MPhil Presentation

8/2/2019 MPhil Presentation

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Research Aim

Directly comparing California Bearing Ratio testwith the new European Volumetric Expansion test.

Materials to be considered are fine grainedstabilised soils

Stabilisation: As the name implies, involves a

ground improvement technique which alters theproperties of the existing soil, so as to create anew site material capable of better meeting thetask in hand.


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Background

Current concerns are that the CBR swelltest may be giving a green light to certain

materials which would, when subjected tosite conditions, react in a different way.

Conversely, the new European test may begiving a red light to potentially suitableprojects.


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The CBR SoakingProcedure

Working Example:

Typical Soil:

Compacted to standard

Proctor DensityPermeability = approx

1x10-7m/s = 25.9mm

in 3days!

If the saturated soilheaves;

5% heave = 1.3mm

in 3days!


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Durability

Testing (G3) Volumetric Expansion New BS

prEN13286-49 Un-tested on UK soils?

Binder suitability Degree of pulverisation

(6.3mm BS Test sieve) Specimen manufacture (96%

of Standard Proctor density) Curing regime (1.5 x

workability of binder) Density related Moisture related Grading related What expectations have we?


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Durability

Testing (G3) Volumetric Expansion New

Modified procedure

Larger specimen size

Wider range of materials

Representative sampling

Degree of pulverisation

Site equipment (MCV) Realistic curing times &

temperatures


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Loss of Strength

on ImmersionLoss of strength on immersion:

B.S. 1924:1975

10 No. specimens prepared5 No. air cured for 14 days

5 No. air cured for 7 days

And totally immersed for afurther 7 days

At 14 days of age the soakedspecimens have achievedover 80% of the strength ofthat achieved by theunsoaked specimens


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Historical

Literature Review In 1962 Sherwood conducted a trial looking at the effects of

sulphates on cement and lime stabilisation. One part of the paper looks at the effect of immersion and

percentage clay fraction against sulphate content. It concludes that under certain conditions lime or cement treated

soils are more likely to disintegrate when the soil contains a high clayfraction, when in the presence of sulphate solution.

It also showed that when the clay fraction is removed, the risk ofdisintegration is also removed.

The report clearly achieved what it set out to achieve, and that was

to create an environment in the laboratory where, when one elementwas added or removed from the mix, a change in characteristicscould be monitored. (Unconfined soaked specimens were used as thecontrol test).


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Historical Literature

ReviewSpecification for Highway Works, 5thEdition, 1976

Included a specification for cementstabilisation, but not for lime stabilisation,and it specified an upper limit of:

< 0.25% total sulphate for cohesive soils

< 1% for granular materials.


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Historical

Literature ReviewIn 1986 the DTp Specification for Highway Works(6th Edition) included for the first time aspecification for lime stabilisation.

This issue of the specification decided to drop thesulphate content as a tool to control the use ofcement stabilised materials and put in its place animmersion test (Loss of strength on immersion).

As for Lime stabilisation at this point there were nodurability tests in place (only an upper sulphatecontent of


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Historical LiteratureReview (Problems

incurred) Lime/Lime and Cement Stabilisation First major problems occurred in the UK in the late 1980s: Saxmunden Bypass (Conclusion better site control required) M40 Banbury IV Contract

Initial views: very hot summer during the period of stabilisation Insufficient water added. Investigation showed CBR specimens did not saturate throughout as had occurred

in the field More water had been absorbed at the top of the CBR specimen than at the

bottom Evident at the end of the tests that the conditions which had occurred in the field

HAD NOT been replicated in the laboratory

Considering the amount of heave recorded on site and the relatively short timethat it took to develop, it does ask questions as to why this could not be repeatedin the laboratory?

The conclusion drawn was that the mineralogy of the soil had the potential todevelop additional sulphate due to the oxidation of sulphides.


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Conclusions from

M40 investigationSnedker quoted:

The most significant test wascarried out on a sample of field

material mixed with lime,compacted into a cylindricalmould and cured. Thespecimen was removed fromthe mould and immersed inwater. Within minutes it beganto disintegrate and withinhours had collapsed

completely.

The M40 failure was put down tothe formation of ettringitewithin the stabilised layer.


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Historical

Literature Review1995 The DTp had issued HA74/95 which clearly set out therecipe for the design and construction of lime stabilisedcapping. As well as checks for total sulphur contents, it

recommended the use of CBR tests to monitor swell.

CBR value is on average > 15% with no individual < 8%,

And must have on average < 5mm heave or swell with noindividual >10mm, after which the material is deemed suitable

for stabilisation.

HA74 refers to Snedkers report but did not acknowledge theshortcomings of the CBR swell test.


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Durability

There are many ways to define durability, but for simplicity I have chosen tosub-divide them into two groups:

Chemical durability, and Design durability

Chemical durabilitycan be defined as the susceptibility of the material todeteriorate in the presence of certain chemical elements (ie. Sulphides,sulphates and Organics etc).

Design durabilitycan be defined as the susceptibility of a material todeteriorate due to the workmanship or design elements (i.e. inadequate

compaction, frost, poor choice of binder, etc)

I believe certain contractors and consultants are currently using the CBR testas both a chemical durability and design durability test.


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TRL Report 505

TRL Report 505 was required to validate or revise the swell limits currently given in HA74/95 (whichwas under review at the same time, and would later become HA74/00).

TRL 505 clearly set out to ensure that only suitable cohesive fills could be permitted for limestabilisation within the Specification for Highway Works.

In section 3 of TRL 505 (Literature Review) it clearly states that the only standard containing swelllimits for acceptability is the current draft CEN Standard, which includes limits for volumetric swelling(accelerated swell test) as an alternative to the current CBR swell test.

It goes on to state that the volumetric values equate to linear swells of 6.35mm (5%) and 12.7mm(10%) of the samples compacted into standard BS1924 CBR moulds (127mm high).

CEN 1997 and the determination of volumetric swelling (Sv):

If Sv < 5% the soil/material is suitable for treatment.

If Sv > 10% the soil/material is unsuitable for treatment.

If Sv > 5% and Sv < 10%, the soil/material warrants further study.

It would seem that if the report was required to validate or revise swell checks, then a comparisonshould have been made between the CBR test and the only other currently acceptable alternative(accelerated swell test).


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TRL 505

The report adopted a testing program based on 7 cohesive soils taken from around the UK, namely:Mercia MudstoneOxford ClayLower Lias ClayLondon ClayGault ClayWeald Clay

Kimmeridge Clay

There was a wide range of total potential sulphates of between


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Conclusions of

Literature ReviewIn 1962 PT Sherwood managed to conduct a regime of testing which created anenvironment which allowed specimens to expand when subjected to high sulphatesolution. At the same time the specimens would not collapse under normal soakingprocedures.

The confined soaking conditions (CBR swell test) adopted by TRL 505 and HA74 do notseem to recreate a site environment.

The experiences gained from the M40 were not fully understood. In 1989 Snedkerconcluded that the CBR test did not replicate the conditions experienced in the field.

TRL 505 did not look at the other alternative testing regime available.

After the 2005 (A10 experience), and the subsequent HA74/07 review, the CBR is stillthe preferred swell test to be used to establish any potential problems that may occur inthe field. And in fact has been changed so as to only test the base of the specimen forCBR value.

My conclusion from the Literature Review is that these two methods(confined andUn-confined) are clearly contradicting one another and further research needs to beconducted.


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The Way Forward

I feel that TRL 447 has clearly set out the sampling and testing regime required for theassessment of a sites chemical elements.

The complexities involved in trying to create an exact environment in which Ettringite andThaumasite are formed, is outside the scope of this paper.

I have, therefore, chosen to look at the mechanical stability tests (Design durability tests)and not the chemical durability tests.

However, to proceed further with the research I need to define the potential durabilityissues that we are hoping to be creating/assessing in the laboratory.

The initial durability tests chosen should be able to fail an item as well as pass it.

Due to the high diversity of potential problems of assessing the durability of a stabilisedmaterial, the initial problem is to choose sufficient boundary conditions within ourlaboratory trial mixes, whilst working within the practical constraints of the researchbudget and time scale.


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Phase 1 Lab Trials


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Conclusions from

Phase 1 Lab trialsMix 1: Low lime content aimed at failing the HA74 guidelines.Mix 1: Material passed the HA74 guidelines, however failed the CEN Sv limits.

Mix 2: High Lime content, and the material passed both HA & CEN Sv limits.

Mix 3: Aimed at a much higher strength, with Cement, to assess the difference in the curing periods.The European curing regime, passed the CEN Sv limits, but showed considerably more swellthan the non standard method used.

Mix 4: High plasticity material, with a low binder content aimed at failing the HA guidelines.Mix 4: Material passed the HA guidelines, however failed the CEN Sv limits.

Mix 5: High Lime content, and the material passed both HA & CEN Sv limits.

Mix 6: Aimed at a much higher strength, with Cement, to assess the difference in the curing periods.The European curing regime, passed the CEN Sv limits, but showed considerably more swellthan the non standard method used.

As can be seen from the above results, the material would pass the HA CBR swell limits, whereas someof the tests fail the CEN Sv limits, and others require the material to be investigated further.

The above results also concur with my conclusions from the literature review that the two tests do notgive the same results, and that further work is needed.


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Phase 2

Classification Tests


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Phase 2 Lab Trials


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FurtherComments/Questions

When stabilising a Soil are we looking for a Permanent average CBR value of >15%

HA74/07 has changed to assess the 28day soaked CBR value (for lab mixes only)

The Current CBR test is at Proctor density yet the field work could be considerably less

The french use very high binders compared to us in the UK (similar to B.A.A. 3% Lime +5% Cement). This could be why their stabilised materials are more stable under soaking,and pass the volumetric test.

Reducing the plastic characteristics of a soil should make a material less susceptible toheave.

By using the CBR swell test as the control for suitability, we could be taking an unduerisk, as it does not seem to fail a material.


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Soil Types

Many different types of soils:GravelSandSiltClay

Clays themselves can be further sub-divided into hundreds of different claymineral types, three principle types are:

Kaolin 1m Non-swelling, Low plasticity, low cohesion

Illite 0.1m Expansive, medium plasticity, low permeability

Montmorillonite 0.01m Highly expansive, Very plastic,(Member of the extremely low permeabilitySmectite group)


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Problematic Soils

Grim 1962 set out two types of swelling characteristics in clay soils, namelyIntercrystalline and Intracrystalline swelling.

Intercrystalline: water in the void spaces between crystals.

Intracrystalline: water enters not only between the crystals but also between the unitslayers, which comprise the crystals.

In less dense soils, expansion initially takes place in void areas before total volumeexpansion takes place (this can be seen as softening of the specimen). In denselypacked soil, with low void space, the soil mass has to swell more or less immediately toaccommodate the volume change.

It also follows that expansive clays normally possess extremely low permeabilities.Whereas moderately expansive clays with higher permeabilities may swell more during asingle wet season (period) than the more expansive clays.

Undisturbed expansive clays often have a high resistance to deformation and swelling.

When the micro structural arrangement of an expansive clay is disturbed (re-mixed orre-moulded) the clay may tend to swell more than that of other undisturbedcounterparts.


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Problematic Soils

If the Plastic Limit of asoil changes from say27% to 47% due tothe addition of Lime,are we creating adesiccated materialwhich is De-stabilisedinstead of Stabilised?


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Discussion

NATURAL MATERIAL

MODIFIED MATERIAL

DE-STABILISED MATERIAL

STABILISED MATERIAL

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