Lime stabilisation : proceedings of the seminar held at Loughborough University Civil & Building Engineering Department on 25 September, 1996

185 Pages·1996·11.978 MB·English

by  Rogers C. D. F., Glendenning S, Dixon N (eds.)

EAST MIDLANDS GEOTECHNICAL GROUP
THE INSTITUTION OF CIVIL ENGINEERS
Lime Stabilisation
Proceedings of the seminar
held at Loughborough University
Civil & Building Engineering Department
on 25 September 1996
Thomas Telford
Organisers: The East Midlands Geotechnical Group of the Institution of
Civil Engineers
Organising Committee: Dr C. D. F. Rogers, Dept of Civil and Building
Engineering, Loughborough University; Dr S. Glendinning, Dept of Civil
and Building Engineering, Loughborough University; R. D. Price,
Engineering Services Laboratory, Northamptonshire County Council;
Dr N. Dixon, Dept of Civil and Structural Engineering, Nottingham Trent
University; Dr E. J. Murray, Murray-Rix Geotechnical
Published for the organisers by Thomas Telford Publishing, Thomas Telford Services Ltd, 1 Heron
Quay, London E14 4JD
First published 1996
Reprinted 2001
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A catalogue record for this book is available from the British Library
Classification
Availability: unrestricted
Content: collected papers
Status: authors' opinions
User: civil and geotechnical engineers and landowners
ISBN: 0 7277 2563 7
© The authors and Thomas Telford Services Limited, 1996, except where stated otherwise
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Printed in Great Britain by The Cromwell Press, Trowbridge, Wiltshire
Acknowledgements
The editors gratefully acknowledge the following:
• Permission to publish Figures 1 and 2 in the paper by H. M. Greaves, which are
reproduced from 'Soil stabilisation with cement and lime' by P. T. Sherwood
(ISBN 0 11 551171 7), published by HMSO, London. Crown copyright is
reproduced with the permission of the Controller of HMSO.
• Permission to publish Figure 5 in the paper by S. Biczysko, which is reproduced
from 'Penetration Testing 1988' Proceedings of the First International Symposium
ISOPT-1, Orlando, 20-24 March 1988, 1096 pp. two volumes, HF1. 440/£180.00.
A. A. Balkema, PO Box 1675, Rotterdam, Netherlands.
• Permission to publish Figures 1 and 2 in the paper by C. D. F. Rogers and
S. Glendinning, which is reproduced from 'Site visit report on the construction of a
lime modified subgrade on highways' Nos 339-01 and 334-02 by D. A. Sweeney,
published by the Geotechnical Engineering Group, Department of Civil
Engineering, College of Engineering, University of Saskatchewan, Sasketoon,
Saskatchewan, November 1987.
All other material that is referred to is fully referenced in the papers in which the reference is
made. Unpublished photographs have been included in the paper by J. H. Smith. These were
supplied by the following organisations: Caterpillar Ltd, Wirtgen Ltd and Bomag Ltd. Their
provision is also gratefully acknowledged.
Preface
Stabilisation of clay soils using lime is a well tried and tested technique in many
overseas countries, but has not been used to its full potential in the UK. The primary
application has traditionally been the improvement of clay subgrades for road pavement
construction using mix-in-place techniques, although novel applications have emerged
to produce a range of geotechnical applications. Associated with the increase in
alternative solutions to geotechnical problems is the increase in environmental and
economic pressure to reduce the demand for quarried aggregates and disposal of
structurally unsuitable or waste materials to landfill sites. The two are not unconnected,
and thus any technique that utilises the soil in situ must be attractive. Stabilisation using
lime is one such technique, regardless of whether the lime is mixed-in-place or
introduced by some other means.
A further growing influence in the construction industry is the need for quality
assurance and certainty, as far as is possible, that design lives will be met. This
mitigates against adoption of new techniques, particularly when the material whose
(altered) properties are ultimately to be relied upon to perform well is initially likely to
be variable to some degree. However engineers, although being necessarily
conservative, also necessarily rely upon the experience of others via technical papers,
reports or books. Thus experience of research programmes and/or practical application
by others allow newer techniques to be adopted. The pressure for consideration of new
techniques derives from the financial (and by implication environmental) demands that
an engineer should adopt the most economical solution that can be assured of producing
the required performance.
The seminar on Lime Stabilisation and this associated publication aim to meet the need
for increased knowledge on a suite of alternative ground improvement techniques using
lime. Publication of papers on the subject is particularly important in light of UK
experience of the techniques which, although generally good, suffered setbacks with
isolated failures including the highly publicised M40 failure. The reasons for these
failures are now known and the lessons learnt have been incorporated in current
practice, yet publication on the subject has been sparse. Allied with this has been a
considerable amount of research effort in the field. The Lime Stabilisation '88 and '90
Seminars organised by BACMI provided an excellent forum for dissemination of such
information, but since then there has been no single occasion at which this could be
done.
It is for these reasons that the East Midlands Geotechnical Group decided to organise
the seminar on the subject in 1996, following an equally successful seminar on
Groundwater Pollution in 1984. The EMGG formed four years ago with the aim of
providing learned society activities on geotechnical subjects for the benefit of engineers
living in the area to either side of the Ml corridor from Northamptonshire to South
Yorkshire. Most of the activity concerns the evening meetings programme, although
the organisation of site visits and seminars complement this activity. Widening of
seminar participation to attract national participation thus provided a logical extension to
the aims of the group. The decision to host the seminar at Loughborough University
was considered appropriate since it has recently completed ten years of research in the
subject area.
The editors wish to acknowledge the considerable support of both the organising
committee and the full EMGG committee. They also wish to thank the contributors for
their excellent papers, particularly since the time to write such a paper appears to be
Contents
The Lime Stabilisation Process 1
Introduction 3
An Introduction to Lime Stabilisation. H. GREAVES 5
Construction of Lime or Lime Plus Cement Stabilised Cohesive 13
Soils. J. H. SMITH
The Uses of Lime In Ground Engineering: a review of recent work 27
undertaken at the Transport Research Laboratory. J. PERRY,
D. J. MACNEIL and P. E. WILSON
Specification and Performance of Lime-Clay Mixes 46
Introduction 48
Lime Treatment of Capping Layers under the Current DoT 51
Specification for Highway Works. C. C. HOLT and
R. J. FREER-HEWISH
Long-Term Performance of Lime Stabilised Road Subgrade. 62
S. J. BICZYSKO
The Structural Performance of Stabilised Road Soil in Road 75
Foundations. B. C. J. CHADDOCK
Novel Applications for Lime Stabilisation 95
Introduction 96
Modification of Clay Soils Using Lime. C. D. F. ROGERS and 99
S. GLENDINNING
Lime Treatment of Metal Contaminated Sludges. 115
D. I. BOARDMAN and J. A. MACLEAN
Deep Stabilisation Using Lime. S. GLENDINNING and 127
C. D. F. ROGERS
Case Studies 139
M40 - Lime Stabilisation Experiences. E. A. SNEDKER 142
Treatment of Silt using Lime and PFA to form Embankment Fill 159
for the New A13. A. NETTLETON, I. ROBERTSON and
J. H. SMITH
Slope Stabilisation using Reinforced Lime Nails. 176
L. THREADGOLD
THE LIME STABILISATION PROCESS
Introduction
An Introduction to Lime Stabilisation
H M Greaves BSc (Hons), CEng, MICE.
Stabilisation Services Manager, Buxton Lime Industries.
Construction of Lime and Lime Plus Cement
Stabilised Cohesive Soils
J H Smith BSc (Hons), CEng, MICE.
Consultant to Powcrbetter Developments Limited.
The Uses of Lime in Ground Engineering:
a review of work undertaken at the Transport
Research Laboratory
J Perry BSc (Hons), MSc, PhD, CEng, MIMM, FGS.
Civil Engineering Centre, Transport Research Laboratory, Crowthorne.
DJMacNeil BSc.
Civil Engineering Centre, Transport Research Laboratory, Crowthorne.
P E Wilson BSc (Hons), CEng, MICE.
Road Engineering and Environmental Division, Highways Agency, London.
Lime stabilisation. Thomas Telford, London, 1996
Introduction
Clay soils notoriously provide a challenge to the geotechnical engineer due to their
considerable variety in terms of composition and properties, and in particular their
variation in properties with time and loading. The latter change in properties is often a
manifestation of clay's ability to develop high pore water pressures, both positive and
negative (suctions). These pressures influence greatly the stresses that a clay can
withstand in engineering practice, whether applied statically or dynamically as a
repeated or cyclic loading.
Two broad categories of clay strata are encountered in the UK. Much of the clay
exposed at the surface is heavily overconsolidated as a result of erosion subsequent to
deposition or glaciation. In their undisturbed state they are generally strong, but when
disturbed they usually undergo stress relief, developing negative pore water pressures
and hence tending to swell. Good examples of this behaviour are the cases of cutting
construction in these clays, embankment construction carried out using these clays and
remoulding of the clays for clay (mineral) liners for landfill sites. In addition such clay
soils can become impassable or unworkable during construction operations that take
place either during or following wet weather. The second broad category concerns
soft, wet clayey and silty alluvial deposits, which are typically normally consolidated or
lightly overconsolidated. These materials generally require improvement before
construction can take place above them.
The properties of a clay soil are largely controlled by the amount and type of clay in the
soil, as determined by the Clay Fraction and clay mineralogy respectively, and its stress
history. The type of clay mineral present in a clay can affect considerably the way in
which it reacts to water. A clay soil containing significant quantities of smectitic
minerals (e.g. montmorillonite), for example, will tend to be highly plastic. This is
because the mineral has a large capacity for water molecules to become associated with
it. The plasticity is measured by the Liquid and Plastic (or Atterberg) Limits, and more
precisely the plasticity index being the difference between the two. Thus smectitic clays
have a large plasticity index. They also have a high Cation Exchange Capacity (CEC),
making them sensitive to the predominant cation present in the soil water. Clay soils
containing predominantly kaolinite will have a much lower plasticity (and CEC), and
those containing illite will tend to have a lower value still. Thus the simple Atterberg
Limit tests provide a good indication of the likely behaviour of a clay soil, and
importantly its likely reaction to water, by giving a crude indication of the minerals
present.
The influence of stress history has been alluded to above and concerns the clay's
consolidated state. The fact that (clay) soils have a memory is a result of their plasticity
(or lack of elasticity). This means that consolidation of a clay under a higher level of
stress than previously experienced will render it permanently more consolidated, or
denser, than prior to the stress application. The stress history is a crucial factor in
determining how a clay soil will react to wetting and to imposed loading or unloading,
for example by excavation or remoulding in situ. The consolidated state of a clay can
be crudely gauged by observation and simple testing on site, but can only be accurately
determined in such equipment as the oedometer or triaxial cell in the laboratory or via
sophisticated testing in situ.
Improvement of the properties of soils for construction purposes can be achieved by a
variety of means, which are broadly covered by
• mechanical improvement, such as densification and drainage,
• chemical improvement, or
• reinforcement by physical inclusion of tensile elements or grouts.
Soil improvement is usually an alternative to the provision of a structural solution to a
practical problem, such as provision of retaining walls or buttresses, thickening of road
pavements or increasing the extent of foundations. Thus the economics of the
alternative solutions will be considered in an engineering design. In the case of clay
soils, chemical improvement is commonly most effective since it can be used to change
the nature of the material. Chemical means can be used to strengthen the soil, but also
to remove its sensitivity both to water and its subsequent stress history. Lime provides
an economic and powerful means of chemical improvement, as demonstrated by the
dramatic transformation that is evident on mixing lime with a heavy clay. It has not,
however, been used to its full potential in the UK. This chapter, and indeed the full
publication, aims to provide an introduction to the methods and applications of the lime
stabilisation in order to engender greater confidence in the technique.
The first paper, by Greaves, provides a brief history of the subject and a summary of
the improvements that can be achieved using lime. Two sets of reactions take place,
known as modification and stabilisation reactions, by which the nature of the clay is
changed and the modified material becomes cemented respectively. They cause the
strength and stiffness of the material to increase markedly and the plasticity, or ductility,
to become progressively lost. An important point to note here is that the clay, once
modified, can no longer be considered to be a clay and thus it must be treated
accordingly as a material in its own right. This material has properties that change with
time after the introduction of lime (however achieved) has taken place, the strengthening
and stiffening for example being progressive. The permeability of the material, which
immediately after treatment could be considered to be a malleable aggregate that
progressively cements with time, increases considerably in the short term but
progressively decreases as the cementing takes place. The susceptibility to water is
greatly reduced, as evidenced by its altered shrinkage and swelling properties and
plasticity index. The material becomes more workable since it is apparently drier (it has
a typically much increased Plastic Limit) and can be effectively compacted only at a
greatly increased water content. The changes in nature are thus considerable.
Greaves goes on to indicate which types of soil are suitable for reaction with lime and
the problems associated with excessive sulphates in the soil. Sulphates can affect the
reactions by modifying the reaction products, thus demonstrating a need to understand
the lime modification and stabilisation processes and to carry out a carefully considered
site investigation. Some of the applications of lime improvement are thereafter
discussed, together with the opportunities of lime as an environmentally friendly
solution to the construction industry's demand for aggregate and apparent need for
landfilling.
In the second paper, Smith presents a more detailed review of the type of soil suitable
for lime improvement using the mix-in-place technique. He thereafter describes in
detail the construction procedures adopted and the safety precautions necessary to
ensure that the effects of a strong alkali are not experienced beyond the soil being
treated. Research has shown that appropriate testing at the site investigation stage is
important for accurate design of the process. It is important on site that sufficient water
is available to ensure that the modification reactions take place fully and that an adequate
period (known as mellowing) is allowed prior to compaction. This is to ensure that the
initial reactions, which are expansive in nature, do not affect the compacted state of the
mixed material, which should be densely compacted with particles in intimate contact in
order for the subsequent stabilisation reactions to be most effective. In this respect
addition of water to the material is usually necessary to ensure that a water content at, or
slightly wet of, the optimum water content is achieved. The important points to note
here are that it is not the same as adding water to a clay, since the material is no longer a
clay, and that the optimum water content of the modified material will be greatly
increased above that of the original clay. These considerations, as Smith points out, are
crucial to the success of the mix-in-place process.
The third paper is jointly authored by the Transport Research Laboratory (TRL) and the
Highways Agency, and discusses wider applications of lime improvement. The
traditional use of lime stabilisation is in the treatment of clay subgrades to create
improved road foundations without the need for large quantities of imported granular
aggregates. In producing a revised specification for this, the TRL conducted a careful
review of the process and the factors affecting it. They provide detailed
recommendations for practice, specifically addressing the identification of possible
sulphate attack, compaction wet of optimum and the influence of organic matter. They
also describe work carried out, or anticipated, in the fields of bulkfill modification of
clays, deep stabilisation and processing of contaminated materials for use as fill. All of
these applications are the subject of current research projects being carried out at
Loughborough University and are described in individual papers later in this book. The
paper provides a good introduction to the subjects, and in the case of bulkfill
modification valuable complementary data. The application to railway foundations is
similar to that of road foundations, yet with important differences since the process
must be completed and the track returned to use within hours. It therefore provides
another good example of an application in which the two stage process of modification
and stabilisation combine to provide both short-term and long-term benefits.