Lime Stabilisation Of Unsaturated London Clay

8/14/2019 Lime Stabilisation Of Unsaturated London Clay

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LIME STABILISATION OF UNSATURATED

LONDON CLAY

by

Colin James Urwin

For the MSc in Civil Engineering

London Southbank University

Faculty of Engineering, Science and the Built Environment

November 2007


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ABSTRACT


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CONTENTS

1. Introduction page 1

2. Clays 2

2.1 Clay Minerals2.2.. London Clay

2.2.1 Kaolinite2.2.2 Montmorillonite2.2.3 Illite

2.3 Summary

3. Lime and Lime-Clay Interaction 5

3.1 Lime3.2.. Mechanisms of Lime-Clay Interaction

3.2.1 Lime Modification Cation Exchange3.2.2 Lime Stabilisation Pozzolanic Reactions

3.3 The Effect of Lime on Clay Fabric3.4 Summary

4. Partially Saturated Soils 11

4.1 The Concept of Suction4.2 Matric Suction4.3 Osmotic Suction4.4 Soil-Water Retention Curves4.5 Summary

5. Measuring Suction 18

5.1 A Comparison of Methods5.2 The Filter Paper Technique5.3 Factors Affecting the Filter Paper Technique


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6. Laboratory Procedure page 23

6.1 Sample Preparation6.2.. Suction Testing Filter Paper Method

6.2.1 Apparatus6.2.2 Procedure Drying Curve6.2.3 Procedure Wetting Curve

6.3.. Particle Density Test Small Pyknometer Method

6.3.1 Apparatus6.3.2 Laboratory Procedure6.3.3 Calculating Saturation

7. Analysis and Justification of Experimental Method 31

7.0.1 Experiment Design7.0.2 Sample Preparation7.0.3 Suction Testing7.0.4 Particle Density Testing7.0.5 Other Tests7.0.6 Results7.0.7 Error Analysis

8. Results 36

8.1 Soil-Water Retention Curves8.2 Volume Change v. Volumetric Water Content

9. Discussion 37

9.1 General Observations on the Clay Samples9.2 Water Content and Volume Change9.3 Soil-Water Retention

10... Conclusions 40

10.1 Recommendations For Further Work

11... References 42

Appendix A Laboratory Data 44


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1.0 INTRODUCTION

All clays, depending on their constituent minerals, are susceptible to swelling and

shrinkage if moisture levels change, as happens naturally over a year. If such clays are

covered by an engineering structure, swelling or shrinkage may occur depending on the

state of desiccation when the clay was covered. These effects can be enhanced by

consequent alteration of surface drainage patterns, leaking pipes, or by moisture removal

caused by heated buildings.

This project is an attempt to understand the interactions between water and partially

saturated London Clay, and how the stability of the latter can be improved by the addition

of lime.

A partially saturated soil exerts a potential negative pressure over moisture in its vicinity.

This is known as suction , and it is responsible for drawing water into a soils structure.

As suction increases, the possibility of substantial volume change increases. In the caseof clay, this process can be retarded by the addition of lime, due to reactions occurring at

different scales within the clay fabric.

This project will also attempt to determine experimentally how on-site stabilisation of

London Clay with lime may compare with laboratory specimens prepared to a British

Standard protocol. The British Standard calls for ground clay and lime to be dry mixed,

then water added prior to compaction. This process is impractical on a construction site,

so a more realistic sample preparation involving adding lime to wet clay has also been

studied.

The subsequent four chapters provide some background into topics relevant to this

project, namely: clays, lime-clay interaction, partially saturated soils, and techniques of

measuring suction. Following this, an account of laboratory procedure, and an evaluation

of the tests performed. Finally the results of the testing are presented and discussed.


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2.0 CLAYS

2.1 Clay Minerals

Clays are principally formed from sheets of crystalline minerals. The sheets are created

through the repetition of one of two basic units: the silicon tetrahedron, or the aluminium

octahedron. [Fig. 1] The aluminium octahedral sheets are not electrically neutral and

cannot exist in nature alone, instead combining with one or two tetrahedral sheets to form

stable layered particles, known as 1:1 minerals and 2:1 minerals respectively. [Fig. 2]

(Barnes 2000)

Figure 1. Basic clay units (after Barnes 2002)

These idealised sheets are not always present; isomorphic substitutions are possible

within the unit sheets, for example, the substitution of a larger aluminium atom in the

place of a tetrahedral silicon atom. The effect of this substitution is to induce an overall

negative charge inside the crystal. This resulting negative charge is balanced by an

adsorption of positive ions (exchangeable cations) and polar water molecules. Various

combinations of substituted atoms, stacking method, exchangeable cations and interlayer

water, create the different varieties of clay.

Figure 2. Formation of stable minerals (after Barnes 2002)


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Exchangeable cations are so-called due to an ability to swap places with other cations on

the surfaces of the minerals. The amount of exchangeable cations is expressed as theCation Exchange Capacity (CEC), and is related to the degree of isomorphic substitution

within the crystal lattice (Montanez 2002). This phenomenon is exploited by the addition

of lime to clay, as the resulting increase in calcium cations drives the exchange process,

the effects of which are discussed in chapter 3.

2.2 London Clay

London Clay is a stiff, overconsolidated clay, formed in the south of England by marine

deposition. It is particularly well developed in the London Basin, reaching an average

thickness of 130m. Three main species of clay minerals make up London clay: illite

(70%), kaolinite (20%) and montmorillonite (10%). (Boswell 1951).

2.2.1 Kaolinite

Kaolinite particles [Fig. 3] are produced from many stacked layers of 1:1 minerals. The

unit layers are held firmly together by hydrogen bonds, preventing interlayer hydration.

This results in very low shrinkage/swelling

characteristics. There is little isomorphic

substitution inside the lattice; accordingly, the

CEC is 3-15 Meq/100g. (Barnes 2000).

Figure 3. Kaolinite (after Barnes 2002)

2.2.2 Montmorillonite

The least common species found in London Clay, but also the most hydraulically and

chemically active. It consists of an octahedral sheet sandwiched between two silica

sheets [Fig. 4]. These layers form stacks of between one to ten layers (MALA), held

together only by weak van der Walls forces. This allows water molecules to enter

between the layers and separate them, making montmorillonite very susceptible to


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swelling and shrinkage. A large specific surface

area, and a high incidence of unbalanced charges

means montmorillonite has a very high CEC, in the

order of 100 Meq/100g (Barnes 2000)

Figure 4. Montmorillonite (after Barnes 2002)

2.2.3 Illite

The main constituent of London Clay, illite shares a similar structure withmontmorillonite, except the unit layers are held together by the positive charges of

potassium cations in the interlayer zone. [Fig. 5] However,

not all layers are necessarily bonded in this manner and

London clay can be said, To be a mineral intermediate

between illite and montmorillonite (Boswell 1951).

Particles show a moderate susceptibility to shrinkage and

swelling, and a CEC of 10-15 Meq/100g (Barnes 2000).

Figure 5. Illite (after Barnes 2002)

2.3 Summary

London clay is prone to heave for two reasons; the nature of overconsolidated clay is to

expand if the moisture content increases above historic levels and the illite and

montmorillonite particles are liable to further expansion due to weak interlayer bonding.

However, the high CEC of these species allows modification of the particles structure

through the introduction of other exchangeable cations as in lime modification.


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3.0 LIME AND LIME-CLAY INTERACTION

3.1 Lime

Lime is a broad term, which is used to describe calcium carbonate (CaCO 3), calcium

hydroxide (CaOH 2) and calcium oxide (CaO). These are commonly known as limestone,

hydrated/slaked lime, and quicklime respectively. It is important to note that this project

will use the term lime to mean hydrated-lime only.

Both lime and quicklime will react with clays, affecting the plasticity, grain size,

compressibility and shear strength (Croce and Russo 2003). The effects are similar given

chemically equivalent amounts (i.e. on a molecular weight basis). However, quicklime

reacts violently with 32% its own weight of water. This can be utilised to remove free

water from soils, and the large amount of heat produced by this reaction can further assist

the drying process. In spite of this, lime is the more widely used soil treatment, as the

highly reactive nature of quicklime can corrode equipment and easily burn skin. (Ingles

and Metcalf 1972)

3.2 Mechanisms of Lime-Clay Interaction

When lime is added to soils, two different phenomena occur that result in structural

change: cation exchange and pozzolanic reactions. These two mechanisms are referred to

as modification and stabilisation respectively, and develop over different timescales.

Rogers and Glendinning (1996) found an immediate initial cation exchange between

calcium ions and clay minerals, causing the aggregation of particles, and a subsequent

development of pozzolanic reactions, forming stable compounds that slowly improved

the soils strength and compressibility. The details of these interactions are discussed in

more detail below.


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3.2.1 Lime Modification Cation Exchange

The ability of a clay particle to hold, and therefore potentially exchange, cations is known

as the Cation Exchange Capacity (CEC). The value of which depends on the type of clay

being considered. In terms of this project, the most significant clay in this respect is

montmorillonite. Although London clay only contains ~10% montmorillonite (Boswell

1951), it is highly susceptible to swelling and shrinkage, and has a CEC approximately

ten times greater than illite and kaolinite, the other main constituents of London clay.

MALA state that montmorillonite particles are usually formed from an aggregate of

between one and ten unit layers. These layers are susceptible to much substitution of

Mg +2 for Al +3 in the octahedral [sheet]. The overall negative charge created by this

substitution must be balanced by a cation. As a result, cations present in solution are

attracted towards the mineral surfaces. These adsorbed cations can be exchanged for

others introduced to the environment.

Bell (1975) asserts that the mechanical properties of clay vary with the type of cations

associated with it. If the clay contains a significant proportion of weakly bonded cationssuch as sodium, it will have a tendency to adsorb large quantities of water between the

surfaces of its particles. On the other hand, if the clay comprises cations of stronger

bonding strength such as calcium, it will adsorb less water and its structure will be more

stable.

Mitchell (1993) contends this decrease in water adsorption is possibly caused by various

means: calcium ions (Ca +2) have twice the charge of sodium ions (Na +1), accordingly

less are required to balance the negative charge held in the mineral layers. This reduces

the tendency of water molecules to diffuse toward the surface in order to equalise

concentrations. Equally, a calcium ion has a smaller hydration shell than other typical

cations, allowing calcium ions to be held closer to the mineral surface, and hence the

mineral surfaces to each other. [Fig. 6]


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Figure 6. Strongly hydrated ions like sodium are surrounded by a shell of water which increases their distance from the surface and decreases the attractive electrical force. Calcium ions are held closer to the

surface and have a double positive charge, and consequently a much greater attraction. (after MALA)

3.2.2 Lime Stabilisation Pozzolanic Reactions

A pozzolana is a material that is capable of reacting with lime in the presence of water to

produce cementitious compounds. (Sherwood 1993). Such materials are common in

volcanic regions the name deriving from Pozzuoli, a Roman ash deposit. Clays are

natural pozzolans, and this can be exploited to increase the clays strength.

According to NAASRA (1986), treating clay with lime creates a highly alkaline

environment, dissolving the edges of the clay plates and producing silica, this reacts with

the lime to form a tough water-insoluble gel of calcium-silicate. The gel has the ability to

bind the clay together, and block off the clays pores. Over time, the gel gradually

crystallises into compounds found in ordinary Portland cement. [Fig. 7] (Ingles and

Metcalf 1972).


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3.3 The Effect of Lime on Clay Fabric

As detailed above, lime causes some clay particles to be immediately drawn together, and

is capable of permanently cementing various clay particles to each other. This bonding

of the particles lessens the effect of water

absorption on the soil structure, due to a

reduced ability of the fabric to swell.

(Sherwood 1993).

A second important effect of thisflocculation and cementation process is an

increase in the clays plastic limit. The

below graph shows how the plastic limit of

London clay increases with lime content.

[Fig. 9] It demonstrates that given an

initial moisture content of 35% the clay

would be sticky and impassable, yet an

addition of 2% lime would raise the plastic

limit and transform the clay into a more

useful, compactable material.

Figure 9. Effect of lime addition to the plastic properties of London Clay (after Sherwood 1993)

The final significant effect of lime treatment is apparent on the water retention properties

of clayey soils. Croce and Russo (2003) noted that whilst the Soil-Water Characteristic

Curves (SWCCs) of untreated clayey soil samples were strongly influenced by initial

(compaction) water content, this effect disappeared in lime-treated samples. They also

observed the apparent contradiction between an increase in grain sizes (due to particle

flocculation), and a increase in the water retention capacity of lime-treated clayey soil,

i.e. larger pore spaces should require less applied suction to remove a given degree of

moisture.


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They further compared the SWCCs of untreated samples compacted wet-of-optimum

with those of lime-treated samples and noted they were very close to each other. From

this, they inferred that the cementation process (in clayey soil) induces a change in pore

structure from interconnected to occluded similar to the pore structure created by wet-

of-optimum compaction.

3.4 Summary

Assuming good mixing, the addition of lime to clay will cause an immediate change in plasticity, followed by a long-term increase in strength. The source of these

improvements is calcium working at different scales within the microscopic structure of

clay. Due to its unique structure, montmorillonite can potentially undergo a large

improvement in mechanical properties, so London clay could be noticeably enhanced by

lime addition due to a probable increase in water retention capacity and a reduced

ability to swell.


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4.0 PARTIALLY SATURATED SOILS

4.1 The Concept of Suction

Soils are typically considered to be either dry, or a fully saturated mixture of soil and

water. Whilst this is a convenient model for many purposes, it does not accurately

represent the real world.

Clays, and other soils in a natural state, commonly display a water table that has dropped below the grounds surface. If this soil pore-water was only under the influence of

gravity, the soil above the phreatic level would be dry. However, physical forces act on

the boundary between soil and water, causing the water to be drawn into and held inside

empty pores in the soil fabric. The pore-water pressure in the ground above the phreatic

level becomes negative with respect to atmospheric pressure this being referred to as

suction.

Desaturation of a soil can be caused either by environmental changes, or by physical

changes such as compaction. When degree of saturation is above ~95%, any air present

is in the form of occluded bubbles, and the soil can be considered to follow Terzaghis

principle of effective stress. Conversely, when the degree of saturation drops below 85-

95%, the air phase becomes continuous. This results in a boundary forming at the air-

water interface which experiences surface tension (Corredor 2004).

Surface tension is a property of a liquid that allows it to exert a contractile force on its

surface. At the surface of a liquid a molecule experiences a resultant force towards the

interior of a liquid. In order to maintain equilibrium a tensile pull is generated along the

surface.

Just as a combination of surface tension, meniscus contact angle and tube radius will

cause water to rise up a small diameter (capillary) tube due to pressure differences, the


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same phenomena (capillarity) draws water above the phreatic level of soil. The parallels

between menisci in soil pores and capillary tubes are demonstrated in Figure 10.

Figure 10. Decreases in pore size and water content cause increases in suction

(after Ridley et al 2003, and Fredlund & Rahardjo 1993)

Changes in the level of suction can cause changes

in soil behaviour. Montanez (2002) considers a

fully saturated soil [Fig. 11a]. Under the

application of external load, internal friction can

be overcome, causing displacement of the grains

[b]. However, if evaporation takes place, menisci

will form. This reduces pore-water pressure, andcompresses the (still saturated) soil [c], increasing

the effective stress. If further drying takes place,

pore-water pressure will reduce, and suction will

drop below the air entry value of the soil [d].

An air-water interface will form, and the remaining

Figure 11. Menisci cause bonding of soil particles due to surface tension effects


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water will develop tensile forces along the menisci. This generates increasing normal

forces between the grains, enhancing the stability of the grain structure, and thus soil

strength.

4.2 Matric Suction

At the air-water interface of an unsaturated soil, the pore-air pressure ( ua) is greater than

the pore-water pressure ( uw). The difference ( ua - uw) is referred to as the soil matricsuction.

Matric suction can be defined as a measure of the energy required to remove a water

molecule from the soil matrix without the water changing state. Matric suction is the

result of two mechanisms, capillarity and adsorption.

In terms of the capillarity, the suction is governed by the size of the soils pores: The

smaller the void, the harder it is to remove water from the soil. Hence, suction will

increase as water content decreases, as initially, water is easily removed from the larger

pores.

Adsorbed water [Fig. 12] is, according to Fredlund & Rahardjo (1993), believed to be

responsible for highly negative pore-water pressures (~7000kPa) demonstrated at low

degrees of saturation. They consider that only adsorptive forces, which hold water

electrostatically to the surface of the soil particles, could maintain such great negative pressures.

Figure 12. Categories of water found in soils

(after Head 2006)


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At a given degree of matric suction water the water content can take a range of values,

dependent on whether the soil is wetting or drying. The relationship is hysteretic, and is

considered by Fredlund & Rahardjo to be so due to the geometrically non-uniform nature

of the pores. This is shown in Figure 13 using the capillary tube analogy. In [a], water

will rise to its maximum height for the tube diameter ( r ). However, the presence of a

larger diameter section in [c] prevents the water rising further by capillary action. Yet,

by holding the capillary tube underwater and raising it to the surface (analogous to

saturating the sample), a larger volume of water can be held [d].

Figure 13. Non-uniform pore sizes causing different levels of suction depending whether the soil is drying or wetting(after Fredlund & Rahardjo 1993)

4.3 Osmotic Suction

Fredlund and Rahardjo (1993) define osmotic potential as a measure of the additional

stress necessary to remove a water molecule from the water phase, due to the presence of

dissolved salts.

An increasing level of dissolved salts in the pore-water will lead to a lower relative

humidity at the air-water interface. The effect of this is to reduce the osmotic potential

aiding the transfer of water molecules. This will seemingly raise the value of suction


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above that provided by the soil matrix. This combination of matric suction and osmotic

suction is referred to as total suction.

However, the significance of osmotic suction is defined by Corredor (2004), who states,

Osmotic suction is difficult to quantify specifically, and is typically not determined in

the majority of soil mechanics applications. Furthermore, Fredlund & Rahardjo assert:

Laboratory data has indicated that a change in total suction is essentially equivalent to a

change in the matric suction for many situations.

4.4 Soil-Water Retention Curves

Soil-water retention curves (SWRCs) define the relationship between suction, and water

content measured in one of several ways. Generally two curves are shown [Fig 14],

denoting either the progressive wetting or drying of the soil. The relationship is

hysteretic, and the two lines represent the boundaries of a full wetting or drying cycle. In

practice an infinite number of intermediate curves known as scanning curves can be

found between the two boundary curves, representing a history of partial wetting and

drying cycles.

Figure 14. Example of hysteretic soil-water retention curve (after Corredor 2004)


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Corredor (2004) states a number of parameters may be identified from a SWRC: the

desaturation point, the air entry value (AEV), and the initial residual condition. [Fig 15]

The desaturation point determines the suction necessary for the formation of

occluded bubbles in the pore-water, caused by dissolved air withdrawing from

solution.

The AEV defines the suction required to draw air into the largest pores. As such,

as particle size, and thus pore-size, decreases, the AEV increases.

The initial residual condition is defined as the moisture content at which

extremely large suction values are needed to remove further water effectively

adsorbed water and water of hydration.

Figure 15. Variables associated with the soil-water retention curve

A SWRC can be used from an engineering design perspective to infer several properties

of soil, such as shear strength, volume change behaviour and permeability. (Fredlund &

Rahardjo 1993)


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A number of different mathematical models have been proposed to quantify the processes

that give a SWRC its shape. Typically these involve three of four independent

parameters, which are adjusted so that the expression will fit a curve derived

experimentally. This method reduces the information needed to give an accurate

description of a soils water-retention characteristics, and in theory can allow the

prediction of an SWRC from particle size data only (Corredor 2004).

4.5 Summary

Suction is negative pore-water pressure, the value of which is related to the amount of

water present, pore size distribution, inter-particle forces and water chemistry.

Matric suction is of particular interest to engineers, because it is the variable which is

strongly influenced by environmental changes encountered in the field.

Suction can be considered as a measure of the energy required to remove water held in asoil, or a measure of a soils affinity for water. This is important, as changing levels of

water in certain clays produces heave. By measuring suction it can be understood which

soils are more susceptible to producing heave effects.


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5.0 MEASURING SUCTION

5.1 A comparison of methods

Techniques of measuring soil suction can be grouped into direct and indirect categories.

Direct techniques involve the instrument used measuring the actual pore water suction,

whilst indirect methods measure a related parameter, that can provide a measurement of

suction through a calibration procedure.

Two instruments are commonly used for direct measure of matric suction: tensiometers

and pressure plate apparatus. Both operate on the principle of measuring negative pore-

water pressures through the interface of a semi-permeable (high air-entry value) porous

ceramic, in contact with the soil fabric. Tensiometers are limited in their usage due to the

possibility of cavitation of water inside the tensiometer below suctions of approximately -

90kPa. Pressure plate (axis-translation) instruments attempt to overcome this problem by

subjecting an unsaturated soil to an external positive pressure. This increases the pore-water pressure by the same amount as the applied increase in air pressure. The difference

between the air and pore-water pressure (i.e. the matric suction) remains constant and can

be measured, yet the positive pressures involved prevent cavitation occurring.

Indirect methods of measuring soil suction include psychrometers, filter paper and

thermal conductivity sensors. A psychrometer is able to determine total suction by

controlling and measuring the condensation and evaporation of water, which in turn

measures the relative humidity either inside the soil, or close to the soils surface. The

filter paper technique is based on the principle that an absorbent material will exchange

either water or water vapour, when in contact with, or in close proximity to a soil, until

equilibrium is reached; allowing the calculation of suction from the weight increase of

the paper. Thermal conductivity sensors perform a measurement of matric suction by

measuring the heat dissipation through a calibrated porous block, the moisture content of


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which has been allowed to equilibrate with a soil in a similar manner to the filter paper

technique.

A summary of the common techniques of measuring suction is below: (adapted from

Fredlund and Rahardjo 1993)

Device Suction componentmeasured

Range (-kPa) Comments

Tensiometer Matric 0 90* Useful in the field, but limited by rangeof measurement.*1500 if internal water is pre-

pressurised

Pressure plate apparatus(axis translation)

Matric 0 - 1500 Requires laboratory apparatus.

Psychrometer Total 100 - ~8000 Temperature of air and soil andapparatus must be controlled to anextreme degree. Dirty or corroded tipscan confuse results.

Filter paper Matric or Total Entire range Results are highly user dependent, must be performed carefully and with a high

degree of repetition.

Thermal conductivitysensor

Matric 0 - ~400 Electronics and porous block commonly deteriorate with time.Porous blocks are also very fragile.Multi-modal, non-linear calibrationcurve.

5.2 The Filter Paper TechniqueLeong et al (2002) note that the idea of indirectly measuring suction by equilibrium with

a known absorbent material can be traced back to 1916, when carefully selected seed

husks were used, following a similar procedure to the modern technique. The method has

been improved since, firstly by substituting blotting paper, and more recently filter paper.

Fredlund & Rahardjo (1993) observe that the technique had not gained general

acceptance at that time, and Head (2006) offers a procedure based upon the ASTM


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standard. It is noted that no equivalent British Standard exists regarding the filter paper

technique. Leong et al , have attempted to optimise the technique, and recommend

various improvements upon the ASTM method, including different calibration curves.

They highlight the need for a fuller understanding of the method, and problems

encountered by users.

The general principle of the filter paper technique is that a standard filter paper is

exposed to a soil sample inside a sealed container, allowing the suctions of the two

materials to reach equilibrium through moisture exchange. If the materials are in direct

contact water will flow between the two, if held apart the only transfer through vapour flow will occur, relating matric and total suction respectively. The filter paper is

removed, and its water content ascertained. This can be related to the calibration curve

for that brand of filter paper, giving a corresponding value of suction. It is a simple and

relatively cheap procedure to perform, that requires less specialised equipment than the

other techniques mentioned.

Ridley et al (2003) have investigated the accuracy of the filter paper technique, and

believe it is possible to measure suction to an accuracy of +/-10% providing the

procedure is followed closely.

5.3 Factors affecting the filter paper technique

Researchers who have studied the filter paper technique (Leong et al , Fredlund &

Rahardjo, Bulut & Wray, Ridley et al ) all regard the strict following of laboratory

procedure as the most important factor in obtaining accurate and repeatable tests.

Furthermore, not only is the same protocol necessary, but it must be performed in a

similar manner each time, for example it is critical that during testing samples are opened

quickly and the damp filter papers hastily sealed to prevent moisture loss to the

atmosphere.


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A second factor of critical importance is the time allowed for contact between the soil

and paper. According to Fredlund & Rahardjo (1993), seven days is a minimum, but also

sufficiently long enough that prolonged contact offers greatly diminishing returns. Leong

et al stated equilibration times of between two and five days were acceptable for matric

suction measurements, yet noted that longer times produced more convergence between

wetting-up and drying calibration curves, especially for total suction measurements.

They also noted that the necessary equilibration time can be lessened by matching the

volume of the container to the sample reducing the volume of air enclosed.

A third significant factor in producing accurate and repeatable results is how the samplesare stored when undergoing equilibration. Fredlund & Rahardjo assert that the

temperature of storage does not affect the results, providing that temperature variations

are minimized. Leong et al agree, stipulating that temperature fluctuations should be

kept below +/- 1 oC.

Filter paper quality is also relevant to the accuracy of the procedure, as filter papers from

the same brand are considered identical, in the sense they will use the same calibration

curve. Hamblin found near-identical calibration curves for two batches of Whatman No.

42 filter papers produced two years apart. A meta-analysis of calibration curves by

Leong et al (2002) showed that Whatman No. 42 papers were more consistent than

another paper recommended by ASTM: Schleicher & Schuell No. 589.

Some researchers have been concerned with bacterial or fungicidal growth adversely

affecting the weight increase of the filter papers, and pre-treated them with various

preparations. However, Leong et al have found no problems of this nature, and suggest

the time-scales are too short for this type of fouling to occur.

Some doubts have been raised about the accuracy of the filter paper technique when used

with saline soils. The equilibrium water content in Whatman No. 42 papers has been

shown to be significantly reduced when salt is present (Ridley et al ), and therefore


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suction may be overestimated. This has been demonstrated in soils that have been

flooded by the sea.


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6.0 LABORATORY PROCEDURE

6.1 Sample Preparation

A representative sample of London Clay was air dried, and crushed by mortar and pestle.

In total six specimens of were prepared, each consisting of London Clay with an

additional 4% lime by weight, and 27% water by weight. (Optimum for compaction).

Two samples were prepared by mixing the powdered London Clay with lime, then adding

water (dry mix). Four other samples were prepared by adding the water to the London

Clay samples, then adding in the lime (wet mix).

All samples were allowed to mellow for one hour before compaction according to

BS1377-4:1990.

Samples were either left to cure in a dessicator (dry cure), or submerged in distilled water

(wet cure), for either 28 or 84 days.

The following samples resulted:

28-day wet cure, wet mix,

28-day wet cure, dry mix,

84-day wet cure, wet mix,

84-day wet cure, dry mix,

28-day dry cure, wet mix,

28-day dry cure, dry mix.


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The samples were extracted from their moulds, and smoothed as far as possible with a

palette knife, and any excess trimming were used to ascertain the moisture content.

6.2 Suction Testing - Filter Paper Method

6.2.1 Apparatus

Analytical balance readable to 0.0001g

Temperature controlled enclosure

Filter papers - Whatman #42 grade, 70mm diameter

Perspex discs, 75mm diameter, 22mm thick

Small sealable Polythene bags

Indelible marker

Tweezers

Scalpel

Cling-film

Sellotape

Bubble-wrap

Large sealable polythene bags

Digital callipers readable to 0.1mm

Laboratory oven

6.2.2 Procedure Drying curve

1. Ensure all surfaces and apparatus are oil, dust and moisture free.

2. Fit filter paper discs. Using tweezers, place three filter papers on the top side of

the sample, and three on the underside. Sandwich sample and filter papers


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between two Perspex discs. Wrap with multiple layers of tight cling-film and

secure with Sellotape.

3. Store sample. Wrap samples in bubble-wrap and seal in large plastic bags. Store

in a temperature controlled environment for seven days. It is desirable to establish

a standard storage time to the hour.

4. Weigh two small polythene bags to 0.0001g using the analytical balance, record

the weight of both ( mbag ) and mark each bag with the indelible marker for future

identification.

5. Remove filter papers. Using the scalpel to cut the cling-film, expose the top

filter papers, and using tweezers, remove only the middle paper. Quickly place

the middle paper in one of the small sealable polythene bags it is critical to

expose the filter paper to the atmosphere for the least time possible. Repeat step

for bottom middle filter paper.

6. Weigh filter papers. Using the analytical scale, immediately weigh the two wet

filter papers in their bags ( mbag + wet paper ). Record weights.

7. Weigh soil sample. Record mass of soil sample to 0.01g ( m sample )

8. Measure soil sample. Using digital callipers measure the diameter and width of

the soil sample to 0.1mm. Record three values for each, and calculate the two

average values.

9. Dry filter papers. Remove the filter papers from their bags, and dry in an oven at

105 oc for 1 hour. Using tweezers quickly remove filter papers from oven and

immediately weigh to 0.0001g using the analytical balance ( m paper ). Minimal

exposure to the atmosphere is critical at this stage.


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10. Calculate the moisture content of the filter papers ( w p) from:

p paper

paper bag wetpaper bag wm

mmm=

+

100

11. Calculate soil suction ( pk ) from:

If w p > 47%: pk = 10(6.05 2.48 log w p) kPa

If w p < 47%: pk = 10(4.84 0.0622 w p) kPa

12. Dry soil sample. Allow a set amount (in this case 3 g) of moisture contained

within soil sample to evaporate into atmosphere at room temperature.

13. Repeat from step 1.

6.2.3 Procedure Wetting curve

1. Ensure all surfaces and apparatus are oil, dust and moisture free.

2. Wet filter paper. Using tweezers fully soak two stacks of five* filter papers with

distilled water. (* The number of filter papers can be adjusted to define the

moisture-mass increase in soil weight per cycle in this case 3g)

3. Fit filter paper discs. Using tweezers, place one set of filter papers on the top side

of the sample, and the second set on the underside. Sandwich sample and filter

papers between two Perspex discs. Wrap with multiple layers of tight cling-film

and secure with Sellotape


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4. Store sample. Wrap samples in bubble-wrap and seal in large plastic bags. Store

in a temperature controlled environment at 20 oC for seven days. It is desirable to

establish a standard storage time to the hour.

5. Weigh two small polythene bags to 0.0001g using the analytical balance, record

the weight of both ( mbag ) and mark each bag with the indelible marker for future

identification.

6. Remove filter papers. Using the scalpel to cut the cling-film, expose the top

filter papers, and using tweezers, remove only the inner three papers. Quickly place the middle paper in one of the small sealable polythene bags it is critical

to expose the filter paper to the atmosphere for the least time possible. Repeat

step for bottom middle three filter papers.

7. Wrap soil sample in cling-film to prevent moisture loss.

8. Weigh filter papers. Using the analytical scale, immediately weigh the two wet

filter papers in their bags ( mbag + wet paper ). Record weights.

9. Weigh soil sample. Record mass of soil sample to 0.01g ( m sample )

10. Measure soil sample. Using digital callipers measure the diameter and thickness

of the soil sample to 0.1mm. Record three values for each, and calculate the two

average values (D av & t av).

11. Dry filter papers. Remove the filter papers from their bags, and dry in an oven at

105 oc for 1 hour. Using tweezers quickly remove filter papers from oven and

immediately weigh to 0.0001g using the analytical balance ( m paper ). Minimal

exposure to the atmosphere is critical at this stage.


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12. Calculate the moisture content of the filter papers ( w p) from:

p paper

paper bag wetpaper bag wm

mmm=

+

100

13. Calculate soil suction ( pk ) from:

If w p > 57.2%: pk = 10(2.094 0.0158 w p) kPa

If 15.5% < w p < 57.2%: pk = 10(4.573 0.0449 w p) kPa

If w p < 15.5%: pk = 10(4.842 0.0622 w p) kPa

14. Repeat from step 1.

6.3 Particle Density Test Small Pyknometer Method

6.3.1 Apparatus

Laboratory oven

Mortar and pestle

2mm sieve

3 Density bottles

Source of vacuumAnalytical balance readable to 0.0001g

Distilled water

Constant-temperature water bath


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6.3.2 Laboratory Procedure

1. Remove dissolved air from water. Boil distilled water for 30min; cool in a strong,

sealed container.

2. Prepare density bottles. Clean each bottle with ethanol, and air dry. Weigh each

bottle and stopper to 0.0001g and record value ( m1).

3. Prepare clay. Dry clay at 80 oc in oven for two hours, crush with mortar and pestle

to pass a 2mm sieve.

4. Place clay in bottles. Fill each bottle to approximately one third full with the clay.

Brush any loose clay off external surface of bottle. Replace stopper. Weigh each

bottle to 0.0001g and record value ( m2).

5. Remove air from clay. Half fill each density bottle with de-aerated distilled

water. Apply vacuum to bottle. Reduce pressure to 2kPa slowly, to prevent dropsof suspension being lost due to violent bubbling. Periodically release vacuum and

stir liquid. Repeat until no further air loss can be seen.

6. Fill density bottles to brim with de-aerated distilled water. Immerse bottles in

constant-temperature bath for 1 hour. Remove from bath, and replace stopper.

Wipe dry all liquid from exterior of bottle.

7. Weigh bottles. Weigh each bottle to 0.0001g ( m3).

8. Calibrate bottles. Clean out each bottle, and fill to brim with de-aerated distilled

water. Immerse in constant-temperature bath for 1 hour. Replace stopper. Wipe

dry exterior of bottle. Weigh to 0.0001g ( m4).


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9. Calculate particle density ( s). In this case l = 1.000 Mg/m 3:

( )( ) ( ) s

l

mmmmmm =

2314

12

6.3.3 Calculating Saturation ( S r )

1. Calculate moisture content ( w), expressed as a fraction. This should be

recalculated for each suction reading:

wm

mm

solids

solids soil =

2. Calculate bulk density ( b). This should be recalculated for each suction reading,

using the average thickness and diameter previously recorded (units: Mg/m 3):

( ) bavav soil

t Dm

=

42

3. Calculate the (partially saturated) void ratio. This should be recalculated for each

suction reading:

( ) ewb

s =+ 11

4. Calculate the degree of saturation ( S r ) for each suction reading, expressed as a

percentage:

100=w

sr e

wS


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7.0 ANALYSIS AND JUSTIFICATION OF

EXPERIMENTAL METHOD

7.0.1 Experiment Design

Two variables were selected for investigation: mixing method and curing time. The

mixing method relates to whether powdered lime is added to wet or dry, powdered

London clay. Previous work has shown a potential difference between the two, possibly

due to hydration effects. It is of interest as BS1377 defines the standard technique to be

dry mixing, but this does not reflect mixing processes that are feasible on-site. The wetmixing technique used is an attempt to replicate on-site mixing of lime and London clay

more realistically. The variation of curing time allows insight into the duration of the

cementation process responsible for stabilising the clay fabric.

Each sample for testing contained 4% lime by weight; chosen to represent a typical

amount used in the field. Lime rather than quicklime was used, as it presented fewer

hazards, due to the caustic nature of the latter.

It was decided to measure the matric suction of the clay only, as this would provide data

relevant to changes in the clays structure and adsorption potential. It was assumed that

the osmotic suction would be mostly constant between the different samples, as they were

of equal chemistry and salinity.

7.0.2 Sample preparationFor the reasons described above, the dry-mixed clay specimens were mixed and

compacted according to BS1377 (Preparation of disturbed samples for testing). The wet-

mixed samples were prepared in a similar and consistent manner, except water was added

prior to the lime.


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The specimens were mixed with a water content of 27% by weight, the optimum for

compaction. This did not account for any surplus water to account for that evaporated

due to exothermic reactions, or used in hydration of the lime. It has been suggested that

an additional 5% water above wopt is normal when adding lime to a soil.

Removing the samples from the circular moulds, and flattening the surfaces was difficult,

especially so with the 90 day water-cured specimens, as their lack of plasticity resulted in

some damage. Although this was repaired, it may have resulted in a less homogenous

fabric than desired. An associated problem was that the 28 day air-cured samples were so

hard that proper surface preparation was effectively impossible, resulting in a lumpy,undulating surface that prevented good contact with the filter papers. It is suspected that

this prevented a true measurement of matric suction, as any voids would have lead to

vapour transfer, resulting in total suction measurement. However, it is doubtful that

seven days would be long enough for equilibration in this respect (Ridley et al 2003). It

was found that this problem lessened as the samples moisture content increased, and

plasticity returned.

7.0.3 Suction Testing

Carrying out the filter paper protocol was relatively trouble free, and could mostly be

performed with little variance between repetitions.

The samples were stored in a temperature controlled room, wrapped in bubble wrap and

double bagged, to smooth any fluctuations in temperature produced by the cooling

system.

Heads (2006) filter paper protocol called for the use of microcrystalline to fully seal the

samples whilst stored. This was deemed unnecessary if the samples were wrapped in a

sufficient amount of cling-film, as per Ridley et al (2003), as although some moisture

would diffuse through the plastic, it would not prevent equilibrium of suctions being

reached. This probably contributed to a lack of moisture content increase over repeated


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weeks testing of the air-cured samples, although a greater factor was likely the dry

protective filter papers competing for the wet filter papers moisture.

7.0.4 Particle Density Testing

This was performed in compliance with BS1377: Part2: 1990 Small pyknometer

method, except it was performed three times, as in Heads (2006) opinion, this offers

greater accuracy. The 84 day water-cured samples were used, as after months of suction

testing, the cementation would have fully developed. These samples were dried at 80 oC,

to prevent evaporation of adsorbed water. The procedure defined in BS1377 called for a

2kPa vacuum to be applied, however the vacuum pressure could not be measured in the

laboratory, and it is doubtful that the required pressure was reached. As such, it is

difficult to be satisfied of the accuracy, especially after comparing the measured values to

textbook values of the particle density of London clay.

7.0.5 Other Tests

Determining the organic content and sulphate content of the clay, may have produced

some relevant results, as these compounds can deplete available lime and also retard or

inhibit the lime-clay reactions (Mitchell & Jardine 2002). However, these tests were not

performed due to time constraints. The same applies to a hydrometer sedimentation test,

which may have given some insight into the detail of lime-clay interaction.

7.0.6 Results

Although there is some disagreement over certain aspects of the drying calibration curves

offered by ASTM for measuring total suction (Leong et al 2002), their standard curves

for matric suction are widely regarded as acceptable. In terms of a separate wetting

calibration curve, ASTM do not propose one, however Corredor (2004) acknowledges

there is a degree of hysteresis between initially wet and initially dry filter papers, and

provides a calibrated drying curve for Whatman No. 42 filter papers.


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Soil Water Retention Curves can be presented in terms of gravimetric water content,

volumetric water content, or degree of saturation. Of these, the degree of saturation

arguably imparts the most information about the state of the soil, although it can be

difficult to measure accurately. In terms of this project, when the degree of saturation

was calculated, the initial values for the water-cured samples were between 136% and

109%. These values are obviously wrong, and probably relate to inaccurate

measurements of sample volume and particle density. A further problem with plotting

the degree of saturation is that as a result of volume change of the samples, the degree of

saturation appears to fluctuate, even though the volumetric water content is steadily

reducing. This is possibly due to inaccurate height measurements affecting the calculated bulk density. To avoid these problems, the volumetric water content has been used,

however it is noted that this also relies on accurate volume measurement.

As mentioned, the samples volumes were difficult to measure, especially with the air-

cured specimens. This was due to the undulating sample surfaces, requiring an average

of several readings to be taken. Because of this, the volume change of the samples is a

function of the change in diameter only.

7.0.7 Error Analysis

By estimating the accuracy of measurement taken, an indication of the overall accuracy

of the results can be obtained through a process of combining the root mean squares of

the initial values. The estimated errors are as follows:

Accuracy of analytical balance +/- 0.0005g

Accuracy of large balance +/- 0.01gEvaporation losses from samples +/- 0.1g

Evaporation losses from filter papers +/- 0.002g

Sample diameter +/- 0.05mm

Sample height +/- 1mm

The potential errors that result from these readings are:

Percentage change in volume +/- 0.1%


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Suction +/- 8%

These values compare with the findings of Ridley et al (2002), who have measured a +/-

10% error in suction measurements taken by the filter paper method when compared to

other techniques.

It was felt that it would be ineffective to try to fit the SWRCs to equations developed by

Fredlund & Xing, or van Genuchten, as only a portion of the SWRC was recorded in each

case.


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8.0 RESULTS


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9.0 DISCUSSION

9.1 General Observations on the Clay Samples

Of the 28-day air-cured samples, the wet-mixed sample displayed a coarser, lumpier

fabric than the dry-mixed sample.

The visual differences between the 28-day water-cured samples were less obvious,

although the wet-mixed sample was able to lose water through evaporation at a greater

rate than the dry-mixed sample.

Both 84-day water-cured samples cracked to some degree upon gradual drying out.

Whilst the dry-mixed sample only suffered from slight cracking at its surface, the wet-

mixed sample developed pronounced cracking, until it catastrophically failed at

approximately 18% volumetric water content.

9.2 Water Content and Volume Change

It is difficult to compare the effects of curing time on the clays ability to change volume.

Because the 28-day water-cured samples began the test with a higher water content, and

underwent a greater loss of water, it was expected that they would experience a greater shrinkage than the 84-day water-cured samples, even before the effects of a progressive

cementation process are considered.

The effect of the mixing procedure on volume change is more pronounced. When

considering both 28-day water-cured samples, it seems the dry-mixed clay reaches its

shrinkage limit at approximately 30% volumetric water content, contracting by about 7%.


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However, the wet-mixed sample continues shrinking past this point, until appearing to

reach its shrinkage limit at roughly 20% volumetric water content, and by this stage its

volume has decreased by around 9%.

A similar pattern was demonstrated

by the 84-day water-cured samples:

The dry-mixed sample performed

better, by reaching its shrinkage limit

earlier. When interpreting this pair

of lines, it must be considered thatthe 84-day water-cured wet-mixed

sample prematurely crumbled, but

the gradient and trend of the graph at

this point suggests this is the case.

The two air-cured samples appear to show the same behaviour, although due to different

initial water contents, it is hard to say this with certainty. The dry-mixed specimen does

appear to have reached a point at roughly 2% of its initial volume were it did not expand

further. The corresponding point on that samples SWRC strengthens the assumption

that the sample was approaching its maximum volumetric water content. On the

contrary, the wet-mixed sample appeared to continue to expand until the end of the

testing period. This maybe suggests a greater degree of porosity, as it was able to hold a

greater volume of water, compared to the dry-mixed sample. This could be compared to

the results of Croce and Russo (2003) [chapter 3.3], who have found the cementation

process induces a change in pore structure from interconnected to occluded.

The above observations suggest definite differences between the samples created by the

method of mixing. It appears that the dry-mixing process of BS1377 produces a much

more intimate mix of lime and clay, resulting in a more homogenous clay fabric, a more

occluded pore structure and better volume change characteristics. Unfortunately it is not

8.2 Volume Change versus Volumetric Water Content

90.0

92.0

94.0

96.0

98.0

100.0

102.0

104.0

0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800

Volumetric Water Content (%)

P e r c e n

t a g e o f

I n i t i a l D i a m e t e

Wet mix - 28 days Water Cure

Dry mix - 28 days Water CureWet Mix - 84 days Water Cure

Dry mix - 84 days Water Cure

Wet mix - 28 days Air CureDry Mix - 28 days Air Cure


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possible to see if these differences reduce with a longer curing time (due to diffusion of

the lime) because of the destruction of the 84-day water-cured dry-mixed sample.

9.3 Soil-Water Retention

The Soil-Water Retention Curves (SWRCs) produced by the water-cured samples

demonstrate two trends: Dry-mixing increases water retention capacity compared to wet-

mixing, and curing time increases the water retention capacity in both cases, although the

differences between the two mixing styles are reduced.

Again, from observation of the soil, it appears that the more homogenous nature of the

dry-mixed samples could provide reasons for this. If the lime and clay are not well

mixed portions of the montmorillonite fraction will remain unmodified, and parts of the

fabric will remain uncemented leading to a more interconnected pore structure. This

would tend to reduce the ability of the clay to retain water, as shown by the SWRCs.

A large difference between the

SWRCs of the two air cured

samples are noted, however due to

the problems encountered in

measuring their volume accurately,

and the lack of close contact with

the filter paper due to their surface

profile, it is difficult to judge the

significance of these two curves.

8.1 Soil-Water Retention Curves

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

1 10 100 1000 10000 100000

Suction (kPa)

V o l u m e t r i c

W a t e r

C o n

t e n t

( % )


Dry mix - 28 days Water Cure


Dry Mix - 84 days Water Cure

Wet mix - 28 days Air Cure

Dry Mix - 28 days Air Cure


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10.0 CONCLUSIONS

Both of the mixing techniques studied create an improvement in the properties of London

clay. Water retention capacity increases, and the potential for volume change decreases.

These changes would the clays ability to cause structural damage by experiencing heave

in response to changing environmental water levels.

The main difference between wet and dry mixing is the degree of intermingling between

the two substances: Crushing powders together results in a better mixing than adding

lime to wet clay, as the aggregation of clay particles will prevent this.

A consequence of this is apparent when on-site mixing occurs, the expected improvement

of the clay will be less than a sample prepared in a laboratory to the British Standard

BS1377. The quality of mixing will determine the clays ability to resist heave.

The clays heave properties will continue to improve over time, as the lime diffusesthrough the clays structure, enabling further cementitious reaction to take place. Given

enough time the improvement of the clays properties may begin to converge with those

found in the laboratory.

Measuring clays suction using the filter paper technique can give good and useful results

provided the procedure is followed closely, and enough data points are collected. Care

must be taken with air-cured samples to ensure a flat surface to provide good contact with

the papers. This could be achieved though a suitable abrasive process.


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10.1 Recommendations for Further Work

Mercury intrusion techniques, and a particle size distribution analysis, may allow greater

insight into the differences in clay fabric created by the two mixing techniques studied.

Furthermore, by allowing enough curing time for the lime to fully diffuse through the

clay, it may be possible to understand how much convergence there is between the

properties developed by BS1377s dry-mixing procedure, and more realistic on-site

mixing procedures.


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11.0 REFERENCES

ASTM D 5298 (1994) Standard Test Method for Measurement of Soil Potential (Suction)Using Filter Paper , American Society for Testing and Materials International, WestConshohocken ( www.astm.org )

Barnes, GE (2000) Soil Mechanics, Principles and Practice (Second Edition) , PalgraveMacmillan, Basingstoke

Bell, FG (1975) Methods of Treatment of Unstable Ground , Butterworth & Co.(Publishers) Ltd, London

Boswell, PGH (1951) The Contribution of Clay Mineralogy to the Study of theDiagenesis of Sediments, Clay Minerals , Vol. 1, Issue 8, Page 246-251

BS1377 (1990) Methods of test for soils for civil engineering purposes , British StandardsInstitute, London

Bulut, R & Wray, WK (2005) Free Energy of Water-Suction in Filter Papers,Geotechnical Testing Journal , Vol. 28, No. 4 (Also: GTJ12307 from www.astm.org )

Corredor, MLM (2004) Laboratory and Numerical Investigations of Soil Retention

Curves , Thesis, Imperial College of Science Technology and Medicine, London

Croce, P & Russo, G (2003) Soil Water Characteristic Curves of Lime StabilizedSoils, International Workshop on Geotechnics of Soft Soils Theory and Practice ,Vermeer, Schweiger, Karstunen & Cudny (Eds.), VGE Verlag, Essen.

Fredlund, DG & Rahardjo, H (1993) Soil Mechanics for Unsaturated Soils , John Wiley& Sons Inc., New York

Hamblin, AP (1981) Filter-Paper Method for Routine Measurement of Field Water Potential, Journal of Hydrology , Vol. 53 pp. 355-360

Head, KH (2006) Manual of Soil Laboratory Testing Volume 1 (Third Edition) ,Whittles Publishing, Caithness

Ingles, OG & Metcalf, JB (1972) Soil Stabilization , Butterworths PTY Ltd, Sydney

Leong, EC; He, L & Rahardjo, H (2002) Factors affecting the Filter Paper Method for Total and Matric Suction Measurements, Geotechnical Testing Journal , Vol. 25, No. 3,

pp. 225-231


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MALA , Lecture Notes, Geol212, Clays , Malaspina University, British Columbia,Canada , Retrieved from: www.mala.bc.ca/~earles/geol212/lectures/unit01/uiuc-clays.pdf ,on 24/09/2007

Mitchell, JK (1976) Fundamentals of Soil Behaviour , John Wiley & Sons Inc., NewYork

Mitchell, JM & Jardine, FM (2002) A Guide to Ground Treatment , ConstructionIndustry Research and Information Association, London

Montanez, JEC (2002) Suction and Volume Changes of Compacted Sand-BentoniteMixtures , Thesis, Imperial College of Science Technology and Medicine, London

NAASRA (1986) Guide to Stabilization in Roadworks , National Association of StateRoad Authorities, Sydney

Ridley, AM; Dineen, K; Burland, JB; Vaughan, PR (2003) Soil Matrix Suction:Some Examples of its Measurement and Applications in Geotechnical Engineering,Geotechnique , Vol. 53, No. 2, pp 241-253

Rogers, CDF & Glendinning, S (1996) Modification of Clay Soils Using Lime, LimeStabilisation , Rogers, Glendinning & Nixon (Eds.), Thomas Telford, London

Sherwood, PT (1993) Soil Stabilization with Cement and Lime , Transport ResearchLaboratory, Department of Transport, HMSO, London


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APPENDIX A LABORATORY DATA

Lime Stabilisation Of Unsaturated London Clay

Documents

Transcript of Lime Stabilisation Of Unsaturated London Clay