2008 rakshya shrestha

7/24/2019 2008 Rakshya Shrestha

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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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

2008 rakshya shrestha

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