelowOptimum

withlime

without lime

withlime

without lime

withlime

without lime

withlime

Withoutlime

Clay1 1,395 124 2,235 120 2,980 280 2,725 225

Clay2 1,293 105 1,935 70 2,765 145 2,458 140Clay3 1,195 50 1,820 85 2,275 160 2,150 155

Effect of Compaction Energy and Molding Moisture Content onUnconfined Compressive Strength

FACTORS AFFECTING THE STABILIZED PROPERTIES

In general most clay soils can be successfully stabilized with portland


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129

In general, most clay soils can be successfully stabilized with portlandcement or lime. However, the achieved engineering properties of a

stabilized soil are dependent upon a number of parameters as discussedin the following sections. Besides all the engineering properties, theclay mineral composition of a soil is one of the most dominant factorsdetermining the chemical and physical properties of a soil. The

presence of a small amount of montmorillonite, with the highest cationexchange capacity, can greatly influence the physical properties ofsoils.Christensen (1969) investigated a total of 11 soils and observed a linearrelationship (see Figure 7) between the clay content of soils and cation

exchange capacity. The characteristics of these soils are shown in Table1. A linear relationship (see Figure 8) was also observed between theclay content and the plasticity indices.

A combination of these two linearities indicates that there 12 should bea linear relationship between cation exchange capacity and thel ti it i d (PI) Th ti l i d h l i fl th


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130

plasticity index (PI). The particle size and shape also influence theproperties of soils. As the ion exchange in illite and kaolinite takes

place primarily at the interface and edges, the cation exchangecapacity of soils in their presence may be different as particle size andshape are changed. Only limited information is available regardinghow various factors influence the engineering properties of a stabilized

soil. While the contributory parameters are many (Felt,1955), some ofthe more important ones are listed below.1. Stabilizer dosage2. Mixing conditions3. Compaction method and effort

4. Gradation and pulverization5. Curing period and conditions6. Delayed compaction7. Climatic conditions


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131

The 28-day unconfined compressive strength of pulverized soils treated withvarious amounts of lime. Size designations: Fine-100% passing No.2.0mmsieve; Medium-80% passing No. 2.0mm; Coarse-60% passing No. 2.0mmsieve. Adapted from Petry and Wohlgemuth, 1988.


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132

The 28-day unconfined compressive strength of pulverized soils treated withvarious amounts of Cement Size designations: Fine-100% passing No.2.0mmsieve; Medium-80% passing No. 2.0mm; Coarse-60% passing No. 2.0mmsieve. Adapted from Petry and Wohlgemuth, 1988.


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133

Variation of unconfined compressive strength, normalized by thedifferences in dry unit weights, with gradation of soil stabilized witheither 10% lime or cement. Adapted from Petry and Wohlgemuth, 1988.

Conductivity Test AnalysisElectrical conductivity test is a test used to study the electrochemical

properties of modified clay and to predict the interaction between the


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134

properties of modified clay and to predict the interaction between theadditive and clay. Although the concept of ion migration from fine-

grained modified soils is easy to understand, the associatedphysicochemical reactions of the modified clay is complex. Theexperimental results show that the approach is a valid step towards a

better understanding the physics and chemistry involved during the

treatment of soft clay. Strong electrolytes are substances that are fullyionised in the modified clay sample solution. As a result, theconcentration of ions in the solution is proportional to the concentrationof the electrolyte added. They include ionic solids and strong acids, forexample Ca(O)2. Solutions of strong electrolytes conduct electricity

because the positive and negative ions can migrate independently largelyunder the influence of an electric field. Weak electrolytes are substancesthat are not fully ionised in the solution. Ionic mobilities of H+ and OH-are considerably higher than that of other ions due to bonding and

debonding between the ions and water molecules (Alberty 1983)

3.15. How is conductivity measured?

Conductivity may be measured by applying an alternating electricalcurrent (I) to two electrodes immersed in a solution and measuring the


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current (I) to two electrodes immersed in a solution and measuring theresulting voltage (V). During this process, the cations migrate to the

negative electrode, the anions to the positive electrode and the solutionacts as an electrical conductor

Plate 3.28 Migration of ions in solution

Plate 3.29 Accumulation of ionic species at electrode surfa

60

70


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136

Unsaturated Lime

0

10

20

30

40

50

6% 5.6 8.9 11.2

12%15.4 30.1 38.5

18% 47.3 51.5 56.3

24% 57.9 63.8 65.1

7 days 56 days 100 days

Conductivity of Unsaturated Lime samples

40

45

50


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137

Saturated Lime

0

5

10

15

20

25

30

35

6% 11.5 8.4 6.5

12% 19.2 15.6 11.9

18% 31 24.2 15.8

24% 41.9 37.6 45.4


Conductivity Values of Saturated Lime samples

Conductivity reading of small, medium and high unsaturated limecontent dosages had shown increasing ionic ability to transfer currentby the time There are more free ions in the sample at day 100 than day


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138

by the time. There are more free ions in the sample at day 100 than day7. This can be attributed to incomplete ongoing reactions; thus allowing

more free ions. The free ions are produced in the debonding process dueto the lack of water to complete the reaction . The high conductivityreading of the high lime content of the unsaturated samples (L18 + L24)was due to the concentration of ions from electrolyte contributed by theCa(O)2 in the solutions as result of uncompleted or broken bond.

The conductivity readings of all saturated lime samples exhibited reversetrend compared to the trend of unsaturated lime samples. All unsaturatedlime sample readings increased by curing time, contrary to the trend of

its saturated counterpart. These indicate that, the saturated samples aremore chemically stable than the unsaturated ones. The conductivityreading of L12 saturated at 7 days had dropped gradually by 38% within100 days, indicating a slow ongoing ionic activity within the sample, and

the strong possibility of being reduced by over time to a lesser value and

20

25


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139

Unsaturated Cement

0

5

10

15

6% 5.1 6.3 6.9

12% 8.4 11.2 12.8

18% 9.9 11.8 12.5

24% 17.1 19.9 22.4


Conductivity Values of Unsaturated Cement Samples

6

7


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140

Saturated Cement

0

1

2

3

4

5

6% 3.1 3.3 3.6

12% 3.9 4.4 4.1

18% 2.8 3.4 3.3

24% 5.5 6.3 5.8


Conductivity Values of Saturated Cement Samples

The range difference in conductivity reading of the unsaturated cementsamples are much less than range of lime samples, which can beinterpreted as less free ions able to conduct electricity; meaning that the


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141

interpreted as less free ions able to conduct electricity; meaning that theunsaturated cement samples are chemically more stable than its lime

counterpart. The general trend indicates slow chemical reaction overtime. Samples with small dosages of cement are chemically more stablethan samples with high dosages. C12 and C18 show degrees ofsimilarities where the difference between 100 days and 7 days

conductivity reading is almost steady.Saturated cement samples have shown great ionic stability from theearly stage where the range of conductivity reading for the all saturatedcement samples was between (3.1) and (6.3). The range of readingdifferences was very small compared to any other samples. Even the

general trend was not really clear as the saturated lime, but theinconsistency can be attributed to the narrow reading range. In limesamples where the high difference in reading of 7 days and 100 days can

be easily detected by the device, it is not the same when it comes to

detecting a difference less than 1 s in saturated cement samples

Determine the effective moisture content (EMC).

Water content of all chemically modified clay samplesd t i d i th l b t th h th


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142

were predetermined in the laboratory through the

mechanical standard proctor compaction test, where theOMC (Optimum Moisture Content) and the MDD(Maximum Dry Density) were calculated for each additivedosage. The reverse conductivity trend between the

unsaturated and saturated sample shows a relation betweenconductivity and water content where the conductivityreading is indicative of the existence of an effective zone

between the two reverse trends, where chemical additive

would have an effective aqueous environment to maximizeits reaction with the clay.

.

Effective Water Content35

40

45


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143

0

5

10

15

20

25

30

OMC=28% 15.4 30.1 38.5

Wc= 35% 12.1 19.9 27.4

Wc=40% 9.8 11.2 12.5

Wc=45 10.2 12.9 15.7

Wc=50% 12.4 12.8 14.4

Saturated 19.2 15.6 11.9

7 56 100

Conductivity values of L12 with different water contents

In brief, it can be concluded that the mechanically predeterminemoisture content (OMC) value for chemically modified clay, wasnot the effective amount of water to maximize the creation of


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144

not the effective amount of water to maximize the creation ofbonding matrix between the chemical additive and the clay. The

conductivity test is a supporting test to determine the effectiveamount of water for chemically modified clay and bettercompressive strength.

THE FLOW OF GROUND

IMPROVEMENT


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INPUT

Existing ground conditions (i.e., strata depth, thickness and

geotechnical properties and groundwater conditions)

Expected foundation loads and allowable settlement

Is weak stratumstressed by

foundation load ?

Is calculated bearing

capacity, stability &

settlement acceptable ?

Treatment notnecessary

NO

NO

YES

YES

Heavy

loading? Consider piled foundationYES


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Large area

treatment ?

Can soil above

competent layer be

improved within

time/budget constraint ?

ConsiderGROUND IMPROVEMENT

YES

YES

NO

NO

NO

CASE STUDY


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of Lime in

Road Construction

The Uses and Value

Lime in Soil Modification

Li B d Mi D i f


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Lime Based Mix Designs for

Different Soil Types

AASHTOGroupClassification

SoilType

UnifiedGroupSymbol

RecommendedAdditives

GW GP GM GC SW SP SM SC ML CL OL MH CH OH PT

A-1-a A-1-a A-1-b A-1-b A-1-bA-1-b

orA-3

A-2-4or

A-2-5

A-2-6or

A-2-7A-4 A-6 A-4 A-5 A-7-6 A-7-5 A-8

Poorlygra

de

dgrav

elsan

dgrave

l

san

dm

ixtures,

little

orno

fines

LIME (Stabilization & Modification)LIME PLUS TYPE F Coal Fly Ash (Stabilization)

We

llgra

de

dgravelsan

dgrave

lsan

d

mixtures,

littleorno

fines

Siltygrave

ls,

grave

l-san

d-s

iltm

ixtures

Clayeygrave

ls,

gra

ve

l-san

d-c

laym

ixtures

We

ll-gra

de

dsands

an

dgrave

llysan

ds,

littleorno

fines

Poorlygra

de

dsand

san

dgrave

lly

san

ds,

littleornofines

Siltysan

ds,

san

d-s

iltm

ixtures

Clayey,

san

ds,

san

d-c

laym

ixtures

Inorgan

ics

ilts,

very

finesan

ds,

roc

k

flour,s

iltyorc

layey

finesan

ds

Inorgan

icc

laysoflow

tome

dium

plas

tic

ity,

grave

llyc

lays,

san

dyc

lays,

siltyc

lays,

leanclays

Organ

ics

iltsan

dorgan

ics

iltyc

layso

f

lowp

las

tic

ity

Inorgan

ics

ilts,

micaceousor

diatomaceous

finesan

dsors

ilts,

elas

tics

ilts

Inorgan

icc

laysofh

ighp

las

tic

ity,

fatc

lays

Organ

icc

layso

fme

dium

tohighp

las

tic

ity

Pea

t,muc

k,

an

dother

highlyorgan

icso

ils

Li ( Li Fl h)


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Lime (or Lime-Flyash)

in asphalt FDR(Full Depth Reclamation) Easy to apply in

FDR process

Provides Pozzolaniceffect to providestrength to thereclaimed basematerial

Water resistance

Strength gain overtime

Old

road

surface

New base

mixture

ready for

compaction

Lime

addedVariable mixing

chamber with milling

and mixing rotor

Working

Direction

S A f A li ti


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Summary Areas of Application

for Lime Stabilization Base Stabilization

Roads (all grades)

Parking lots / Public areas

Upgrades marginal base materialmaking it usable

Asphalt FDR

Structural Fills and Embankments

Site Preparation


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Scarification before lime application

Soil windrow used to containlime before mixing


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Example of lime slurry application

Scarification after lime spreading


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Dry lime application with mechanical spreader4


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Example of lime slurry application

Scarification after lime spreading


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Adding water after dry lime

application

Rotary mixer used for initial mixing


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Rotary mixer with water truck attached

Mixing and pulverization


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Sheepsfoot (above) & padfoot

(below) rollers

Steel roller

MIXING TOOL


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The function of the tool is to remold the clay at thedrilling phase downwards and to mix the binder and thesoil as well as to compact the mixed soil during theuplift.

The blade have an angle towards the rotation, like aboot propeller.

By using a rotation speed high enough and a restrictedlifting speed, it is possible to compact the mix soil as

well as provide the mixing. Usually 100 to 200 rotationsper minute (rpm) are used, with a lifting speed equal to15 to 25 mm per revolution.

The binders are injected through hollow, rotated mixing shaftstipped with some type of cutting tool.

Th h ft b th t l m b f rth r ipp d ith


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The shaft above the tool may be further equipped withdiscontinuous auger lights and/or mixing blades or paddles.

These shafts a remounted vertically on a crawler-mounted, andrange in number from one to eight (typically two to four) percarrier, depending on the nature of the project, the particular

variant of the method, and the contractor.

Column diameters typically range from 0.6 to 1.5 m, and mayextend to 40 m in depth.

In some methods, the mixing action is enhanced bysimultaneously injecting fluid grout at high pressure throughnozzles in the mixing or cutting tools.

The mixing level is expressed by the number of mixing per meterin depth against the amount of the stabilizer injected into theground

SKECTHES FOR PRAPARATIONOF INSTRUCTION DRAWING


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Sketches of Representative

Mixing Mechanism

Example of Augers


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p g


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Schematic showing mixing operation in dry DSM process

Rate of rotation ranges between 120 and 150rpm

Rate of withdrawal ranges between 15 and 30mm per revolution

Dry deep soil mixing construction sequences


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The Soil mixing

tool is rotated intothe ground at a

predetermined

location

Once the tools has reached

the required depthcementitious powder begins

to be jetted into the

disturbed soil from a nozzle

located above the blade

The tool is rotated at

high speed during itswithdrawal to blend

the dry mix materials

with the soil


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Sketches of Drilling PatternCompletedoverlapping and complete treatment or known asWall Type Treatment Pattern in Marine Conditions(Yang, 1997)

Description

R i f l i l i h f


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- Rotation of multiple axis shafts create

relatively movement and shear in soil forsoil reagent mixing.

Number of mixing shafts

- 4 shafts

Major additives

- Lime and cement

MATERIAL SPECIFICATION


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Lime cement are widely referred to as binders and can be

introduced in dry or slurry form.

Table: Chemical Composition

CONSTRUCTION / INSTALLATIONMETHODOLOGY


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Bearing capacity of the Lime claycolumn


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Ultimate bearing capacity

H

Proposed Three

storey house

Proposed Column

2, 2.25ult soil col uQ dH d C

B = Width cf column group

L = Length of column group

H = Height of column group

d= Diameter of ColumnCu= Ave. undrained shear strength of the surrounding soft clay

Lime as a column (cont.)


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2, 2.25ult soil col uQ dH d C Assumption:

Cu= 20 Kpa

H col = 12 m

d = 0.3 m

2, 2.25ult soil col uQ dH d C

Lime as a column (cont.)


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a = relative column area (NA col/BL)

N= Total number of column

q= applied unit load

M col = confined modulus of column

material

M soil = confined modulus of untreated

soil.

1(1 )col soil

qHh

aM a M

Settlement of the column;

Schematic of plate load test


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Schematic of plate load test

Typical Result of plate load test

Documents

Hafez Clay Minerals - 2011 Hafez