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UNIVERSITY GHENT
UNIVERSITEIT
GENT
INTERUNIVERSITY PROGRAMME
MASTER OF SCIENCE IN
PHYSICAL LAND RESOURCES
Universiteit Gent
Vrije Universiteit Brussel
Belgium
Soil Mixing: A Study on Brusselian Sand
Mixed with Slag Cement Binder
September 2008
Promotor: Master dissertation in partial fulfilment
Prof. J. Wastiels of the requirements for the Degree of
Master of Science in
Physical Land Resources
by: Rakshya Shrestha
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PREFACE
The Geo-technical and Structural Division of the BBRI (Belgian Building Research Institute)
has planned to prepare Guidelines or Directives for the Design, the implementation and the
monitoring of different supporting techniques for underground constructions as a two-year
project (01.07.2007-30.06.2009).The supporting techniques that would be incorporated in the
Guidelines would be concerned with almost all types of Traditional Supporting Techniques
existing and the New Supporting Techniques developing (the ground improvement
techniques).The Soil Mix Technology will be incorporated as one of the recent ground
improvement techniques as a part of this project. This thesis finds its origin with this
aforementioned project.
This thesis comprises the review of literature and gives an overview of The Soil Mix
Technology, as one of the most striking renewals today in the field of Geotechnical and Geo-
environmental ground improvement. Majority of the thesis incorporates the laboratory work
which focuses on two important aspects Effect of Binder dosage in the strength of soil mixed
columns, and the Effect of Curing time in the strength of soil mixed columns. It also studies
the effect of total water in the strength gain parameter and efforts to take into account the
workability parameter. The dissertation also has attempted to accomplish the research and
development activities during the past few years and highlights the facts of what has been
done on a regional basis in Asia, in North America and especially in Europe. It further
highlights the current practices and the future needs in this area.
The work thus aims to be a part of the lesson or as a part of the technical information note
capable of being guiding the contractors in Belgium during the construction work and aims to
be useful for all those interested in this field.
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This work is an unpublished M.Sc thesis and is not worked out for further distribution. The
author and promoter give authorization for this thesis consultation and availability of the copy
for personal use. Any other use falls within the restrictions of copyright, particularly with
regard to the obligation to state explicitly the source when quoting the results from this thesis.
The Promoter, The Author,
Prof.Dr.Jan Wastiels Rakshya Shrestha
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i
ACKNOWLEDGEMENT
Firstly, I would like to thank my promoter and supervisor Professor Jan Wastiels for his
encouraging attitude and valuable advice throughout my studies. I am also grateful to Mr.
Patrick Ganne and Ir. Noel Huybrechts of the BBRI for supporting me in carrying my work
out.
A number of people have supported me in various ways during the course of this studies and I
would like to express my sincere gratitude to them.
Rene, for keeping excellent track and helping me in whatever ways he could in the lab.Gabriel, Frans, all the people of MeMC, Edward and Anja without whom the work
would have been incomplete.
My friends and the colleagues at the lab for their friendly assistance.
My sincere thanks to VLIR, and the people of Physical Land Resources Program for
the uninterrupted support throughout my studies.
Last but not the least; I would like to thank my family for their endless support and
encouragement in my studies and for always standing by my side.
August 25, 2008
Rakshya Shrestha
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ii
SUMMARY
Names such as Soil Mixing, Jet Grouting, Cement Deep Mixing (CDM), Soil Mixed Wall
(SMW), Geo-Jet, Deep Soil Mixing, (DSM), Hydra-Mech, Dry Jet Mixing (DJM), and Lime
Columns are known to many. Each of these methods has the same basic root, finding the most
efficient and economical method to mix cement (or in some cases fly ash or lime) with soil
and cause the properties of the soil to become more like the properties of a soft rock
(Nicholson, 1998).
Strength of the soil mixed material is one of the most important factors in soil mixing. It is
important because of its wide spectrum of diverse applications in construction projects
including highways, railroads, embankments, building and bridge foundations, retaining
structures, support of excavation and wide range of increasing applications. Almost all factors
that have influential effects on strength should be studied. Binder dose, curing time and total
water content are some of the influential factors studied in this thesis.
In this study, Brusselian sand specific to Belgium, a dense, cohesionless soil (Schittekat,2003) from the BBRI site in Limelette, Brabant was used. The binder used was Holcim
cement labeled, CEM III/A 42.5 NLA, a mixture of Portland cement clinker and blast
furnace slag.Holcim is one of worlds leading producers of cement and aggregates.
(www.holcim.com).
Binder doses of 200 kg/m3, 300kg/m
3, 400 kg/m
3, 500 kg/m
3, 600 kg/m
3and even up to 700
kg/m3was mixed with the sand in the laboratory mixing set up to prepare series of soil mixed
specimen/columns. The strength gain attained after 7 days of curing was then tested with
standard unconfined compression test machine. The study further attempted to inspect the
effect of total water on the strength parameter. The total water varied with the water content in
the soil and the water added to cement ratio, which was varied in the lab. Also included in the
study was, an additional series of specimens, which attempted to study the effect of curing
time 3 days, 7 days, 14 days and 28 days on the strength of soil mixed columns, mixed with
specific binder doses.
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iii
The strength gain at the end of 7 days of curing tested for different binder doses mentioned
above were found to increase almost linearly with increasing doses of binder. Strength as high
as about 10 MPa was obtained for binder dose of 600 kg/m
3
. A considerable decrease instrength was found with an increase in the total water content. The strength increased with
increase in curing time with a value of about 20 MPa at 28 days of curing for a binder dose of
600 kg/m3.
Workability, the ease with which the mix can be mixed, placed, compacted and finished
(ACI, 2000) is a parameter, which is broadly defined and very difficult to be determined
quantitatively. Moreover, workability requirement varies depending upon the application and
requirement in the field. Nevertheless, another parameter assessed in this study wasworkability. The workability of the soil mix was evaluated as a function of the total water to
total solids ratio in the mix. The best workability was determined based on the ease
experienced while preparing the specimens (neither too dry nor too wet). The total water to
total solids ratio for this particular mix was calculated. The mix with the total water to total
solids ratio of 0.3 was rendered the most workable mix during the study.
Binder doses as high as 600 kg/m3and even 700 kg/m
3, which accounts for 40% to about 50
% respectively of the weight of the natural soil might not prove economical. Nonetheless,
taking into account the proven record (this study) that very high strength (up to about 20
MPa) can be gained, doses like 500 kg/m3 or 600 kg/m
3 could be practiced. These doses
might prove economical, in some cases where deep mixing and excavations in a large area of
land may otherwise simply prove to be much more expensive than the higher doses of binder.
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iv
TABLE OF CONTENTS
PREFACE ............................................................................................................................................... I
ACKNOWLEDGEMENT ..................................................................................................................... I
SUMMARY ........................................................................................................................................... II
TABLE OF CONTENTS .................................................................................................................... IV
LIST OF FIGURES ............................................................................................................................ VI
LIST OF TABLES ............................................................................................................................ VII
LIST OF TABLES ............................................................................................................................ VII
LIST OF ABBREVIATIONS AND SYMBOLS ............................................................................ VIII
LIST OF ABBREVIATIONS AND SYMBOLS ............................................................................ VIII
CHAPTER 1: INTRODUCTION ........................................................................................................ 1
1.1. Background ..................................................................................................................... 1
1.2. Problem Definition .......................................................................................................... 2
1.3. Objectives of the thesis ................................................................................................... 3
1.4. Overview/Outline of the thesis layout ........................................................................... 4
CHAPTER 2: LITERATURE REVIEW ............................................................................................ 5
2.1. Ground Improvement ..................................................................................................... 5
2.2. What is In situ Soil Mixing? ........................................................................................... 62.3. In situ Soil Mixing vs. few other methods of Ground Improvement ......................... 8
2.4. The state of art (What has been done so far?) ........................................................... 14
2.5. Soil Mixing and its suitability to various soil types.................................................... 25
2.6. Soil Mixing and its suitability to various binder types .............................................. 26
2.7. Some Research Efforts specific to the Strength of Soil Mixed Columns ................. 28
CHAPTER 3: SCOPE OF THE STUDY .......................................................................................... 32
3.1. Extent of the studies ...................................................................................................... 32
3.2. Material and Methods .................................................................................................. 33
3.2.1. The Brusselian sand................................................................................................. 33
3.2.2. The Binder............................................................................................................... 34
3.2.3. Soil Parameters Estimation in the Laboratory........................................................ 35
3.2.4. The Test Procedure .................................................................................................. 38
3.2.5. Workability Assessment of the Mix.......................................................................... 42
CHAPTER 4: RESULTS AND DISCUSSION ................................................................................. 44
4.1. Experimental Results .................................................................................................... 44
4.1.1. Series I..................................................................................................................... 44
4.1.2. Series II.................................................................................................................... 46
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4.1.3. Series III................................................................................................................... 47
4.1.4. Series IV................................................................................................................... 49
4.1.5. Series V.................................................................................................................... 51
4.1.6. Series VI................................................................................................................... 54
4.1.7. Series VII................................................................................................................. 56
4.1.8. Series VIII................................................................................................................ 58
4.2. Discussion and Critical assessment ............................................................................. 59
CHAPTER 5: CONCLUSIONS AND RECOMMENDATION ...................................................... 61
REFERENCES .................................................................................................................................... 63
APPENDIX A ...................................................................................................................................... 69
APPENDIX B ....................................................................................................................................... 75
APPENDIX C ...................................................................................................................................... 77
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LIST OF FIGURES
Figure 1. Main applications for deep mixing method in Japan ................................................ 15
Figure 2. Combination mixing method of Jet grout and deep mixing ..................................... 16
Figure 3. Set of one to four mixing tools top driven by hydraulically or electrically powered
motors ....................................................................................................................................... 19
Figure 4. Application of deep mixing methods ........................................................................ 23
Figure 5. Grain size Distribution curve of The Brusselian Sand ............................................. 36
Figure 6. Illustration of the laboratory procedure .................................................................... 41
Figure 7. Strength variation with binder doses for Series I ...................................................... 45
Figure 8. Total water to total solids ratio variation with the binder dose for Series I .............. 45
Figure 9. Strength variation with binder doses for Series II .................................................... 46
Figure 10. Total water to total solids ratio variation with the binder dose for Series II .......... 47
Figure 11. Strength variation with binder doses for Series III ................................................. 48
Figure 12. Total water to total solids ratio variation with the binder doses for Series III ....... 48
Figure 13. Strength variation with binder doses for Series IV ................................................. 50
Figure 14. Total water to total solids ratio variation with the binder dose for Series IV ......... 50
Figure 15. Strength variation with binder doses for Series V .................................................. 51
Figure 16. Total water to total solids ratio variation with the binder dose for Series V .......... 52
Figure 17. Strength variation with total water to total solids ................................................... 53
Figure 18. Contour lines showing the strength variation with total water for specific binder
doses ......................................................................................................................................... 53
Figure 19. Strength variation with binder doses for Series VI ................................................. 55
Figure 20. Best fit for Strength vs. water added to cement ratio .............................................. 55
Figure 21. Total water to total solids ratio variation with the water added to cement ratio ..... 56
Figure 22. Strength variation with binder doses for Series VII ............................................... 57
Figure 23. Best fit for Strength vs. binder dose ....................................................................... 58
Figure 24. Strength variation with curing time for Series VIII ................................................ 59
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LIST OF TABLES
Table 1. Factors affecting the strength increase of treated soil .................................................. 2
Table 2. General application of Deep soil mixing for each Asian country .............................. 15
Table 3. Typical strength and permeability characteristics of treated soils ............................. 26
Table 4. Binder combinations and their notations .................................................................... 29
Table 5. Binders, their mixtures and notations ......................................................................... 30
Table 6. Chemical composition of the binders ......................................................................... 30
Table 7. Physical properties of the soil at Limelette ................................................................ 34
Table 8. Results of sieving ....................................................................................................... 35
Table 9. Chart of the Unified Soil Classification System ........................................................ 37
Table 10. Classes of Workability Measurement ...................................................................... 42
Table 11. UCS test results for Series I ..................................................................................... 44
Table 12. UCS test results for Series II .................................................................................... 46
Table 13. UCS test results for Series III ................................................................................... 48
Table 14. UCS test results for Series IV .................................................................................. 49
Table 15. UCS test results for Series V .................................................................................... 51
Table 16. UCS test results for Series VI .................................................................................. 54
Table 17. UCS test results for Series VII ................................................................................. 57
Table 18. UCS test results for Series VIII ................................................................................ 58
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viii
LIST OF ABBREVIATIONS AND SYMBOLS
CEN/TC European Committee for Normalization/Technical Committee
DM Deep Mixing
QA/QC Quality Assurance/Quality Control
MeMC Mechanics of Materials and Constructions
DSM Deep Soil Mixing
SSM Shallow Soil Mixing
SMW Soil Mixed Wall
NCSEA National Council of Structural Engineers Association
CASE American Council of Engineering Companies
SEI Structural Engineering Institute of the American Society of Civil
Engineers
CA/T Central Artery/Tunnel Project
TCE TriChloroEthane
PCB Polychlorinated Biphenyls
FHWA Federal Highway Administration
EU European UnionEC European Commission
EC7 Euro code 7
BBRI Belgian Building Research Institute
ASTM American Society for Testing and Materials
m.y. million years
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Chapter 1: Introduction 1
1. Chapter 1: INTRODUCTION
1.1. Background
Ground Improvement is the enhancement of the properties of weak compressible strata in
order to render them competent to carry load from structures. (Westcott et.al, 2003). Ground
improvement methods are used to change the characteristics of soil or rock to provide
foundation support for structures, protection from earthquake-induced soil liquefaction,
subsidence remediation, site improvement, and similar applications. There are a large number
and variety of ground improvement or ground modification methods, many of which are
specific to soil types and applications.
In situ Soil Mixing is one of the Ground Improvement Techniques in which a variety of
chemical additives is used to improve the properties of soil. A method which was originally
developed in Sweden and Japan more than thirty years ago and was normally used for soft
cohesive soils but can be used for any type of soil and is becoming well established in an
increasing number of countries. (Ahnberg, 2006) It is also referred to as auger mixing, deep
mixing method, soil cement columns / piles, SMW, cement soil mixing, Trevimix, rotary
mixing, and simply, soil mixing.
In the mid 1970s when soil mixing was first used in practice in Europe that was in Sweden,
only lime in the form of quicklime was used, whereas today, a mixture of lime and cement is
the dominating binder. Other binders are also used though on a small scale. Other binders
mainly include slag in combination with cement, primarily for the stabilization of organic
soils. However, the use of binders is likely to increase in the years to come. Other types of
binders are increasingly used internationally, primarily for shallow stabilization of capping
layers and sub-bases, but also for deep soil stabilization. Besides slag, other industrial by-
products, such as different types of ash, may be of interest. Apart from possible environmental
benefits of using industrial by-products, there may be economic as well as technical reasons
for incorporating alternative binders.
An understanding of the properties and behavior of the mixed soil is of vital importance for
the design of the mixing. Strength gain is one of those important properties, which depend
upon the type of soil and binder, their quantity, geotechnical properties, chemical
composition, and construction of mixing equipment. Several other factors like the mixing
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Chapter 1: Introduction 2
procedure, curing conditions, binder dose and curing time influence the strength gain. The
elastic moduli and the strength gain in soil mixed material is up to 1/5th
to 1/10th
of that of
concrete. (Nicholson, 1998).
According to the information obtained from ir. Noel Huybrechts of the BBRI in Belgium,
today, the soil mix technology has been one of the most striking renewals. This technology is
already adopted by several contractors in few sites (at least 5). Mixing tools were in some
cases developed by the contractors themselves and in some cases, this was done with the tools
already available in the market (such as Cutter Soil Mixer). Today, this technology finds its
place in the Belgian domain, but still a lot of research related to various important aspects like
strength gain, permeability, deformation, compressibility, binder and soil types and theireffect on these parameters and much more is necessary for its development and successful
implementation.
1.2. Problem Definition
The strength of the stabilized soil is an important property. It is important because of the wide
range of spectrum of applications in the construction industry (Probaha et al., 1998) e.g.
retaining wall systems, foundation support systems, seismic strengthening systems wherestrength plays the vital role. Thus, it is very important to understand the strength behavior of
the stabilized soil. This will help us develop a design method specific to particular soil and
binder type or specific to a construction method adopted. A number of factors affect the
strength gain of the mixed soil. Some of them after (Terashi, 1997) are listed in the Table 1.
Table 1. Factors affecting the strength increase of treated soil
I Characteristics of hardening
agent
1. Type of hardening agent
2. Mixing water and additives
II Characteristics of soil 1. Physical, chemical and mineralogical properties of soil
2. pH of pore water
3. Water content and organic matter content
III Mixing conditions 1. Degree of mixing
2. Timing of mixing/re-mixing
3. Quality of hardening agent
IV Curing conditions 1. Temperature
2. Curing time
3. Humidity
4. Wetting and drying/freezing and thawing, etc.
(Source: Terashi, 1997)
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Chapter 1: Introduction 3
Although a number of investigations have been performed regarding different aspects of the
strength of soil mixed material, there was a need for further studies, particularly concerning
the effects of different types and doses of soils and binders. However, not only the type of soiland binder but also the mixing procedure and the curing conditions (temperature, humidity) as
listed in Table 1, affect the strength of the stabilized soil columns. Furthermore, the strength
property of stabilized soil columns may considerably vary with time, mainly due to different
chemical reactions taking place. In addition, external factors such as foundation loading or
changes in the surrounding soil and ground water conditions influence and change the
strength. Studies of all kind of influencing factors are thus called for as far as possible in order
to understand well the strength behavior of the stabilized soil, which forms the basis for safer
and more cost-effective designs of soil/ground improvement by soil mixing.
Within this framework, the study of some of the factors (binder dose, total water to total
solids and curing time) and their effect on the strength parameter has been regarded as the
main work of this thesis, with an aim to be of some contribution to the aforementioned project
and to those who are interested in this field in one way or the other.
1.3. Objectives of the thesis
The overall objective of the research presented in this thesis was to study the strength
parameter of soil mixed columns prepared by mixing the Brusselian sand specific to
Belgium with Holcim (one of the worlds leading producers of cement and aggregates)
cement, CEM III/A 42.5 N LA which is mixture of ordinary Portland cement clinker and
blast furnace slag, as a function of binder dosage, total water to total solids ratio and curing
periods.
The general strength behavior (strength evolution) was investigated in the laboratorywith various binder doses and curing periods. The workability of the soil mix was also
addressed in this respect.
The investigations were also intended to include the evaluation and verification of
other important soil properties such as water content, density, specific gravity,
atterberg limits which has an effect on the strength behavior.
A laboratory procedure for making and curing the soil mixed column specimen was
attempted to be formulated.
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Chapter 1: Introduction 4
1.4. Overview/Outline of the thesis layout
The thesis is presented in the form of five chapters, each chapter trying to conclude one
particular aspect. After the introductory chapter, the information gathered during the literature
survey that was performed as part of this research is presented under the title Literature
Review in Chapter 2, but the literature survey is also integrated and related with the related
results where relevant. The scope of the research is presented in Chapter 3, giving the extent
of the study, a description of the approach used for studying the strength parameter of the soil
mixed columns, and the materials used in the study. Some relevant soil parameters are also
intended to be assessed. An attempt to formulate the laboratory procedure for the mixing,
curing and testing of the soil mixed specimens is also presented, followed by some definitionsof workability at the end of this chapter. In Chapter 4, the results of the laboratory tests are
presented and summarized and the important results obtained in the study are discussed and
analyzed. The discussion focuses on the strength achieved in the soil and its evolution
depending on binder dose, total water to total solids and curing time. The trend lines obtained
could potentially be used for preliminary estimation of the doses of binder to attain a desired
strength for similar soil types in the future studies. Conclusions and Recommendations for
further research are presented in Chapter 5.References and Appendices are included in the last
part.
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Chapter 2: Literature review 5
2. Chapter 2: LITERATURE REVIEW
2.1. Ground Improvement
Ground improvement is the enhancement of the properties of weak compressible strata in
order to render them competent to carry loads from structures (Westcott et al., 2003). Ground
improvement, as mentioned in the chapter Ground Improvement, of the Geotechnical
Design Manual published by the Washington State Department of Transportation (WSDOT,
2006), is used to address a wide range of geotechnical engineering problems, including, but
not limited to, the following:
Improvement of soft or loose soil to reduce settlement, increase bearing resistance,
and/or to improve overall stability for structure and wall foundations and/or for
embankments
To mitigate liquefiable soils
To improve slope stability for landslide mitigation
To retain otherwise unstable soils
To improve workability and usability of fill materials
To accelerate settlement and soil shear strength gain
Types of ground improvement techniques are also cited in this Manual to include the
following:
Vibro-compaction techniques such as stone columns and vibro-flotation, and other
techniques that use vibratory probes that may or may not include compaction of gravel
in the hole created to help densify the soil
Deep dynamic compaction
Blast densification
Geo-synthetic reinforcement of embankments
Wick drains, sand columns, and similar methods that improve the drainage
characteristics of the subsoil and thereby help to remove excess pore pressure that can
develop under load applied to the soil
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Chapter 2: Literature review 6
Grout injection techniques and replacement of soil with grout such as compaction
grouting, jet grouting, and In situ soil mixing
Lime or cement treatment of soils to improve their shear strength and workability
characteristics
Permeation grouting and ground freezing
Each of these methods has limitations regarding their applicability and the degree of
improvement that is possible. Each of the above-mentioned techniques can however be
broadly classified into three categories even though several of the techniques could fall into
more than one of the following three categories. (Hussin, 2006):
Compaction: techniques that typically are used to compact or densify soil in situ;
Reinforcement: techniques that typically construct a reinforcing element within the
soil mass without necessarily changing the soil properties. The performance of the soil
mass is improved by the inclusion of reinforcing elements;
Fixation: techniques that fix or bind the soil particles together thereby increasing the
soils strength and decreasing its compressibility and permeability.
As referred in the Structure magazine, a joint publication of NCSEA,CASE and SEI, (2004),
in many situations, ground improvement can be used to support new foundations or increase
the capacity of existing foundations in place of bypass systems, such as piling, caissons, or
remove and replace. In doing so, the ground improvement system reduces the overall
foundation cost by allowing the new structure to be built on spread footings with a slab on
grade rather than pile caps and a structural slab. It has been estimated that a saving of four to
eight dollars per square foot of building can be realized. For a large super market, department
store or home improvement store the savings can be in excess of one million dollars. In the
case of an existing structure, ground improvement allows the use of existing foundations with
little to no modification.
2.2. What is In situ Soil Mixing?
In situ Soil Mixing is a Ground Improvement Technique originated and developed to
reinforce the native soils and strengthen them.
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Chapter 2: Literature review 7
According to Nicholson (1998), various methods of soil mixing, mechanical and hydraulic,
with and without air and combinations of both types have been used widely in Japan for about
30 years and more recently have gained wide acceptance in the United States and Europe. Thesoil mixing, ground modification technique, has been used for many diverse applications
including building and bridge foundations, retaining structures, liquefaction mitigation,
temporary support of excavation and water control. Ground Improvement techniques such as
Jet Grouting, Soil Mixing, Cement Deep Mixing (CDM), Soil Mixed Wall (SMW), Geo-Jet,
Deep Soil Mixing, (DSM), Hydra-Mech, Dry Jet Mixing (DJM), and Lime Columns are
known to many. Each of these methods has the same basic root, finding the most efficient and
economical method to mix cement (or in some cases fly ash or lime) with soil and cause the
properties of the soil to become more like the properties of a soft rock.
In situ Soil Mixing is a construction technique that uses augers to mix the binders with the
existing soil to form a soil-crete mixture that creates a continuous and impervious wall prior
to excavation. A wet or dry binder is introduced into the ground and is blended with the soil
by mechanical or rotary mixing tools. The result of mixing is a hardened ground with
improved engineering properties such as strength, compressibility and permeability compared
to the native ground (Bruce et.al.,2003).This method allows the site to be excavated under
dry conditions, improves the water proofing of the structure being constructed and limits draw
down of the water table. The intent of the soil mixing is to achieve improved character,
generally a design compressive strength or shear strength and/or permeability. Soil mixing
can also be used to immobilize and/or fixate contaminants as well as a treatment system for
chemical reduction to a more friendly substrate (Hayward Baker, 2003a).
Components of In situ Soil Mixing:
Soil
Binder
Mixing Equipment/Plant
o Mixing Tools/Augers.
o Equipment/Plant Operator, Monitoring and Control System
Typically, the Binder also called the Reagent is delivered in a slurry form (i.e. combined with
water), although dry delivery is also possible. Depending on the soil to be mixed, the volume
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Chapter 2: Literature review 8
of slurry necessary normally ranges from 20 to 30 percent by volume as mentioned in the
services offered by Hayward Baker, a leading Geotechnical construction company of North
America. The Binder can be a variety of materials including:
Cement
Lime
Ground Blast Furnace Slag
Fly ash
Lime
Additives
Combination of the above
The Mixing Tools are The Augers. The augers may be:
Multiple Shaft tools /augers
Single Shaft tools/augers
Both types have cutting and mixing blades/paddles. These mixing tools are top driven
by either hydraulically or electrically powered motors.
Different construction companies have however, developed different innovative and standard
equipments as mixing equipments.
This method can be used for almost all soil types. However, laboratory testing prior to
construction is recommended for all projects. (Hayward Baker, 2003a)
2.3. In situ Soil Mixing vs. few other methods of Ground Improvement
When a suitable foundation has to be designed for a superstructure, the foundation engineer
typically follows a decision-making process in selecting the optimum type of foundation. The
important steps of that decision process is based on the principle that cost-effective
alternatives must be sought first before considering relatively costly foundation alternatives
by considering specific techniques applicable to the site.
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Chapter 2: Literature review 10
Two types of In situ soil mixing can be distinguished:
Dry soil mixing is a low-vibration, quiet, clean form of ground treatment technique
that is often used in very soft and wet soil conditions and has the advantage of
producing very little spoil. The high-speed rotating mixing tool is advanced to the
maximum depth disturbing the soil on the way down. The dry binder is then pumped
with air through hollow stem as the tool is rotated on extraction. It is very effective in
soft clays and peats.Soils with moisture content, greater than 60% are most
economically treated. This process uses cementacious binders to create bond among
soil particles and thus increase the shear strength and reduces the compressibility of
weak soils.
Wet soil mixingis similar technique except that a slurry binder is used making it more
applicable with dryer soils with moisture contents less than 60%.The slurry is pumped
through hollow stem to the trailing edge of the mixing blades both during penetration
and extraction. Depending on the in situ soils, the volume of slurry necessary varies
from 20 to 40 % of the soil volume. The technique produces a similar amount of spoil
(20 to 40 %) which is essentially excess mixed soil, which, after setting up, can be
used as structural fill. The grout slurry can be composed of Portland cement, fly ash,
and ground granulated blast furnace slag.
In situ soil mixing can also be subdivided into two general categories (Topolnicki, 2004):
Deep Soil Mixing (DSM/DMM) also referred to as Column Mixing.
Shallow Soil Mixing (SSM/SMM) also referred to as Mass Mixing.
Both DSM and SSM include a variety of proprietary systems.
The more frequently used and better developed DMM is applied for the stabilization of the
soil to a minimum depth of 3 m(CEN/TC 288,2004) and is currently limited to a treatment
depth of about 50 m.The binders are injected into the soil in dry or slurry form through hollow
rotating mixing shafts tipped with various cutting tools. The mixing shafts are equipped with
discontinuous auger flights, mixing blades or paddles to increase the efficiency of the mixing
process.
The complementary SMM has been specially developed to reduce the cost of improving loose
or soft superficial soils overlying substantial areas, including land disposed dredged sediments
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and wet organic soils a few meters thick. It is also a suitable method in the in situ remediation
of contaminated soils and sludges. In such applications, the soils have to be thoroughly mixed
in situ with an appropriate amount of wet or dry binders to ensure stabilization of entirevolume of treated soil. Therefore, this type of soil mixing is often referred to as mass
stabilization. Mass Stabilization can be achieved by installing vertical overlapping columns
with up and down movement of rotating mixing tools, as in case of DMM, and is most cost
effective when using large diameter mixing augers or multiple shaft arrangements. With this
kind of equipment, it is generally possible to stabilize soils to a maximum depth of about
12m.
More recently, however, another method of mass stabilization has been implemented, and themixing process can now be carried out repeatedly in vertical and horizontal directions through
the soil mass using various cutting and mixing arrangements that are different from the tools
originally developed for DMM. The depth of treatment for this relatively new system is
generally limited to about 5 m.
It is important to note that the differentiation between SMM and DMM is not solely attributed
to the available depth of treatment criterion because in principle, soil mixing at shallow depth
can also be performed with DMM.
According to Jasperse (2003), DSM is a relatively simple process involving standard
construction equipment rearranged for the process. The equipment is a crane supported set of
leads that guide a series of one to four hydraulically driven augers 450 to 900 mm in diameter.
As penetration occurs, a bentonite, cement, lime or other slurry is injected into the soil
through the tip of the hollow stemmed augers. The auger flights penetrate and break loose the
soil, sand lift it to mixing paddles, which blend the slurry and soil. As the auger continues to
advance, the soil and slurry are re-mixed by additional paddles attached to the shaft.
Referring to Broomhead et.al.(1992), DSM can be used to treat soil more than 30 m deep. A
zone of contaminated soil or a complete block of contaminated soil can be treated. Water
table elevation has no effect on the process. If the work is performed under the water table,
the groundwater is mixed into the treated soil mass. If the work is performed above the water
table, then the slurry waste-solids ratio can be adjusted to allow for the lack of water in the
final soil-mixed product. The ability to perform under the water table is the key advantage to
using a soil mixing system because dewatering is not required. This saves on the cost,
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particularly when groundwater is contaminated and would have to be treated or could not be
lowered.DSM has many excellent civil and geotechnical applications such as structural cut-
off walls, on-structural cut-off walls, block treatment for foundations and low strengthpiles.However,for large, shallow applications e.g. to provide foundation for large effluent
storage tanks as well as to contain foundation soils in the event of liquefaction from an
earthquake,DSM is not economical.
Because economics is one of the deciding factors, SSM is developed for treating large soil
masses. Shallow Soil Mixing (SSM) is, the derivative of Deep Soil Mixing (DSM) a sister
technology to DSM developed to more economically improve soils within ten meters of the
surface and to provide cost effective foundation systems for geotechnical, civil applications.Shallow Mixing was developed to improve soft and compressible soft, but also dredged
sediments and waste deposits. The treatment depth is limited to a few meters. Shallow Mixing
is also a suitable method for in situ remediation of contaminated soils and sludges.In such
applications, the soils have to be thoroughly mixed in situ with an appropriate amount of wet
or dry binders to ensure stabilization of the entire volume of the treated material.
The SSM system uses a single, large-diameter (2 to 4 m) mixing auger, which, by benefit of
scale, provides the most economical system available. Although technically feasible to greater
depths and larger diameters, torque limitations and soil consistency usually limit application
depths to about 12 m. SSM, like DSM, uses a crane-mounted mixing system with reagents fed
into a mixing auger as the auger penetrates the soil. Additives and reagents, typically mixed at
the batch plant, can be transferred pneumatically, or pumped. Reagents are volumetrically
measured to allow the correct proportions to be mixed with the soil. The mixing augers
advance through the total depth of the soil in an up and down motion. Upon completion of a
mixed soil column, the auger is repositioned to overlap the previous soil column and theprocess is repeated.
SSM has both geotechnical and environmental applications. It can be used for foundation
elements, block stabilization, gravity walls and fixation/solidification of contaminated soils.
Columns can be arranged in-situ up to 35-40 feet, into gravity retaining walls or mat
foundations.
Some merits and drawbacks of In situ Soil Mixing as described in the Soil Mixing Brochure
of Hayward Baker (2003b), are listed as:
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Merits
Economic
Flexibility
Savings of materials and energy
Rapidity
Can be flexibly linked with other structures and with the surroundings (no harmful
settlement differences), avoids destruction of or harmful effects to existing structural
facilities bridges that still has a long useful life remaining
Flexible improved engineering properties of the soil
Low noise and vibration level
No excavation is required
Reduces off-site disposal problems
Reduces surface exposure
Additional ground improvement of contaminated soils
Exploiting of the properties of the soil at the site
Soil remains in place. Zero spoils production. No transfer of the natural soil elsewhere.
Drawbacks
Not for high embankments
Limited possibilities to increase stability of high embankments
Poorly stabilisable soils
Time needed for curing
Maximum depths: for mass stabilization 5, 0 meters; columns 40, 0 meters (Euro
Soil Stab,2002)
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2.4. The state of art (What has been done so far?)
What has been done so far regarding the soil mixing technology in the world is attempted to
be summarized in this section on a continental basis.
In Asia
What has been done in Asia on a regional basis was described by M.Nozu of the Fudo
Construction Co., Ltd in the International Conference on Deep Mixing which was held in
Sweden in 2005, is reviewed and summarized in this section.
In Asian region, the soil mixing method has been developed in Japan since 1960s, and it has
been widely used in Thailand since 1998.Publications of Reference manuals and Standardsdocuments, Efforts for standardization and development and the needs in future has been
worked, and their validation is searched and researched and these works are undergoing. It is
becoming popular due to its applicability with time. The level of research and development
activity in Japan in relation to deep soil mixing remains the highest in the world today.
General application of deep soil mixing methods (wet and dry) in the Soft clay deposits of
Southeast Asia are shown in Table 2. Soft clay is widely spread especially in Large River
Delta, and the potential demand of ground improvement will be increased due to supplyingthe infrastructure.
Typical applications of wet soil mixing in foundation engineering applications on land,
marine and offshore, earthquake and soil dynamics and environmental applications in Japan
are shown in Figure 1.
In Japan, the accumulative volume of treated soil using wet-type deep soil mixing from 1977
to1998 reached 38 million cubic meters. The volume of the treated soil includes that of the
land application and marine application. For on land applications, the method has mainly been
applied to improve slope stability, to prevent building subsidence and to improve the bearing
capacity of foundations. In approximately 50% of marine applications, it has been applied to
improve the foundations of revetments.
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Table 2. General application of Deep soil mixing for each Asian country
Nations Type of
Mixing
Diameter
(m)
Maximum
depth
Main purpose and Construction records
Japan Wet 1.0-1.6 50m
(-70m, from
sea level,
off-shore)
Many kinds of purposes, such as port
structure (quay-wall, breakwater) foundation,
Self standing retaining wall, building
foundation, anti-liquefaction with lattice type
pile arrangement, and so on
Dry 1.0-1.3 33m Road embankment and river dike foundation
for increasing stability and reducing
settlement.
It is difficult for Dry method to be applied in
the sandy layer with low natural water
content, less than 30%.
Thailand Wet,
Dry
0.6 20m Road embankment foundation for increasing
stability and reducing settlement.
Application for self-standing retaining wall is
now considering for some projects.
Singapore Wet 1.0-1.3 20m or less Self-standing retaining wall for excavation
work for building foundation.
Vietnam Wet 0.6-1.3 30m or less Road embankment and river dike foundationfor increasing stability and reducing
settlement
(Source: Nozu, M., 2005)
Figure 1. Main applications for deep mixing method in Japan
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With regard to the Quality control, the Asian Region adopts the soil mixing quality control in
three stages such as The Mix Design, Construction Control, and Check Boring.
In the Mixing Design, the standard of Summary of the Practice for Making and Curing
Stabilized Soil Specimen without compaction (JGS0821) was established by Japanese
Geotechnical Society (Kitazume, 2002), and has been widely used. In the Construction
Control, blade rotation number (Kitazume, 2002) and cement volume are controlled during
mixing procedure. In the Check Boring, Core boring and unconfined compression test is
widely applied in Japan, normally with every 500 columns. Pull up column and unconfined
compression test or Column Loading Test has been used in Thailand.
In Japan, the application of soil mixing has been diversified such as foundation of many kinds
of building and bridge abutment, self-standing retaining wall, and countermeasure against
liquefaction due to earthquake. Large diameter and high strength column are required and
developed in each companies and groups.JACSMAN is a new large-diameter deep-mixing
method that combined the advantages of mechanical mixing and jet stirring (Kawanabe et al.,
2002), see Figure 2. Control of the improved area is made possible by dual, cross-jetting
nozzles that emit a hardening agent. Cross jet streams affect a more uniform area than
conventional jet mixing, giving precise control over the diameter of the improved. In future,
the quality of Soil Mixing method will be more improved and widely used in many aspects.
Figure 2. Combination mixing method of Jet grout and deep mixing
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In America
According to a regional report presented in the International Conference on Deep Mixing held
in Stockholm, Sweden, by Probaha et.al, (2005), the development in the field of Soil Mixing
in North America is summarised in this section.
In 1987, the first US use of deep mixing was applied to aliquifaction mitigation project for
the Bureau of Reclamation beneath Jackson Lake Dam in Wyoming.(Probaha
et.al,2005).According to this Regional Report published by the Deep Mixing 05 conference,
the construction beginning in the 1990s,of the Central Artery in Boston,Massachusetts,a
depressed highway constructed in a very urbanized and crowded central business district,
provided an opportunity for contractors and engineers to provide unique solutions in a very
difficult geotechnical setting and a showcase of DM technology. Deep soil mixing was chosen
to provide excavation support and mass stabilization or buttressing of the constructed new
alignment. As the quantity of deep mixing on this project exceeded half a million cubic
meters, it provided significant insight in the possibilities and problems with implementation
and costs associated with this technology. In addition, in connection with the reconstruction
of Interstate 15 in Salt Lake City, dry mix lime-cement columns were used to stabilize a high
embankment and decrease settlement, serving as a laboratory and showcase for this allied
technology (Dimillio, 2003).
Also this regional report describes the typical equipment with which North America practices
Deep Mixing consists of a set of one to four mixing tools, top driven by hydraulically or
electrically powered motors. These motors and the shafts they power ride up and down a
specially designed lead, which in turn is supported by a crane or may be structurally
integrated into the crane body itself. The mixing tools consist of thick-walled rods, usually
200-300 mm (8-12 in) diameter, with 50-75 mm (2-3 in) diameter center holes for slurry
conveyance. In-situ soil mixing practiced in North America consist of a set of one to four
mixing tools and top driven by either hydraulically or electrically powered motors is shown in
the Figure 3.The set of tools shown in the figure is obtained from Condon-Johnson and
Associates,Geo-Con,Hayward Baker,Ration,Schnable and Seiko.
Organizations involved with the Deep Mixing like the NDM (National Deep Mixing)
facilitate advancement and implementation of deep mixing technology through partnered
research and dissemination of international experience. It serves as the forum to identify
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current best practices and guide new developments in the design and construction. In addition,
the NDM research program has initiated collaborative efforts with the international
community involved with deep mixing, including Swedish Geotechnical Institute andCambridge University. As part of outreach to the practitioners/users of the technology, the
NDM program has organized a number of workshops and one symposium to increase public
awareness and users confidence. These events were held in Transportation Research Board
and annual conferences of Geo-Institute of American Society of Civil Engineers (Porbaha et
al., 2005).
The Deep Foundations Institute (DFI) established a Soil Mixing Committee in 1998
(www.dfi.org). Committee members, including several international members, are engineers,contractors and owners who desire to work together to improve the planning, design and
construction of deep mixing projects. Committee efforts are directed towards eliminating
roadblocks to the use of deep mixing methods and to educating the North American
engineering community. They are working to establish realistic quality expectations for
different applications and to develop recommended QA/QC procedures for the wet method.
The Committee has sponsored seminars and is currently working on a Guide Specification for
the wet-method.
Other organizations like The US Army Corps of Engineers (USACE) have been involved
with solidification or stabilization of contaminated ground. In addition, USACE has used DM
for cutoff wall systems for flood control of levees. The US Environmental Protection Agency
(EPA) has been involved in the remediation of the sites improved by DM for environmental
applications. The Portland Cement Association (PCA) has been involved in developing
cement-based grouts for the stabilization and solidification of contaminated soils. Several
universities are currently involved with research on deep mixing, including Virginia Tech,University of Texas at Arlington, Texas A & M, University of Kansas, University of Nevada,
and Wentworth Institute of Technology, among others. These universities are involved in
research for the NDM research program, the State Department of Transportation, and private
sponsors.
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Figure 3. Set of one to four mixing tools top driven by hydraulically or electrically powered motors
Distinctive features of soil mixing are the wide spectrum of applications in the construction
industry (Porbaha et al., 1988).Typical applications of wet soil mixing projects in North
America include six main application categories viz hydraulic barrier systems, retaining wall
systems, foundation support systems, excavation support systems, seismic strengthening
systems, and environmental remediation systems.
A quick summary of the representative applications for each category is presented here:
Hydraulic barrier systems
Flood control for levee
Extending the crest level of an existing dam
Dewatering of high-rise building close to harbor
Cutoff wall for a dam spillway
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Dewatering of an elevated roadway below sea level
Retaining wall systems
Reinforced gravity structure
Gravity wall for river front
Sea wall for a port
Secant walls
Deep water bulkhead
Foundation support systems
Heavy machinery foundation Highway embankment foundation
Storage tank foundations
Deep foundation for light rail system
Dome silo foundation
Foundation of parking garage
Bridge abutment foundation
Excavation support systems
Excavation for CA/T project
Excavation for depressed highway section projects
Excavation for vibratory machinery
Excavation for building
Braced excavation
Excavation for cut & cover tunnel
Trench excavation for railway tracks
Seismic strengthening systems
Seismic retrofit of dam foundation
Alleviation of lateral spreading
Liquefaction mitigation of culvert foundation
Strengthening around an excavation
Seismic stabilization of dune deposits
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Liquefaction mitigation of river bank
Seismic strengthening of levees
Environmental remediation systems
TCE remediation
PCB stabilization
Hydrocarbon contamination
Stabilization of Lagoon sludge
Stabilization of steel factory disposal pond
Leachate control for sediment pond
Remediation of site contaminated with heavy metals
As per the standardization and guide documents, North American practice lacks standard
procedures for laboratory sample preparation, coring, and testing of soil cement. However, the
work plan of the NDM research program includes addressing these deficiencies. Filz et al.,
(2005) discussed the standardized definitions and laboratory procedures. Overall, in the North
American practice, codification of deep mixing design and construction is not encouraged
due to complexity and the judgment associated with the real-world problems. In the
meantime, several guide documents have been developed to address issues related to
design, construction and quality control. Engineering guide documents produced by various
organizations involved with deep mixing are presented to include NDM, SOA reports,
USACE, USEPA, FHWA, PCA, and WTC.
Despite being huge, the US market tends to be tough for adoption of a new technology due to
a variety of reasons, including: availability of various alternate technologies, large
geographical size with many regional specialty geotechnical contractors, a risk averseengineering and construction profession, contracting method, and lack of centralized decision
making (good or bad !?) in comparison with other countries.
Because the deep mixing industry is still in its early stages and acceptance has been gradually
increasing, there is still much debate over how the technology is implemented. With the
availability of appropriate equipment, deep mixing has become a viable method in the
American construction market. North American practice often requires the penetration of
dense coarse-grained soils and stiff to hard fine-grained soils. Mixing tools have been adapted
to enable these soils to be cut.
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As verification methods for deep mixing work improve and expectations that are more
realistic are established, the amount of deep mixing work is expected to grow. The hope is
that the products of the NDM guide documents and its outreach program will enhance theusers confidence in taking full advantage of the capabilities of the technology.
In Europe
Due to the variable geotechnical conditions in Europe, different deep and shallow mixing
methods have been developed in different (countries) parts of Europe. The optimal mixing
method for a specific project depends on a variety of factors, such as the geological and
geotechnical conditions, the structural requirements, the experience of the design engineer and
the availability of suitable equipment and qualified personnel.
Areas of Application:
Soil mixing is being used increasingly in Europe. However, the areas of application vary for
different reasons, such as geotechnical conditions (soil type and soil strength), design
considerations (stability, settlements, containment etc.), cost of competing foundation
methods, availability of equipment and material, past experience etc. Examples of the
application of deep mixing for different purposes like foundation support, retention systems,
ground treatment, hydraulic cut-off walls, and environmental remediation are listed here and
illustrated in Figure 4.
(1) Road Embankment: stability/settlement
(2) High embankment: stability
(3) Bridge Abutment: uneven settlement
(4) Cut Slope: stability
(5) Reducing the influence from nearby construction
(6) Braced Excavation: earth pressure/heave
(7) Pile foundation: lateral resistance
(8) Sea wall: bearing capacity
(9) Break-water: bearing capacity
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Figure 4. Application of deep mixing methods
Standardization work in Europe:
A Technical Code for Deep Mixing - prEN 14679 - "Execution of special geotechnical
works was prepared by CEN/TC 288 Working Group 10.The working group -comprising
delegates from 9 European countries -commenced work in February 2000. In addition, experts
from Japan took part in the meetings of the working group and contributed to the formulation
of the final draft. The document has passed the CEN Enquiry, formal voting. The document is
intended to stand alongside Euro code 7.The first part includes, Geotechnical design, general
rules and Part 2 includes Geotechnical design, ground investigation and testing) by 2010
(CEN/TC 288, 2004).
The standard addresses execution aspect and expands on design only where necessary, but
provides full coverage of the construction and supervision requirements. It establishes general
principles for the execution, testing, supervision and monitoring of deep mixing works carried
out by two different methods: dry mixing and wet mixing.
Deep mixing considered in this Standard is limited to methods, (Hansbo, 2002) which
involve:
Mixing by rotating mechanical mixing tools where the lateral support provided to thesurrounding soil is not removed;
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Treatment of the soil to a minimum depth of 3 m;
Different shapes and configurations, consisting of either single columns, panels, grids,
blocks, walls or any combination of more than one single column, overlapping or not;
Treatment of natural soil, fill, waste deposits and slurries, etc;
Other ground improvement methods using similar techniques exist.
The Euro code 7 is developed with an aim to be applied to the geotechnical aspects of the
design of buildings and civil engineering works. It is concerned with the requirements for
strength, stability, serviceability and durability of structures. It covers the following topics:
Basis of geotechnical design; Geotechnical data; Supervision of construction, monitoring and
maintenance; Fill, dewatering, ground improvement and reinforcement; Spread foundations;
Pile foundations; Anchorages; Retaining structures.
Research Efforts:
a. EuroSoilStab Project
On the European level, the EuroSoilStab research project (1997-2001), which was carried out
by 17 partners and which was funded by the EU, addressed Development and design of
construction methods to stabilize soft organic soils. The objective of the project was to
develop and prove novel competitive design and construction techniques, backed by guidance
documents, to stabilize soft organic soils for the construction of rail, road and other
infrastructure, thereby enabling economic construction on land that was previously considered
unsuitable. The project involved laboratory studies and field trials and aimed to cover the
development of binders, laboratory testing of binders and soils, full-scale testing using both
dry and wet mixing, measurement and back analysis of the full-scale behavior and the
completion of a design guide to EC7. The findings of the project, which included several fieldtests, are documented in the Final Report of Design Guide Soft Soil Stabilization (Holm,
1999).
b. Swedish Deep Stabilization Research Centre
The most comprehensive Research and Development effort in the area of dry mixing in
Europe during the past decade was initiated and financed by the Swedish Deep Stabilization
Research Centre (SD). The activities of SD ended in 2001 and resulted in a large number of
publications related to soil mixing and different aspects related to it.
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Construction equipments and construction methods:
Regarding the construction equipments and construction methods, different mixing
equipments and different methods of deep and shallow soil mixing has been developed in
different countries of Europe.
Several innovative and currently developed methods can be listed as:
The Bauer Mixed-In-Place (MIP) Method
The Nordic Dry Deep Mixing Method
The COLMIX Method
The TREVIMIX Method
The Bauer Cutter Soil Mixing (CSM) System
Recently, Hybrid methods, the methods which may combine conventional piling,
grouting, and jet grouting and mechanical mixing are also under development like The
TURBOJET Wet Mixing System.
Currently a method is aimed to be developed in the UK by the SMiRT project, a
Cambridge University, UK launched project.Project SMiRT aims to achieve significanttechnical advancement and cost-savings by developing an innovative single soil mix
technology (SMT) system for integrated remediation and ground improvement, with
simultaneous delivery of wet and dry additives, and with advanced quality assurance
system (Al- Tabbaa, 2008).
2.5. Soil Mixing and its suitability to various soil types
The intent of most soil mixing is to modify the soil so that its properties become similar to
that of soft rock such as clay shale or lightly cemented sandstone. The modulus of elasticity
and unconfined compressive strengths are typically 1/5th
to 1/10th
that of normal concrete
(Nicholson, 1998). Almost all soil types are amenable to treatment; however, soils containing
more than 10 % peat must be tested thoroughly prior to treatment. Mixing of soft, clay soils
must be carefully controlled to avoid significant pockets of untreated soils. However, there are
methods readily available to insure competent mixing and methods of testing to insure that
adequate mixing and treatment has been achieved.Cohesionless soils are typically easier to
mix and blend than cohesive soils. Depending on many factors, the unconfined compressive
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strength of the soil mixed material ranges from 0.3 to 2 MPa for cohesive soils and much
higher for cohesionless soils (Hayward Baker, 2006).Soil Mixing is also commonly used as a
stabilization or in situ fixation method for soils containing hazardous wastes andsludges.Containment walls can be constructed with permeability of approximately 5X10
-7
cm/sec, similar to that achieved by most slurry wall techniques. Typical strength and
permeability characteristics of treated soils are listed in Table 3.
Table 3. Typical strength and permeability characteristics of treated soils
Soil Type Cement dosage(kg/m3) UCS(KPa) Permeability(cm/sec)
Sludge 240 to 400 70-350 1x10-6
Organic Silts and Clays 150 to 260 350-1400 5x10-7
Cohesive Silts 120 to 240 700-2100 5x10-7
Silty sands and Sands 120 to 240 1400-3500 5x10-6
Sands and Gravels 120 to 240 3000-7000 1x10-5
(Source: Nicholson, 1998)
2.6. Soil Mixing and its suitability to various binder types
Different types of binder that has been used in soil mixing and that can be used in soil mixing
are Cement, Lime, Slag, Fly Ash, Gypsum, Bentonite and many more.
All the above-mentioned binders have almost the same chemical constituents viz CaO, SiO2,
Al2O3, Fe2O3, MgO, K2O, Na2O, SO3.The only difference between them is that the
constituents vary in proportion or quantities. Lime and cement have been the most commonly
used binder so far, whereas other binders have been scarcely used.
The suitability of almost all types of binders and their combination and their use in soil
mixing is determined based on the strength gain of the soil treated with these binders. The
strength gain with time finally depends upon the principal chemicals, the reactions and the
type and amount of reaction products formed which differs depending upon the type of
binders used. Ahnberg et.al(2005), describes the major binders that is in use for soil mixing
as follows:
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reactive material in itself. However, the silica and alumina in fly ash are often more
easily accessible for reactions with any CH added through the binders, compared with
the same minerals in the soil. The reaction products generated are much the same asthose of soils containing silica and alumina, i.e. mainly CASH, CSH and/or CAH.
In order to further understand the way in which the various reaction products generated from
different types of binder affect the increase in strength with time after mixing, rough estimates
can be made of the amounts of bonding being formed. The amount of reaction products
formed when adding a certain quantity of binder is assessed based on the mole weights of the
principle chemical elements involved (Ahnberg, 2006).
2.7. Some Research Efforts specific to the Strength of Soil Mixed Columns
So far, the Euro soil stab project studied the effect of binder quantity of up to 300 kg/m3 on
the strength of the soft soils like clay, gyttja and peat stabilized by soil mixing.
The Euro soil stab project also studied the effect of curing time up to 1 year on the strength of
soils stabilized by soil mixing. It was then concluded from this project that when only pure
cement was used as binder the strength gain was faster with the almost final strength gained
within the first month. Whereas when cement mixed with blast furnace slag as in our studies
was used, the reactions continued several months later. Thus short or long-term strength gain
studies are encouraged depending on the type of binder used (Euro Soil Stab, 2002).
The Swedish Deep Stabilization research centre has also studied the effect of different types
of binder on the strength of soft soils like clays and organic soils.
Few other projects in the United States also tested the strength parameter of almost all types
of soil as expressed in the Table 3 but binder doses higher than 400 kg/m3 have not been
tested so far, as learnt from the literature.
This study (thesis) affords to investigate if construction material with strength value ranging
from 2MPa to 20 MPa can be obtained in cohesionless soils via in situ soil mixing. Higher
binder doses up to 700 kg/m3 of soil are used during the investigation in the laboratory.
Few Research projects, which studied the different types of binders and soils and their relation
on the strength of mixed soil, are summarized as below:
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binders give different bondings and different reaction products and the strength gain is
dependent on the type and amount of reaction products formed.
In this way, different project has been launched in local and national level with several
different types of soil and several different binders and their combinations. Studies so far have
focused on soft and cohesive soils, lime and cement as binders but the use of cohesionless soil
and other binders like slag, fly ash, gypsum that are very scarcely studied has to be
investigated. Though cohesionless soil might not prove useful in case of deep mixing projects,
its ability to gain high strengths should not be neglected and its use in construction of not very
deep mixing projects like sub bases should be given a priority for further studies.
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Chapter 3: Scope of the study 32
3. Chapter 3: SCOPE OF THE STUDY
3.1. Extent of the studies
Mixing binders into a soil will bring about significant changes in most of the soil properties.
The strength properties of stabilized soil are affected by several different factors. The factors
regarded as being important in this research were the type and quantity of binder, the type of
soil, the total amount of water in the mix, the amount of solids in the mix and the curing time.
The investigations comprised laboratory testing of Brusselian soil, dense, cohesionless soil
stabilized with the binder, Holcim cement, CEM III/A 42.5 N LA.Complementary data from
other investigations presented in the literature were also used in the analysis of stabilized soil
behavior. The tests performed were all laboratory tests. Comparisons that could be made with
the field behavior would be based on the similar earlier projects learnt via literature. The
laboratory tests performed were all physical tests. The physical tests in the laboratory
involved the testing of physical parameters, which was restricted to the equipment availability
in the laboratory. However, almost all geotechnical or engineering properties that have a
relation with the strength gain were attempted to be investigated. The chemical testing of the
soil or binder composition or the reaction products was not included.
The Brusselian sand used in the test was brought from the BBRI site at Limelette, Brabant.
The geological and paleogeological process determines the soil type of the area. The
Brusselian sand from depth greater than 8m was taken for laboratory experiment. Clays and
organic soils, which are so far more commonly studied, were not studied in the work.
Although the more coarser soil type have been considered as less relevant for deep mixing
applications( Ahnberg,2006), the use of these soils for the improvement of sub bases and the
high strength that can be achieved with this soil type should not be underestimated.
The binder was readily available from the BBRI.The binder was used directly from the sealed
bags without any further refinement.
In all approximately about 80 samples, which after unmoulding and rectification were divided
into 160 samples each of shape factor 1, were prepared for testing in the laboratory.
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Chapter 3: Scope of the study 33
3.2. Material and Methods
3.2.1. The Brusselian sand
The Brusselian sand is a dense sand. Actual behavior of the sand is strongly dependent on its
composition, which is varies even at the site scale. However, to understand the geomechanical
behavior of the sand, it is important to have a better understanding of the geological
framework (Schittekat, 2003).
The subsoil of the area around Limelette, south of Brussels is built up of a series of Lutetian
sand, about 46 m thick, covering 20 m Landenian clay and sand underlined by sandstone of
Cambrian age. This sand is known as Brusselian sand (Laga, 1998) belonging to the Eocene.
These sediments are covered by Quaternary silt formations with a thickness ranging up to 6
m.
Also called the Lutetian sand, the Brusselian sand is of Middle Eocene age (43 m.y.).It is
characterized by numerous facies changes. The kind, which is in Brabant, has at the bottom
gravel, sometimes glauconitic coarse sand with marl and rounded pieces of the older Ypresian
formations, coarse glauconitic quartzitic sand, fine calcitic sand, very fine glauconitic calcitic
sand (Schittekat, 2003). As a rule, the above-mentioned faces are found from the bottom to
top.
The Brusselian sand in Belgium is found over a large area from Charleroi at the south to the
border of the Netherlands at the north, throughout Brabant area. It is outcropping (but mostly
covered by 5 to 10 m silt) over two Brabant provinces and the North East of the Hainaut
province.
The Brusselian sand is important and relatively well known for 3 different reasons:
It is a major aquifer at the south east of Brussels and since it is vulnerable and
contaminated by nitrates recently investigated from a hydro geological point of view.
It is an important source of construction material; many pits have been opened, some
of them later filled with waste. The faces of the pits could be observed. When filled
with waste the contamination plume has been observed or predicted.
It is an important layer for geotechnical or civil works in the whole outcropping area
including Brussels.
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Chapter 3: Scope of the study 34
An extensive soil investigation campaign was conducted at the Limelette site by the BBRI in
1998-2002 under the framework of a research project on Soil Displacement Screw Piles.
Standard tests, which characterize the soil at the site including a boring with undisturbedsampling, were executed in order to define through laboratory tests the physical and
mechanical properties of the soil (Gauthier et.al 2003). The results of the tests, which
determined the physical characteristics of the soil at the depth of 10 m to 11 m, which
characterizes the soil used in this study, are listed in Table 6.
Table 7. Physical properties of the soil at Limelette
Site Limelette
Depth 10 m -11 m or more
Soil type Slightly Clayey sand
Dry density 13.8 kN/m3
Natural Density 15.0 kN/m3
Water content 9 %
Saturation water content 27.0 %
Liquid Limit 23.4 %
Plastic Limit 20.7 %
Plasticity Index 2.7
(Source: Gauthier et.al 2003)
3.2.2. The Binder
The binder used is cement from the Holcim Company, labeled CEM III /A 42.5 N LA.
According to Belgian standard, EN 197-1 and NBN B12-109, the cement CEM III/A 42.5 N
LA is blast furnace cement, with main constituents as Portland clinker (K) and granulated
blast furnace slag (S). The percentage of granulated blast furnace slag is between 36% and
65%. The cement CEM III/A 42.5 N LA is cement with limited alkali percentage (LA).The
term CEM indicates the cement, III represents high slag blast furnace cement, A represents
the slag percentage and 42.5 typify the characteristic strength in MPa at 28 days of that
particular cement mix. The Na2O-equivalent is smaller than 0.90%.The main chemical
composition is CaO(51.3%), SiO2(23.5%), Al2O3(8.1%), Fe2O3(2.6%), MgO(4.4%),
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Chapter 3: Scope of the study 35
Na2O(0.36%), K2O(0.65%), Na2O(0.79%), SO3(3.2%), Cl(0.03%), Loss on ignition(1.8 %),
Insoluble rest(0.6%).
It is generally recognized that the rate of hardening of Portland blastfurnance slag cement is
somewhat lower than that of Portland cement during the first 28 days, but thereafter increases
so that at 12 months the strength becomes close to, or even exceeds that of Portland cement.
(Hewlett, 1998).
The binder was mixed with water first and used in slurry form while mixing. The quantity of
binder varied from 200 kg/m3 to up to 700kg/m3 of wet soil.
3.2.3. Soil Parameters Estimation in the Laboratory
Soil Type:In order to characterize the soil, sieve analysis was performed by sieving the soil in
sieve sizes with standard diameter. Results of Sieve Analysis are listed in the table 7 below:
Table 8. Results of sieving
Diameter of sieve
openings (mm)
Fraction of the particles >
Diameter (%)
Diameter of sieve
openings (mm)
Fraction of the particles >
Diameter (%)
28.000 0.00 0.212 1.70
19.000 0.00 0.150 2.31
14.000 0.00 0.106 49.94
10.000 0.00 0.075 82.63
7.1000 0.00 0.0547 86.68
6.300 0.00 0.0390 88.63
4.000 0.00 0.0238 89.60
2.411 0.00 0.0138 89.93
0.850 0.28 0.0098 90.25
0.600 0.67 0.0072 90.90
0.425 1.36 0.0035 93.50
0.300 1.52 0.0014 93.83
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Chapter 3: Scope of the study 37
Table 9. Chart of the Unified Soil Classification System
Group symbol Group name
GWwell graded gravel, fine tocoarse gravel
GP poorly graded gravel
GM silty gravel
GC clayey gravel
SWwell graded sand, fine to
coarse sand
SP poorly-graded sand
SM silty sand
SC clayey sand
ML silt
CL clay
OL organic silt, organic clay
MHsilt of high plasticity, elastic
silt
CH clay of high plasticity, fat clay
organic OH organic clay, organic silt
Pt
inorganic
Highly organic soils
Sand 50% of coarse
fraction passes No.4sieve
Gravel > 50% of
coarse fraction
retained on No.4 (4.75
mm) sieve
Coarse grained soils
more than 50%
retained on No.200
(0.075 mm) sieve
Fine grained soils more
than 50% passes
No.200 sieve
silt and clay
liquid limit < 50
silt and clay
liquid limit 50
Major divisions
clean gravel
gravel with >12%
fines
clean sand
sand with >12%
fines
(Source: ASTM D-2487-69)
Specific Gravity: Specific gravity was determined in the lab by Pycnometer method following
the ASTM (1984), standard document D 854 and was found to be 2.66.
Water content: The water content of the soil was measured before the preparation of the
samples for each of the series. When the total workability of the soil mix material was to be
determined, the water content played a very important role. Thus, the water content measured
in the laboratory for the soil varied from 12.44 % for Series I, 15.29 % for Series II, 13.67 %
for Series III, 11.27 % for Series IV, 9.26 % for Series V, 9.0% for series VI and 8.17% for
Series VII and Series VIII.
Densities: A natural density of 1500 kg/m3as from Table 6 was used during the calculation of
the soil mix proportions for each series for ease.However,to verify this density value, the
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Chapter 3: Scope of the study 39
5. The binder and water was mixed to make a slurry. To ensure proper mixing, a small
Hobart Mixer was used and the slurry was prepared in 3-5 minutes.
6. The slurry was then added to the soil while mixing and each batch was mixed for 10
minutes in the Hobart Mixer as shown in Figure 6(a), with a relative level of mixing
energy. (Speed of the mixer set at 1).However, how much mixing energy the
contractor will employ in field is unknown. Variation of the mixing energy may
cause scatter of the test results and
Recommended