Improvement of Dredged Sediments1131128/FULLTEXT01.pdf · My special thanks to Assoc. Professor ......

Improvement of Dredged Sediments-A laboratory study on dredged sediments with different types of binders

ABDUL SIDDIK HOSSAIN

Civil Engineering, master's level (120 credits)

2017

Luleå University of Technology

Department of Civil, Environmental and Natural Resources Engineering

Thesis submitted in conformity with the requirements for the degree of

Master of Science

Authored by: Abdul Siddik Hossain

Supervised by: Chaired Professor Jan Laue

Department of Civil, environmental and natural resources engineering

Luleå University of Technology

2017

Improvement of Dredged Sediments

-A laboratory study on dredged sediments with different types of binders

This dissertation work is dedicated to my loving Grandfather who is always being a great

source of mental strength and inspiration since my childhood. I miss him a lot in each

success of my life.

i

ACKNOWLEDGMENTS

First of all, the author wishes to express his gratitude to the almighty Allah for giving him the

opportunity and for enabling him to accomplish this research work. This thesis work would not have

been possible to finish without the support of many people. I would like to give heartiest gratitude and

profound indebtedness to my supervisor Chaired Professor Jan Laue for supervised me without knowing

me before. I honestly believe this thesis work would not be possible to accomplish without your

continuous guidance, invaluable ideas, inspirational motivation and encouragement at every stage of

this research work.

This thesis work has also given me the opportunity to work with other researchers in Geotechnical

engineering division of Lulea University of Technology (LTU). My special thanks to Assoc. Professor Hans

Mattsson to appoint me for this challenging research work. I am very much thankful to research

engineer Dr. Gregory Makusa, for his patient guidance, technical assistance and excellent collaboration,

while performing laboratory tests at CompLab in Lulea University of Technology.

I would like to give my thanks to Dr Mohammad Sazzad Mosharrof, Dr Minhaj Alam, Dr Nowshir Fatima,

Mr Mohammad Khairul Islam, Dr Ifthekhar Uddin Bhuiyan, Dr Asif Saleh Qureshi, Mr Syed Alley Hassan,

Mr Riaz Hussain Bhanbhro and all other friends in Lulea city for their company and support during my

entire stay in Sweden.

Last but not least, I would like to express my deep gratitude to my parents who always encourage me

for higher studies and educated me with their unconditional love. I would like to give thanks to my

respectable Mother in Law for keeping faith in me. Finally, My deepest gratitude and love to my better

half, Dr Shawlin Sultana for her endless tolerance, love and continuous motivation.

Abdul Siddik Hossain Luleå, February 2017

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ABSTRACT

Stabilization and solidification (S/S) technique have been the most frequently used method for dredged

sediment improvement in Sweden and worldwide. As dredging activities are essential for safe navigation

of ships and vessels that may processes harmful substances or organic pollutants to cause

contamination of the surrounding environment. Stabilization/solidification technology has been

identified as the most beneficial handling strategy for contaminated dredged sediments and treated

stabilized materials can be used in civil engineering applications (e.g. backfill or embankment). This (S/S)

technique is the easiest way of improving high water content dredged sediments using different types of

binders. During the stabilization process, dredged sediments are mixed with commonly used binders,

such as Portland cement, fly ash and ground granulated blast furnace slag (Merit 5000). Nowadays,

supplementary cementitous materials such as (fly ash and blast furnace slag) are being used increasingly

considering long term strength development of stabilized dredged materials instead of using more

cement. Generally, cement hydration is a complex chemical-reactions. By addition of supplementary

cementitious materials, it becomes more complex because of cement hydration and pozzolanic

reactions. The overall objective of this thesis work is to improve the understanding of compressibility

and strength behavior of stabilized dredged materials. To achieve these objectives, a series of

unconfined compressive strength tests and consolidation tests were performed on stabilized dredged

materials (SDM) with different types and mixing ratios of binders. These lab tests have been focused on

the compressibility and strength properties of stabilized materials. The UCS test determines the amount

of binders and curing time needed to achieve the required shear strength of SDM. The outcomes of this

thesis work show that the stabilized dredged sediments constitute of binder mixing ratio (Cement:Fly

ash:Merit 5000 as a proportion of 10:10:5) which is 25% of the total fresh dredged sediments can’t

sustain any superstructure or surcharge load but it can only be used as backfill materials on site.

Whereas, stabilized dredged material with binder mixing ratio (Cement:Fly ash:Merit 5000 as a

proportion of 20:20:10) which is 50% of the total fresh dredged Sediment becomes stiff after 28 days

curing and becomes very stiff after 91 days curing. It becomes obvious that the unconfined compressive

strength of SDM increases with higher amount of binders and longer curing time. The pozzolanic

reaction continues after 28 days curing period. The presence of supplementary cementitous materials

(fly ash, blast furnace slag and merit 5000) can improve the ductility of stabilized dredged materials

(SDM) in the post-peak strength degradation zone without changing the unconfined compressive

strength. It is also obvious from the test results that the UCS values of stabilized dredged materials

increase with decreasing moisture content/increasing bulk density. The consolidation properties of SDM

are greatly influenced by the binder mixing ratio, curing time and preloading weight. Due to preloading

weight, the deformation in stabilized dredge sediments is irreversible because of cementation and

pozzolanic effects. Considering both curing time and binder ratio, compression index (Cc) and swelling

index (Cs) values for SDM with binder ratio (20:20:10) have been lowered approximately by 75% and

67%, respectively than SDM with binder ratio (10:10:5). After 91 days curing of SDM with binder ratio

(20:20:10), the maximum value of tangent modulus is estimated about 9624 kPa which indicates that

the superstructure can be erected on stabilized dredged materials. It is also concluded that physico-

chemical variables control the consolidation behavior of stabilized dredge materials (SDM) as the

coefficient of consolidation (Cv) value decreases with increasing consolidation pressure.

iii

Table of Contents

ACKNOWLEDGMENTS .................................................................................................................................... i

ABSTRACT ...................................................................................................................................................... ii

List of Tables ................................................................................................................................................. v

List of Figures ............................................................................................................................................... vi

List of Symbols and Acronyms ................................................................................................................... viii

1 Introduction ............................................................................................................................................... 1

1.1 Problem statement ....................................................................................................................... 2

1.2 Investigation objectives ................................................................................................................ 4

2 Theoretical Background ........................................................................................................................ 5

2.1 Dredged Sediment Stabilization and Solidification Technology ................................................... 5

2.2 Environmental Effects of Dredged Sediment ................................................................................ 7

2.3 Geotechnical Structures and Design Considerations .................................................................... 7

3 Materials and Methods ......................................................................................................................... 9

3.1 Dredged Sediment types ............................................................................................................... 9

3.2 Organic content ............................................................................................................................ 9

3.2.1 Loss on ignition (LOI) method ............................................................................................. 10

3.3 Initial water content ................................................................................................................... 11

3.4 Percentage (%) sieve ................................................................................................................... 11

................................................................................................................................................................ 13

3.5 Binders ........................................................................................................................................ 13

3.5.1 Cement ....................................................................................................................................... 13

3.5.2 Fly ash ........................................................................................................................................ 16

3.5.3 Blast furnace slag (merit 5000) .................................................................................................. 17

3.5.4 Binder recipe .............................................................................................................................. 17

3.6 Samples preparation for laboratory tests ................................................................................... 18

3.6.1 Unconfined Compressive Strength Test..................................................................................... 19

3.6.2 One – Dimensional Consolidation or Oedometer Test .............................................................. 22

iv

4 Results ...................................................................................................................................................... 26

4.1 Unconfined Compression Test .......................................................................................................... 26

4.2 Consolidation Test............................................................................................................................. 30

5 Discussion ............................................................................................................................................ 44

6 Conclusions and Future Work .................................................................................................................. 47

6.1 Stiffness behavior .............................................................................................................................. 47

6.2 Consolidation behavior ..................................................................................................................... 47

6.3 Future work ....................................................................................................................................... 48

References .................................................................................................................................................. 49

Appendix ..................................................................................................................................................... 52

A.1 Test results of samples with binder ratio (20:20:10) from UCS test: ............................................... 52

A.2 Test results of samples with binder ratio (10:10:5) from UCS test: ................................................. 53

B.1 Analysis of test results of samples with binder ratio (20:20:10) from Oedometer test: .................. 54

B.2 Analysis of test results of samples with binder ratio (10:10:5) from Oedometer test: .................... 56

v

List of Tables

Table 3.4.1. Shows the U.S. standard sieve numbers corresponding opening sizes. .................................. 12

Table 3.5.1. Distinguishing characteristics associate with IP, NCP and HP that affect the compressibility

of SDM. ...................................................................................................................................................... 15

Table 3.5.4.1 Chemical composition for binders: FA = fly ash, GBBS = ground granulated blast furnace

slag (Data: courtesy of SSAB) and Cement (Makusa et al. 2016). ............................................................. 17

Table 3.5.4.2. Suggested binder recipe for stabilized dredged material. C = cement, FA = fly ash, GGBS =

ground granulated blast furnace slag. ......................................................................................................... 17

Table 3.6.1.1. General relationship of consistency and unconfined compression strength. ....................... 19

Table 3.6.1.2. Sample data sheet from the UCS test. .................................................................................. 21

Table 3.6.2.1. Consolidation test (Void Ratio-Pressure, Coefficient of consolidation, Coefficient of

volume compressibility and Permeability Calculation) .............................................................................. 24

Table 4.1.1. Peak strength from UCS tests and corresponding strain values. ............................................. 29

Table 4.2.2 Primary consolidation, coefficient of consolidation and coefficient of volume compressibility

at different stresses according to curing time of stabilized materials with binder ratio (20:20:10). ........... 40


at different stresses according to curing time of stabilized materials with binder ratio (10:10:5). ............. 41

vi

List of Figures

Figure 1. Implementation rate of S/S treatment compared to other technologies used at U.S. superfund

sites (USEPA 2001). ....................................................................................................................................... 2

Figure 1.1. Stabilization/Solidification with process stabilization in port of Gävle (G. Holm 2012). ............ 3

Figure 2.1.1. Mass stabilization technique as deep mixing (Ideachip and Ramboll 2005). Method is

applicable for soft soils like peat, mud and clay. .......................................................................................... 6

Figure 2.1.2.Stabilization in layers. Here the binder is spread on the upper surface or fed through the

rotating mixing head. During the mixing process the excavator shaft is taking the mixed soil towards the

excavator. The stabilization depth is not limited by the length of the arm (Ideachip and Ramboll 2005). . 6

Figure 2.1.3. Combining mass- and column stabilization techniques; e.g. for a road. ................................. 7

Figure 2.3.1. Principle sketch of geotechnical structure including monolith stabilized/solidified

contaminant dredged sediments. ................................................................................................................. 8

Figure 3.2.1 Classification of soil organic matter. ....................................................................................... 10

Figure 3.4.1. Grain size distribution plot for pure dredged sediments with organic content. ................... 13

Figure 3.5.1. A pictorial representation of cross-section of a cement grain. ............................................. 14

Figure 3.5.2. Heat evolution curve produced in cement hydration. .......................................................... 14

Figure 3.5.2.1. functions of a boiler, A) coal or bio fuel goes into furnace, B) combustion chamber, C)

bottom ash accumulated, D) flue gases with suspended fly ash, E) fly ash is collected in filter, F) flue

gases is emitted. ......................................................................................................................................... 16

Figure 3.6.1. Stabilized dredged materials (SDM) samples curing for unconfined compression and

oedometer test. .......................................................................................................................................... 18

Figure 3.6.2. Variation of temperature during curing of samples. ............................................................. 19

Figure 3.6.1.1. Unconfined compression strength test: a) curing of treated dredged sediment samples

under fixed load, b) sample placement for UCS test, C) removing sample after test, d) failure modes of

samples. ...................................................................................................................................................... 20

Figure 3.6.1.2. (a) Unconfined compression test, (b) Typical stress Vs strain plot from UCS test. ............ 22

Figure 3.6.2.1. Samples have been placed in Oedometer setup for test. .................................................. 23

Figure 3.6.2.2. Determination of t90 by square root of time method (ASTM 2003). .................................. 23

Figure 3.6.2.3. Plot of void ratio against pressure of the specimen (e-logp) graph. .................................. 25

Figure 4.1.1. Stress-strain plot of stabilized dredged materials with binder ratio 20:20:10 ...................... 27

Figure 4.1.2. Stress-strain plot for stabilized dredged materials with binder ratio 10:10:5 ....................... 27

vii

Figure 4.1.3. Curing period and binder ratio effect on UCS values of stabilized dredged sediments. ....... 28

Figure 4.1.4. Plotting strain values over curing time for binder ratio (20:20:10). ...................................... 28

Figure 4.1.5. Plotting strain values over curing time for binder ratio (10:10:5). ........................................ 29

Figure 4.1.6. Variations of unconfined compressive strength with bulk density & water content followed

by curing time 7, 14, 28 and 91 days. ......................................................................................................... 30

Figure 4.2.1. Void ratio variation (Δe) with log (pressure) for a given curing period. ................................ 31

Figure 4.2.2. Void ratio variation (Δe) with log (pressure) for a given curing period. ................................ 32

Figure 4.2.3. Binder contents and curing time effect on compression index. ............................................ 33

Figure 4.2.4. Binder contents and curing time effect on recompression/swelling index. .......................... 33

Figure 4.2.5. Tangent modulus (Et)-vertical stress (σ) behavior of SDM during consolidation test. .......... 34

Figure 4.2.6. Tangent modulus (Et)-vertical stress (σ) behavior of SDM during consolidation test. .......... 34

Figure 4.2.7. Constrained modulus (M)-vertical stress (σ) behavior of SDM during consolidation test. ... 35

Figure 4.2.8. Constrained modulus (M)-vertical stress (σ) behavior of SDM during consolidation test. ... 36

Figure 4.2.9. Coefficient of consolidation (Cv)-vertical stress (σ) behavior of SDM during consolidation

test. ............................................................................................................................................................. 37


test. ............................................................................................................................................................. 37

Figure 4.2.11. Permeability (K)-vertical stress (σ) behavior of SDM during consolidation test. ................ 38

Figure 4.2.12. Permeability (K)-vertical stress (σ) behavior of SDM during consolidation test. ................ 39

Figure 4.2.13. Stress-strain curves of SDM subjected to various consolidation stresses. .......................... 42

Figure 4.2.14. Stress-strain curves of SDM subjected to various consolidation stresses. .......................... 43

viii

List of Symbols and Acronyms

SMOCS Sustainable Management of Contaminated Sediments

UCS Unconfined compressive strength

WC Water content

SDM Stabilized dredged materials

S/S Stabilization/Solidification

M Constrained Modulus

Cv Coefficient of consolidation

Cu Undrained shear strength

Cc & Cs Compression and Swelling index

DS Dredged sediments

PC Portland cement

FA Fly ash

GGBS Ground granulated blast furnace slag

K Coefficient of permeability

Et Tangent modulus

1 Introduction

Dredging is the process of digging up sediments from the river bed for widening and deepen the

navigational channels or waterways. Dredging activities are essential for safe navigation of ships and

vessels at ports and harbors. By the nature of dredging activities, it changes the surrounding

environment and affects the aquatic ecosystem. So, it is recommended to consider the positive and

negative effects of dredging activities on the surrounding and the aquatic environment. These dredging

and disposal processes may release harmful substances into the environment, making them available to

be taken up by animals and plants with the potential to cause contamination or poisoning. So, proper

treatment is inevitable prior to disposal the waste sediments. According to (EPA 2001), “dumping wastes

at sea is forbidden”. High cost and scarcity of landfill creates demand for beneficial reuse of

contaminated dredged sediments. Sustainable Management of Contaminated Sediments (SMOCS)

projects in the Baltic Sea region was funded by the European Union during 2007-2013. The purpose of

the project was to establish a guideline on sustainable management of contaminated sediments within

dredging projects in Baltic Sea. The main goal was beneficial reuse of dredged sediments in expanding

port area constructions and SMOCS in collaboration with port of Gävle in Sweden identified a sediment

stabilization/ solidification technology as potential method (Holm et al. 2013). In fact,

stabilization/solidification technology is using widespread around the world as a remedial technology for

amending and improving high water content contaminated dredged sediments. According to (Bates and

Hills 2015), with the determination of an effective binders mixing ratio and proper implementation,

stabilization-solidification technology can be used to treat a wide range of organic and inorganic

contaminants in dredged sediments and sludge. However, in Europe implementation of S/S technology

is increasing due to its availability and cost of landfill space, and the restrictions placed upon the ‘digging

and dumping’ of waste and soil. Considering low-cost management of soil and waste, S/S methods

become more widely appreciated and implemented technology in the world. According to EPA,

stabilization-solidification technology performs the following tasks: improve handling and geotechnical

properties of waste, reduce surface area of stabilized mass thus decreasing contaminants leakage path

and limit solubility of hazardous elements in the waste (EPA 1989). The S/S method can be implemented

either in in-situ or ex-situ. Excavation and backfilling is done while performing ex-situ operations.

Whereas, the in-situ process involves injecting of binder agents (e.g. Portland cement, lime, fly ash,

ground granulated blast furnace slag and organic binder such as asphalt) into the contaminated soils.

The U.S Environment Protection Agency (EPA) considers stabilization-solidification (S/S) an established

remedial technology and wastes are regulated in U.S under the Resource Conservation and Recovery Act

(RCRA). EPA has invented S/S as the Best Demonstrated Available Technology (BDAT) for 57 types of

hazardous wastes mentioned in RCRA (Means 1995). S/S was the most frequently used remedial method

for controlling the source of environmental contamination at superfund sites and about 25% of selected

remediation sites were treated by this technology at shown in Figure 1.

Figure 1. Implementation rate of S/S treatment compared to other technologies used at U.S. superfund sites (USEPA 2001).

(EuroSoilStab 2002) describes that geotechnical properties of stabilized soil such as stiffness and

compressibility are obtained from laboratory test results which can be utilized to predict in-situ

performance of stabilized dredged materials. Unconfined compressive test and Oedometer test are the

most commonly used laboratory tests for determination of strength and compressibility parameters of

stabilized dredged materials (SDM). During design analysis of geotechnical engineering, it should

consider that laboratory evaluated properties of SDM may differ significantly from the in-situ

stabilization (G.Makusa 2013).

1.1 Problem statement

Due to increased sea transport at the port of Gävle as shown in Figure 1.1, the fairway needed to be

widen and deepen for larger and deeper ships. The fairway had to be dredged to get the proper depth

and the upper part of dredged sediments (0-0.5m) was contaminated. To investigate the suitability of

S/S method regarding the type of dredged sediments, laboratory tests need to be

Figure 1.1. Stabilization/Solidification with process stabilization in port of Gävle (G. Holm 2012).

performed in order to seek geotechnical properties. (Lagerlund 2010a, 2010b) completed laboratory

tests on natural dredged sediments from the port of Gävle with average water content of 450%. For

stabilization of high moisture content of dredged sediments, Cement/Merit 5000/Bio fly ash were used.

Merit 5000 is ground granulated blast furnace slag (GGBS) which was collected from Merox AB, Sweden.

Fly ash was a bio fly ash provided by vattenfall power plant. These Merit 5000 and bio fly ash were used

in sample preparation as supplementary cementing material (G. Holm 2012). In general, two types of

design recipes were used with proportion by weight 40:20:40 (cemen:merit5000:fly ash) and

35:30:35(cement:merit5000:fly ash) (Lagerlund 2010a, 2010b). The desired unconfined compressive

strength (UCS) is 140 kPa after 91 days of curing time to carry the load from superstructure and surface

load by containers and mobile cranes. The expected hydraulic conductivity (HC) is 10-9 m/s after 91 days

of curing time. The laboratory test results have shown that S/S method is applicable on dredged

sediments to obtain required strength and permeability properties. As it is proven that stabilized

contaminated dredged material meet most of the geotechnical and environmental criteria, it can be

used as construction material. Besides, it successfully re-act with other structures like as retaining wall,

sheet pile wall etc.

In this dissertation work, consolidation test and unconfined compression test have been performed on

dredged sediments which have been collected from port of Gävle. This study seeks to evaluate the

mixing ratio of binders with dredged sediments to attain required geotechnical properties. Although

selection of binders and mixing ratio depend on many factors such as, soil mineralogy, organic matter

present, leachability, pH, desired strength and stiffness of the final material. In this study, the freshly

dredged sediments have been treated with cement, fly ash and merit 5000 according to a mixing ratio of

20:20:10 (50% of the total fresh dredged sediment) and 10:10:5 (25% of the total fresh dredged

sediment).

1.2 Investigation objectives

The objectives of this dissertation work are to assess the main engineering parameters of stabilized

dredged sediments for design purposes such as compressive shear strength, modulus of elasticity

(stiffness), hydraulic conductivity, the coefficient of consolidation as well as compressibility. Generally,

design parameters depend on design method and analysis. But the most common design calculations

carried out in geotechnical engineering are settlement analysis and stability calculations. It is assumed

that stress Vs strain curve is linear if soil is elastic under working load. In stability calculations, complete

failure of soil mass is considered. This causes ultimate failure of the structure along with large

deformations and the stress Vs strain behavior become rigid and perfectly plastic. It is also important to

understand the mechanical behavior of stabilized dredged sediments and possible modes of failure

under undrained conditions during geotechnical design process.

2 Theoretical Background

Stabilization–solidification (S/S) technology is a combination of two separate methods namely as

stabilization and solidification according to (USEPA 1993). The stabilization method involves chemical

reactions that reduces leachability of contaminants. The chemical reactions cause contaminants to be

less mobile by reducing its solubility. Solidification technology encapsulates the contaminants through

chemical reactions between the dredged sediments and binders that increased compressive strength

and reduced permeability.

2.1 Dredged Sediment Stabilization and Solidification Technology

Stabilization and solidification (S/S) techniques can transform waste, soil, sediment or sludge to a more

stable material chemically and physically. During the stabilization process, dredged sediments are mixed

with cement or admixtures of cement or other stabilizing agents. This technique can prevent or delay

the mobility of pollutants in the material. The stabilization technique creates more physically and

chemically stable constituents which reduce potential environmental risk without changing its physical

structure. The solidification technique converts sediment to a stable, monolithic structure involving

chemical interaction between contaminants and solidification agents. In-fact solidification is a suitable

technique for contaminated soils, sediments and other types of waste material to interlock and reduce

mobility of the contaminants by reducing of excess air and water by achieving reduced permeability and

porosity of the material. Additional reduction of mobility of contaminants is achieved through

stabilization technique using cement or composites of cement or other stabilizers.

S/S treatments include a wide range of process that usually involves mixing inorganic binders into the

soil or waste to transform it into a new, solid and non – leachable material. Mixing of binders usually

selected by mix design criteria which depends on the application. This application could be ordinary

infrastructure construction on weak ground, development of contaminated site, reuse of waste in

construction or land filling.

S/S treated material has many advantages, it reduces risk, increase reliability and reduce process costs.

Moreover, S/S is an environmentally beneficial technology, both by reducing contaminant flux and the

exchange and transport of materials. There are different types of S/S techniques, mixing methods and

usages. Nowadays three main techniques are used worldwide such as column stabilization, mass

stabilization and layer stabilization as shown in Figure 2.1.1, Figure 2.1.2 and Figure 2.1.3. These

methods serve different purposes, e.g. improving strength of subsoil and prevent leaching of

contaminants from soil. Therefore, different purposes require different stabilizers or mixtures of

stabilizers and mixing technology. As we know that different S/S techniques require different mixing

methods. This mixing can be done in-situ or ex-situ. In situ operation takes place within the ground or

site where the processed material originally was locked (originally contaminated site). The ex situ

operation takes place away from the original contaminated location. There are many systems to classify

the different S/S technique regarding mixing method and type of binders being used. (Massarsch and

Topolnicki 2005) classify deep mixing methods as wet/dry, rotary/jet-based, auger based or blade based

and the type of binder as wet or dry. Mass and column stabilization can be performed as a deep or

shallow stabilization process.

Figure 2.1.1. Mass stabilization technique as deep mixing (Ideachip and Ramboll 2005). Method is

applicable for soft soils like peat, mud and clay.

Figure 2.1.2.Stabilization in layers. Here the binder is spread on the upper surface or fed through the

rotating mixing head. During the mixing process, the excavator shaft is taking the mixed soil towards the

excavator. The stabilization depth is not limited by the length of the arm (Ideachip and Ramboll 2005).

Figure 2.1.3. Combining mass- and column stabilization techniques; e.g. for a road.

2.2 Environmental Effects of Dredged Sediment

Usually dredging activities have some impact on the environment. (Murray 1994) stated that, most of

the dredged materials contain some contamination despite lightly contaminated. Generally, seabed

sediments in ports carry harmful substances such as organic (oil, petrol, TBT, PCBs, PAH), heavy metals

(Pb, Cd, Cr, Hg, As, Cu, Zn) and pesticides. The sources of these contaminants can be from long distance

source or historic origin. During dredging and disposal processes, these contaminants can be released

into water. Thus, contaminants become available for plants and animals to be taken up. However, the

possibility of this phenomenon largely depends on the type and degree of contamination. Usually

dredged sediments from port and harbor contain the highest level of contaminations. The dredging

process causes alteration of water-system that could impact on the aquatic ecosystem. So, it is wise to

assess the positive and negative effects on the environment when planning dredging activities.

The aim of S/S method is to provide treated dredged sediments with good strength and lower hydraulic

conductivity. Surface leakage may occur from the treated dredged sediments. It is obvious that leaking

contaminants in the treated sediments should be lower or equal than the untreated dredged sediments.

2.3 Geotechnical Structures and Design Considerations Geotechnical design should verify that no relevant limit state is exceed as defined in (EN 1997-1 2004).

Limit states are related to design situations and design situations can be classified as persistent,

transient and accidental. There are two types of limit states: Ultimate limit states that concern

- The safety of people

- The safety of the structure

And Serviceability limit states that concern

The functioning of the structure and structural members under normal use

- The comfort of people

- The appearance of the construction works

Besides limit states, (EN 1997-1 2004) has established geotechnical design requirement based on three

geotechnical categories. Geotechnical Category 1 only includes small and relatively simple structures.

Geotechnical category 2 deals with conventional types of structure and foundation with no exceptional

risk or difficult soil or loading conditions. Geotechnical Category 3 include structures or part of

structures which fall outside the limits of geotechnical categories 1 and 2. Geotechnical category 3

includes the following examples:

- Very large or unusual structures

- Structures involving abnormal risks or exceptionally difficult ground or loading conditions

- Structures in highly seismic areas

- Structures in areas of probable site instability or persistent ground movements that require

separate investigation

Design of structure with stabilized/solidified contaminant dredged sediments should be regarded as an

unusual structure and consequently geotechnical category 3 shall be used. The required geotechnical

properties of the stabilized/solidified dredged sediments are based on the type of construction,

governing limit state and the use of the area. Figure 2.3.1 shows the exemplified application of

stabilized/solidified contaminant dredged sediments.

Figure 2.3.1. Principle sketch of geotechnical structure including monolith stabilized/solidified

contaminant dredged sediments.

3 Materials and Methods

3.1 Dredged Sediment types

The physical properties of fresh dredged sediments determine the required type of binders, activity and

gained strength. Thus, compressibility and strength behavior of stabilized dredged materials relate to

physical properties of fresh dredged sediments (water content, particle sizes, organic matter, bulk

density etc.).

3.2 Organic content

In many cases, large amounts of organic matter constitute the top layer of soil. However in well drained

soils organic matter may extend to a depth of 1.5m (Sherwood 1993). Most soil index properties

(including water content, gas content, bulk density, specific gravity, particle size distribution, Atterberg

limits, shrinkage potential, and two chemical indices: cation exchange capacity and acidity) and

engineering properties (including compaction behavior, strength, permeability and compressibility) of

organic soils are related to organic content. (F. J. Stevenson 1974) stated, soil organic matter includes

“the total organic material in soils, including litter, light fraction, microbial biomass, water-soluble

organics, and stabilized organic matter” Given the complexity of soil organic matter, it can be normally

classified into two major categories as shown in Figure 3.2.1. Living organic matter can be defined as

bacteria, fungi, algae, fresh and un-decomposed animal or plant debris. On the other hand, non-living

organic matter is the major portion of the total organic components in soils include plant or animal

debris at different stages of decomposition and transformation. Non-living organic matter is usually

divided into humic and non humic substances due to various chemical components (Hayes and Swift

1990). Non-humic substances refer to amino acids (including polypeptides), carbohydrates (including

monosaccharide, oligosaccharide and polysaccharide), and lipids (including fats, waxes, resins and so

on). Humic substances are classified as fulvic acid, humic acid and humin. (SSSA 2008) strictly stated

that, soil organic matter refers to only those organic components that accompany soil particles which

are smaller than 2 mm.

Soil organic matter

Non-living organic

Living organic

Non-humic substance

Humic substance

Amino acid

Carbohydrates Lipids

Humin

Humic acidFulvic acid

Figure 3.2.1 Classification of soil organic matter.

3.2.1 Loss on ignition (LOI) method

Based on existing literature shows that there is no universally accepted method to determine the

organic content in soils. In this report, most commonly used test has been presented. The measurement

of organic content of soil required to remove the organic matter from the soil and quantify it. Several

methods have been proposed to perform this measurement which is classified into two major groups:

direct methods and indirect methods. In direct methods, the organic content of soil is directly measured

whereas in indirect methods, the quantity of organic content is determined by multiplying the

concentration of organic carbon (measured by chemical methods) by a factor which varies with soil type

and depth. Loss on ignition and hydrogen peroxide (H2O2) digestion are the two primary methods

belonging to direct methods. The loss on ignition method direct estimates the organic matter in soils

based on the thermal decomposition of organic matter. In this method, high temperature is used to

remove organic matter. The results of the loss on ignition test are sensitive to the heating temperature

and oven drying the soil sample before ignition test (Landva et al. 1983). The freshly dredged sediments

were dried in oven over 24 hours at a temperature of 1050C. Approximately 10g mass of oven dry

sample that entirely passing through No. 10 sieve was placed in a crucible and kept in a well

temperature control furnace. The percentage loss on ignition (LOI %) is the weight loss of soil sample

due to oxidation of organic matter and can be obtained from the following:

= 𝑊𝑒𝑖𝑔ℎ𝑡105 − 𝑊𝑒𝑖𝑔ℎ𝑡440

𝑊𝑒𝑖𝑔ℎ𝑡105×100

Where, Weight105 is the weight of soil sample after oven-dry to 1050C for 24 hours and Weight440 is the

weight of soil sample after ignition to 4400C. According to ASTM D 2974 Method C, the temperature of

4400C is used for ignition of organic soil.

3.3 Initial water content

Moisture content is essential in stabilized soils for both hydration process and compaction. (Sherwood

1993) stated that fully hydrated cement can takes up 20% of its own weight of water and quicklime

(Cao) takes up 32% of its own weight of water from the surrounding. Usually organic soils have a great

affinity for water which might lead to retardation of hydration process due to insufficient moisture

content. The fibrous structure of organic soil creates large voids and high cation exchange capacity of

organic matter increases the attraction for water molecules. Both properties cause high water content

in organic soils. Most of the laboratory tests in soil mechanics demand for determination of water

content. Just after mixing with binders of freshly dredged sediments, test samples were taken in

containers and weighted. After that, samples were placed in oven and dried for 24 hours at a

temperature of 105oC and then weighted again. Water content is defined as following:

𝑊 =𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑎 𝑔𝑖𝑣𝑒𝑛 𝑠𝑜𝑖𝑙 𝑚𝑎𝑠𝑠

𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑜𝑖𝑙

Normally water content is expressed in percentage (%).

3.4 Percentage (%) sieve analysis

Grain size analysis belongs to the oldest soil tests which is used in soils classification and specifications of

soil for airfields, earth dams, roads and other soil embankment construction. Grain size distribution or

particle size analysis determines the relative proportions of different grain size as they are distributed

among certain size ranges and Sieve analysis does not provide any information about the shape of

particles. This is accomplished in two steps:

- A sieve analysis which is also called mechanical analysis or screening process that consider

particle sizes retained on the No. 200 sieve.

- A hydrometer analysis which is also known as sedimentation process that consider particle sizes

passing through the No.200 sieve.

The sieve number increases as the size of the openings decreases according to table 3.4.1.

Table 3.4.1. Shows the U.S. standard sieve numbers corresponding opening sizes.

Sieve No Opening (mm) Sieve No Opening (mm)

4 4.75 35 0.500 5 4.00 40 0.425 6 3.35 45 0.355 7 2.80 50 0.300 8 2.36 60 0.250

10 2.00 70 0.212 12 1.70 80 0.180 14 1.40 100 0.150 16 1.18 120 0.125 18 1.00 140 0.106 20 0.85 200 0.075 25 0.71 270 0.053 30 0.60 400 0.038

Particle size distribution indicates the state of soil aggregation which belongs to index properties of soil.

Aggregation and dispersion are two main mechanisms that affected particle size distribution. On the

other hand, organic matter content of soil influences both aggregation and dispersion mechanisms.

Sieve analysis was performed on the stabilized dredged sediment soils. Although No.200 sieve with

smallest opening is used for the test in all practical purposes. Finally, the grain size distribution obtained

from sieve analysis is plotted in a semi-logarithmic graph paper as shown in Figure 3.4.1. Where percent

finer is plotted on the normal scale and grain size is plotted on the log scale. The graph data can be

prepared in a few steps as following:

- The percent of soil retained on the nth sieve should be count from the top

=𝑚𝑎𝑠𝑠 𝑟𝑒𝑡𝑎𝑖𝑛𝑒𝑑, 𝑊𝑛

𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠, 𝑊×100 = 𝑅𝑛

- The cumulative percent of soil retained on the nth sieve

= ∑ 𝑅𝑛

𝑖=𝑛

𝑖=1

- The cumulative percent passing through the nth sieve

= 𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑓𝑖𝑛𝑒𝑟 = 100 − ∑ 𝑅𝑛

𝑖=𝑛

𝑖=1

And the other two important steps are:

- Determination of grain size diameter D10, D30 and D60 corresponding to percent finer of 10%,

30% and 60% from the semi-logarithmic graph paper

The uniformity coefficient (Cu) and the coefficient of gradation (Cc) can be calculated using

equations:

𝐶𝑢 =𝐷60

𝐷10

𝐶𝑐 =𝐷302

𝐷60×𝐷10

Figure 3.4.1. Grain size distribution plot for pure dredged sediments with organic content.

3.5 Binders

(Sherwood 1993) defines binders as hydraulic (primary binders) or non-hydraulic (secondary binders)

materials which form cementitious composite materials in presence of pozzolanic minerals. The binders

can be mixed either by wet method or dry method. A slurry of binders and water are used in wet

method whereas in dry method, whereas in dry binder powder reacts chemically with pore water during

curing. Therefore, dry method reduces the water content of Stabilized dredged materials (EuroSoilStab

2002). Only dry binders have been used in laboratory tests following dry method. Usually 3 component

binders are effective for many cases. The most important components are cement, fly ash and blast

furnace slag (merit 5000).

3.5.1 Cement

Portland cement is a widely used primary stabilizing agent. In the manufacture of Portland cement,

clinker comes from a hot kiln which is basically anhydrous. The clinker of Portland cement generally

contains 67% CaO, 22% SiO2, 5% Al2O3, 3% Fe2O3 and 3% other components. The reactions of cement

with water is termed as “hydration”. (H.F.W. Taylor 1997) stated that in anhydrous state of cement, four

main minerals are present such as alite (C3S), belite (C2S), aluminate (C3A) and ferrite (C4AF) as shown in

Figure 3.5.1 adapted from Cement Microscopy, Halliburton Services, Duncan, OK. These four minerals

have different impacts during hydration process that transform the dry cement into hardened cement

paste.

Figure 3.5.1. A pictorial representation of cross-section of a cement grain.

This cement hydration process is exothermic, that’s mean reactions produce heat. By using conduction

Calorimetry technique, it is possible to assess the rate of reactions in minerals by monitoring at which

heat is evolved as shown in Figure 3.5.2.

Figure 3.5.2. Heat evolution curve produced in cement hydration.

The three main end products of cement hydration are calcium hydroxide (CH), calcium silicate hydrate

(C-S-H) and calcium aluminate hydrate (C-A-H). Almost immediately after mixing, aluminate (C3A)

mineral (the most reactive mineral in clinker) reacts with water. Finally, this aluminate (C3A) creates

aluminate-rich gel which is strongly exothermic but does not last long. This reaction refers to stage I as

shown in Figure 3.5.2 and terminates within few minutes. Stage I is followed by a period of relatively low

heat evolution for few hours which is known as dormant or induction phase (IP). Finally, alite and belite

in cement clinker start to react while induction phase ends. This refers to main hydration period (stage

III) with formation of calcium silicate hydrate (C-S-H) and calcium hydroxide (CH). During this phase,

mixture gains strength and all the individual anhydrous minerals react from the surface to inwards. The

main binding phases in cement hydration for both calcium silicate and aluminate based pastes are the

calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) gels (H.F.W. Taylor 1997).

However, the alite (C3S) reacts with water much quicker than belite (C2S) and thus is responsible for

early strength development. Both aluminate and ferrite also hydrate but the products that are formed

impact very little to the properties of cement paste. Finally, three phases of hydration mechanism that

effects on compressibility of stabilized dredged sediments namely, induction phase (IP), nucleation and

crystallization phase (NCP) and hardening phase (HP). The distinguishing characteristics associate with

IP, NCP and HP that affect the compressibility of SDM has shown in Table 3.5.1(G.Makusa 2015).

Table 3.5.1. Distinguishing characteristics associate with IP, NCP and HP that affect the compressibility of

SDM.

Phase Characteristics

IP

i. Occurs immediately after mixing.

ii. A protective layer is formed on the particle surface of binder, which prevent

penetration of water.

iii. The unhydrated portion of binder behaves like solid particles which increase

resistance to compression.

iv. Tangent modulus increases due to increasing resistance to vertical deformation

v. The maximum effective vertical stress which is required to reduce the initial water

content of untreated dredged sediments to a value below plastic limit, defines the

apparent preconsolidation stress of the SDM

NCP

i. Occurs when the protective layer become more permeable, which allows

penetration of water.

ii. Plasticity of the SDM decreases due to increasing plastic limit.

iii. Loss of apparent presonsolidation stress and tangent modulus occurs.

iv. The tangent modulus increases about linearly with applied effective vertical stress.

v. Normally consolidated clay settlement behavior dictates the compressibility behavior

of the SDM.

i. Occurs because of solidification, hardening and loss of plasticity on protective layer.

ii. Protective layer become impermeable and water may become lodged in.

HP iii. The apparent preconsolidation stress has increased to the value equal to the UCS.

iv. The tangent modulus increases exponentially with applied effective vertical stress.

v. Silt-sand soil compression behavior describes the deformation behavior of the SDM.

3.5.2 Fly ash

Fly ash can be found as a by-product of coal burning power stations and burning of hard coal or bio fuels

in a boiler. From boiler, two types of ash particles are generated. The heavier ash particles are

accumulated below the furnace and are called bottom ash. On the other hand, smaller ash particles are

suspended in flue gases. Later flue gases can pass through a filter and the smaller particles remain in

filter which is called fly ash. These processes are depicted in Figure 3.5.2.1. Fly ash contains pozzolanic

materials. pozzolana as “a siliceous or siliceous and aluminous material which possesses little or no

cementitious value but will, in finely divided form and in the presence of moisture, chemically react with

calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties”.

The pozzolanic materials in fly ash reacts with pore water and CaO in cement. This reaction is very slow

and impacts on strength development of stabilized dredged materials mainly depends on chemical

composition of fly ash. According to Table 3.5.4.1, the fly ash used in SDM contains 21% of calcium oxide

(CaO) characterized by ‘’Class C’’ fly ash with some self-cementing properties. Moreover, the used fly

ash has 43% of silicon dioxide (SiO2) that indicates strong pozzolanic properties.

Figure 3.5.2.1. functions of a boiler, A) coal or bio fuel goes into furnace, B) combustion chamber, C)

bottom ash accumulated, D) flue gases with suspended fly ash, E) fly ash is collected in filter, F) flue

gases is emitted.

3.5.3 Blast furnace slag (merit 5000)

Secondary stabilizing agents do not possess any cementitious properties but can be used with lime or

cement. Blast furnace slag is a by-product of pig iron production and is consisting of siliceous

constituents of the iron ore with the limestone flux used for smelting iron. It has been used as secondary

stabilizing agents in SDM in association with cement and fly ash. Blast furnace slag contains same

chemical elements as Portland cement which are not cementitous but it possesses latent hydraulic

properties that can be activated by addition of an activator such as lime or cement (Sherwood 1993).

Blast furnace slag can have three different forms depending on cooling conditions after leaving the blast

furnace. Firstly “air-cooled slag” is cool slowly in open air. Secondly “granulated slag” is subjected to

abrupt cooling using water or air. Thirdly “expanded slag” is cooled by water under specific conditions.

3.5.4 Binder recipe

Stabilization and solidification (S/S) techniques largely depends on the proper selection of binders and

amount of binders added correspond to dredged sediment quantity. S/S technique is fruitful for soft

soils such as organic soils, clayey or silty soils. During the laboratory tests three binder components were

chosen, namely cement, fly ash and ground granulated blast furnace slag (Merit 5000). Cement, fly ash

and merit 5000 were provided by Cementa AB, Billerud paper mill and SSAB steel industry in Sweden.

The chemical composition of three main binders used is given in Table 3.5.4.1 (G.Makusa 2015). Two

types of mixing ratio were used for stabilization of dredged sediments according to Table 3.5.4.2. The

binder recipes were chosen from economic point of view.

Table 3.5.4.1 Chemical composition for binders: FA = fly ash, GBBS = ground granulated blast furnace

slag (Data: courtesy of SSAB) and Cement (Makusa et al. 2016).

Chemical compound (%) FA GGBS Cement

CaO 21 31 63 SiO2 43 34 18 Al2O3 10 13 5 MgO 4 17 K2O 5

Table 3.5.4.2. Suggested binder recipe for stabilized dredged material. C = cement, FA = fly ash, GGBS =

ground granulated blast furnace slag.

Sample ID

Binder Binder Ratio (%) per unit weight of DS Curing Time (Days)

A C, FA, GGBS 20:20:10 (50% of total mass of DS) 7, 14, 28, 91 B C, FA, GGBS 10:10:5 (25% of total mass of DS) 7, 14, 28, 91

3.6 Samples preparation for laboratory tests

In this thesis work, fresh dredged sediments have been analyzed which were collected from port of

Gävle in Sweden. With the help of mechanical dredges, the contaminated dredge sediments (DS) were

collected from underwater down to a depth of 0.5m of sediments. The initial water content of this fresh

dredged sediment is 420%. To perform laboratory tests, Portland cement, fly ash and ground granulated

blast furnace slag were mixed with it. After rigorous mixing, samples have been poured in cylindrical PVC

tubes of size (5cm×17cm). These PVC tubes were filled with stabilized dredged materials by creating a

vibration of its bottom end. No external compaction force was applied during filling up time. After that,

filter plugs and consolidation cell lower porous disc were inserted on top and bottom end of each PVC

sample tube. Thus, drainage facility was provided to these samples during the curing period from top

and bottom. The inside walls of PVC tubes were greased to prevent friction during the consolidation and

extrusion of soil specimens. It is essential to apply a minimum preloading weight of 18 kPa on stabilized

dredged materials immediately after mixing. A preloading weight of 22 kPa was placed on top of each

filter plug as shown in Figure 3.6.1. This vertical curing stress can represent the soil overburden pressure

and helps to blow off trapped air during mixing and brings soil particles together for better hydration

reactions. Thereafter, all PVC sample tubes were cured and stored under drinking water in a sealed glass

box at 18-210C as shown in Figure 3.6.2.

Figure 3.6.1. Stabilized dredged materials (SDM) samples were cured for unconfined compression and

oedometer test.

Finally, in preparation of test specimens was extremely difficult. In some cases, small chip has been

broken from the edge of the specimen. For instance, while doing UCS test small chips were carefully

placed back into original position. The most common and popular laboratory tests for determination of

stiffness and compressibility of stabilized dredged materials (SDM) are unconfined compression and

oedometer tests. In order to perform a full scale project, it is common practice to conduct some

advance tests in laboratory to obtain adequate data concerning stiffness of stabilized dredged materials

(EuroSoilStab 2002).

Figure 3.6.2. Variation of temperature during curing of samples.

3.6.1 Unconfined Compressive Strength Test

The Unconfined compression test was performed on Stabilized/Solidified contaminated dredged

sediment samples. It is a quick test to determine the shear strength parameters of cohesive fine-grained

soils. This test is mainly strain controlled test. Water within the soil sample do not get enough time to

dissipate because of rapid loading. As a result, the test replicates of soils in construction sites where the

construction is very fast and the pore water does not have enough time to dissipate. The results from

the test also gives the relative consistency of the soil according to Table 3.6.1.1 (Braja M. Das 2002).

Table 3.6.1.1. General relationship of consistency and unconfined compression strength.

Consistency qu (kN/m2)

Very soft 0 – 25 Soft 25 - 50

Medium 50 - 100 Stiff 100 - 200

Very stiff 200 - 400 Hard > 400

Finally, undrained cohesion or undrained shear strength can be determined using the equation, Cu =

qu/2. Soil specimens were obtained from the treated contaminate dredged sediments based on both

curing time (7 days, 14 days, 28 days and 91 days) and mixing ratio (Cement 20%, Fly ash 20%, Merit

10% and Cement 10%, Fly ash 10%, Merit 5%). It is recommended that length to diameter (L/D) ratio of

the cylindrical soil specimen should be 2:1 to prevent the Saint - Venant’s end effect. In the laboratory

UCS test, most of the soil samples have been trimmed to size (diameter 5cm and length 10cm) by using

the specimen trimmer. After that, the sample was placed centrally on the bottom plate of the

unconfined compression testing machine and the top loading plate was just touching the top surface of

sample as depicted in Figure 3.6.1.1. During the test, top loading plate was operated as strain-controlled

method with a constant rate of vertical deformation 1.5 mm/min. Vertical deformation was continued

until the load reached the peak and then decreased. The crashed sample was removed from the

machine by lowering the bottom plate and then placed in an oven to determine the moisture content.

No unimproved dredged sediments were tested due to having higher water content by weight, this

excessive water content made the unimproved pure dredged materials unsuitable for UCS test. There

are three direct influences on UCS tests, namely, curing time, vertical curing stress and composite

binders.

(a) (b) (c)

(d)

Figure 3.6.1.1. Unconfined compression strength test: a) curing of treated dredged sediment samples

under fixed load, b) sample placement for UCS test, C) removing sample after test, d) failure modes of

samples.

Time

(sec)

Sample

Deformation ∆L

(mm)

Vertical Strain

(ε = ∆L/L)Strain (%) Load (N)

Corrected Area

Ac=Ao/(1-ε) (mm2)

Stress σ

(N/mm2)

Stress σ

(kN/m2)

0 0 0 0 0.00 0 0 0

1 0.025 0.0003 0.03 0.82 1963.99 0.0004 0.42

2 0.05 0.0005 0.05 3.70 1964.48 0.0019 1.89

3 0.075 0.0008 0.08 10.08 1964.97 0.0051 5.13

4 0.1 0.0010 0.10 14.61 1965.46 0.0074 7.43

5 0.125 0.0013 0.13 18.52 1965.95 0.0094 9.42

6 0.15 0.0015 0.15 21.40 1966.44 0.0109 10.88

7 0.175 0.0018 0.18 24.90 1966.94 0.0127 12.66

8 0.2 0.0020 0.20 29.42 1967.43 0.0150 14.96

9 0.225 0.0023 0.23 33.95 1967.92 0.0173 17.25

10 0.25 0.0025 0.25 38.48 1968.42 0.0195 19.55

11 0.275 0.0028 0.28 43.00 1968.91 0.0218 21.84

12 0.3 0.0030 0.30 47.74 1969.40 0.0242 24.24

13 0.325 0.0033 0.33 52.26 1969.90 0.0265 26.53

14 0.35 0.0035 0.35 56.79 1970.39 0.0288 28.82

15 0.375 0.0038 0.38 61.94 1970.89 0.0314 31.43

16 0.4 0.0040 0.40 66.46 1971.38 0.0337 33.71

17 0.425 0.0043 0.43 71.61 1971.88 0.0363 36.31

18 0.45 0.0045 0.45 76.75 1972.37 0.0389 38.91

19 0.475 0.0048 0.48 82.51 1972.87 0.0418 41.82

20 0.5 0.0050 0.50 87.66 1973.36 0.0444 44.42

Table 3.6.1.2. Sample data sheet from the UCS test.

The test results were extracted from the PC-loggers and saved as an EXCEL sheet containing date, time

and load. Based on these data, calculation has been made stepwise as follows:

1) Vertical strain, ε = ∆L/L where ∆L = total vertical deformation of sample

L = original length of sample

2) Corrected area of the sample,Ac =𝐴𝑜

(1−ε ) (mm2) where A0 = initial area of cross section of the Sample

= π

4 D2

3) The stress on the sample, σ = 𝐿𝑜𝑎𝑑

𝐴𝑐 (kN/m2)

Finally, a graph has been plotted by axial stress, σ Vs axial strain, ε. The unconfined compressive

strength, qu of the sample is defined as the peak stress from this Figure 3.6.1.2. The undrained cohesion

or undrained shear strength of the sample can be determined using equation Cu = qu/2 (kN/m2).

(a) (b)

Figure 3.6.1.2. (a) Unconfined compression test, (b) Typical stress Vs strain plot from UCS test.

3.6.2 One – Dimensional Consolidation or Oedometer Test

Oedometer test was performed on Stabilized/Solidified contaminated dredged sediment samples to

determine its consolidation properties. In this method, a laterally confined soil specimen is subjected to

an increased axial loading to estimate the magnitude and rate of consolidation settlement.

Consolidation test results are dependent upon the duration of each load increment and the magnitude

of load increment. The specimens have been prepared by trimming the SDM samples obtained in PVC

tubes. These specimens were molded in oedometer rings (40mm × 20mm) according to curing period.

After that, some excess SDM samples have been collected for determination of moisture content and

specific gravity respectively. A lower and upper porous stone were placed on the specimen in

oedometer ring. Only axial deformation was allowed while restraining lateral deformation.

Subsequently, water was added to the consolidometer base to submerge the specimens and kept it

saturated for the entire period of test as shown in Figure 3.6.2.1. The loading of the specimen was

applied through a mechanical lever arm capable of vertical effective stress of 640 kPa. Loading device

was connected to the consolidometer ring maintaining sustained increment load (IL) ratio of 1. The

initial vertical loading of 1.25 kg equivalent to vertical stress of 10 kPa was applied on the specimens.

Hence, the vertical load was doubled to obtain a value of 20, 40, 80, 160, 320, 640 kPa respectively.

Traditionally, each load increment is maintained for 24 hours until excess pore water pressure has

completely dissipated. In these tests, no unloading-reloading was applied to the specimens. Finally, after

7 days specimens were removed from the consolidometer base and moisture content was determined.

Figure 3.6.2.1. Samples have been placed in Oedometer setup for test.

After completion of tests, data has extracted from PC-loggers and using these data calculation has been

done stepwise as following:

1) All the time Vs. vertical dial readings data have been collected for each load increment from p =

10 kPa to p = 640 kPa.

2) For each set of time Vs. vertical dial readings, t90 (90% primary consolidation) has been

determine as shown in Figure 3.6.2.2.

Figure 3.6.2.2. Determination of t90 by square root of time method (ASTM 2003).

3) Height of solids (Hs) of the specimen has calculated using the following equation

Hs = 𝑊𝑠

(𝜋

4𝐷2)×𝐺𝑠×𝑃𝑤

Where, Ws = dry mass, D = diameter, Gs = specific gravity and Pw = density of water.

Table 3.6.2.1. Consolidation test (Void Ratio-Pressure, Coefficient of consolidation, Coefficient of volume

compressibility and Permeability Calculation)

4) In Table 3.6.2.1, determination of change in specimen height (ΔH) and final height, Ht(f) due to

load increments from p to p+Δp. For instance,

p = 10 kPa, final dial reading = 0.102 mm

p+Δp = 20 kPa, final dial reading = 0.181 mm

Hence, ΔH = 0.181 – 0.102 = 0.079 mm

The final specimen height, Ht(f) = 19.904 mm for p = 10 kPa. Due to change in load from 10 to 20

kPa, final specimen height Ht(f) = 19.904 – ΔH = 19.904 – 0.079 = 19.825 mm

5) For each given load, height of void of specimen has been calculated at the end of consolidation

as, Hv = Ht(f) – Hs

6) Final void ratio at the end of consolidation for each loading was determined as, 𝑒 =𝐻𝑣

𝐻𝑠

7) Coefficient of consolidation, Cv was calculated for each loading using equation,

𝑇𝑣 = 𝐶𝑣×𝑡90

𝐻2

Where, Tv = time factor t90 = 0.848, H = maximum length of drainage path = 𝐻𝑡(𝑎𝑣)

2 (the specimen

was drained at top and bottom)

So, Cv = 0.848Ht(f)2

4t90 (m2/s)

8) Coefficient of volume compressibility mv was determined from initial void ratio and change in

void ratio correspond to load increments.

mv =𝑒1−𝑒2

𝑝2−𝑝1×

1

1+𝑒0 (m2/kN)

9) Coefficient of permeability, K of the specimen was calculated using equation, K = CvmvΥw (m/s)

Pressure, ρ

(kPa)

Final dial

reading, mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height, Ht(f)

(mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Coefficient of

Consolidation

Cv*10-6

(m2/s)

Coefficient of

Volume

Compressibility

mv

(m2/kN)

Coefficient of

Permeability

K*10-8

(m/s)

0 0.006 20 14.02 2.34

0.096 19.95 29 2.910 0.00048 1.37

10 0.102 19.904 13.924 2.33

0.079 19.86 39 2.145 0.00040 0.83

20 0.181 19.825 13.845 2.32

0.111 19.77 49 1.691 0.00028 0.46

40 0.292 19.714 13.734 2.30

0.172 19.63 49 1.667 0.00022 0.35

80 0.464 19.542 13.562 2.27

0.23 19.43 60 1.334 0.00014 0.19

160 0.694 19.312 13.332 2.23

0.266 19.18 73 1.068 0.00008 0.09

320 0.96 19.046 13.066 2.18

0.376 18.86 86 0.877 0.00006 0.05

640 1.336 18.67 12.69 2.12

10) Compression index, Cc was calculated from the semi-logarithmic graph Figure 3.6.2.3.

Cc = 𝑒1−𝑒2

log(𝑝2

𝑝1)

Figure 3.6.2.3. Plot of void ratio against pressure of the specimen (e-logp) graph.

4 Results

4.1 Unconfined Compression Test

The unconfined compression test is a relatively quick method of determining the value of undrained

cohesion Cu for a saturated clayey soil. Laboratory tests have shown that unconfined compressive

strength (qu) of stabilized dredged materials (SDM) is increased with curing time, types and amount of

binders used as shown in Figure 4.1.3. The tests are conducted on two identical specimens and the

average value of qu is considered as the representative value. Figure 4.1.1 and Figure 4.1.2 show the

stress-strain curves of UCS tests for stabilized dredged materials with binder ratio 20:20:10 and 10:10:5,

respectively. The peak strength of SDM is increasing with curing time as illustrated in Figure 4.1.1. There

is a significant difference between the peak strength of stabilized dredged materials based on curing

time 14 days, 28 days and 91 days. Figure 4.1.1 illustrates that the UCS value of SDM after 91 days curing

period (CP) is about 10 times the UCS value of 14 days CP and almost 2.5 times of 28 days CP. It also

appears that SDM specimen tends to reach peak strength at lower strain after 91 days in comparison

with 28 days of curing time. Whereas, stabilized soil reaches at peak strength at higher strain values

after 14 and 7 days of curing period. Thus, stabilized soil mass may not gain enough strength after 28

days of CP but has better ductility property. After 91 days of CP stabilized soil mass becomes stiff and

brittle. A major difference between 28 and 91 days CP of specimens is the strength degradation rate

after failure strength is reached. Specimen, which is cured for 91 days indicated rapid post-peak strength

degradation over a small range of strain due to increased brittleness of stabilized dredged materials.

Moreover, the specimen is being cured after 28 days showed that post-peak strength degradation

occurs over a large range of strain due to increased ductility of the stabilized dredged materials. Table

4.1.1 outlines the decrease in failure strain with increasing unconfined compressive strength. Figure

3.6.1.1 shows the failure mode and crack propagation in specimens during the UCS tests. From Table

3.6.1.1, the consistency of stabilized dredged materials after 28 days CP with qu value of 130 kPa

indicates stiff and after 91 days CP becomes very stiff with qu value of 310 kPa. So, it is suggested that

stabilized dredged materials can’t be used before 28 days curing period because of its consistency

remains soft both after the curing period of 7, 14 days.

Figure 4.1.1. Stress-strain plot of stabilized dredged materials with binder ratio 20:20:10 (50% of the total DS)

Figure 4.1.2. Stress-strain plot for stabilized dredged materials with binder ratio 10:10:5 (25% of total

DS)

The value of unconfined compressive strength (qu) of stabilized dredged materials with a binder ratio of

10:10:5 (25% of the total fresh dredged sediment) is significantly smaller than binder ratio 20:20:10

(50% of the total fresh dredged sediment). Figure 4.1.2 shows that maximum (qu) value of SDM can be

achieved 21 kPa after 91 days of curing time, which falls in a very soft soil category in terms of

consistency. Unfortunately, with this amount of binder mixing ratio, no superstructure or surcharge load

can be applied to stabilized dredged materials. It can only be used as backfill materials on site.

Figure 4.1.3. Curing period and binder ratio effect on UCS values of stabilized dredged sediments.

Binder ratio (20:20:10) and (10:10:5) has very little impact on shear strength of stabilized dredged

sediments up to 14 days of curing time as shown in Figure 4.1.3. But the difference continues increasing

and becomes significant till 91 days curing period. It is obvious that the amount of cement and

pozzolanic materials increased with higher binder ratio, which accelerates cement hydration till 28 days

after that pozzolanic reaction continues till 91 days.

Figure 4.1.4. Plotting strain values over curing time for binder ratio 20:20:10 (50% of total DS).

Figure 4.1.5. Plotting strain values over curing time for binder ratio 10:10:5 (25% of total DS).

Figure 4.1.4 & Figure 4.1.5 present the UCS values and strains over curing time both for binder ratio

20:20:10 and 10:10:5. There appears a big difference between the peak strength of stabilized dredged

soil at given curing time in terms of strain values. It can be seen from Figure 4.1.4 that failure strength

lies between 2% strain and 3% strain. On the other hand, Figure 4.1.5 has shown that shear strength

keeps increasing beyond 3% strain and failure strength occurs in between 3% & 4% strain from Table

4.1.1. However, the stabilized soil mass becomes stiffer with curing time increased and peak strength

can reach at a smaller strain as shown in Figure 4.1.4. Thus, post-peak strength degradation rate occurs

rapidly.

Table 4.1.1. Peak strength from UCS tests and corresponding strain values.

Binder Ratio

Curing Time (Days)

Peak Strength (kPa)

Strain at Peak Strength (%)

20:20:10 (50% of total DS)

7 26 3.6

14 30 3.5

28 126 2.6

91 310 2.3

10:10:5 (25% of total DS)

7 14 4.5

14 15 4.8

28 18.5 3

91 21.5 3.5

Figure 4.1.6. Variations of unconfined compressive strength with bulk density & water content followed

by curing time 7, 14, 28 and 91 days.

The initial water content of fresh dredged sediments was 420%. Later, binders were mixed based on per

unit weight of this fresh dredged sediments. Finally, the water content of SDM with binder ratio

(20:20:10) decreases to 110 % from 420%. After 28 days of curing period, water content drops to 99%

and 95% after 91 days of curing time. Besides, bulk density of freshly mixed stabilized materials

increases from 1407 kg/m3 to 1436 kg/m3 after 28 days of curing and after 91 days bulk density

increases to 1456 kg/m3. The curing time (7→14 days) plays a significant role over increasing bulk

density along with very little increasing on UCS value. It is obvious from the Figure 4.1.6 that UCS values

of stabilized dredged materials increased with decreasing moisture content and increasing bulk density.

4.2 Consolidation Test

The characteristics of a stabilized dredged soil during one dimensional consolidation can be determined

by consolidation or oedometer test. The consolidation test results for stabilized dredged sediments are

analyzed in the form of e-logσ curves as shown in Figure 4.2.1 and Figure 4.2.2, respectively. Stabilized

dredged materials with binding ratio 20:20:10 (50% of total DS) will help in lowering overall

consolidation settlement along with lower rebound height if loads are removed. Stabilized dredged

sediments a with higher binder ratio have much less change in void ratio than SDM with a lower binder

ratio as shown in Figure 4.2.1 and Figure 4.2.2. It is also seen that initial resistance to consolidation in

SDM samples increases with higher binding components which is caused by the formation of cemented

bonds within stabilized materials. Besides, hydration reaction is time dependent and cemented bonds

develop in stabilized dredged materials with curing time. The e-log σ curve after 14 days and 28 days of

curing time has been overlapped as shown in Figure 4.2.2. Dormant or induction phase (IP) of cement

hydration occurs during that time, which might be a possible cause for this kind of behavior of stabilized

material. According to (Yilmaz et al. 2013), cemented bonds in stabilized mass can resist applied

consolidation stress until the yield stress is reached. Beyond the yield stress of SDM, cemented bonds in

stabilized mass started to break down because of decreasing void ratio. As the loading continues in

oedometer test, the consolidation stress exceeds the yield stress of SDM sample and consolidation

curve becomes steeper. Another consolidation parameter is preconsolidation stress which varies with

curing time, binder ratio and overburden pressure during curing period. The settlement of this particular

untreated dredge sediments increases linearly with consolidation stress up to 80 kPa and no further

settlement occur beyond 80 kPa of consolidation stress (G.Makusa 2015). Due to preloading weight, the

deformation occurred in stabilized dredge sediments is irreversible because of cementation effect.

Figure 4.2.1illustrates that SDM samples show rigidity behavior up to consolidation stress of 80 kPa and

compressibility trend begins under consolidation stress above 80 kPa. Thus, it can be assumed that

apparent preconsolidation stress of stabilized dredged materials is equal to 80 kPa. The stabilized

materials behave like overconsolidated soil while the consolidation stress is lower than preconsolidation

stress and behaves like normally consolidated soil when the consolidation stress is higher than

preconsolidation stress (Ahnberg 2006).

Figure 4.2.1. Void ratio variation (Δe) with log (pressure) for a given curing period.

Figure 4.2.2. Void ratio variation (Δe) with log (pressure) for a given curing period.

The consolidation properties of stabilized dredged sediments are greatly influenced by binder types and

curing time. The consolidation properties of SDM are improved with longer curing time and higher

binder ratio. Compressibility parameters such as compression index (Cc) and swelling index (Cs) are

obtained from linear portion of consolidation curve (e-log p). The value of either the compression index

or coefficient of volume compressibility is required to estimate settlement of soft soil. Improved

consolidation properties mean lower value of compression index, Cc and swelling index, Cs which will

eventually reduce the consolidation settlement. Figure 4.2.3 and Figure 4.2.4 illustrate the change in

compression index and swelling index of stabilized dredge materials which are influenced by curing time

and binder contents. 91 days Curing period of specimens with binder ratio 20:20:10 (50% of total DS)

have reduced the compression index and swelling index values by approximately 80% and 83% than 7

days curing time. On the other hand, 91 days Curing period of specimens with binder ratio 10:10:5 (25%

of total DS) have reduced the compression index and swelling index values by approximately 58% and

70% than 7 days curing time. By considering both curing time and binder ratio, Cc and Cs values for

specimen with mixing ratio (20:20:10) have lowered by approximately 75% and 67%, respectively than

specimen with mixing ratio (10:10:5). Stabilized dredged materials with binding ratio (20:20:10) will help

in lowering overall consolidation settlement along with lower rebound height if loads are removed.

Thus, the compression index along with swelling index of SDM samples decrease with increasing binder

contents and curing time because of increasing stiffness by formation of more cemented bonds within

the particles.

Figure 4.2.3. Binder contents and curing time effect on compression index.

Figure 4.2.4. Binder contents and curing time effect on recompression/swelling index.

There is a discrepancy between the in-situ and laboratory test values of compression index. Due to

effects of sample preparation, oedometer test results show a slight decrease in the slope of the virgin

compression line. Therefore, it is assume that the slope of the virgin compression line of in-situ soil will

be slightly greater than the slope of virgin line obtained in a laboratory test (G.Makusa 2013).

Figure 4.2.5. Tangent modulus (Et)-vertical stress (σ) behavior of SDM during consolidation test.

Figure 4.2.6. Tangent modulus (Et)-vertical stress (σ) behavior of SDM during consolidation test.

The tangent modulus is defined as the slope of strain vs stress curve which also represents the stiffness

of sediments. Usually normally consolidate (NC) stabilized dredged sediments show a linear relationship

between tangent modulus and vertical stress. Figure 4.2.5 and Figure 4.2.6 illustrate the tangent

modulus against vertical stress for each load step on stabilized dredged sediments. Both of those graphs

have some similarities and dissimilarities. The tangent modulus shows a linear relationship with vertical

stress up to apparent preconsolidation stress in both graphs. In Figure 4.2.6, suddenly this modulus

reaches a minimum value, then it starts increasing nonlinearly with further increase in vertical stress. In

contrary, Figure 4.2.5 shows a linear relationship between modulus and vertical stress till apparent

preconsolidation stress and continues to increase non-linearly without any downward movement. The

maximum value of tangent modulus is estimated about 9624 kPa after 91 days curing time of SDM with

binder ratio (20:20:10). On the other hand, stabilized dredged materials with binder ratio (10:10:5) gives

the tangent modulus value of about 1800 kPa after 91 days curing period. Figure 4.2.5 shows a

significant difference in tangent modulus value between 28 days and 91 days of curing time. After 91

days of curing time, stabilized sediments with binder ratio (20:20:10) can increase tangent modulus by

approximately 200% than 28 days of curing time. In the case of SDM with binder ratio (10:10:5), this

modulus value is increased by 20% after 91 days of curing than 28 days curing time.

Figure 4.2.7. Constrained modulus (M)-vertical stress (σ) behavior of SDM during consolidation test.

Figure 4.2.8. Constrained modulus (M)-vertical stress (σ) behavior of SDM during consolidation test.

Constrained modulus is another compressibility property of sensitive clayey soil. It is possible to

measure constrained modulus by using the coefficient of volume compressibility, mv (determined from

Oedometer test). Figure 4.2.7 and Figure 4.2.8 show the relationship of constrained modulus and

vertical stress both for stabilized dredged materials with binder ratio (20:20:10) & (10:10:5) respectively.

In both cases, the constrained modulus values increase linearly with vertical stress and suddenly

changed when vertical stress approaches apparent preconsolidation stress. (Janbu 1967) stated that the

constrained modulus of sensitive clay tends to increase non-linearly from linear when applied effective

vertical stress approaches the preconsolidation stress, σc’ value.


test.

Figure 4.2.10. Coefficient of consolidation (Cv)-vertical stress (σ) behavior of SDM during consolidation test.

The process of volume reduction due to drainage is called consolidation (R.F. Craig 2004). Coefficient of

consolidation of a soil defines compression rate at which pore water is lost. Once the coefficient of

consolidation value is determined from oedometer test, the coefficient of permeability can be

calculated. The variables with coefficient consolidation values against effective vertical stresses are

shown in Figure 4.2.9 and Figure 4.2.10. Both graphs show that (Cv) values, variation become uniform

while consolidation stress over 200 kPa. Samples with binder ratio (20:20:10) have higher (Cv) values

than (10:10:5) samples. The coefficient of consolidation (Cv) value is not constant which varies with

consolidation pressure. It is also seen that the coefficient of consolidation (Cv) decreases with increasing

effective stress. After completion of oedometer test, the value of (Cv) range (0.807-0.523) ×10-6 (m2/s)

corresponds to 91 & 7 days of curing time as shown in Figure 4.2.9. On the other hand, this (Cv) values

for binder ratio (10:10:5) variables between (0.310 - 0.306)×10-6 (m2/s) after 91 & 7 days of curing period

as shown in Figure 4.2.10. (Robinson and Allam 1998) describes that coefficient of consolidation (Cv) of

clays is mainly affected by mechanical variables (surface friction & flexibility of particles) and physico-

chemical variables (surface charge density and distribution). If mechanical variables control the

consolidation behavior of soil then Cv increases with consolidation pressure. On the other hand, Cv

decreases with consolidation pressure if physico-chemical variables control the consolidation behavior

of soil. Figure 4.2.9 and Figure 4.2.10 show that physico-chemical variables control the consolidation

behavior of stabilized dredge materials (SDM).

Figure 4.2.11. Permeability (K)-vertical stress (σ) behavior of SDM during consolidation test.

Figure 4.2.12. Permeability (K)-vertical stress (σ) behavior of SDM during consolidation test.

Most of the contaminated dredged sediments are considered as soft soils. After implementation of

stabilization/solidification method, dredged sediments gain shear strength and reduce permeability.

Figure 4.2.11 and Figure 4.2.12 demonstrate the permeability behavior of SDM while applying vertical

pressure. The coefficients of permeability of soft soils are mainly controlled by mechanical variables and

physic-chemical variables (Robinson and Allam 1998). The mechanical variables impact on permeability

by controlling the size, shape and geometrical arrangement of the soil particles whereas physico-

chemical variables influence on coefficient of permeability by controlling the tendency of soil particles

dispersion or to form aggregates. It is obvious from the above graphs that after exceeding vertical stress

of 300 kPa, binder ratio and curing period have little impact on the permeability behavior of stabilized

dredged materials. Although curing time and binder ratio play a significant role over permeability up to

100 kPa consolidation stress. The permeability is smaller for a longer period of cured specimens as

compared to the short period of cured specimens. Which indicates less water and higher particles

packing density in more mature specimens than fresh specimens. The water in stabilized dredged

materials gets squeezed out with each load increment causing the reduction in permeability.


at different stresses according to curing time of stabilized materials with binder ratio 20:20:10 (50% of

total DS).

Binder mixing ratio 20:20:10 (50% of total DS)

Curing Time (days)

Stress (kPa)

Primary Consolidation (mm)

Cv ×10-6

(m2/s) mv

(m2/kN)

7

10 0.356 2.872 0.00178

20 0.271 2.123 0.00136

40 0.455 1.586 0.00114

80 0.694 1.219 0.00087

160 1.336 0.895 0.00083

320 1.439 0.644 0.00045

640 1.776 0.523 0.00028

14

10 0.402 3.777 0.00201

20 0.33 2.761 0.00165

40 0.26 2.043 0.00065

80 0.353 1.253 0.00044

160 0.528 1.195 0.00033

320 0.828 0.911 0.00026

640 1.523 0.674 0.00024

28

10 0.185 0.977 0.00092

20 0.137 0.612 0.00069

40 0.262 0.942 0.00066

80 0.42 0.663 0.00052

160 0.598 0.628 0.00037

320 0.96 0.932 0.00030

640 1.529 0.807 0.00024

91

10 0.096 2.910 0.00048

20 0.079 2.145 0.00040

40 0.111 1.691 0.00028

80 0.172 1.667 0.00022

160 0.23 1.334 0.00014

320 0.266 1.068 0.00008

640 0.376 0.877 0.00006

Table 4.2.2 & Table 4.2.3 demonstrate the change in Cv and mv of SDM with binder ratio (20:20:10) and

(10:10:5) as a function of curing time for different loading steps. Coefficient of consolidation (Cv) was

estimated using Taylor root time method and Oedometer test results were used to determine

coefficient of volume compressibility (mv) for each load increment using the following equation: 𝑚𝑣 =

1

1+𝑒0×

𝑒0−𝑒1

𝜎1−𝜎0

The value of co. of volume compressibility (mv) is not constant but depends on the consolidation

pressure range over which it is measured. It is also seen from Table 4.2.2 that almost 50% of total

displacement in stabilized dredged specimens occur during 160 kPa of loading. The total settlement of

SDM sample has a decreasing behavior with curing time, which indicates the effect of hardening process

in stabilized materials over time as shown in Table 4.2.2. For instance, 6.65% settlement occurs in the

SDM sample after 91 days of curing time as compared to 31.6% settlement after 7 days of curing time,

respectively. It is obvious that settlement decreases with curing time as the hydration process takes

place and provides sufficient stiffness and strength for SDM to carry more consolidation pressure.

(Robinson and Allam 1998) describes that coefficient of consolidation (Cv) of clays is mainly affected by

mechanical variables (surface friction & flexibility of particles) and physico-chemical variables (surface

charge density and distribution). If mechanical variables control the consolidation behavior of soil then

Cv increases with consolidation pressure. On the other hand, Cv decreases with consolidation pressure if

physico-chemical variables control the consolidation behavior of soil. Table 4.2.2 shows that physico-

chemical variables control the consolidation behavior of stabilized dredge materials (SDM).

Nevertheless, ion concentration in SDM increases with time and pressure.


at different stresses according to curing time of stabilized materials with binder ratio 10:10:5 (25% of

total DS).

Binder mixing ratio 10:10:5 (25% of total DS)

Curing Time (days)

Stress (kPa)

Primary Consolidation (mm)

Cv ×10-6 (m2/s)

mv (m2/kN)

7

10 0.411 3.776 0.00206

20 0.406 2.747 0.00203

40 0.703 1.978 0.00176

80 0.965 1.144 0.00121

160 1.762 0.804 0.00110

320 2.468 0.520 0.00077

640 2.281 0.310 0.00036

14

10 0.396 2.867 0.00198

20 0.718 1.602 0.00359

40 1.391 1.169 0.00348

80 1.546 0.587 0.00193

160 1.746 0.408 0.00109

320 1.87 0.316 0.00058

640 1.201 0.216 0.00019

10 0.131 2.905 0.00066

20 0.534 1.662 0.00267

40 1.312 1.233 0.00328

28 80 1.707 0.727 0.00213

160 1.918 0.581 0.00120

320 2.024 0.322 0.00063

640 1.024 0.253 0.00016

91

10 0.21 1.712 0.00105

20 0.4 2.141 0.00200

40 0.82 1.559 0.00205

80 1.08 1.149 0.00135

160 1.48 0.815 0.00093

320 2.03 0.554 0.00063

640 1.85 0.306 0.00029

Figure 4.2.13. Stress-strain curves of SDM subjected to various consolidation stresses.

Figure 4.2.14. Stress-strain curves of SDM subjected to various consolidation stresses.

The stress-strain curves of treated dredged sediments subjected to oedometer tests are illustrated in

Figure 4.2.13 and Figure 4.2.14. It is clearly visible that amount of binders and curing time have a great

influenced over the stress-strain behavior of stabilized dredged materials. All the samples of SDM with

binder ratio (20:20:10) show relatively reduced vertical deformation compared to SDM with binder ratio

(10:10:5). Sample with binder ratio (20:20:10) after 7 days of curing time shows 32% strain while

samples after 91 days of curing time show 7% strain from Figure 4.2.13. This increase in vertical

deformation in short time cured samples could be a result of slow hydration process. In (solidification/

stabilization process) immediately after mixing with cement, calcium silicate hydrate (C-S-H) is formed

around each cement particle surface (Mollah 1995). After that, calcium silicate minerals break down into

charged silicates and calcium ions. Thus, charged silicate ions accumulate on cement particle surface to

prevent the interaction of water with cement particle. The reaction between water and cement particle

begins from the surface of cement grain and continued until central cement grains are fully hydrated.

5 Discussion

The main aim of this research work is to investigate the mechanical behavior of stabilized dredged

materials. A series of unconfined compressive strength tests and consolidation tests were performed on

(SDM) to gain a basic knowledge of mechanical behavior of stabilized dredged materials. Based on UCS

tests that the improved strength of stabilized dredged materials was influenced by the amount of binder

ratio in the mixture and curing time, respectively. It is seen that binder ratio 20:20:10 (50 % of total DS)

can achieve significant improvement in strength of the stabilized dredged materials compared to binder

ratio 10:10:5 (25% of total DS). It is also recommended that SDM with binder ratio (10:10:5) can be used

as backfill materials after 28 days curing period. Figure 4.1.2 shows that maximum (qu) value of SDM can

be achieved 21 kPa after 91 days of curing time, which falls in a very soft soil category in terms of

consistency. Thus, with the amount of binder mixing ratio 10:10:5 (25% of total DS), no superstructure

or surcharge load can be applied to stabilized dredged materials. In general, only cement-improved

dredged materials become stiff and brittle, but the partial substitution of cement with fly ash and blast

furnace slag can greatly increase the ductility of SDM. After 91 days of curing, the peak strength and

strain of SDM with binder ratio (20:20:10) are 310 kPa and 2.3%, which is well above the required

strength (140 kPa). On the other hand, the peak strength and strain of SDM with binder (10:10:5) after

91 days curing are 21.5 kPa and 3.5%, respectively. Thus, stabilized dredged materials with binder ratio

(10:10:5) can only be used as backfill materials on-site. A major difference between the 28 and 91 days

of curing of stabilized dredged sediments with binder ratio (20:20:10) is the strength degradation rate

after failure strength is reached. A specimen which is cured for 91 days indicated rapid post-peak

strength degradation over a small range of strain due to increased brittleness of stabilized dredged

materials. Moreover, the specimen is being cured after 28 days showed that post-peak strength

degradation occurs over a large range of strain due to increased ductility of the stabilized dredged

materials. While looking at the curves of Figure 4.1.1, one important thing is to note that more fly ash

and blast furnace slag contribute to the strength increase between 28 and 91 days of curing time. Which

indicates here that the slow pozzolanic reactions contribute to the strength increase of stabilized

materials. The stiffness of dredged sediments can be significantly increased under preloading weight

during curing time compared with the stabilized sediments without preloading curing weight. On the

other hand, there is no unique correlation between the achieved UCS values and the amount of

composite binder ratio, as relationships vary with types of soil and binder.

Oedometer test results of stabilized dredged sediments were evaluated to gain better knowledge about

the impact of binders, curing time, hydration process and preloading weight on the consolidation

behavior of SDM. Binder contents have a large impact on the initial void ratio of freshly mixed dredged

sediments. The initial voids of SDM decrease with higher binder contents. By adding more binders

(cement, fly ash and GGBS) that accelerated hydration process and tend to reduce compressibility

during consolidation. Furthermore, the initial resistance to the consolidation of stabilized sediments also

increases with higher binder contents. The compressibility behavior of treated dredged sediments is

influenced by three hydration mechanisms as described in

Table 3.5.1. By analysis oedometer test results, it is seen that curing time has a significant impact on

void ratio as shown in Figure 4.2.1 and Figure 4.2.2. The void ratio decreases with longer curing time

because of higher initial resistance to consolidation pressure. According to (Yilmaz and Belem 2007),

more cemented bonds are developed within stabilized materials that can resist consolidation pressure

during the oedometer test until the yield stress of SDM is reached. With the increment of consolidation

pressure, cemented bonds are started to collapse that causing decrease in void ratio. Thus, when the

consolidation pressure exceeds the yield stress of SDM, the consolidation curve becomes steeper.

Stabilized dredge materials behave like as overconsolidation soil when the consolidation pressure is

lower than the apparent preconsolidation pressure. On the other hand, it behaves like as normally

consolidated soil when the consolidation pressure is higher than the apparent preconsolidation pressure

(Ahnberg 2006). Irrespective of the curing time, all specimens from stabilized dredged materials with

binder ratio (10:10:5) have shown that increasing in tangent modulus value followed by suddenly drop

to lower tangent modulus value (Figure 4.2.6). On the other hand, Figure 4.2.5 shows a linear

relationship between tangent modulus and vertical stress till apparent preconsolidation stress and

continues to increase non-linearly without any downward movement. Figure 4.2.5 illustrates a

significant difference in tangent modulus value between 28 days and 91 days of curing time. After 91

days of curing time, stabilized sediments with binder ratio (20:20:10) can increase tangent modulus by

approximately 200% than 28 days of curing time. Cement hydration produces calcium silicate hydrate

(C-S-H) and calcium hydroxide (CH). Calcium silicate hydrate is the main reaction product that develops

early strength in stabilized dredged materials. (Richardson, G.R., Groves 1997) observed that main

hydration products and core binding phases in all calcium silicate- based pastes are the calcium silicate

hydrate (CSH) gels. There is no fixed ratio of SiO2/CaO in (C-S-H) membrane but somewhat variable in

between 0.45-0.50 in hydrated Portland cement and increases up to 0.6 if fly ash or GGBS is present

(Understanding Cement 2005). Calcium hydroxide (CH) is another reaction product from cement

hydration which reacts with pozzolans such as fly ash and blast furnace slag. This reaction is called

pozzolanic reaction which is very slow and influences on strength development of stabilized dredged

materials. The consolidation properties of stabilized dredged sediments are greatly influenced by binder

types and curing time. The consolidation properties of SDM are improved with longer curing time and

higher binder ratio. It has been observed from oedometer test results that compressibility parameters

such as compression index (Cc) and swelling index (Cs) are decreased with increasing curing time and

higher binder ratio. Thus, stiffness of SDM increases when more cemented bonds developed within

stabilized particles. It is widely regarded that compressibility of clays is mainly influenced by mechanical

variables (surface friction & flexibility of particles) and physico-chemical variables (surface charge

density and distribution), depending on mineral types, cation concentration and pore fluid (Robinson

and Allam 1998). If mechanical variables control the consolidation behavior of soil, then Cv increases

with consolidation pressure. On the other hand, Cv decreases with consolidation pressure if physico-

chemical variables control the consolidation behavior of soil. Figure 4.2.9 and Figure 4.2.10 shows that

physico-chemical variables control the consolidation behavior of stabilized dredge materials (SDM).

6 Conclusions and Future Work

The main objectives of this dissertation were to investigate the effects of binder content, curing time on

the strength and consolidation behavior of stabilized dredged materials. To achieve the objectives,

oedometer tests and UCS tests were carried out which provided essential information about physico-

chemical changes in stabilized dredged sediments. The main outcomes of this research work are

following:

6.1 Stiffness behavior

The shear strength of stabilized dredged materials a with binder ratio of 10:10:5 (25% of total DS) is

significantly smaller than binder ratio 20:20:10 (50% of total DS). After 91 days of curing, the achieved

shear strength of SDM with binder ratio (10:10:5) is 21 kPa which falls in very soft soil category in terms

of consistency. Unfortunately, with this amount of binder mixing ratio, no superstructure or surcharge

load can be applied to stabilized dredged materials, but it can only be used as backfill materials on site.

The consistency of stabilized dredged materials with binder ratio (20:20:10) after 28 days curing with a

qu value of 130 kPa indicates stiff and after 91 days of curing becomes very stiff with a qu value of 310

kPa as shown in Table 3.6.1.1. So, it is suggested that stabilized dredged materials can’t be used before

28 days of curing period because of its consistency remains soft both after the curing period of 7, 14

days. Besides, the stabilized soil after 91 days of curing indicates rapid post-peak strength degradation

over a small range of strain due to increased stiffness and brittleness. Moreover, specimen being cured

after 28 days shows that post-peak strength degradation occurs over a large range of strain due to

increased ductility of SDM.

Binder ratio (20:20:10) and (10:10:5) has very little impact on shear strength of stabilized dredged

sediments up to 14 days of curing time as shown in Figure 4.1.3. But the difference continues increasing

and becomes significant upto 91 days curing period. It is obvious that the amount of cement and

pozzolanic materials increased with higher binder ratio, which accelerates hydration reaction till 28 days

after that pozzolanic reaction continues till 91 days.

It is obvious from the Figure 4.1.6 that UCS values of stabilized dredged materials increased with

decreasing moisture content and increasing bulk density.

6.2 Consolidation behavior

The consolidation properties of stabilized dredged sediments are greatly influenced by the binder mixing

ratio and curing time. The value of either the compression index or coefficient of volume compressibility

is required to estimate settlement of soft soil. Improved consolidation properties mean lower value of

compression index, Cc and swelling index, Cs which will eventually reduce the consolidation settlement.

By considering both curing time and binder ratio, Cc and Cs values for specimen (20:20:10) are lowered

by approximately 75% and 67%, respectively from specimen (10:10:5).

Higher binder ratio, preloading weight and longer curing time, improve the bonding between particles of

SDM because of the reduced void ratio during consolidation. Due to preloading weight, the deformation

occurred in stabilized dredge sediments is irreversible because of cementation effect.

The maximum value of tangent modulus is estimated about 9624 kPa after 91 days curing of SDM

(20:20:10). On the other hand, SDM (10:10:5) gives the tangent modulus value of about 1800 kPa after

91 days curing period. However, after 91 days of curing, shallow foundation can be placed upon

stabilized dredged materials with binder ratio (20:20:10).

The coefficient of consolidation (Cv) value is not constant but varies with consolidation pressure. After

91 days of curing, binder ratio (20:20:10) can achieve (Cv) value of 0.523×10-6 (m2/s) whereas binder

ratio (10:10:5) can reach (Cv) value of 0.306×10-6 (m2/s). It is also seen that the coefficient of

consolidation (Cv) decreases with increasing effective stress. It is also seen that the coefficient of

consolidation (Cv) decreases with increasing effective stress. Thus, physico-chemical variables control

the consolidation behavior of stabilized dredge materials (SDM).

6.3 Future work

Future work should focus on developing a comprehensive numerical model considering

loading/unloading behavior of stabilized dredged materials. There are many factors must to be

investigated for better understanding the effects on the consolidation process in stabilized materials,

including:

➢ Selection of binder types and mixing ratio are estimated by trial and error method. Further

research should be done to make a correlation between required strength of SDM and binders

(amount & mixing ratio) based on the initial water content and bulk density of fresh dredged

sediments.

➢ Choose a binder ratio in between 20:20:10 (50% of the total fresh dredged sediment) which is

overestimated and 10:10:5 (25% of the total fresh dredged sediment) which is underestimated.

➢ A Numerical model should develop considering primary and secondary consolidation

settlement.

References

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doi:10.1108/ijshe.2001.24902bab.006.

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methods to stabilize soft organic soils.

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Swedish).

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Swedish).

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Appendix

A.1 Test results of samples with binder ratio (20:20:10) from UCS test:

A.2 Test results of samples with binder ratio (10:10:5) from UCS test:

B.1 Analysis of test results of samples with binder ratio (20:20:10) from Oedometer test:

Specific Gravity, Gs = 2.49

Pressure, ρ

(kPa)

Final dial

reading, mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height, Ht(f)

(mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Coefficient of

Consolidation

Cv*10-6

(m2/s)

Coefficient of

Volume

Compressibility

mv

(m2/kN)

Coefficient of

Permeability

K*10-8

(m/s)

0 0.006 20 14.02 2.34

0.096 19.95 29 2.910 0.00048 1.37

10 0.102 19.904 13.924 2.33

0.079 19.86 39 2.145 0.00040 0.83

20 0.181 19.825 13.845 2.32

0.111 19.77 49 1.691 0.00028 0.46

40 0.292 19.714 13.734 2.30

0.172 19.63 49 1.667 0.00022 0.35

80 0.464 19.542 13.562 2.27

0.23 19.43 60 1.334 0.00014 0.19

160 0.694 19.312 13.332 2.23

0.266 19.18 73 1.068 0.00008 0.09

320 0.96 19.046 13.066 2.18

0.376 18.86 86 0.877 0.00006 0.05

640 1.336 18.67 12.69 2.12

1.33

Curing time (91 days)

Description of soil = grey black soil Location = Gävle port

Specimen Diameter = 4cm =40mm Initial specimen height, Ht(f) = 2cm = 20mm Height of solids, Hs = 0.598 cm = 5.98 mm

Total Settlement

Moisture content: Beginning of test = 95.3% End of test = 69.88% Mass of dry soil specimen, Ms = 18.72g

Pressure, ρ

(kPa)

Final dial

reading,

mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height, Ht(f)

(mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Cv*10-6

(m2/s)

mv

(m2/kN)

Permeability

K*10-8

(m/s)

0 0.005 20 12.41 1.64

0.185 19.91 86 0.977 0.00092 0.89

10 0.19 19.815 12.225 1.61

0.137 19.75 135 0.612 0.00069 0.41

20 0.327 19.678 12.088 1.59

0.262 19.55 86 0.942 0.00066 0.61

40 0.589 19.416 11.826 1.56

0.42 19.21 118 0.663 0.00052 0.34

80 1.009 18.996 11.406 1.50

0.598 18.70 118 0.628 0.00037 0.23

160 1.607 18.398 10.808 1.42

0.96 17.92 73 0.932 0.00030 0.27

320 2.567 17.438 9.848 1.30

1.529 16.67 73 0.807 0.00024 0.19

640 4.096 15.909 8.319 1.10

4.091





Total Settlement

Moisture content: Beginning of test = 99.5% End of test = 77.43% Mass of dry soil specimen, Ms = 25g

Pressure, ρ

(kPa)

Final dial

reading, mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height, Ht(f)

(mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Cv*10-6

(m2/s)

mv

(m2/kN)

Permeability

K*10-8

(m/s)

0 0.003 20 12.76 1.76

0.402 19.80 29 2.866 0.00201 5.65

10 0.405 19.598 12.358 1.71

0.33 19.43 22 3.639 0.00165 5.89

20 0.735 19.268 12.028 1.66

0.26 19.14 38 2.043 0.00065 1.30

40 0.995 19.008 11.768 1.63

0.353 18.83 60 1.253 0.00044 0.54

80 1.348 18.655 11.415 1.58

0.528 18.39 60 1.195 0.00033 0.39

160 1.876 18.127 10.887 1.50

0.828 17.71 73 0.911 0.00026 0.23

320 2.704 17.299 10.059 1.39

1.523 16.54 86 0.674 0.00024 0.16

640 4.227 15.776 8.536 1.18

4.224


Description of soil = grey black soil Location = Gäble port


Mass of dry soil specimen, Ms = 24.52g


Total Settlement

Moisture content: Beginning of test = 105.2% End of test = 74.42%

Pressure, ρ

(kPa)

Final dial

reading,

mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height,

Ht(f) (mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Cv*10-6

(m2/s)

mv

(m2/kN)

Permeability

K*10-8

(m/s)

0 0.006 20 14 2.33

0.356 19.82 29 2.872 0.00178 5.01

10 0.362 19.644 13.644 2.27

0.271 19.51 38 2.123 0.00136 2.82

20 0.633 19.373 13.373 2.23

0.455 19.15 49 1.586 0.00114 1.77

40 1.088 18.918 12.918 2.15

0.694 18.57 60 1.219 0.00087 1.04

80 1.782 18.224 12.224 2.04

1.336 17.56 73 0.895 0.00083 0.73

160 3.118 16.888 10.888 1.81

1.439 16.17 86 0.644 0.00045 0.28

320 4.557 15.449 9.449 1.57

1.776 14.56 86 0.523 0.00028 0.14

640 6.333 13.673 7.673 1.28

6.327




Total Settlement

Description of soil = grey black soil Location = Gäble port


Pressure, ρ

(kPa)

Final dial

reading,

mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height,

Ht(f) (mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Cv*10-6

(m2/s)

mv

(m2/kN)

Permeability

K*10-8

(m/s)

0 0.01 20 12.08 1.53

0.21 19.90 49 1.712 0.00105 1.76

10 0.22 19.79 11.87 1.50

0.4 19.59 38 2.141 0.00200 4.20

20 0.62 19.39 11.47 1.45

0.82 18.98 49 1.559 0.00205 3.13

40 1.44 18.57 10.65 1.34

1.08 18.03 60 1.149 0.00135 1.52

80 2.52 17.49 9.57 1.21

1.48 16.75 73 0.815 0.00093 0.74

160 4 16.01 8.09 1.02

2.03 15.00 86 0.554 0.00063 0.34

320 6.03 13.98 6.06 0.77

1.85 13.06 118 0.306 0.00029 0.09

640 7.88 12.13 4.21 0.53

7.87


Mass of dry soil specimen, Ms = 24.78g


Total Settlement



Moisture content: Beginning of test = 170.6% End of test = 90.67%

Pressure, ρ

(kPa)

Final dial

reading, mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height,

Ht(f) (mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Cv*10-6

(m2/s)

mv

(m2/kN)

Permeability

K*10-8

(m/s)

0 0.271 20 15.6 3.55

0.131 19.93 29 2.905 0.00066 1.87

10 0.402 19.869 15.469 3.52

0.534 19.60 49 1.662 0.00267 4.35

20 0.936 19.335 14.935 3.39

1.312 18.68 60 1.233 0.00328 3.97

40 2.248 18.023 13.623 3.10

1.707 17.17 86 0.727 0.00213 1.52

80 3.955 16.316 11.916 2.71

1.918 15.36 86 0.581 0.00120 0.68

160 5.873 14.398 9.998 2.27

2.024 13.39 118 0.322 0.00063 0.20

320 7.897 12.374 7.974 1.81

1.024 11.86 118 0.253 0.00016 0.04

640 8.921 11.35 6.95 1.58

8.65





Total Settlement


B.2 Analysis of test results of samples with binder ratio (10:10:5) from Oedometer test:

Pressure, ρ

(kPa)

Final dial

reading,

mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height,

Ht(f) (mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Cv*10-6

(m2/s)

mv

(m2/kN)

Permeability

K*10-8

(m/s)

0 0.006 20 15.98 3.98

0.396 19.80 29 2.867 0.00198 5.57

10 0.402 19.604 15.584 3.88

0.718 19.25 49 1.602 0.00359 5.64

20 1.12 18.886 14.866 3.70

1.391 18.19 60 1.169 0.00348 3.99

40 2.511 17.495 13.475 3.35

1.546 16.72 101 0.587 0.00193 1.11

80 4.057 15.949 11.929 2.97

1.746 15.08 118 0.408 0.00109 0.44

160 5.803 14.203 10.183 2.53

1.87 13.27 118 0.316 0.00058 0.18

320 7.673 12.333 8.313 2.07

1.201 11.73 135 0.216 0.00019 0.04

640 8.874 11.132 7.112 1.77

8.868





Total Settlement


Pressure, ρ

(kPa)

Final dial

reading, mm

Change in

specimen

height, ΔH

(mm)

Final

specimen

height, Ht(f)

(mm)

Height of

void, Hv

(mm)

Final Void

ratio, e

Avg height

during

cosolidaion,

Ht(av)

Fitting

time, sec

t90

Cv*10-6

(m2/s)

mv

(m2/kN)

Permeability

K*10-8

(m/s)

0 0.003 20 16.08 4.10

0.411 19.79 22 3.776 0.00206 7.61

10 0.414 19.589 15.669 4.00

0.406 19.39 29 2.747 0.00203 5.47

20 0.82 19.183 15.263 3.89

0.703 18.83 38 1.978 0.00176 3.41

40 1.523 18.48 14.56 3.71

0.965 18.00 60 1.144 0.00121 1.35

80 2.488 17.515 13.595 3.47

1.762 16.63 73 0.804 0.00110 0.87

160 4.25 15.753 11.833 3.02

2.468 14.52 86 0.520 0.00077 0.39

320 6.718 13.285 9.365 2.39

2.281 12.14 101 0.310 0.00036 0.11

640 8.999 11.004 7.084 1.81

8.996




Total Settlement



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