Geotechnical characteristics and admixture stabilization ......ADMIXTURE STABILIZATION OF BIOSOLIDS Visvalingam Suthagaran This thesis is submitted for the Degree of Doctor of Philosophy

Faculty of Engineering and Industrial Science

Department of Civil Engineering

GEOTECHNICAL CHARACTERISTICS AND

ADMIXTURE STABILIZATION OF BIOSOLIDS

Visvalingam Suthagaran

This thesis is submitted for the Degree of Doctor of Philosophy

of

Swinburne University of Technology

OCTOBER 2010

ii

DECLARATION

This thesis contains no material which has been accepted for the award of any other

degree or diploma in any university. To the best of my knowledge and belief this thesis

contains no material previously published by any other person except where due

acknowledgment has been made.

The following publications have resulted from the work carried out for this degree.

Copies of selected published or in print refereed journal papers are presented in

Appendix 1. Copies of published refereed conference papers are presented in Appendix

2.

Refereed Journal Papers:

1. Suthagaran, V., Arulrajah, A., Bo, M. W. and Wilson, J. (2009a). “Stabilisation

of Biosolids with Admixtures for Potential Use as an Embankment Fill Material”,

Australian Geomechanics, Journal of the Australian Geomechanics Society, Vol.

44, No. 3, September 2009, pp. 63-70.

2. Suthagaran, V., Arulrajah, A. and Bo, M. W. (2009b). “Geotechnical

Engineering Properties of Biosolids”, International Journal of Geotechnical

Engineering; J. Ross Publishing Inc, Issue. 3, July 2010, pp. 417-424.

iii

Refereed Conference Papers:

1. Suthagaran, V., Arulrajah, A., Wilson, J. and Bo, M. W. (2007). "Field Testing

to Determine The Suitability of Biosolids for Embankment Fill", 12th European

Biosolids and Organic Resources Conference, Manchester, UK, November.

2. Suthagaran, V., Arulrajah, A., Bo, M. W. and Wilson, J. (2008a). “Biosolids as

a Construction Material for Engineered Fills", 10th International Conference on

Applications of Advanced Technologies in Transportation (AATT 2008), Athens,

Greece, May.

3. Suthagaran, V., Arulrajah, A., Lamborn, J. and Wilson, J. (2008b).

"Geotechnical Testing to Determine the Suitability of Biosolids for Embankment

Fill", Biosolids Speciality IV Conference, Adelaide, Australia, June.

4. Disfani, M. M., Arulrajah, A., Suthagaran, V. and Bo, M. W. (2009a).

"Geotechnical Characteristics of Recycled Glass-Biosolid mixtures", 62nd

Canadian Geotechnical Conference and 10th Joint Canadian Geotechnical Society

(CGS) and Canadian National Chapter of the International Association of

Hydrogeologists (IAH-CNC) Ground Water Speciality Conference

(GeoHalifax2009), Halifax, Nova Scotia, Canada, September.

5. Disfani, M. M., Arulrajah, A., Suthagaran, V. and Bo, M. W. (2009b). "Shear

Strength Behaviour of Recycled Glass-Biosolids Mixtures”, 17th International

Conference on Soil Mechanics and Geotechnical Engineering (17th ICSMGE),

Alexandria, Egypt, October.

6. Suthagaran, V., Arulrajah, A., Bo, M. W. (2009c). "Settlement Behaviour of

Biosolids Stabilised with Bauxsol in Road Embankment”, 1st International

Conference on Sustainable Infrastructure and Built Environment (SIBE-2009),

Bandung, Indonesia, November.

Signature : ………………………..

Date :…………………………

iv

ABSTRACT

Biosolids are defined as appropriately treated sewage sludge which consists of organic

slurry residue derived from wastewater treatment processes. The sustainable usage of

waste materials such as biosolids in engineering applications is of social and economic

benefit to industrialized nations. Due to the shortages of natural mineral resources and

increasing waste disposal costs, recycling solids wastes has become significant in recent

years. This thesis presents research on the geotechnical properties of biosolids and

investigates their sustainable usage as an embankment fill material,

Field sampling of biosolids was conducted at three stockpiles at Biosolids Stockpile

Area, Western Treatment Plant in Melbourne. An extensive suite of geotechnical

laboratory tests were undertaken on untreated biosolids and biosolids stabilised with

various additives. The geotechnical laboratory tests undertaken included index tests as

well as more detailed tests. These tests included consolidation, triaxial, particle density,

particle size analysis, Atterberg limits, compaction, California bearing ratio (CBR),

hydraulic conductivity tests on untreated and well stabilised with admixtures such as

lime, cement, bauxsol and fly-ash were determined and analysed in this research study.

The Plaxis finite element analysis software was used to analyse the behaviour of various

heights of embankments using stabilised biosolids with lime, cement, bauxsol and fly-

ash. The primary, secondary and also the creep settlement were determined from the

finite element analysis and analysed.

In addition to the primary and secondary settlement, biodegradation settlement of the

biosolids were also analysed by adapting theories that are presently used for landfills.

As biodegradation is sensitive to pH values of the biosolids, a sensitivity analysis was

undertaken by varying the pH value of the untreated biosolids and also the stabilised

biosolids with admixtures.

The laboratory testing results indicate that the biosolids stabilised with the required

proportions of additives possess sufficient shear strength and bearing capacity to make

them suitable for use as fill material. The results of the finite element analysis agree

well with the laboratory results and indicate that biosolids, when stabilised with

additives to the required percentages, can be used as stabilised fill in embankments.

v

ACKNOWLEDGEMENTS

I would first like to express my sincere gratitude to my supervisor Associate Professor

Arul Arulrajah of the Faculty of Engineering and Industrial Science at Swinburne

University of Technology for his constant support, invaluable technical guidance, and

understanding throughout the period of my research studies. I thank him for the

technical development for this research and also his availability for discussion, thesis

editing, despite his heavy workload, is very much appreciated. I thank him for

constantly encouraging me to publish the finding of this research in the form of journal

and conference papers. I thank Dr. Arulrajah for his support to me during difficult times

in my personal life. I am thankful to him for getting the opportunity to work with him

and the experience gained have been both enlightening and memorable.

I am greatly indebted to my co-supervisor Dr. M. W. Bo, Principal/Director

(Geoservices) at DST Consulting Engineers Inc. (Canada) for his invaluable technical

advice and guidance for my studies. Dr M.W. Bo provided key input at all stages of this

PhD thesis works and I thank him for his invaluable technical input.

I wish to thank my co-supervisor Prof. John Wilson, Professor at the Faculty of

Engineering and Industrial Science, Swinburne University of Technology for his

valuable advice and assistance for my study.

My special thanks go to the Smart Water Fund for funding this research project (Project

No: 42M-2059). The Smart Water Fund is an initiative of the Victorian Government

and the Victorian water industry in Australia aimed at encouraging innovative solutions

to water conservation, water management and biosolids management. I would also like

to thank VicRoads, Melbourne for providing the field data of Deer Park Bypass project

in order to determine parameters for finite element analysis of embankment in this

study.

I thanks to Mr. Alec Papanicolaou for his valuable assistance to complete laboratory

tests successfully and thanks are extended to my colleagues Mr. M. M. Disfani and Mr.

T. Aatheesan for their valuable assistance for lab test and my research studies.

vi

I wish to acknowledge Mr. Stephen Darmawan the Managing Director at Geotesta Pty

Ltd. for being a constant source of encouragement and assistance for past three years of

my career and studies. I thank him for his interest and for his advice to me in my work

and studies.

I extend my gratitude to my friends Mr. L. Charley, Mr. S. Sivaniruban, Mr. S.

Baraneetharan, Mr. J. Vinoth for their support and social interaction outside the

University. I extend my gratitude to Dr. Manivannan and Mr. S. Ajanthan for their

moral support for my work, studies and personal life.

Finally, I wish thankful to my mother Mrs. S. Visvalingam and my siblings for their

considerable encouragement throughout these studies. In addition I also thank them for

being supportive in my pursuit of further studies.

vii

TABLE OF CONTENTS

DECLARATION .................................................................................................................. ii

ACKNOWLEDGEMENTS ................................................................................................. v

TABLE OF CONTENTS ................................................................................................... vii

LIST OF FIGURES .......................................................................................................... xiii

LIST OF TABLES ........................................................................................................... xxii

1 INTRODUCTION .................................................................................................... 1

1.1 Problem Statement ...................................................................................................... 1

1.2 Objectives and Scope .................................................................................................. 2

1.3 Research Approach ..................................................................................................... 3

1.4 Thesis Outline ............................................................................................................. 4

2 LITERATURE REVIEW ........................................................................................ 6

2.1 Geotechnical Characteristics of Sludge and Biosolids................................................ 6

2.2 Laboratory Testing of Biosolids and Sludge ............................................................. 10

2.2.1. Classification Test........................................................................................... 10

2.2.2. Laboratory Vane Shear Test ........................................................................... 16

2.2.3. Compaction Test ............................................................................................. 17

2.2.4. California Bearing Ratio Test (CBR Test) ..................................................... 18

2.2.5. Consolidation Test .......................................................................................... 21

2.2.6. Hydraulic Conductivity Test ........................................................................... 22

2.2.7. Triaxial Test .................................................................................................... 23

2.3 Biosolids Stabilisation ............................................................................................... 25

2.3.1. Stabilisation with Lime ................................................................................... 25

2.3.2. Stabilisation with Cement ............................................................................... 27

2.4 Finite Element Analysis of Biosolids Embankment ................................................. 29

2.5 Local Road Works Specifications for Engineered Fill ............................................. 30

2.5.1. Type A Material .............................................................................................. 30

viii

2.5.2. Type B Material .............................................................................................. 31

2.6 Conclusions: Literature Review ................................................................................ 32

3 SITE DESCRIPTION AND FIELD TESTING ................................................... 34

3.1 Site Description ......................................................................................................... 34

3.2 Field Testing.............................................................................................................. 38

3.2.3. Borehole Sampling and Testing ...................................................................... 39

3.2.3. Dynamic Cone Penetration Test ..................................................................... 43

3.2.3. Bulk Sampling ................................................................................................ 43

3.3 Assessment and Discussion of Field Testing ............................................................ 46

3.3.1. Standard Penetration Test Results .................................................................. 46

3.3.2. Field Vane Shear Test Results ........................................................................ 47

3.3.3. Dynamic Cone Penetrometer Test Results ..................................................... 49

3.4 Conclusions: Field Works ......................................................................................... 51

4 LABORATORY EXPERIMENTAL PROGRAM ................... ........................... 52

4.1 Overview ................................................................................................................... 52

4.2 Stabilizing Admixtures.............................................................................................. 53

4.2.1. Lime ................................................................................................................ 53

4.2.2. Cement ............................................................................................................ 54

4.2.3. Bauxsol ........................................................................................................... 55

4.2.4. Fly ash ............................................................................................................. 57

4.3 Laboratory Testing Methodology ............................................................................. 58

4.3.1. Moisture content ............................................................................................. 58

4.3.2. Specific gravity (Particle Density) .................................................................. 58

4.3.3. Particle size analysis ....................................................................................... 58

4.3.4. Atterberg limit test .......................................................................................... 59

4.3.5. Standard compaction test ................................................................................ 59

4.3.6. Consolidation test ........................................................................................... 60

4.3.7. Triaxial test ..................................................................................................... 60

4.3.8. California Bearing Ratio (CBR) test ............................................................... 61

4.3.9. Hydraulic Conductivity test ............................................................................ 61

ix

5 GEOTECHNICAL CHARACTERISTICS OF UNTREATED BIOSOLDIS .. 62

5.1 Index Properties ........................................................................................................ 62

5.2 Standard Compaction Test Results ........................................................................... 66

5.3 California Bearing Ratio (CBR) Test Results ........................................................... 67

5.4 Triaxial (Consolidated Drained) Test Results ........................................................... 69

5.5 Triaxial (Unconsolidated Undrained) Test Results ................................................... 71

5.6 One Dimensional Consolidation Test Results ........................................................... 72

5.7 Rowe Cell Consolidation Test Results ...................................................................... 75

5.8 Hydraulic Conductivity Test Results ........................................................................ 78

6 GEOTECHNICAL CHARACTERISTICS OF STABILISED BIOSOLID S ... 80

6.1 Geotechnical Characteristics of Biosolids Stabilised with Lime .............................. 80

6.1.1. Index properties .............................................................................................. 80

6.1.2. Standard compaction test results..................................................................... 84

6.1.3. California Bearing Ratio (CBR) test results ................................................... 87

6.1.4. Triaxial (Consolidated Drained) test results ................................................... 89

6.1.5. One dimensional consolidation test results ..................................................... 90

6.1.6. Rowe Cell consolidation test results ............................................................... 92

6.1.7. Creep consolidation test results ...................................................................... 93

6.1.8. Hydraulic conductivity test results ................................................................. 94

6.2 Geotechnical Characteristics of Biosolids Stabilised with Cement .......................... 98

6.2.1. Index properties .............................................................................................. 98

6.2.2. Standard compaction test results................................................................... 102

6.2.3. California Bearing Ratio (CBR) test results ................................................. 104

6.2.4. Triaxial (Consolidated Drained) test results ................................................. 106

6.2.5. One dimensional consolidation test results ................................................... 108

6.2.6. Rowe Cell consolidation test results ............................................................. 110

6.2.7. Creep consolidation test results .................................................................... 111

6.2.8. Hydraulic conductivity test results ............................................................... 113

6.3 Geotechnical Characteristics of Biosolids Stabilised with Bauxsol ....................... 117

6.3.1. Index properties ............................................................................................ 117

x



6.3.4. Triaxial (Consolidated Drained) test results ................................................. 124

6.3.5. One dimensional consolidation test results ................................................... 125

6.3.6. Rowe Cell consolidation test results ............................................................. 128

6.3.7. Creep consolidation test results .................................................................... 129


6.4 Geotechnical Characteristics of Biosolids Stabilised with Fly-ash......................... 135

6.4.1. Index properties ............................................................................................ 135




6.5 Analysis of Laboratory Test Results for Untreated and Stabilised Biosolids ......... 146

6.5.1. Moisture content ........................................................................................... 146

6.5.2. Atterberg Limits ............................................................................................ 148

6.5.3. Compaction characteristics ........................................................................... 152

6.6 Conclusions: Laboratory Testing ............................................................................ 154

7 FINITE ELEMENT MODELLING OF STABILISED BIOSOLID

EMBANKMENTS ................................................................................................ 156

7.1 Overview of Finite Element Modelling .................................................................. 156

7.2 Finite Element Modelling Theory ........................................................................... 157

7.2.1. Geometry model ........................................................................................... 157

7.2.2. Finite element mesh for embankment ........................................................... 159

7.2.3. Soil models ................................................................................................... 160

7.2.4. Material properties of subsoil and fill material ............................................. 163

7.3 Finite Element Analysis of Embankments using Biosolids Stabilised with Lime .. 164

7.4 Finite Element Analysis of Embankments using Biosolids Stabilised with

Cement .................................................................................................................... 169


Bauxsol .................................................................................................................... 176

xi

7.6 Finite Element Analysis of Embankments using Untreated Biosolids ................... 183

7.7 Conclusions: Finite Element Modelling.................................................................. 186

8 BIODEGRADATION SETTLEMENT OF BIOSOLIDS AND

CORROSIVITY .................................................................................................... 188

8.1 Methodology and Approach of Biodegradation settlement of Biosolids ................ 188

8.2 pH and Electrical Conductivity Tests ..................................................................... 193

8.3 Corrosivity Analysis of Biosoilds ........................................................................... 196

8.4 Sensitivity Analysis of Biodegradation Settlement................................................. 200

8.5 Biodegradation Settlement of Untreated Biosolids ................................................. 201

8.6 Biodegradation Settlement of Stabilised Biosolids with Lime ............................... 203

8.6.1 Biodegradation settlement of stabilised biosolids with 5% Lime .............. 203

8.7 Biodegradation Settlement of Stabilised Biosolids with Cement ........................... 208

8.7.1 Biodegradation settlement of stabilised biosolids with 3% cement ........... 208

8.7.2 Biodegradation settlement of stabilised biosolids with 5% cement ........... 213

8.8 Biodegradation Settlement of Stabilised Biosolids with Bauxsol ........................... 218

8.8.1 Biodegradation settlement of stabilised biosolids with 3% bauxsol .......... 218

8.8.2 Biodegradation settlement of stabilised biosolids with 5% bauxsol .......... 223

8.9 Discussion on Biodegradation Settlement of Biosolids .......................................... 228

8.10 Conclusion: Biodegradation Settlement of Biosolids and Corrosivity ................... 230

9 CONCLUSION AND RECOMMENDATION .................................................. 232

9.1 Literature Review .................................................................................................... 232

9.2 Field Testing............................................................................................................ 232

9.3 Laboratory Testing on Untreated and Stabilised Biosoldis with Admixtures ......... 233

9.4 Finite Element Modelling of Embankment using Stabilised Biosolids with

Admixtures .............................................................................................................. 234

9.5 Biodegradation Settlement Analysis of Untreated and Stabilised Biosolids with

Admixtures .............................................................................................................. 236

xii

9.6 Corrosivity Settlement Analysis of Untreated and Stabilised Biosolids with

Admixtures .............................................................................................................. 237

10 REFERENCES...................................................................................................... 238

APPENDIX 1: Published refereed journal papers resulting from this study

APPENDIX 2: Published refereed conference papers resulting from this study

xiii

LIST OF FIGURES

Figure 2.1. Dry sludge granulometry curve in Spain, (Valls et al., 2004). .................... 14

Figure 2.2. Density-water content relationships for compaction in United Kingdom,

(Kelly, 2004). .................................................................................................. 17

Figure 2.3. Relationship between optimum moisture Contents (OMC) and dry density

with addition of lime and fly ash in Korea, (Lim et al., 2002). .................... 18

Figure 2.4. The relationship between permeability and void ratio of the sludge samples

in Korea, (Lim et al., 2002). ............................................................................ 23

Figure 2.5. Variation of undrained shear strength with water content in United

Kingdom, (Kelly, 2005). ................................................................................. 24

Figure 2.6. Micrographs of original waterworks and wastewater sludge in Korea,

(Lim et al.,2002).............................................................................................. 26

Figure 2.7. Micrographs of modified sludge mixtures by lime and fly ash in Korea,

(Lim et al., 2002)............................................................................................. 26

Figure 2.8. Compressive strength according to sludge content for concrete with three

different curing times in Spain, (Valls et al., 2004). ....................................... 27

Figure 2.9. Flexural strength according to the sludge content with three different curing

times in Spain, (Valls et al., 2004). ................................................................. 28

Figure 2.10. Elastic modulus of concrete according to the sludge content after 90 days

in Spain, (Valls et al., 2004). ........................................................................... 28

Figure 3.1. Location of the Western Treatment Plant, Werribee,

(Melways Map 205, 12F). ............................................................................... 35

Figure 3.2. Systematic diagram of the production of biosolids at the Western Treatment

Plant ................................................................................................................ 36

Figure 3.3. Aerial view of Western Treatment Plant, Werribee, Victoria,

(Melbourne Water Corporation, 2000) ........................................................... 37

Figure 3.4. Biosolids stockpiles at the Western Treatment Plant, Werribee, Victoria. .. 37

Figure 3.5. Location of boreholes at the Biosolids Stockpile Area ................................ 39

Figure 3.6. Augering for biosolid samples at a borehole location .................................. 40

Figure 3.7. Sample tube retrieved from a biosolids stockpile. ........................................ 41

Figure 3.8. Standard penetration test (SPT) at a borehole location ................................ 42

Figure 3.9. Field vane shear tests (FVT) at a borehole location ..................................... 42

Figure 3.10. Dynamic cone penetration (DCP) tests at a field test location ................... 43

xiv

Figure 3.11. Locations of bulk sampling in stockpiles ................................................... 44

Figure 3.12. Collection of biosolid bulk samples ........................................................... 45

Figure 3.13. Bulk sampling bags..................................................................................... 45

Figure 3.14. Layout diagram of dynamic cone penetrometer

(Australian Standards, AS1289). .................................................................... 49

Figure 4.1. The colour and physical appearance of biosolids ......................................... 52

Figure 4.2. The colour and physical appearance of lime ................................................ 54

Figure 4.3. The colour and physical appearance of cement ............................................ 55

Figure 4.4. Process to get a uniform consistency of bauxsol,

(Department of Environmental Protection, 2008)........................................... 56

Figure 4.5. The colour and physical appearance of bauxsol ........................................... 56

Figure 4.6. The colour and physical appearance of fly ash ............................................. 57

Figure 5.1. Plasticity chart for biosolids samples ........................................................... 62

Figure 5.2. Testing progress of sieves analysis on untreated biosolids .......................... 63

Figure 5.3. Biosolids passing various sizes of sieves...................................................... 65

Figure 5.4. Particle size distributions of biosolids samples ............................................ 66

Figure 5.5. Variation of dry density of untreated biosolids with moisture content ........ 66

Figure 5.6. Testing progress of CBR test on untreated biosolids.................................... 67

Figure 5.7. CBR results of untreated biosolids ............................................................... 68

Figure 5.8. Swell results after 4 days for untreated biosolids ......................................... 68

Figure 5.9. Triaxial sample (after the shearing failure) .................................................. 69

Figure 5.10. Consolidated drained triaxial test results for biosolids in stockpile 1 ........ 70



Figure 5.13. Consolidation sample preparation process ................................................. 72

Figure 5.14. Consolidation testing arrangement ............................................................. 73

Figure 5.15. Compressed untreated biosolids sample (before oven dried) ..................... 74

Figure 5.16. Compressed untreated biosolids sample (oven dried sample) .................... 74

Figure 5.17. Variation of void ratio with vertical stress for biosolids in stockpiles 1, 2

and 3 ................................................................................................................ 75

Figure 5.18. Rowe Cell test result for biosolids in stockpile 1 ....................................... 76

Figure 5.19. Rowe Cell test results for biosolids in stockpile 2 ...................................... 76

Figure 5.20. Rowe Cell test results for biosolids in stockpile 3 ...................................... 77

Figure 6.1. Moisture content variation with percentage of lime added to biosolids ....... 80

xv

Figure 6.2. Atterberg limits variation with percentage of lime added to biosolids in

stockpile 1 ....................................................................................................... 81


stockpile 2 ....................................................................................................... 81


stockpile 3 ....................................................................................................... 82

Figure 6.5. Particle size distribution of biosolids samples stabilised with lime in

Stockpile 1....................................................................................................... 83


Stockpile 2....................................................................................................... 83


Stockpile 3....................................................................................................... 84

Figure 6.8. Compaction curves for the stabilised biosolids with lime ............................ 85

Figure 6.9. Variation of Maximum Dry Density (MDD) with percentage of lime ......... 85

Figure 6.10. Variation of Optimum Moisture Content (OMC) with percentage of lime 86

Figure 6.11. CBR results of biosolids stabilised with lime ............................................. 87

Figure 6.12. Swell results after 4 days for biosolids stabilised with lime ....................... 88

Figure 6.13. Consolidated drained triaxial test results for stabilised biosolids with 3%

lime.................................................................................................................. 89


lime.................................................................................................................. 89

Figure 6.15. Variation of void ratio with vertical stress for biosolids in stockpile 1 ...... 90



Figure 6.18. Rowe Cell test results for stabilised biosolids with 3% lime ..................... 92

Figure 6.19. Variation of secondary consolidation for biosolids stabilised with 5% lime

......................................................................................................................... 93

Figure 6.20. Permeability of stabilised biosolids with lime ............................................ 94

Figure 6.21. Moisture content variation with percentage of cement added to biosolids 98

Figure 6.22. Atterberg limits with percentage of cement added to biosolids in

stockpile 1 ....................................................................................................... 99


stockpile 2 ....................................................................................................... 99

xvi


stockpile 3 ..................................................................................................... 100

Figure 6.25. Particle size distribution of biosolids stabilised with cement in Stockpile 1

....................................................................................................................... 101


....................................................................................................................... 101


....................................................................................................................... 102

Figure 6.28. Compaction curves for the stabilised biosolids with cement ................... 103

Figure 6.29. Variation of Maximum Dry Density (MDD) with percentage of cement 103

Figure 6.30. Variation of Optimum Moisture Content (OMC) with percentage of cement

....................................................................................................................... 104

Figure 6.31. CBR results for biosolids stabilised with cement ..................................... 105

Figure 6.32. Swell results after 4 days for biosolids stabilised with cement ................ 106


cement ........................................................................................................... 107


cement ........................................................................................................... 107

Figure 6.35. Variation of void ratio with vertical stress for biosolids in stockpile 1 .... 108



Figure 6.38. Rowe Cell test results for stabilised biosolids with 3% cement ............... 110

Figure 6.39. Variation of secondary consolidation for biosolids stabilised with 3%

cement ........................................................................................................... 112


cement ........................................................................................................... 112

Figure 6.41. Permeability of biosolids stabilised with cement ..................................... 113

Figure 6.42. Moisture content variation with percentage of bauxsol added to biosolids

....................................................................................................................... 117

Figure 6.43. Atterberg limits with percentage of bauxsol added to biosolids in

stockpile 1 ..................................................................................................... 118


stockpile 2 ..................................................................................................... 118

xvii


stockpile 3 ..................................................................................................... 119

Figure 6.46. Compaction curves for the stabilised biosolids with bauxsol ................... 120

Figure 6.47. Variation of Maximum Dry Density (MDD) with percentage of bauxsol 121

Figure 6.48. Variation of Optimum Moisture Content (OMC) with percentage of

bauxsol .......................................................................................................... 121

Figure 6.49. CBR results of biosolids stabilised with bauxsol ..................................... 122

Figure 6.50. Swell results after 4 days for biosolids stabilised with bauxsol. .............. 123


bauxsol .......................................................................................................... 124


bauxsol .......................................................................................................... 125




Figure 6.56. Rowe Cell test results for stabilised biosolids with 3% bauxsol .............. 128


bauxsol .......................................................................................................... 130


bauxsol .......................................................................................................... 130

Figure 6.59. Permeability of untreated and stabilised biosolids with bauxsol .............. 131

Figure 6.60. Moisture content variation with percentage of fly ash added to biosolids 135

Figure 6.61. Atterberg limits with percentage of fly ash added to biosolids in stockpile 1

....................................................................................................................... 136


....................................................................................................................... 136


....................................................................................................................... 137

Figure 6.64. Compaction curves for the stabilised biosolids with fly ash .................... 138

Figure 6.65. Variation of Maximum Dry Density (MDD) with percentage of fly ash . 139

Figure 6.66. Variation of Optimum Moisture Content (OMC) with percentage of fly ash

....................................................................................................................... 139

Figure 6.67. CBR results of biosolids stabilised with fly ash ....................................... 140

Figure 6.68. Swell results after 4 days for biosolids stabilised with fly ash. ................ 141

xviii

Figure 6.69. Permeability of untreated and stabilised biosolids with fly ash ............... 142

Figure 6.70. Correlation of natural water content with percentage of additives added to

the biosolids .................................................................................................. 146

Figure 6.71. Correlation of natural water content with percentage of fly ash added to the

biosolids ........................................................................................................ 147

Figure 6.72. Correlation of atterberg limits with percentage of lime added to the

biosolids ........................................................................................................ 148

Figure 6.73. Correlation of atterberg limits with percentage of cement added to the

biosolids ........................................................................................................ 149

Figure 6.74. Correlation of atterberg limits with percentage of bauxsol added to the

biosolids ........................................................................................................ 150

Figure 6.75. Correlation of atterberg limits with percentage of fly ash added to the

biosolids ........................................................................................................ 151

Figure 6.76. Correlation of dry density with water content in the biosolids ................. 152

Figure 7.1. Coordinate system of geometry. ................................................................. 157

Figure 7.2. Typical geometry of embankment with stabilised biosolids on basalt

formation. ...................................................................................................... 157

Figure 7.3. Typical geometry model for a 5m high embankment using stabilised

biosolids. ....................................................................................................... 158

Figure 7.4. Finite element mesh for the geometry model of a 5m high embankment. . 159

Figure 7.5. Finite element mesh with nodes for the geometry model of a 5m high

embankment. ................................................................................................. 159

Figure 7.6. Finite element mesh with stress points for the geometry model of a 5m high

embankment. ................................................................................................. 160

Figure 7.7. Derivation of elastic modulus from triaxial tests. ....................................... 161

Figure 7.8. Typical geometry for embankment using biosolids stabilised with 5% lime

....................................................................................................................... 165

Figure 7.9. Deformation mesh of 5 m embankment using biosolids stabilised with 5%

lime................................................................................................................ 166

Figure 7.10. Vertical settlement of 5 m embankment using biosolids stabilised with 5%

lime................................................................................................................ 166

Figure 7.11. Variation of vertical settlement of 5 m embankment using biosolids

stabilised with 5% lime. .............................................................................. 167

xix

Figure 7.12. Variation of vertical settlement of various embankments using biosolids

stabilised with 5% lime. ................................................................................ 168

Figure 7.13. Typical geometry for embankment using biosolids stabilised with cement.

....................................................................................................................... 170


cement. .......................................................................................................... 171

Figure 7.15. Vertical settlement of 5m embankment using biosolids stabilised with 3%

cement. .......................................................................................................... 171


stabilised with 3% and 5% cement. ............................................................ 172


stabilised with 3% cement............................................................................. 173



Figure 7.19. Typical geometry for embankment using biosolids stabilised with bauxsol.

....................................................................................................................... 177


bauxsol. ......................................................................................................... 178

Figure 7.21. Vertical settlement of 5 m embankment using biosolids stabilised with 3%

bauxsol. ......................................................................................................... 178


stabilised with 3% and 5% bauxsol. ............................................................ 179


stabilised with 3% bauxsol. ........................................................................... 180



Figure 7.25. Typical geometry for embankment using untreated biosolids. ................. 184

Figure 7.26. Collapsed deformation mesh of 5 m embankment using untreated biosolids.

....................................................................................................................... 185

Figure 8.1. The effect of solution pH upon the corrosion rate of iron (Scully, 1990). 197

Figure 8.2. Biodegradation settlement of 5m height embankment using untreated

biosolids. ....................................................................................................... 202

Figure 8.3. Biodegradation settlement of 5m height embankment using stabilised

biosolids with 5% lime. ................................................................................. 204

xx








biosolids with 3% cement. ............................................................................ 208
















biosolids with 3% bauxsol. ........................................................................... 219











xxi





Figure 8.23. Time taken for biodegradation with pH values. ...................................... 228

Figure 8.24. Trend of biodegradation process with pH values. .................................. 229

xxii

LIST OF TABLES

Table 2.1. Summary of moisture content testing of biosolids treated with lime in

Victoria, (Golders Associates, 2006). ............................................................. 7

Table 2.2. Summary of average UCS test results on cement treated biosolids in stockpile

23 in Victoria, (Golders Associates, 2006). ...................................................... 7

Table 2.3. Summary of average UCS test results on cement treated biosolids in stockpile

7 and 14 in Victoria, (Golders Associates, 2006). ............................................ 8

Table 2.4. Unconfined compressive strength (kPa) for each modified mixture in Korea,

(Lim et al., 2002)............................................................................................. 10

Table 2.5. Statistical summary of geotechnical tests in Victoria,

(Golders Associates, 2006). ............................................................................ 12

Table 2.6. Some properties of slurry direct from wastewater plant in United Kingdom,

(Kelly, 2006). .................................................................................................. 13

Table 2.7. Some properties of the tested sewage sludge in Trinidad (Stone et al., 1998).

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

Table 2.8. Index properties of sludge and each modifier in Korea, (Lim et al., 2002). .. 15

Table 2.9. Index properties of modified sewage sludge in Korea, (Lim et al., 2002)..... 16

Table 2.10. Summary of CBR tests results on trial embankment material in stockpile 23

in Victoria, (Golders Associates, 2006). ......................................................... 19

Table 2.11. Summary of CBR tests results on trial embankment material in stockpile 7

and 14 in Victoria, (Golders Associates, 2006). ............................................. 20

Table 2.12. Results of CBR of modified wastewater sludge mixture in Korea,

(Lim et al., 2002)............................................................................................. 20

Table 2.13. Comparison of coefficient of volume compressibility (mv) from oedometer

test in Victoria, (Golders Associates, 2006). .................................................. 21

Table 2.14. Comparison of secondary consolidation values (c∝) from oedometer test in


Table 2.15. Summary of triaxial undrained compression testing on treated biosolids in


Table 2.16 pH values of modified sludge with curing time in Korea, (Lim et al., 2002).

......................................................................................................................... 25

Table 2.17. Engineering properties requirement for Type A fill material ...................... 30

Table 2.18. Engineering properties requirement for Type B fill material ...................... 31

xxiii

Table 3.1. SPT values of the biosolids at selected borehole location ............................. 47

Table 3.2. Summary of field vane shear test results ....................................................... 48

Table 3.3. Summary of dynamic cone penetrometer test results .................................... 50

Table 5.1. Summary of Unconsolidated Undrained triaxial test results of untreated

biosolids .......................................................................................................... 71

Table 5.2. Falling head permeability of untreated biosolids ........................................... 78

Table 5.3. Summary of geotechnical characteristics of untreated biosolids ................... 79

Table 6.1. Secondary consolidation (creep) values for biosolids stabilised with lime. .. 93

Table 6.2. Summary of geotechnical characteristics of biosolids stabilised with 1% lime

......................................................................................................................... 95


......................................................................................................................... 96


......................................................................................................................... 97

Table 6.5. Secondary consolidation (creep) values for biosolids stabilised with cement.

....................................................................................................................... 111

Table 6.6. Summary of geotechnical characteristics of biosolids stabilised with 1%

cement ........................................................................................................... 114


cement ........................................................................................................... 115


cement ........................................................................................................... 116

Table 6.9. Consolidation (creep) values for the biosolids stabilised with bauxsol. ...... 129


bauxsol .......................................................................................................... 132


bauxsol .......................................................................................................... 133


bauxsol .......................................................................................................... 134


fly ash ............................................................................................................ 143


fly ash ............................................................................................................ 144

xxiv


fly ash ............................................................................................................ 145

Table 7.1.Summary of finite element model parameters for basalt and engineered fill.

....................................................................................................................... 163

Table 7.2. Material properties of biosolids stabilised with 5% lime. ............................ 165

Table 7.3. Summary of total and residual settlement of embankments using biosolids

stabilised with 5% lime. ................................................................................ 168

Table 7.4. Material properties of biosolids stabilised with 3% and 5%cement. ........... 170





Table 7.7. Material properties of biosolids stabilised with 3% and 5% bauxsol. ......... 177





Table 7.10. Material properties of untreated biosolids. ................................................ 184

Table 7.11. Summary of residual settlement, total settlement and unit weight of

biosolids. ....................................................................................................... 187

Table 8.1. Settlements and residual thickness of the biosolids layer after the primary,

secondary and creep consolidation. .............................................................. 190

Table 8.2. Assumed residual thickness of the biosolids layer for biodegradation

settlement computation. ................................................................................ 191

Table 8.3. Assigned biosolids parameters for biodegradation settlement analysis. ...... 192

Table 8.4. pH and electrical conductivity test results of untreated biosolids. ............... 194

Table 8.5. pH and electrical conductivity test results of biosolids stabilised with lime.

....................................................................................................................... 194

Table 8.6. pH and electrical conductivity test results of biosolids stabilised with cement.

....................................................................................................................... 195

Table 8.7. pH and electrical conductivity test results of biosolids stabilised with

bauxsol. ......................................................................................................... 195

Table 8.8. pH and electrical conductivity test results of biosolids stabilised with fly-ash.

....................................................................................................................... 196

xxv

Table 8.9. Soil corrosivity classification. ...................................................................... 197

Table 8.10. Soil corrosivity classification for biosolids based on conductivity values. 198

Table 8.11. Soil corrosivity classification for biosolids based on pH values. .............. 199

Table 8.12. Biodegradation settlement of 5m height embankment using untreated

biosolids. ....................................................................................................... 202

Table 8.13. Biodegradation settlement of 5m height embankment using stabilised




























xxvi













1

1 INTRODUCTION

1.1 Problem Statement

This research involves expertise in the areas of civil engineering and geotechnical

engineering. By the application of advanced soil mechanics concepts, it is aimed to

obtain geotechnical strength properties of aged biosolids (with and without the addition

of additives) at a major treatment plant in Victoria for the future design of biosolids for

stabilized fill applications.

Biosolids refers to dried sludge having the characteristics of a solid typically containing

50% to 70% by weight of oven dried solids. Sludge refers to solids-water mixture

pumped from wastewater treatment lagoons having the characteristics of a liquid or

slurry typically containing between 2% to 15% of oven dried solids.

Currently, the majority of biosolids in Victoria is treated through air-drying for three

years at which point the biosolids are available for beneficial use. It is estimated that the

annual production of biosolids in Victoria is approximately 67,000 dry tonnes per

annum. A large quantity of this is produced by various major treatment plants in

Victoria. There is believed to be significant stockpiles of aged biosolids (air-dried for

greater than 3 years) at various major treatment plants in Victoria that are suitable for

this research.

The short and long term geotechnical characteristics of biosolids with and without the

addition of additives were investigated in the field as well as in the laboratory. A

geotechnical finite element software will be used to study the deformation

characteristics of biosolids and to develop a geotechnical model of the biosolids

stabilized fill. The project will also develop a technical note or specification for the use

of biosolids as stabilized fill.

EPA Victoria has identified that biosolids should be investigated as a beneficial,

sustainable resource rather than as being treated as a waste material that requires

disposal. This study would be environmental and social benefit as it pertains to the

2

sustainable use of biosolids and provides for biosolids to be used for engineering

applications.

The determination of the engineering properties of aged biosolids will enable design

parameters were obtained for using the biosolids as an engineered stabilized fill

material. Finite element modelling of the biosolids deformation is a new area covered

by this research. A holistic approach was used for this applied research project which

encompasses laboratory testing, in-situ testing and finite element modelling of

biosolids.

1.2 Objectives and Scope

This research study provides a contribution to Environmental and Geotechnical

Engineering particularly with regards to the geotechnical characteristics of biosolids,

admixture stabilization of biosolids and utilization of biosolids in geotechnical

engineering applications. The objectives for this research study is outlined as follows:

• Characterization of physical, mechanical, strength, consolidation, hydraulic

conductivity of untreated and stabilised biosolids with admixtures.

• Utilization of disposed biosolids in highway embankment construction in order

to maximize its beneficial use and thus reduce the disposal problem.

• Finite element modelling of highway embankment and compare the

embankment design criteria with the finite element modelling results.

• Develop a model for the biodegradation of biosolids to determine the

biodegradation settlement of biosolids in embankments.

• Develop a technical guideline for road governing authority in Victoria,

Australia.

3

1.3 Research Approach

This research aim to determine the geotechnical characteristics of untreated and

stabilised biosolids with lime, cement, bauxsol and fly ash with various percentages and

also evaluate their suitability for use in embankment construction. To accomplish this

aims, bulk samples of biosolids were collected from the Western Treatment Plant

(WTP), Victoria, Australia and subjected to an extensive laboratory investigation.

First, a series of laboratory tests were performed on untreated biosolids to characterise

and also stabilised biosolids with the admixtures. Following the characterization of

biosolids , the experiments focused on the investigation of mechanical behaviour of the

mixture of biosolids stabilised with admixtures. The evaluation is accomplished by

performing various engineering property tests on stabilised biosolids with admixtures

with different mixture ratio. Lime, cement and bauxsol contents of 1%, 3% and 5%

were used for this investigation and also fly ash contents of 10%, 20% and 30% were

used for this investigation. The mixtures of higher contents of fly ash such as 10%, 20%

and 30% were also used in this research.

The total experimental program consisted of the following:

• Material Characteristics

o Moisture content

o Organic content

o Particle size distribution

o Atterberg limits

o Particle density

• Mechanical and Hydraulic Characteristics

o Compaction (moisture density relationship)

o Bearing

o Hydraulic conductivity

o Compressibility

o Shear strength

The results obtained from the laboratory investigations can be used for the finite

element analysis and stability assessment of embankment which is constructed by using

4

stabilised biosolids with admixtures. In order to examine suitable admixture and

biosolids mixture compositions and embankment geometries, slope stability analysis

and finite element modelling by using geotechnical engineering software Plaxis V8

were performed on embankment with different geometries.

1.4 Thesis Outline

The thesis has been divided into various chapters to highlight the various aspects of the

study:

Chapter 1 consists of an introduction into the entire research study in general and

highlights the problem statement, scope, objectives, methodology and organization of

the study.

Chapter 2 consists of literature review of the following: geotechnical characteristics of

untreated sludge and biosolids and also stabilised sludge and biosolids with admixtures,

finite element modelling with soft soils materials and biodegradation of biosolids.

Chapter 3 describes the field testing and sampling. This chapter describes the overview

of the waste water treatment plant and also biosolids stockpile area, geotechnical field

testings (standard penetration tests, dynamic cone penetration test and field vane shear

test). The bulk sampling of biosolids is also described in this chapter.

Chapter 4 introduce the experimental program followed in this study. The testing

materials, the testing methods and procedures are also discussed.

Chapter 5 discuss and summarizes the test results of all laboratory tests. They include

the biosolids characterization and mechanical properties, including compaction bearing,

hydraulic conductivity, shear strength and compressibility, of untreated biosolids. The

geotechnical characteristics of untreated were summarised and discussed in this chapter.

Chapter 6 discusses and summarizes the geotechnical characteristics of stabilised

biosolids with admixtures, such as lime, cement, bauxsol and fly-ash with various

5

percentages were compared in this chapter. The correlation of the geotechnical

characteristics is also presented in this chapter.

Chapter 7 address the application of the test results of this study to the design and

construction of embankment using stabilised biosolids with admixtures. The results of

finite element analysis from Plaxis V8 are presented. The settlement and slope stability

analyses are also presented in this chapter. The modelling results are also compared

with calculation with conventional settlement calculations.

Chapter 8 summaries the settlement due to the biodegradation process in the biosolids.

Biodegradation settlement was very sensitive with temperature, moisture content, and

pH of the biosolids mixture.

Chapter 9 concludes the findings of this research study.

6

2 LITERATURE REVIEW

2.1 Geotechnical Characteristics of Sludge and Biosolids

Geotechnical aspects of sewage sludge have been studied in recent years in various

countries. Similarly, a few studies investigating the geotechnical aspects of biosolids

have been published internationally. This could be due to varying treatment processes

for sewage sludge such as in the case of the United Kingdom and Hong Kong where

untreated sludge is disposed of directly in landfills and not treated to enable them to be

termed as biosolids.

Golders Associates (2006) reported that, clay-rich biosolids samples were collected

from the Eastern Treatment plant (ETP), Victoria. The clay rich biosolids samples were

collected from three different stockpiles in the ETP and the samples were used for

various type of geotechnical testing. Bulk sample were collected from the top, middle

and bottom of the each stockpile by digging test pits with excavators. The laboratory

results of these tests are discussed later in Section 4.2.

Golders Associates (2006) reported that the moisture content of many of the sample

recovered from the stockpiles in the Eastern Treatment Plant (ETP), Victoria were

above optimum moisture content. Golders Associates (2006) also reported on the

moisture content of biosolids stabilized with lime and cement. Table 2.1 presents the

average, optimum moisture content and the maximum dry density of the cement treated

biosolids samples. The moisture content of the sample close to the optimum moisture

content was denoted as dry biosolids material. The moisture content of the sample

higher than the optimum moisture content was denoted as medium and wet biosolids

materials respectively.

Golders Associates (2006) reported that the addition of lime is most effective where the

moisture content is close to optimum moisture content (dry biosolids material). The

difference between average and optimum moisture content of dry sample is 12.5% for

0% lime addition and the moisture content reduces to 8.7% for 5% lime addition. The

addition of lime to wet biosolids material was reported to be less effective in reducing

7

the moisture content. The difference between average and optimum moisture content of

wet sample is 21.8% for 0% lime addition and 19.0% for 5% lime addition.

Table 2.1. Summary of moisture content testing of biosolids treated with lime in Victoria, (Golders Associates, 2006).

Relative MC Dry Medium Wet

Lime Added 0% 3% 5% 0% 3% 5% 0% 3% 5%

Avg MC (%) 41.5 39.4 37.7 39.0 37.5 36.2 54.8 54.4 52.0

MDD (t/m3) 1.37 1.32 1.28 1.38 1.34 1.32 1.19 1.15 1.14

OMC (%) 29.0 27.0 31.0 25.5 21.5 23.0 33.0 33.0 32.0

Avg OMC (%) 12.5 10.4 8.7 13.5 12.0 10.7 21.8 21.4 19.0

Golders Associates (2006) reported that the unconfined compressive strength (UCS) of

the modified biosolids increases with the percentage of the cement. Table 2.2 represents

the unconfined compressive strength of the trial embankment material in stockpile 23 at

ETP. The unconfined compressive strength of the reference trial embankment material

was obtained 50kPa. The UCS of the sample with 3% of cement, increased from

150kPa after two days of curing to 240kPa after 14 days of curing. Between the same

numbers of curing days, the UCS of the sample with 5% of cement rose from 200 kPa

to 270kPa.

Table 2.2. Summary of average UCS test results on cement treated biosolids in stockpile 23 in Victoria, (Golders Associates, 2006).

Days Cured Samples 0% Cement 3% Cement 5% Cement

0 9 50 kPa - -

2 6 - 150 kPa 200 kPa

7 6 - 220 kPa 260 kPa

14 6 - 240 kPa 270 kPa

Table 2.3 represents the unconfined compressive strength (UCS) of the trial

embankment material in stockpile 7 and 14 at the ETP. 100kPa of UCS was obtained

for the reference trial embankment material. The UCS after two days of curing, was 90

kPa for 1% of cement addition and to 110 kPa for 5% of cement addition. The UCS

8

after fourteen days of curing, increased to 110 kPa for 1% of cement addition and to 210

kPa respectively for 5% of cement addition.

Table 2.3. Summary of average UCS test results on cement treated biosolids in stockpile 7 and 14 in Victoria, (Golders Associates, 2006).

Days Cured Samples 0% Cement 1% Cement 3% Cement 5% Cement

0 2 100 kPa - - -

2 6 - 90 kPa 80 kPa 110 kPa

7 6 - 100 kPa 150 kPa 170 kPa

14 6 - 110 kPa 140 kPa 210 kPa

Chu et al. (2005) has reported on the consolidation properties of cement-treated sewage

sludge in the Republic of Singapore with the use of prefabricated vertical drains. Chu et

al. (2005) and Goi (2004) have reported on the geotechnical properties of sewage sludge

in Singapore and proposed the option of using cement-treated sewage sludge as a fill

material for land reclamation activities in Singapore. Pore pressure dissipation of the

sewage sludge was measured during the consolidation process in a large-consolidometer

to enable than to study the consolidation behaviour of prefabricated vertical drain.

Ordinary Portland cement and hydrated lime were used as binder materials for the

consolidation test that lasted 550 hours. The Asaoka (1978) and Hyperbolic methods

(Tan 1995, 1996) were used to determine the ultimate settlement and degree of

consolidation of the cement-treated sludge in Singapore.

Lo et al. (2002) reported on the geotechnical characterisation of dewatered sewage

sludge generated from the Stonecutters Island treatment plant in Hong Kong.

Compaction tests carried out indicated that the dewatered sewage sludge exhibits

compaction characteristics similar to that of clayey soils. The practice in Hong Kong is

noted to be similar to the United Kingdom in that raw untreated sewage sludge is

disposed into landfills. Lo et al. (2002) also confirms on the findings of Klein and

Sarsby (2000) that sludge once placed in landfills can be considered as geotechnical

material similar to non-consolidated cohesive material with high organic contents. In

addition to consolidation and compaction tests, direct shear tests were also carried out

on the sludge mixtures.

9

Kelly (2004, 2005, 2006) reported on the various geotechnical characteristics of sludge

at the Tullamore wastewater treatment plant in the United Kingdom in terms of their

strength, compaction, compressibility and other geotechnical properties. Kelly (2004)

reported that in the United Kingdom, the sewage sludge is eventually disposed in

landfills (sludge-to-landfill) which is different from the typical requirement of 3 year

air-drying and subsequent stockpiling of biosolids in Australia. Kelly (2004) stated that

sludge material in various treatment plants can have different engineering properties due

to different input levels of domestic and industrial wastewater. Kelly (2006) reported on

consolidation tests conducted on liquid sludge and compacted sludge with oedometers

and Rowe hydraulic consolidation cells. Lab vane shear tests were used to obtain the

undrained shear strength of the sludge. Klein (1995) has also reported on the

geotechnical characteristics of lagoon sewage sludge in the United Kingdom.

Lim et al. (2002) have reported in Korea, the unconfined compressive strength of the

waterworks and wastewater sludge with lime, fly ash and loess in various mixing

proportion, by the unconfined compression test.

Table 2.4 represents the unconfined compressive strength for each modified mixture, it

clearly states that the unconfined compressive strength of modified wastewater sludge

mixture increases as the amount of lime and fly ash increases. Similarly, the unconfined

compressive strength of the modified sludge increase with the curing time. Further, the

unconfined compressive strength of the construction materials in Korea is 100 kPa

achieved by adding lime and fly ash in specific ratio (by weight).

Vajirkar (2000) reported on the strength characteristics of biosolids when mixed with

municipal solid waste based on cone penetration tests carried out in Florida, USA whilst

Kocar et al. (2003) has reported on the use of fly ash as an additive in the stabilisation

of biosolids and sludge in Turkey.

10

Table 2.4. Unconfined compressive strength (kPa) for each modified mixture in Korea, (Lim et al., 2002).

Sludge Lime (%) Ash (%) Loess (%) 0 Day 7 Days 28 Days

Waterworks 0 0 0 9.8 25.3 41.3

5 0 0 17.1 56.0 99.4

10 0 0 20.9 74.0 123.9

15 0 0 26.7 79.5 155.7

0 0 10 4.0 40.0 62.0

0 0 20 5.0 55.0 90.0

0 0 50 10.0 101.0 112.0

0 0 100 28.0 105.0 118.0

10 0 20 22.0 79.0 91.0

10 0 50 28.0 100.0 113.0

10 0 100 32.0 117.0 127.0

Wastewater 0 0 0 8.4 9.3 18.0

10 50 0 5.9 98.3 161.0

2.2 Laboratory Testing of Biosolids and Sludge

The determination of the geotechnical parameters is required to calculate the bearing

capacity, slope stability, earth pressure and settlement of the structures. Laboratory tests

will help to find these geotechnical parameters.

2.2.1. Classification Test

Golders Associates (2006) has presented the moisture content, organic matter and total

organic content of the clay rich biosolids sample in three different locations such as top,

middle and base of the stock pile from the Eastern Treatment Plant (ETP), Victoria.

Generally the moisture content in the middle of the stockpile had higher value than top

and base of the stockpile. The organic matter and the total organic content in the base

were found to be higher than that at the other parts of the stockpile.

11

Golders Associates (2006) further reported the geotechnical properties of the clay rich

biosolids based on laboratory testing and this is summarised in Table 2.5. The sludge in

ETP had 25.9% of average value of moisture content for test pits sample and 29.7% for

the composites sample. Also it had 64 %, 25% and 40% of liquid limit, plastic limit and

plastic index respectively. The maximum dry density has the lowest standard deviation

and liquid limit and the plasticity index have higher standard deviation among the

geotechnical properties from the number tests which they used to find these properties.

Kelly (2006) has reported the index and physical properties of slurry direct from the

wastewater plant in United Kingdom. He indicated a liquid limit of 315 %, plastic limit

of 55%, specific gravity of solid of 1.55 (measured using pyknometer method) as

tabulated in Table 2.6 along with other properties.

12

Table 2.5. Statistical summary of geotechnical tests in Victoria, (Golders Associates, 2006).

Test Samples Average Std Dev Max. Min.

Organic Content (%) - test pits 264 7.8 4.1 29.9 0.9

Moisture Content test

Moisture Content (%) - test pits 264 25.9 8.5 44.8 5.8

Moisture Content (%) - composites 28 29.7 10.0 46.1 6.0

Atterberg Limit and Linear Shrinkage Test

Liquid Limit (%) 23 64 13 78 23

Plastic Limit (%) 23 25 8 38 11

Plasticity Index (%) 23 40 10 54 12

Linear Shrinkage (%) 23 14.8 2.9 17.0 3.5

PSD Test

% Gravel 28 3 2 7 0

% Sand 28 48 9 78 33

% Fines (< 75micron) 28 49 9 66 19

Compaction Test

MDD1 (t/m3) 28 1.35 0.16 1.76 1.14

OMC2 (%) 28 29.98 8.33 43.00 15.00

CBR Test

CBR Swell3 (%) 28 3.23 1.27 5.50 1.50

CBR Value4 (%) 28 3.04 1.84 7.90 0.53

Notes : 1-MDD- Standard Maximum Dry Density, 2-OMC- Standard Optimum Moisture Content

3-CBR Swell After Applied at the end of Soak Period, 4-CBR Value at 95% MDD at OMC

13

Table 2.6. Some properties of slurry direct from wastewater plant in United Kingdom, (Kelly, 2006).

Properties of Sludge Value

Liquid Limit 315%

Plastic Limit 55%

Shrinkage Limit 10%

Plasticity Index 260%

Specific gravity of solids 1.55

Ignition loss 70%

Water content 720%

Void ratio 11

Bulk unit weight 10.2 kN/m3

Dry unit weight 1.3 kN/m3

pH 8.0

Stone et al. (1998) has stated physical properties of the sewage sludge in five different

locations in Trinidad. Liquid limit of the sewage sludge in the Trinidad was reported to

vary between 66% and 165% and saturated hydraulic conductivity of the four sewage

sludge varies between 0.11 to 0.56 cm/h. Other physical properties of the sewage

sludge in five various treatment plants in Trinidad are also tabulated in Table 2.7.

Table 2.7. Some properties of the tested sewage sludge in Trinidad (Stone et al., 1998).

Lo

catio

n o

f se

wag

e

slu

dg

e

So

urc

e o

f w

aste

wat

er

Organic matter

content (%)

Air

-dry

wat

er c

on

ten

t

/(%

,w/w

)

Air

-dry

bu

lk d

ensi

ty

/(M

g/m

3 )

So

lid c

on

ten

t / (

%)

Pla

stic

lim

it /(

%,w

/w)

Liq

uid

lim

it /(

%,w

/w)

Sat

ura

ted

hyd

rau

lic

con

du

ctiv

ity /(

cm/h

)

Oxi

dat

ion

met

ho

d

Lo

ss-o

n-

ign

itio

n

met

ho

d

Valencia Residential 30.9 67.2 40.3 0.41 71.3 117 165 16.6

San Fernando Residential 25.3 49.1 24.1 0.4 80.6 114 144 0.56

Trincity

Residential

and

Industrial

13 33.1 52.8 0.37 65.4 - 80 0.16

Arima Residential 21.4 41.7 28.9 0.54 77.6 101 104 0.13

Santa Cruz Residential 10.8 14.3 10.8 0.83 90.3 57 66 0.11

14

Valls et al. (2004) have reported physical, chemical and mechanical properties of the

dry sewage sludge from a sewage treatment plant in Spain. The sludge had been totally

dried for the grading, because of residual humidity of the sludge. Valls et al. (2004)

reported that, the granulometry of the dry sludge is similar to that of fine agglomerate

and also it was a very spongy material with a very low density in the order of 10 kN/m3.

The granulometry of the dry sludge is given in Figure 2.1. Valls et al. (2004) further

reported that, there were no clays in the dry sludge from the mineralogical

characterization of sludge by X-ray diffraction analysis.

Figure 2.1. Dry sludge granulometry curve in Spain, (Valls et al., 2004).

Lim et al.(2002) have reported the characteristics of the waterworks sludge in Korea,

shows relatively uniform but the characteristics of the wastewater treatment sludge

shows the seasonal variation. Further they have found both had high water content, up

to 450% for the waterworks sludge and 250% for the wastewater treatment sludge.

Also hydrated lime had a higher value (48.26) of uniformity coefficient (Cu) and

Coefficient of gradation (Cc) than fly ash (16.44). Table 2.8 describes the index

properties of the hydrated lime, fly ash and sludge from waterworks and wastewater in

Korea.

Lim et al. (2002) reported that the modified-wastewater sludge mixtures have better

engineering properties than the modified-waterworks sludge mixtures. They further

reported the all index properties of the modified waterworks and wastewater sludges

15

decreased with the increasing percentage of additives. Positive effect was encountered

on the plastic index (PI), except for 200% of fly ash by adding lime.

Table 2.8. Index properties of sludge and each modifier in Korea, (Lim et al., 2002).

Test Waterworks

sludge

Wastewater

sludge

Hydrated

lime Fly ash

Specific gravity 2.495 2.059 2.199 2.173

Water Content (%) 270.0 217.0 - -

Classification (UIUC) MH OH/Peat - -

Cu (uniformity coefficient) 8.45 9.34 48.26 16.44

Cc (coefficient of gradation) 0.68 1.18 2.75 0.63

Mean Size(µm) 119.4 123.7 232.4 111.0

Standard deviation 158.0 171.0 244.0 135.0

Coefficient of variation (%) 133.0 139.0 105.0 122.0

The index properties of the modified sludge mixtures in South Korea with the different

percentage of lime and fly ash are given in Table 2.9 from the Lim et al. (2002), where

LL, PL, PI, NP and SL refer as liquid limit, plastic limit, plastic index, non plastics

material and shrinkage limit respectively. The large dosage of fly ash can make

modified-sludge mixtures, as non-plastic materials.

16

Table 2.9. Index properties of modified sewage sludge in Korea, (Lim et al., 2002).

Sludge Lime (%) Fly ash (%) LL PL PI SL

Waterworks 0 0 262.7 132.0 130.7 -

5 0 257.6 113.9 143.7 -

15 0 199.3 109.8 89.5 -

Wastewater 0 0 233.3 182.2 51.1 39.6

10 0 193.5 180.0 13.5 43.3

10 50 140.5 129.8 10.7 46.5

10 100 120.0 115.0 5.0 46.5

10 200 88.0 NP NP NP

15 0 182.0 175.0 7.0 52.3

15 50 136.8 128.9 7.9 54.1

15 100 126.5 120.0 6.5 54.6

15 200 88.4 NP NP NP

The details of the experimental procedure used for the particle size distribution tests

(sieve and hydrometer analysis) is described in the Australian Standard for Soil

classification (AS 1289.3.6.1-1995 and AS 1289.3.6.2-1995).

2.2.2. Laboratory Vane Shear Test

The laboratory vane is a small scale device with a blade height of about 12.7mm and a

width of about 12.7mm.The small size of the laboratory vane makes the device

unsuitable for testing samples with fissuring or fabric, and therefore it is not very

frequently used. The laboratory vane test will be carried out according to British

Standards (BS 1377, 1990). Head (1994) has described the preparation of the sample,

type of testings and guide lines for the measurements of the experiment.

Kelly (2006) has reported the undrained shear strength properties of sludge decreases

with increasing water content. Undrained shear strength properties of the sewage sludge

can be determined by the laboratory vane apparatus and unconsolidated-undrained

17

triaxial compression test. The current knowledge of the geotechnical properties and in

particular the shear strength properties of sewage sludge and biosolids are limited.

2.2.3. Compaction Test

Laboratory compaction tests are intended to model the field process and to indicate the

most suitable moisture content for compaction (the 'optimum moisture content') at

which the maximum dry density will be achieved for a particular soil. The testing

procedure of standard compaction test is outlined in the Australian Standards (AS

1289.5.1.1-2003).

In the United Kingdom, Kelly (2004) has achieved the maximum dry density of 0.56

tonne/m3 and optimum moisture content of 85% (54% of solid contents) for the air dried

sludge material by the standard compaction test. Kelly (2004) has reported that bulk

density and dry density values are low but consistent with the low range of specific

gravity of solid values measured. Figure 2.2 illustrates the density variation with the

water content by compaction. The bulk density increase from 0.65 tonne/m3 for dry

sludge material, which compacted poorly, to 1.10 tonne/m3 for sludge material with

moisture content values above optimum moisture content.

Figure 2.2. Density-water content relationships for compaction in United Kingdom,

(Kelly, 2004).

18

Lim et al. (2002) in Korea has reported that, the optimum moisture content and the

maximum dry density of the sludge are 68.4% and 8.1kN/m3, the values of the optimum

water content decreases and also the value of dry density increase with the increasing of

mixing of lime and fly ash in percentage. Figure 2.3 illustrates the variation of the dry

density with the water content and the percentage of the lime and cement from Lim et

al. (2002).

Figure 2.3. Relationship between optimum moisture Contents (OMC) and dry density with addition of lime and fly ash in Korea, (Lim et al., 2002).

2.2.4. California Bearing Ratio Test (CBR Test)

Golders Associates (2006) has reported the CBR value of reference biosolids (0% of

modifier) and modified biosolids in the ETP, Victoria. The test was carried out on

samples compacted to about 95% maximum dry density at optimum moisture content.

Table 2.10 shows the CBR test results of stockpile 23 in ETP. The CBR values of

biosolids in stockpile 23 at ETP increase with the percentage of the cement addition

with the biosolids. The CBR values at 18 days of the modified biosolids rose from 5%

to 12 % for 3% of cement addition and from 14% to 15% for 5% cement addition

respectively.

19

Table 2.10. Summary of CBR tests results on trial embankment material in stockpile 23 in Victoria, (Golders Associates, 2006).

Sample Location Samples Trial Embankment Materials

% Gravel 9 0

% Sand 9 48 - 70

% Fines (<75microns) 9 30 - 52

Maximum Dry density (t/m3) 2 1.37

Optimum Moisture Content (%) 2 20.0 - 20.5

Percentage Organics (%) 2 12.3 - 13.5

CBR Value with Cement Added 0% 3% 5%

CBR @ 0 Days+ (%) 3 1.5 – 5.0 - -

CBR @ 18 Days (%) 4 - 5 - 12 14 - 16

CBR Swell After Soak (%) 7 1.43 - 3.2 0.62 - 1.41 0.05 - 0.19

Note: + Number of Days curing before 4 days soak

Table 2.11 represents the test results at stockpile 7 and 14. The CBR values of biosolids

in stockpile 7 and 14 at ETP was reported to increase with the percentage of the cement

addition with the biosolids. The CBR values at 14 days of the modified biosolids

increased from 5.5% to 6.5 % for 1% of cement addition with biosolids and from 19%

to 20 % for 5% cement addition respectively.

Lim et al. (2002) have reported the CBR, swelling and absorbed water content for the

modified waste water sludge mixture with lime and fly ash in Korea. Table 2.12 shows

the values of CBR, swelling and absorbed water content for the modified sludge in

Korea, the value of the CBR represents that an alternative method needs to be sought

for the use of construction materials due to its low CBR. But CBR value of modified

sludge increase with the percentage of the added modifier.

20

Table 2.11. Summary of CBR tests results on trial embankment material in stockpile 7 and 14 in Victoria, (Golders Associates, 2006).

Sample Location Samples Biosolids Materials

% Gravel 2 0

% Sand 2 51 - 53

% Fines (<75microns) 2 47 - 49

MDD1 (t/m3) 2 1.15

OMC2 (%) 2 42

Organics (%) 2 9.6 - 12.4

CBR4 Value 0% Cement 1% Cement 3% Cement 5% Cement

CBR @ 0 Days (%) 2 3.5 - - -

CBR @ 14 Days (%) 6 - 5.5 - 6.5 11.0 - 12 19 - 20

CBR Swell3 (%) 8 0.91 - 1.20 0.27 - 0.53 0.15 - 0.38 0.1 - 1.11

Notes : 1-MDD- Standard Maximum Dry Density, 2-OMC- Standard Optimum Moisture Content

3-CBR Swell After Applied at the end of Soak Period, 4-CBR Value at 95% MDD at OMC

Table 2.12. Results of CBR of modified wastewater sludge mixture in Korea, (Lim et al., 2002).

Lime (%) Fly ash (%) Absorbed water (%) Expansion (%) CBR (%)

0 0 3.70 1.37 2.74

10 50 6.45 2.39 3.49

10 100 9.33 2.31 4.52

10 200 10.0 2.30 5.13

California Bearing Ratio test will be carried to find the CBR value for the compacted

specimen and also the swelling index of the specimen. The method and the procedures

of California Bearing Ratio test are stated in the Australian Standard (AS1289.6.1.1-

1998).

21

2.2.5. Consolidation Test

Golders Associates (2006) has reported the consolidation parameters by conducting the

oedometer test on biosolids. Table 2.13 compares the primary consolidation properties

of the natural clay, untreated biosolids and the treated biosolids. The coefficient of

volume compressibility (mv) values inferred from the oedometer test results for both

treated and untreated biosolids indicate that the biosolids samples are slightly more

compressible than the natural clay under the applied loads. The mv values for biosolids

with high moisture content indicate that they are more compressible than the cement

treated biosolids. Golders Associates (2006) further reported that, the biosolid samples

behave more typical of organic materials than typical clays, and also they mentioned it

not possible to distinguish the primary and secondary consolidation phases of the

biosolids.

Table 2.13. Comparison of coefficient of volume compressibility (mv) from oedometer test in Victoria, (Golders Associates, 2006).

Soil Type

Natural

Clay

Soils

Untreated

Biosolids

Biosolids

High

MC1

Biosolids

+ 1%

Cement

Biosolids

+ 3%

cement

Biosolids

+ 5%

cement

Loading Stage Coefficient of Volume Compressibility - inferred mv (m2/year)

0 to 50 kPa

0.00018

-

0.00028

0.00029 -

0.00054

0.00002 -

0.00134

0.00036 -

0.00056

0.00027 -

0.00031

0.00016 -

0.00050

50 to 100 kPa 0.00004 0.00006 -

0.00008

0.00001 -

0.00056

0.00002 -

0.00020

0.00012 -

0.00017

0.00006 -

0.00007

100 to 150 kPa 0.00003 0.00005 -

0.0010

0.00001 -

0.00036

0.00014 -

0.00048 0.00008

0.00004 -

0.00008

Note : 1 - MC - Moisture Content

Table 2.14 compares the long term creep properties of the natural clay, untreated

biosolids and the treated biosolids. The secondary consolidation values (c∝) indicates

that the natural clay samples have c∝ values of 0.46% to 0.70% , which are less than the

values for the biosolids (0.60% to 2.05%). The c∝ values for biosolids with high

moisture content values are higher than those for normal biosolids. The cement

22

stabilised biosolids samples have generally lower c∝ values than both the natural clay

and untreated biosolids. The rate of secondary consolidation doest not appears to be

load dependent, which is accordance with pre-trial expectations.

Table 2.14. Comparison of secondary consolidation values (c∝) from oedometer test in Victoria, (Golders Associates, 2006).

Average c∝∝∝∝ (% Strain/Log Cycle Time) Load Stage (kPa)

0 - 50 50 - 100 100 - 150

Untreated Biosolids Composite 0.76 0.91 0.72

Untreated Biosolids Composite (High Moisture

Content) 2.05 1.68 1.11

Biosolids Composite + 1% Cement - 0.51 0.66

Biosolids Composite + 3% Cement 0.76 1.07 0.70

Biosolids Composite + 5% Cement 0.60 0.73 0.92

Natural Clay Sample 0.70 0.49 0.46

Rowe (1966) and Head (1975) have described the details of the Rowe Cell

consolidation apparatus and testing procedure. The Rowe cell has many advantages over

the traditional oedometer consolidation apparatus. The main features responsible for

these improvements are the hydraulic loading system, the control facilities and ability to

measure pore water pressure, and the capability of testing large diameter samples.

2.2.6. Hydraulic Conductivity Test

Lim et al. (2002) reported that the permeability of modified sludge in Korea varies

between 1× 10-8 cm/s to 1× 10-4 cm/s. Lim et al. (2002) identified the permeability of

the modified waterworks sludge was greater than that of the modified wastewater sludge

because of the large amount of added fly ash.

Figure 2.4 represents the relationship between permeability and void ratio of the

modified sludge. It states that, void ratio of the reference sludge (unmodified) has the

highest void ratio whilst sludge with 10% of lime and 20% of fly ash has the lowest

void ratio.

23

Figure 2.4. The relationship between permeability and void ratio of the sludge samples in Korea, (Lim et al., 2002).

2.2.7. Triaxial Test

Golders Associates (2006) has reported the friction angle, cohesion and undrained shear

strength of the treated biosolids sample in the Eastern Treatment Plant (ETP) estimated

from undrained triaxial compression testing. Table 2.15 represents the summary of

undrained triaxial compression testing on treated biosolids with 3% added lime and 3%

added cement in ETP, Victoria. The biosolids with 3% added lime and 3% added

cement achieved an average friction angle of 49° and a maximum friction angle of 75°

as well as an average cohesion of 29 kPa and a maximum cohesion of 32 kPa.

Table 2.15. Summary of triaxial undrained compression testing on treated biosolids in Victoria, (Golders Associates, 2006).

Parameter Average Standard Deviation Max Min

Friction angle, φ’ 49° 22° 75° 33°

Cohesion, c’ 29 kPa 3 kPa 32 kPa 27 kPa

Undrained shear strength, Su 208 kPa 23 kPa 230 kPa 185kPa

24

Kelly (2004) reported that the undrained shear strength of the sludge increases

exponentially with reducing water content. He reported that sludge which was wetter

than 180% of water content had negligible shear strength. Kelly (2005) has proposed

Equation 2.1 to find the solid content (SC) from the water content (WC) of the sludge

material.

( ) ( )%100/1

100

+=

WCSC Equation 2.1

The undrained triaxial compression test and the laboratory vane shear test provided

similar characteristics for the shear strength of the sludge. Figure 2.5 from Kelly (2005)

illustrates the behaviour of the undrained strength of the sludge with water content. The

effective angle of friction has been reported by Kelly (2004) to range between 32° and

37° for moderate and strong levels of sludge digestion, whilst the effective cohesion is

reported as zero.

Figure 2.5. Variation of undrained shear strength with water content in United Kingdom, (Kelly, 2005).

25

2.3 Biosolids Stabilisation

2.3.1. Stabilisation with Lime

Lim et al (2002) reported in Korea, that hydrated lime was used for the purpose of

sterilizing micro-organisms in sludge. Lim et al (2002) has determined the optimum

mixing ratio of lime by measuring the pH value of the sludge. Further it was reported

that high pH was obtained by modified waste water sludge mixing with 10% to 15% of

lime. Lim et al (2002) determined that the optimum mixing ratios of lime was 15% for

the waterworks-sludge and 10% for the wastewater-sludge respectively. Table 2.16

illustrates clearly the pH values with curing time for two different sludges with the

different percentage of lime as mentioned by Lim et al. (2002).

Table 2.16 pH values of modified sludge with curing time in Korea, (Lim et al., 2002).

Sludge Lime (%) Curing Time (min)

0 30 60 120 180 240

Waterworks 5 10.2 10.1 10.2 10.1 10.0 10.0

10 11.2 11.3 11.4 11.4 11.4 11.3

15 11.8 11.9 12.0 12.0 11.9 11.9

Wastewater 8 12.1 12.1 12.0 11.8 11.7 11.6

10 12.4 12.4 12.3 12.2 12.1 12.0

15 12.5 12.5 12.4 12.2 12.1 12.0

Lim et al. (2002) also presented the microstructure of the original sludge and the

modified sludge mixtures with lime and fly ash. The micrographs of the sludge are

shown in Figure 2.6 (a) and (b). The black area represents the voids in the sludge and

indicates that the microstructure of the sludge is not dense.

Figure 2.7 (a), (b), (c) and (d) represents the modified sludge with lime and fly ash after

28 days of curing, it indicates that an increase of calcium compounds induced the

increase in strength of the modified-sludge mixtures.

26

Figure 2.6. Micrographs of original waterworks and wastewater sludge in Korea, (Lim et al.,2002).

Figure 2.7. Micrographs of modified sludge mixtures by lime and fly ash in Korea, (Lim et al., 2002).

27

2.3.2. Stabilisation with Cement

Valls et al. (2004) in Spain have reported on the compressive strength, flexural strength

and elastic modulus of concrete with added dry sludge which would be similar to the

behaviour of biosolids stabilized with cement. Figure 2.8 illustrates the compressive

strength according to sludge content for concrete with three different curing times. The

compressive strength decreased appreciably as the proportion of sludge increased with

the curing time. The flexural strength also decreased with the increase in the amount of

sludge in the different samples and increases with curing time, as illustrated in Figure

2.9.

Figure 2.8. Compressive strength according to sludge content for concrete with three different curing times in Spain, (Valls et al., 2004).

28

Figure 2.9. Flexural strength according to the sludge content with three different curing times in Spain, (Valls et al., 2004).

Valls et al. (2004) further reported that, the elastic modulus of the concrete with added

dry sludge decreased to 20000 MPa for specimens with 10 % of dry sludge content

compared with approximately 30000 MPa for the reference specimen with 0 % of dry

sludge. Figure 2.10 shows the variation of the elastics modulus of concrete with the

proposition of the added dry sludge.

Figure 2.10. Elastic modulus of concrete according to the sludge content after 90 days in Spain, (Valls et al., 2004).

29

2.4 Finite Element Analysis of Biosolids Embankment

From the various geotechnical parameters obtained, finite element models are proposed

to be developed with the Plaxis (2002) geotechnical finite element code to model the

behaviour of biosolids as engineered fill in embankments. Finite element modelling to

predict biosolids deformation and behaviour is an innovative modelling technique that

has not been previously reported for biosolids either nationally or internationally and

this will be another innovative feature of this research. Finite element modelling will be

used to predict settlement and pore pressure dissipation of biosolids when subjected to

fill loads.

The finite element modelling technique used for soft soils will be used to model the

biosolids, since soft soils and biosolids are similar from a geotechnical perspective.

Finite element modelling of soft soils has been investigated by various authors

including Arulrajah (2004) and Lin et al. (2000). These modelling techniques will be

revisited and modified when developing a geotechnical finite element model for

biosolids.

Karstunen et al. (2006) reported the numerical and finite element modelling of an

embankment on soft clay using five different models to analyse the behaviour of the

embankment on soft clay. Two of the models were isotropic elasto-plastic models whilst

the other three were plastic anisotropy. Three plastic anisotropy models were analysed

using the Plaxis geotechnical software.

Vajirkar (2000) reported on the slope stability analysis of a landfill in Florida, USA

with municipal solid waste only as well as municipal solid waste and biosolids using

SLOPE/W geotechnical software analysis. The minimum factor of safety for the landfill

batter slopes for was reported as 1.5 (Shafer, 2000).

30

2.5 Local Road Works Specifications for Engineered Fill

Fill material should be capable of being spread and compacted and should have

adequate shear strength and bearing capacity to carry traffic loads. The VicRoads

specifications for earthworks (VicRoads, 2006), defines three types of engineered fill

material: Type A, Type B and Type C. The scope of this project is to investigate the

usage of untreated and stabilised biosolids as a Type B fill material. Type C fill material

is a lesser quality material which does not meet the requirements of Type A and Type B.

2.5.1. Type A Material

Type A fill material should be spread and compacted in layers not exceeding a

compacted thickness of 200 mm. It should be a superior quality material and should be

free of topsoil, deleterious and /or perishable matter. The requirements for Type A fill

material as specified by VicRoads is presented in Table 2.17.

Table 2.17. Engineering properties requirement for Type A fill material

Engineering properties Unit VicRoads

Requirements

CBR (min) % 6

Swell (max) % 1.0 – 2.5

Permeability(max) m/s 5 x 10-7

Limits of Grading (% passing)

Post Compaction Sieve Size AS (mm)

75 mm % 100

4.75 mm % 40 – 80

0.075 mm % 10 - 40

Plasticity Index (PI) x percentage passing 0.425 mm Post

Compaction % 1000

Plasticity Index post compaction % 6 - 25

31

2.5.2. Type B Material

This project will investigate the usage of untreated and stabilised biosolids as a Type B

fill material. Type B fill material is a lesser quality material than fill material Type A.

Type B fill material shall have a minimum assigned CBR of 2 to 5 % and should be free

of topsoil, deleterious and /or perishable matter. The particle dimension is to be not

more than 150 mm within 400mm of subgrade level after compaction. The only

requirements for Type B fill material as specified by VicRoads are presented in Table

2.18.

Table 2.18. Engineering properties requirement for Type B fill material

Engineering properties Unit VicRoads Requirements

CBR (min) % > 2

Swell (max) % < 2.5

Permeability(max) m/s N/A

Limits of Grading (% passing)

Post Compaction Sieve Size AS

(mm)

75 mm % N/A

4.75 mm % N/A

0.075 mm % N/A

Maximum Particle Size (mm)

< 150 (within 400mm of the subgrade)

< 400 (depths greater than

400 mm below subgrade)

Plasticity Index (PI) x percentage passing

0.425 mm Post Compaction %

N/A

Plasticity Index post compaction % N/A

32

2.6 Conclusions: Literature Review

There were various research studies available on geotechnical characteristics of sludge

from United Kingdom, Singapore, Hong Kong, Korea and Trinidad. The geotechnical

properties of sludge varied from each other country, mainly based on the treatment

process and effluent process of waste-water.

Only a few research studies from Australia and USA were available on the geotechnical

properties of the biosolids. As water and solids content in biosolids are different from

the sludge, the geotechnical properties of the biosolids specially index geotechnical

properties shows a large variations from geotechnical properties of sludge. However

there are limited publications on finite element modelling and geotechnical analyses of

biosolid embankments worldwide.

This Literature Review chapter has been prepared based on laboratory testing and

research studies conducted on sludge and biosolids locally and around the world and

discuss the geotechnical characteristics of the sludge and the biosolids.

The stabilisation of sludge and biosolids by using additives such as lime, fly-ash and

cement are also discussed in this report together with the finite element modelling and

analysis conducted on sludge and soft soil in recent decades.

The major findings of this literature review include:

• Geotechnical sampling and testing of clay-rich biosolids has been carried out

previously at the Eastern Treatment Plant, Victoria.

• For the clay-rich biosolids at the Eastern Treatment Plant, stabilisation of the

biosolids was carried out with lime and cement.

• The geotechnical characteristics of the clay-rich biosolids at the Eastern

Treatment Plant have been reported by Golders Associates.

• There is limited information on the geotechnical characteristics of biosolids in

other countries.

33

• There is no information to date of the regarding the acceptability of biosolids

(without clay) as a geotechnical fill based on current literature available. Current

literature available internationally reports more on stabilised sewage sludge than

on biosolids.

• Geotechnical characteristics of sewage sludge stabilized with lime, cement and

fly-ash has been reported in various countries.

• The geotechnical characteristic of sewage sludge in Australia has not been

reported on previously.

34

3 SITE DESCRIPTION AND FIELD TESTING

3.1 Site Description

The Biosolids Stockpile Area is located at the Western Treatment Plant (WTP),

Werribee in Victoria, which is located approximately 50 km to the west of Melbourne

CBD. The Biosolids Stockpile Area is approximately 18 ha in size and was recently

constructed on a parcel of land in Melbourne Water’s Western Treatment Plant. The

biosolids stockpile area is located on a parcel of land in an area immediately north of the

existing Sludge Drying Pans (SDP) 1-16. The Biosolids Stockpile Area is bounded by

Tyquin’s Lane and 160 South Road in the North West corner. Following the

construction, approximately 150,000 m3 of biosolids were harvested from sixteen

existing Sludge Drying Pans and stockpiled in the Biosolids Stockpile Area.

A further 150,000 m3 of biosolids from an additional thirteen existing Sludge Drying

Pans is expected to be harvested in the near future. The Biosolids Stockpile Area was

constructed with provision for the stockpiling up to 7 rows of biosolid stockpiles in 5

meters high and separated by access roads. To date, 3 rows of stockpiles have been

constructed and the field sampling and testing were carried out on these stockpiles.

Figure 3.1 shows the location of the Western Treatment Plant in Werribee, Victoria

(Melways Map 205,12F).

35

Figure 3.1. Location of the Western Treatment Plant, Werribee, (Melways Map 205, 12F).

The Eastern and Western treatment plants are the main treatment plants in Victoria for

sewage treatment. The Eastern Treatment Plant treats sewage from about 1.5 million

people in Melbourne’s south-eastern and eastern suburbs. About 92% of the sewage that

flows into the Eastern Treatment Plant each year is from residential and commercial

sources, and the remaining 8% is from trade waste.

The Western Treatment Plant at Werribee is a significant public asset, with more than

100 years of history. Before the construction of Western Treatment Plant, Melbourne’s

sewage was collected in open channel and discharged into the Yarra River and Hobsons

Bay. In 1892 the newly established metropolitan works began buying land at Werribee

and developing the site. The first Melbourne homes were connected to the sewage

system in 1897 (Melbourne Water Corporation, 2000). The systematic diagram of the

production process of biosolids at the Western Treatment Plant is presented in Figure

3.2.

36

Figure 3.2. Systematic diagram of the production of biosolids at the Western Treatment Plant

The Western Treatment Plant continues to provide essential public health service,

treating approximately 456 million litres a day (Melbourne Water Corporation, 2006).

This serves about 1.6 million people in the central and northern and western suburbs.

The Western Treatment Plant is almost 11,000 hectares in area and is a world leader in

environmentally friendly sewage treatment. Sewage is now treated at the Western

Treatment Plant through the lagoon systems. Treated effluent is discharged under

licence or recycled to various on and off-site customers.

Figure 3.3 shows the aerial view of the Western Treatment Plant in Werribee, Victoria

(Melbourne Water Corporation, 2000). Figure 3.4 shows biosolids stockpiles at the

Western Treatment Plant in Werribee, Victoria.

Sludge

Water

Biogas

Raw Sewage 52% of Melbourne Sewage

Domestic Waste

Trade Waste

Enhanced Lagoon Treatment

Power Generation

Recycled Water Supply

Sludge

90% WaterSludge Drying PanBiosolids Stockpile

30% Water

Evaporation

37

Figure 3.3. Aerial view of Western Treatment Plant, Werribee, Victoria, (Melbourne Water Corporation, 2000)

Figure 3.4. Biosolids stockpiles at the Western Treatment Plant, Werribee, Victoria.

38

3.2 Field Testing

Swinburne University of Technology engaged Connell Wagner Pty Ltd to undertake the

geotechnical testing and sampling of biosolids. Field tests were carried out at the

Biosolid Stockpile Area at Melbourne Water’s Western Treatment Plant, Werribee. The

field investigation was carried out to determine the field geotechnical properties as well

as to obtain biosolid samples for laboratory testing. This report is based on the site

investigation works carried out in the Biosolids Stockpile Area at the Western

Treatment Plant.

The collection of biosolids samples from the field with the use of drilling rigs and bulk

samples as well as field testing with field vane shear tests, standard penetration tests and

dynamic cone penetrometer tests. The collected bulk and tube samples were

subsequently stored in the lab for the geotechnical laboratory investigation.

The scope of the field testing and sampling carried out in this phase was as follows;

• Sample collection with a geotechnical drilling rig.

o Twelve boreholes were carried out from the top of the biosolids stockpile

area for the full depth of the biosolids (estimated at 4-5 meters high).

o Four undisturbed samples were obtained with 100 mm diameter sample

tubes in each borehole (total of 48 nos.).

o All samples collected were appropriately labelled.

• Standard Penetration Test (SPT)

o Four SPT test were carried out at four borehole locations.

• Field vane shear tests (FVT)

o Twenty field vane shear tests were carried out at six borehole locations.

o Field vane shear tests were carried out at 1 m depth intervals.

• Dynamic Cone Penetrometer (DCP) tests

o Twelve DCP tests were carried out at locations just adjacent to the

boreholes to a depth of 1.6 m.

39

• Bulk sample collection

o Total of 2500 kg of biosolids was obtained from the biosolids stockpile

area.

o Bulk samples were collected in 130 bags which were sealed with rubber

bands to retain the natural moisture content of the biosolids in the field.

3.2.3. Borehole Sampling and Testing

The boreholes (BH) location for this investigation is presented in Figure 3.5. The

standard penetration tests, field vane shear tests and tube sampling were carried on the

boreholes.

Figure 3.5. Location of boreholes at the Biosolids Stockpile Area

Chadwick T&T Ltd was engaged by Connell Wagner to carry out the drilling of the

boreholes on the site. A wheel mounted Edson 100 drilling rig was used to carry out

augering of the boreholes. The Edson 100 drilling rig was considered suitable for the

investigation due to its small size and ability to dry auger. Dry augering works were

preferred in order to get actual field moisture of biosolids at stockpile. All works were

carried out under the full-time supervision of Connell Wagner. Research engineers from

40

Swinburne University were present throughout the works. Each borehole was drilled to

approximately 4.0 m to 5.2 m depth. Figure 3.6 shows augering at a borehole location.

Figure 3.6. Augering for biosolid samples at a borehole location

Sample tubes of 100 mm diameter samples were collected at 1 m interval for each

borehole. Both ends of the sample tubes were filled with wax to retain the in-situ

moisture content. Figure 3.7 shows a sample tube collected during borehole drilling

operation at the Biosolids Stockpile Area.

Standard penetration tests were undertaken at four borehole locations at the Biosolids

Stockpile Area. Figure 3.8 shows the standard penetration test being carried out at a

borehole location. The Geotechnique Geovane with the dimensions of 19 mm in width

41

and 30 mm in height was used in the investigation. Figure 3.9 shows the field vane

shear test being carried out at a borehole location.

Figure 3.7. Sample tube retrieved from a biosolids stockpile.

42

Figure 3.8. Standard penetration test (SPT) at a borehole location

Figure 3.9. Field vane shear tests (FVT) at a borehole location

43

3.2.3. Dynamic Cone Penetration Test

In total, twelve numbers of Dynamic Cone Penetrometer (DCP) tests were carried out at

locations just adjacent to each borehole at top of stockpile area. The dynamic cone

penetration test which was conducted on the biosolids stockpile is shown in Figure 3.10.

Figure 3.10. Dynamic cone penetration (DCP) tests at a field test location

3.2.3. Bulk Sampling

Bulk samples that totalled approximately 2500 kilograms of biosolids in total (130

bags) were collected from the Biosolids Stockpile Area. The samples were sent to the

Geotechnical Laboratory at Swinburne University of Technology for future laboratory

testing. The approximate location of the bulk sampling is indicated in Figure 3.11.

Bulk samples were collected in polythene bags and the bags were tightened with rubber

bands to maintain the in-situ moisture content. Figure 3.12 shows the collection of

biosolids bulk samples while Figure 3.13 shows the bulk sampling bags with biosolids.

44

Figure 3.11. Locations of bulk sampling in stockpiles

45

Figure 3.12. Collection of biosolid bulk samples

Figure 3.13. Bulk sampling bags

46

3.3 Assessment and Discussion of Field Testing

The approximate height of the biosolids in the stockpiles varied between 5.0 m to 5.2 m.

Generally the material encountered in the twelve boreholes can be classified as being

firm to very stiff.

3.3.1. Standard Penetration Test Results

The standard penetration test (SPT) was used to determine the resistance of biosolids to

the penetration of a sampler, and to obtain disturbed samples of the biosolids for

identification purposes. The SPT test was performed by driving a standard spilt spoon

sampler into the stockpile by blows from a drop hammer of mass 64 kg falling 760 mm.

The number of blows (N) recorded for a depth of 300 mm (the initial 150 mm is

ignored) is called the standard penetration value. From the standard penetration value,

the allowable bearing capacity of the biosolids was determined.

Table 3.1 summarises the geotechnical engineering parameters for various depths at

four different borehole locations based on the field investigation and SPT tests results.

The firm layer of the biosolids (4< SPT <8) was encountered in BH3, BH5 and BH11 at

depths ranging from 1.5 m to 3.0 m. The very stiff layer of the biosolids (16< SPT <30)

was encountered in BH7 at depth of 4.0 m.

The allowable bearing capacity of the biosolids was found to vary between 70 to 80 kPa

at a depth of 1.5 m to 3.0 m in BH3, BH5 and BH11. The allowable bearing capacity of

the biosolids in BH7 was found to be 230 kPa at depth of 4.0 m.

47

Table 3.1. SPT values of the biosolids at selected borehole location

Borehole

Stockpile

No. Depth

(m) Material

SPT

“N”

(blows)

Allowable

Bearing

Capacity

(kPa)

Consistency

BH3 1 1.5 Biosolids 7 70 Firm


BH7 2 4.0 Biosolids 23 230 Very Stiff


3.3.2. Field Vane Shear Test Results

The field vane shear test was used to determine the shear strength of biosolids in the

field. This was done by measuring the torque required to cause a vane blade to shear the

biosolids at various depths. The vane shear device consists of four thin metal blades

welded orthogonally (90 degree) to a rod. The vane is pushed to the desired depth and a

torque is applied at a constant rate (approximately 6 degree per minute) by a torque head

device. Rotation is continued until the material is sheared and a maximum torque value

has been reached. From the test results, the undrained shear strength, sensitivity and

consistency of the biosolids was determined. The term sensitivity is defined as the ratio

between peak and residual shear strength

Table 3.2 summaries the field vane shear peak and residual strengths and the

consistency of the biosolids. The field vane shear tests results indicate that the

undrained shear strength of biosolids generally increases with the depth of stockpile.

Consistency of the biosolids can be classified as very stiff to hard. The sensitivity of the

biosolids was found to vary between 2.3 to 6.8.

48

Table 3.2. Summary of field vane shear test results

Borehole

No.

Stockpile

No.

Depth

Peak

Shear

strength

(kN/m2)

Residual

Shear

strength

(kN/m2)

Sensitivity Consistency

BH2 1 1.0m 190 - - Very Stiff

2.0m 113 49 2.31 Very Stiff

3.0m 224 - - Hard

4.0m 222 76 2.92 Hard

BH4 1 1.1m 174 33 5.27 Very Stiff

2.1m 206 48 4.29 Hard

3.1m 157 49 3.20 Very Stiff

4.1m 222 54 4.11 Hard

BH6 2 1.0m 49 21 2.33 Firm

2.0m 143 21 6.80 Very Stiff

3.0m 209 48 4.35 Hard

4.0m 97 30 3.23 Stiff

BH8 2 1.0m 127 29 4.38 Very Stiff

2.0m 190 36 5.27 Very Stiff

3.0m 193 51 3.78 Very Stiff

4.0m 141 35 4.02 Very Stiff

BH10 3 1.0m 78 17 4.59 Stiff

2.0m 209 48 4.35 Hard

3.0m 224 65 3.44 Hard

4.0m 128 33 3.88 Very Stiff

BH12 3 1.0m 49 17 2.88 Firm

2.0m 89 22 4.04 Firm

3.0m 151 36 4.19 Very Stiff

4.0m 222 63 3.52 Hard

49

3.3.3. Dynamic Cone Penetrometer Test Results

The dynamic cone penetrometer (DCP) is an instrument designed to determine the

penetration resistance of a soil to the penetration of a steel cone (30 degree angle and 20

mm diameter) driven with a 9 kg mass dropped a height of 510 mm (Figure 3.14). The

number of blows per graduation interval (100 mm) is counted and this is defined as the

DCP value or the penetration resistance. DCP values were used to determine the in-situ

California bearing ratio (CBR) and allowable bearing capacity of the biosolids.

Dynamic cone penetrometer tests results are summarised in Table 3.3.

Figure 3.14. Layout diagram of dynamic cone penetrometer (Australian Standards, AS1289).

The table indicates the approximate California Bearing Ratio (CBR) and allowable

bearing capacity values based on the DCP blows counts. The DCP test results obtained

from stockpiles 1 and 2 indicate that the biosolids is firm to very stiff at depths from 0

to 0.5 m. Below the depth of 0.5 m, the biosolids are found to be stiff to hard. The DCP

test results obtained from Stockpile 3 indicate that the biosolids is firm to stiff at depths

50

from 0 to 0.5 m. Below the depth of 0.5 m, the biosolids are found to be stiff to very

stiff.

Table 3.3. Summary of dynamic cone penetrometer test results

Stockpile

No.

DCP

No.

Depth

(m) CBR

Allowable

Bearing

Capacity

(kN/m2)

Consistency

1 DCP1 0.0 – 0.5 2 – 9 46 – 183 Firm – Very Stiff 0.5 – 0.9 14 – 17 275 – 320 Very Stiff – Hard 0.9 – 1.6 17 – 25 320 – 458 Hard

DCP2 0.0 – 0.5 2 – 9 46 – 183 Firm – Very Stiff 0.5 – 0.9 14 – 17 275 – 320 Very Stiff – Hard 0.9 – 1.6 14 – 17 275 – 320 Very Stiff – Hard

DCP 3 0.0 – 0.5 2 – 6 46 – 137 Firm –Stiff 0.5 – 0.9 6 – 14 137 – 275 Stiff – Very Stiff 0.9 – 1.6 14 – 17 275 – 320 Very Stiff – Hard

DCP 4 0.0 – 0.5 2 – 11 46 – 229 Firm – Very Stiff 0.5 – 0.9 6 – 17 137 – 320 Stiff – Hard 0.9 – 1.6 9 – 17 183 – 458 Very Stiff – Hard

2 DCP 5 0.0 – 0.5 2 – 11 46 – 229 Firm – Very Stiff 0.5 – 0.9 6 – 9 137 – 183 Stiff – Very Stiff 0.9 – 1.6 9 – 17 183 – 320 Very Stiff – Hard

DCP 6 0.0 – 0.5 2 – 9 46 – 183 Firm – Very Stiff 0.5 – 0.9 9 183 Very Stiff 0.9 – 1.6 9 – 17 183 – 320 Very Stiff – Hard

DCP 7 0.0 – 0.5 2 – 9 46 – 183 Firm – Very Stiff 0.5 – 0.9 6 – 11 137 – 229 Stiff – Very Stiff 0.9 – 1.6 6 – 11 137 – 229 Stiff – Very Stiff

DCP 8 0.0 – 0.5 2 – 9 46 – 183 Firm – Very Stiff 0.5 – 0.9 6 – 11 137 – 229 Stiff – Very Stiff 0.9 – 1.6 11 – 17 229 – 320 Very Stiff – Hard

3 DCP 9 0.0 – 0.5 2 – 4 46 – 92 Firm – Stiff 0.5 – 0.9 2 – 4 46 – 92 Stiff – Stiff 0.9 – 1.6 2 – 11 46 – 229 Firm – Very Stiff

DCP

10

0.0 – 0.5 2 – 4 46 – 92 Firm – Stiff 0.5 – 0.9 4 – 6 92 – 137 Stiff 0.9 – 1.6 4 – 11 92 – 229 Stiff – Very Stiff

DCP

11

0.0 – 0.5 2 – 9 46 – 183 Firm – Very Stiff 0.5 – 0.9 6 – 9 137 – 183 Stiff – Very Stiff 0.9 – 1.6 6 – 11 137 – 229 Stiff – Very Stiff

DCP

12

0.0 – 0.5 2 – 6 46 – 137 Firm – Stiff 0.5 – 0.9 4 – 11 92 – 183 Stiff – Very Stiff 0.9 – 1.6 9 – 19 183 – 366 Very Stiff – Hard

51

3.4 Conclusions: Field Works

This chapter is based on field testing and sampling works which were undertaken by

Connell Wagner for Swinburne University at the Western Treatment Plant in Werribee.

This phase describes the collection of biosolids with 100 mm diameter tube samples

from the field with the use of drilling rigs as well as bulk sample collection. This

chapter also presents the field testing results and presents the results obtained from field

vane shear tests, standard penetration tests and dynamic cone penetrometer tests. The

height of the three biosolid stockpiles at the site ranges between 5.0 m to 5.2 m.

The standard penetration test (SPT) results indicated that the estimated allowable

bearing capacity of the biosolids in the stockpiles was found to vary between 70 to 80

kPa at a depth of 1.5 m to 3.0 m in boreholes BH3 (Stockpile 1), BH5 (Stockpile 2) and

BH11 (Stockpile 3). The allowable bearing capacity of the biosolids in borehole BH7

(Stockpile 2) at depth of 4.0 m was found to be 230 kPa. The standard penetration test

results indicate that the consistency of the biosolids in all the stockpiles is firm to very

stiff.

The field vane shear test results indicate that the consistency of the biosolids is very stiff

to hard. The undrained shear strength of biosolids was found to generally increase with

the depth.

In general, the estimated California Bearing Ratio (CBR) values from dynamic cone

penetrometer tests increases with the depth of the biosolids stockpile. The CBR results

indicate that the consistency of the biosolids in the stockpiles is firm to hard.

It is noted that the various field testing methods consistently indicate that the biosolids

at the stockpiles are firm to hard. The slight variability between the various field testing

methods is expected due to the various assumptions and empirical equations used in

each test methods.

The next chapter of this project is the laboratory testing phase which will accurately

confirm the geotechnical engineering characteristics of the untreated biosolids as well as

determine the engineering characteristics of biosolids when treated with additives.

52

4 LABORATORY EXPERIMENTAL PROGRAM

4.1 Overview

This chapter introduces the laboratory experimental program followed in the present

study. The main objective of this program is to evaluate the geotechnical engineering

characteristics of untreated and stabilised biosolids with various admixtures. The

experimental program is designed to first characterize the untreated biosolids sampled

from the Western Treatment Plant in Victoria, Australia and then investigate various

mechanical properties of untreated and also the stabilised biosolids with various

admixtures. The colour and physical appearance of the biosolids used in this research is

shown in Figure 4.1.

Figure 4.1. The colour and physical appearance of biosolids

For the material characterization, untreated biosolids and stabilised biosolids with

admixtures are subjected to a series of characterization tests, consisting of moisture

content, organic content, particle density, particle size distribution and Atterberg limits

tests. Extensive geotechnical engineering characteristics tests, including compaction,

hydraulic conductivity, shear strength, compressibility and bearing, are then performed

on untreated and also stabilised biosolids with various admixtures for the evaluation of

their Mechanical behaviours.

53

In this chapter, a detailed description of the testing material, specification for the

existing fill material, the testing methods and the procedures is presented.

4.2 Stabilizing Admixtures

Various percentages of admixtures being lime, cement, bauxsol and fly ash were added

by weight to the biosolids to improve the biosolids physical and strength properties.

4.2.1. Lime

1%, 3% and 5% of lime were used to stabilise the biosolids in this project. Hydrated

lime was used in this project which is principally calcium hydroxide (85-95%). It is a

strong alkali, derived from limestone by expelling carbon dioxide and hydrating the

resulting quicklime with water. This material is then stabilised by a mechanical

separation process to remove impurities. The resulting clean white powder (hydrated

lime) is used in a large numbers of industrial, agricultural and construction applications

(National Lime Association, 2007).

Lime can be used for chemically transforming unstable soils into structurally sound

construction foundations. Lime is particularly important in road construction for

modifying and improving the engineering properties of subgrade soils, subbase

materials, and base materials to improve engineering characteristics of biosolids

(Austroads, 1998).

Lime stabilization creates a number of important engineering properties in soil,

including improved strength, improved resistance to fracture, fatigue, permanent

deformation, improved resilient properties, reduced swelling and resistance to the

damaging effects of moisture (Little, 1999). The colour and physical appearance of the

lime used in this research is shown in Figure 4.2.

54

Figure 4.2. The colour and physical appearance of lime

4.2.2. Cement

1%, 3% and 5% of cement were used to stabilise the biosolids in this project. Portland

cement is composed of calcium-silicates and calcium-aluminates that, when combined

with water, hydrate to form the cementing compounds of calcium-silicate-hydrate and

calcium-aluminate-hydrate, as well as excess calcium hydroxide.

Because of the cementitious material, Portland cement may be used successfully in

stabilizing both granular and fine-grained soils, as well as aggregates (Herzog, 1963). A

pozzolanic reaction between the calcium hydroxide released during hydration and soil

alumina and soil silica occurs in fine-grained clay soils and is an important aspect of the

stabilization of these soils.

The permeability of cement stabilized material is greatly reduced as compared to

untreated material. The result is a moisture-resistant material that is highly durable and

resistant to leaching over the long term. Portland cement can be used either to improve

and modify the quality of soil or to transform the soil into a cemented mass, which

significantly increases its strength and durability (Austroads, 1998). The colour and

physical appearance of the cement used in this research is shown in Figure 4.3.

55

Figure 4.3. The colour and physical appearance of cement

4.2.3. Bauxsol

1%, 3% and 5% of Bauxsol were used to stabilise the biosolids in this project. Bauxsol

is an inert stabilised by-product of the aluminium industry and is a carefully modified

residue from alumina refineries, also known as red mud.

The first application of this product was to treat contaminated acid mine water to

convert it to drinking water standards or better. Subsequently it was experimentally

added to soil for agricultural and construction purposes (Maddocks et al., 2004). Figure

4.4 illustrates the process to attain the uniform consistency of bauxsol material for

several applications.

56

Figure 4.4. Process to get a uniform consistency of bauxsol, (Department of Environmental Protection, 2008)

Bauxsol typically is a dark reddish colour, and the contrast of the colour is usually

varying for each alumina refineries. The colour and physical appearance of the bauxsol

used in this research is shown in Figure 4.5.

Figure 4.5. The colour and physical appearance of bauxsol

57

4.2.4. Fly ash

10%, 20% and 30% of fly ash were used to stabilise the biosolids in this project. Fly ash

is the finely divided residue that results from the combustion of pulverized coal and is

transported from the combustion chamber by exhaust gases. Currently, over 20 million

metric tons (22 million tons) of fly ash are used annually in a variety of engineering

applications (American Coal Ash Association, 2003).

The consistency and abundance of fly ash in many areas present unique opportunities

for use in structural fills and other highway applications. Fly ash is typically finer than

portland cement and lime. Fly ash consists of silt-sized particles which are generally

spherical, typically ranging in size between 10 and 100 micron. Fineness is one of the

important properties contributing to the pozzolanic reactivity of fly ash (ACAA, 2003).

Fly ash can be tan to dark grey, depending on its chemical and mineral constituents. Tan

and light colours are typically associated with high lime content. A brownish colour is

typically associated with the iron content. A dark grey to black colour is typically

attributed to elevate unburned carbon content. Fly ash colour is usually very consistent

for each power plant and coal source (ACAA, 2003). The colour and physical

appearance of the fly ash used in this research is shown in Figure 4.6.

Figure 4.6. The colour and physical appearance of fly ash

58

4.3 Laboratory Testing Methodology

The following geotechnical tests were performed on untreated and stabilised biosolids

samples to determine their geotechnical engineering characteristics. Laboratory tests

were performed according to the Australian Standards (AS) methods of testing soils for

engineering purposes. The triaxial tests were undertaken in accordance to American

Society for Testing and Material (ASTM).

4.3.1. Moisture content

The moisture content (or water content) is the ratio of the mass of water to the mass of

the biosolids sample. The moisture of the biosolids was determined using AS

1289.2.1.1, “Determination of the moisture content of a soils – Oven dried method”.

This parameter is of interest for the geotechnical characterisation of biosolids.

4.3.2. Specific gravity (Particle Density)

Specific gravity is the ratio of the density of solid particles to the density of water.

Particle density can be measured by using any other liquid such as kerosene for soluble

solid material. Kerosene was used to determine the specific gravity of biosolids,

because it was identified as a partly soluble material in water. The specific gravity

(particle density) of biosolids was measured using AS 1289.3.5.1, “Determination of the

particle density of a soil – Standard method”. The specific gravity of inorganic soil

generally varies from 2.5 to 2.7. Organic soils generally possess lower specific gravity

values as compared to inorganic soils.

4.3.3. Particle size analysis

Particle size analysis consists of sieve and hydrometer analysis. Sieve analysis was used

to determine the distribution of coarse fraction (>0.075mm) of biosolids and hydrometer

analysis was performed to determine the distribution of fine fraction (<0.075mm) of

59

biosolids. The coarse and fine fractions of biosolids were determined from particle size

distribution curves.

Sieve analysis was performed using AS 1289.3.6.1, “Determination of the particle size

distribution of soil – Standard method of analysis by sieving” and hydrometer analysis

was carried out using AS 1289.3.6.3, “Determination of the particle size distribution of

a soil – Standard method of fine analysis using a hydrometer”.

4.3.4. Atterberg limit test

Atterberg limits are used to define the consistency of soil and it comprises of liquid

limit (LL) and plastic limit (PL). Liquid limit is defined as the threshold water content

at which soil changes from the plastic state to the liquid state. Plastic limit is defined as

the threshold water content at which a soil changes from the semi plastic state to the

plastic state. Plasticity index (PI) is the difference between the liquid limit and plastic

limit.

Liquid limit was determined using AS 1289.3.1.1, “Determination of the liquid limit of

a soil – Four point Casagrande method”. Plastic limit was determined using AS

1289.3.2.1, “Determination of plastic limit of a soil – Standard method” and Plastic

index was calculated using AS 1289.3.3.1, “Calculation of the plasticity index of a

soil”.

4.3.5. Standard compaction test

Compaction refers to the removal of air voids from material by the application of

mechanical energy. Basically there are two types of compaction methods available in

engineering practices which are the standard and modified compaction. The compaction

method is selected according to the engineering application of the material. The

standard compaction method was selected to compact the biosolids material as per the

VicRoads requirement for Type B fill.

60

The optimum moisture content (OMC) is the moisture content at which maximum dry

density (MDD) will develop and this can be determined from compaction tests. The

OMC and MDD are used to express compaction criteria for a material. Moisture–

density relationships for biosolids were determined using standard proctor testing

procedure in accordance with AS 1289.5.1.1, “Determination of the dry

density/moisture content relation of a soil – Standard compaction effort”.

4.3.6. Consolidation test

Consolidation parameters are required to estimate the settlement of embankments. The

rate of settlement of soils depends on the rate of dissipation of pore water pressure

created by the increased loading. One dimensional consolidation and Rowe

consolidation tests were undertaken to evaluate the consolidation properties of the

biosolids.

One dimensional consolidation characteristics of biosolids were determined using AS

1289.6.6.1, “Determination of one dimensional consolidation properties of a soil –

Standard method”. Rowe consolidation tests were performed using AS 1289.6.6.1,

“Determination of one dimensional consolidation properties of a soil – Standard

method” and BS 1377: Part 6, “Consolidation and permeability tests in hydraulic cell

and with pore pressure measurement”.

4.3.7. Triaxial test

Shear strength of biosolids is an important engineering properties used in the design of

bearing capacity, slope stability and pavement design. Shear strength can be defined as

the ultimate or maximum shear stress a soil can withstand. Shear strength is dependent

on the applied consolidation and drainage conditions. Consolidated-Drained (CD) and

Unconsolidated-Undrained (UU) triaxial compression tests were conducted to determine

the shear strength of biosolids.

Consolidated-Drained (CD) triaxial compression tests were carried out in accordance

with ASTM D 4767, “Standard test method for consolidated-drained triaxial

61

compression test on cohesive soil”. Unconsolidated-Undrained (UU) triaxial

compression tests were carried out in accordance with ASTM D 2850, “Standard test

method for unconsolidated-undrained triaxial compression test on cohesive soil”.

4.3.8. California Bearing Ratio (CBR) test

California Bearing Ratio (CBR) of biosolids was determined using AS 1289.6.1.1,

“Determination of the California Bearing Ratio of a soil – standard laboratory method

for a remoulded specimen”. CBR values are useful to evaluate the suitability of

biosolids as engineered fill material. The samples were prepared at the optimum

moisture content which was obtained from the standard compaction test. Standard

compaction effort was applied to the sample to measure the suitability of biosolids as

fill material in accordance with the VicRoads specification.

4.3.9. Hydraulic Conductivity test

The hydraulic conductivity of the construction material is an important characteristic in

embankment and road construction. The hydraulic conductivity of biosolids was

measured from falling head permeability tests in accordance to AS 1289.6.7.2, “Soil

strength and consolidation test – Determination of the permeability of soil – Falling

head method for remoulded specimen”. The samples were prepared at the optimum

moisture content which was obtained from the standard compaction test.

62

5 GEOTECHNICAL CHARACTERISTICS OF UNTREATED BIOSOLDIS

5.1 Index Properties

Figure 5.1 shows a plot of the Atterberg limits of biosolids samples at the three

stockpiles on the Plasticity Chart. Atterberg limit tests conducted on air-dried biosolids

indicated Liquid Limits (LL) ranging between 100 and 110 and Plasticity Index (PI)

ranging between 21 and 27. Figure 5.1 indicates that the biosolids can be classified as

organic fine-grained soil of medium to high plasticity “OH” based on Australian

standard for geotechnical site investigation (AS1276, 1993).

Figure 5.1. Plasticity chart for biosolids samples

The particle size analysis of the untreated biosolids was derived from the sieve and

hydrometer tests on two different samples at three stockpiles. Figure 5.2 is shows the

testing progress of the sieve analysis on untreated biosolids samples. The size and

quantity of the biosolids samples passing on each specified sieves for a single sieve

analysis is presented in Figure 5.3. The results of particle size analysis is summarised in

Table 5.3.

63

Figure 5.2. Testing progress of sieves analysis on untreated biosolids

64

(a) Biosolids passing 6.7mm and 4.75mm sieve

(b) Biosolids passing 2.36mm and 1.18mm sieve

(c) Biosolids passing 600µm and 425µm sieve

65

(d) Biosolids passing 300µm and 150µm sieve

(e) Biosolids passing 75µm sieve

Figure 5.3. Biosolids passing various sizes of sieves

Figure 5.4 shows a combined grained-size distribution plot for the biosolids at the three

biosolid stockpiles. The biosolids samples in the three stockpiles contain 2% to 4% of

gravel sized particles; 44% to 58% sand sized particles; 34% to 51% silt sized particles

and 1% to 4% clay sized particles respectively.

66

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0.0001 0.001 0.01 0.1 1 10 100 1000

Particle Size (mm)

Per

sen

tag

e P

assi

ng

(%

)Stockpile 1- Sample 1

Stockpile 1- Sample 2





20.002 0.06 60

GravelSandSiltClay Cobbles & Boulders

Figure 5.4. Particle size distributions of biosolids samples

5.2 Standard Compaction Test Results

Figure 5.5 shows the variation of biosolids with the moisture content when standard

compaction effort was applied to the biosolids sample. The maximum dry density

(MDD) varies between 0.83 t/m3 to 0.87 t/m3 and the optimum moisture content (OMC)

ranges between 48% and 56%.

0.70

0.75

0.80

0.85

0.90

40 45 50 55 60 65 70Moisture Content (%)

Dry

Den

sity

(t/m

3)

Stockpile 1-Sample 1






Figure 5.5. Variation of dry density of untreated biosolids with moisture content

67

5.3 California Bearing Ratio (CBR) Test Results

California Bearing Ratio (CBR) tests were conducted on two samples in each stockpile.

The CBR tests were performed on automated laboratory test equipment and the testing

progress of CBR test on untreated biosolids is shown in Figure 5.6 . The CBR test

results are summarised in Table 5.3. Figure 5.7 summaries the CBR results for the

untreated biosolids. CBR values of untreated biosolids varied from 0.8 to 1.1 %. The

swell value of the untreated biosolids varies between 0.3 and 0.73.

Figure 5.6. Testing progress of CBR test on untreated biosolids

From the results in Figure 5.7, it is apparent that untreated biosolids does not satisfy the

VicRoads minimum requirement of 2% CBR for Type B fill material.

68

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 1 2 3

Stockpile Number

CB

R v

alue

(%

)

Figure 5.7. CBR results of untreated biosolids

Figure 5.8 shows the CBR swell results after 4 days for untreated biosolids in three

stockpiles. The swell value of untreated biosolids varied from 0.30% to 0.73% for

biosolids sample from all 3 biosolids stockpiles.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

1 2 3Stockpile Number

Sw

ell (

%)

Figure 5.8. Swell results after 4 days for untreated biosolids

69

5.4 Triaxial (Consolidated Drained) Test Results

In order to study stress-strain and volumetric behaviours of compacted biosolids under

shearing and to determine their shear strength, consolidated drained triaxial tests were

performed on untreated compacted biosolids samples. The friction angle of the

untreated compacted samples was determined from the triaxial tests.

The untreated sample was compacted in layers in a spilt mould with a collar using a

standard manual sleeve compaction rammer. The samples were compacted to 95% of

relative compaction at the optimum compaction moisture content and maximum dry

density was achieved by the standard compaction effort.

The tri axial tests were performed on three untreated biosolids samples and results are

summarised in Table 5.3. Triaxial sample after the shearing failure is presented in

Figure 5.9. The failure plane of shearing and the direction of shearing also denoted in

Figure 5.9.

Figure 5.9. Triaxial sample (after the shearing failure)

Failure Plane

Shearing Direction

70

Figure 5.10 presents the Mohr coulomb circle for consolidated drained triaxial test on

the compacted untreated biosolids in stockpile 1. From the consolidated drained triaxial

test of the compacted untreated biosolids, the effective friction angle was 18.2 degrees

while the effective cohesion was 0 kPa.

Figure 5.10. Consolidated drained triaxial test results for biosolids in stockpile 1






71






5.5 Triaxial (Unconsolidated Undrained) Test Results

Unconsolidated undrained (UU) triaxial test were performed on untreated biosolids after

standard compaction. Table 5.1 summarises the unconsolidated undrained triaxial test

results for the untreated biosolids after compaction. The cohesion results for the

untreated biosolids varied between 24-25 kPa while the friction angle varied between 9

and 10 degrees.

Table 5.1. Summary of Unconsolidated Undrained triaxial test results of untreated biosolids

Stockpile Stockpile 1 Stockpile 2 Stockpile 3

Cohesion (kN/m2) 24 25 24

Friction Angle (Degree) 9.0 10.0 10.0

72

5.6 One Dimensional Consolidation Test Results

One dimensional consolidation tests were conducted on one sample in each stockpile.

Each sample was compacted to 95% of relative compaction at the optimum compaction

moisture content. An untreated biosolids samples were compacted in a spilt mould with

the standard compaction effort. The compacted samples were carefully trimmed using a

knife and a wire was and inserted into the consolidation ring, and extreme care was

taken in this process to minimize any disturbance in the sample. The sample preparation

process for the consolidation test is presented in Figure 5.13.

The sample with the consolidation ring was placed in a consolidometer and small

seating load was applied to record the initial zero reading. A total of five incremental

loading was used in the compression so that the vertical stress on each sample increased

from zero to 800 kPa. Each incremental load was maintained for 24hr prior to the

increment of the vertical load.

Figure 5.13. Consolidation sample preparation process

73

The sample deformation by incremental loads was measured by a LVDT positioned on

the loading frame which changes together as the sample height changes. A data

acquisition system was used for the LVDT data reading. The consolidation testing

arrangement with the loading frame is presented in Figure 5.14 .

A texture of the compressed untreated biosolids sample after the consolidation is

presented in Figure 5.15 and Figure 5.16. The sample in Figure 5.15 shows the texture

of compressed untreated biosolids before oven dried. The sample in Figure 5.16, was

placed in the oven to determined the moisture content of the sample after the test.

Figure 5.17 presents the behaviour of the void ratio with the vertical stress of untreated

biosolid samples from the one dimensional consolidation test. Standard compaction

effort was applied to the untreated samples prior to commencing the consolidation test.

Pre-consolidation pressures of between 190 kN/m2 to 210 kN/m2 were obtained from

stockpiles 1, 2 and 3.

Figure 5.14. Consolidation testing arrangement

74

Figure 5.15. Compressed untreated biosolids sample (before oven dried)

Figure 5.16. Compressed untreated biosolids sample (oven dried sample)

75

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

10 100 1000Vertical Stress (kN/m2)

Voi

d R

atio

(e)

Stockpile 1

Stockpile 2

Stockpile 3

Figure 5.17. Variation of void ratio with vertical stress for biosolids in stockpiles 1, 2 and 3

5.7 Rowe Cell Consolidation Test Results

Figure 5.18 presents the behaviour of the displacement with the vertical stress of

untreated biosolid samples in stockpile 1 from the Rowe Cell consolidation test.

Standard compaction effort was applied to the untreated samples prior to commencing

the consolidation test. A pre-consolidation pressure of 200 kN/m2 was obtained from the

untreated biosolids in stockpile 1.

76

Figure 5.18. Rowe Cell test result for biosolids in stockpile 1


untreated biosolid samples in stockpile 2 from the Rowe consolidation test. Standard

compaction effort was applied to the untreated samples prior to commencing the

consolidation test. A pre-consolidation pressure of 100 kN/m2 was obtained from the


Figure 5.19. Rowe Cell test results for biosolids in stockpile 2

77


untreated biosolid samples in stockpile 3 from the Rowe consolidation test. Standard

compaction effort was applied to the untreated samples prior to commencing the

consolidation test. A pre-consolidation pressure of 110 kN/m2 was obtained from the


Figure 5.20. Rowe Cell test results for biosolids in stockpile 3

78

5.8 Hydraulic Conductivity Test Results

Falling head permeability test results indicated that there was little variation in the

permeability of the untreated biosolids. Standard compaction effort was applied to

untreated biosolids before commencing the permeability tests. The hydraulic

conductivity of untreated biosolids is presented in Table 5.2 and ranges between 1.24 x

10-7 m/s to 1.60 x 10-7 m/s.

Table 5.2. Falling head permeability of untreated biosolids

Stockpile Stockpile 1 Stockpile 2 Stockpile 3

Coefficient of Permeability (m/s) 1.60 x 10-7 1.24 x 10-7 1.31 x 10-7

Table 5.3 summarises the geotechnical characteristics of untreated biosolids which were

collected from 3 stockpiles in the Biosolids Stockpile Area at the Western Treatment

Plant in Victoria.

The natural moisture content shows that untreated biosolids have high moisture content

and have 25% of organic content. Atterberg limits indicate that the biosolids having

high liquid and plastic limit. Therefore based on the geotechnical classification of soil,

the untreated biosolids could be categorised as organic soil. The results show that the

untreated biosolids having low California bearing ratio and shear strength and also the

coefficient of permeability from falling head and consolidation test indicate that it have

low permeability.

79

Table 5.3. Summary of geotechnical characteristics of untreated biosolids

Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3

Natural Moisture Content % 47.6 53.5 58.6 56.6 49.2 46.8

Organic Content % 24.8 25.2 24.9 28.1 24.4 27.6

Particle density of biosolids t/m3 1.79 1.76 1.75

Particle Size

Analysis

60.0mm to 2.0mm % 4 4 4 2 4 2

2.0mm to 0.06mm % 58 44 54 50 58 46

0.06mm to 0.002mm % 34 51 40 46 34 51

<0.002mm % 4 1 2 2 4 1

Atterberg

Limit

Liquid Limit % 100 104 110

Plastic Limit % 79 80 83

Plasticity Index % 21 24 27

Compaction

Type of Compaction effort Standard Standard Standard

Maximum Dry Density t/m3 0.84 0.86 0.84 0.83 0.87 0.83

Optimum Moisture Content % 56 54 51 55 48 52

CBR CBR Swell* % 0.36 0.47 0.56 0.43 0.30 0.73

CBR Value % 0.8 0.9 1.0 1.0 0.9 1.1

Laboratory

Vane Shear

Vane Shear Strength kN/m2 N.O N.O N.O

Remoulded Vane Shear

Strength kN/m2 N.O N.O N.O

Consolidation

- Oedometer

e0 0.911 0.865 1.048

Coefficient of

Consolidation m2/year 0.5 0.5 0.4

Coefficient of Permeability m/s 10.1x 10-11 8.8 x 10-11 4.2 x 10-11

Preconsolidation Pressure kN/m2 190 195 210

Compression Index 0.625 0.563 0.640

Recompression Index 0.044 0.038 0.045

Consolidation

- Rowe Cell Preconsolidation Pressure kN/m2 200 100 110

Triaxial

Compression

Type of Test UU CD UU CD UU CD

Cohesion kN/m2 24 0 25 0 24 0

Phi Angle Degree 9.0 18.2 10.0 10.2 10.0 16.8

Falling Head

Permeability Permeability m/s 1.60 x 10-7 1.24 x 10-7 1.31 x 10-7

* - CBR swell after load applied at the end of soak period

N.O - Not Obtainable

UU – Unconsolidated Undrained Triaxial test

CD –Consolidated Drained Triaxial test

80

6 GEOTECHNICAL CHARACTERISTICS OF STABILISED BIOSOLIDS

6.1 Geotechnical Characteristics of Biosolids Stabilised with Lime

6.1.1. Index properties

Moisture content tests were undertaken on samples of biosolids stabilised with 1%, 3%,

and 5% of lime. The results as shown in Figure 6.1 indicate variation in moisture

content between biosolids stabilised with lime and the untreated biosolids. Moisture

content was noted to decrease with increasing percentages of lime.

0

10

20

30

40

50

60

70

0 1 2 3 4 5

Percentage of lime added to biosolids (%)

Moi

stur

e C

onte

nt (

%)

Untreated biosolids

Stablised biosolids with 1%Lime



Figure 6.1. Moisture content variation with percentage of lime added to biosolids

Liquid limit, plastic limit and plastic index tests were undertaken on the biosolids

stabilised with various percentages of lime. Figure 6.2 to 6.4 presents the atterberg

limits results of biosolids from stockpiles 1 to 3 after stabilisation with 1%, 3% and 5%

of lime as compared to untreated biosolids. It was noted that the liquid limit, plastic

limit and plastic index in all three stockpiles decreased with the addition of increasing

amounts of lime.

81

0

20

40

60

80

100

120

0 1 3 5Percentage of lime added to biosolids (%)

Moi

stur

e co

nten

t (%

)Liquid Limit

Plastic Limit

Plastic Index

Figure 6.2. Atterberg limits variation with percentage of lime added to biosolids in stockpile 1

0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)

Liquid Limit

Plastic Limit

Plastic Index


82

0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)Liquid Limit

Plastic Limit

Plastic Index


Figure 6.5 to 6.7 shows a combined grained-size distribution plot for the untreated and

stabilised biosolids with lime in stockpile 1, stockpile 2 and stockpile 3 respectively. All

three figures indicate that there are only little changes in the percentage of sand and silt

particles when lime added to the biosolids.

The biosolids samples stabilised with 1% lime contain 4% to 6% of gravel sized

particles; 45% to 56% sand sized particles; 38% to 51% silt sized particles and up to 2%

clay sized particles respectively. The biosolids samples stabilised with 3% lime contain

4% to 6% of gravel sized particles; 45% to 55% sand sized particles; 39% to 51% silt

sized particles and up to 2% clay sized particles respectively. The biosolids samples

stabilised with 5% lime contain 4% to 6% of gravel sized particles; 44% to 54% sand

sized particles; 40% to 52% silt sized particles and up to 2% clay sized particles

respectively.

83

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10 100 1000

Particle Size (mm)

Per

cen

tag

e P

assi

ng

(%

)

Sample 1- 0% Lime Sample 2- 0% Lime




0.060.002 2 60

Clay Silt Sand Gravel Cobbles & Boulders

Figure 6.5. Particle size distribution of biosolids samples stabilised with lime in Stockpile 1

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10 100 1000

Particle Size (mm)

Per

cen

tag

e P

assi

ng

(%

)





0.060.002 2 60



84

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10 100 1000

Particle Size (mm)

Per

cent

age

Pas

sing

(%

)





0.060.002 2 60



6.1.2. Standard compaction test results

The Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) results was

obtained from the standard compaction test results of biosolids stabilised with 1%, 3%

and 5% of lime. The compaction curves for the biosolids stabilised with 1%, 3% and

5% of lime are presented in Figure 6.8. The compaction test results are summarised in

Table 6.2 to 6.4 and also the variation of the maximum dry density and optimum

moisture content with the percentage of lime added for the stabilisation is presented in

Figure 6.9 and Figure 6.10 respectively.

Figure 6.9 presents the maximum dry density of biosolids stabilised with various

percentages of lime as compared to untreated biosolids. The maximum dry density of

stabilised biosolids varied from 0.88t/m3 to 0.91t/m3 with the addition of 1% of lime;

0.90t/m3 to 0.93t/m3 with the addition of 3% of lime and between 0.89t/m3 to 0.91t/m3

with the addition of 5% of lime. In general, increasing the proportion of lime had little

effect on the maximum dry density of the biosolids.

85

0.80

0.85

0.90

0.95

1.00

1.05

1.10

20 25 30 35 40 45 50 55 60

Moisture Content (%)

Dry

Den

sity

(t/m

3)Biosolids + 1% LimeBiosolids + 3% LimeBiosolids + 5% LimeZAV (G=1.5)ZAV (G=1.75)

Figure 6.8. Compaction curves for the stabilised biosolids with lime

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0 1 2 3 4 5


Max

imum

Dry

Den

sity

(t/m

3)

0% Lime1% Lime3% Lime5% Lime

Figure 6.9. Variation of Maximum Dry Density (MDD) with percentage of lime

86

Figure 6.10 shows the optimum moisture content of biosolids stabilised with various

percentage of lime as compared to untreated biosolids. The optimum moisture content

of stabilised biosolids was 40% to 43% with 1% of lime; 38% to 42% with 3% of lime

and 39% to 42% with 5% of lime. The addition of lime had little effect on the optimum

moisture content of the biosolids as compared with the untreated biosolids.

10

20

30

40

50

60

70

0 1 2 3 4 5


Opt

imum

Moi

stur

e C

onte

nt (

%)

0% Lime1% Lime3% Lime5% Lime

Figure 6.10. Variation of Optimum Moisture Content (OMC) with percentage of lime

87

6.1.3. California Bearing Ratio (CBR) test results

Figure 6.11 presents the CBR results for biosolids stabilised with 1%, 3% and 5% of

lime as compared to untreated biosolids. The CBR value of stabilised biosolids varies

from 1.2% to 1.6% with the addition of 1% of lime; 1.4% to 1.7% with the addition of

3% of lime and 3.3% and 4.7% with the addition of 5% of lime. In general, the

stabilisation of biosolids with lime increases the CBR value of biosolids.

From the results in Figure 6.11, it is apparent that biosolids stabilised with 5% lime

satisfies the VicRoads minimum requirement of 2% CBR for Type B fill material

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 1 2 3 4 5


CB

R V

alue

(%

)

0% Lime 1% Lime 3% Lime 5% Lime

Figure 6.11. CBR results of biosolids stabilised with lime

Figure 6.12 shows the CBR swell results after 4 days for biosolids stabilised with 1%,

3% and 5% of lime. The swell value of stabilised biosolids varied from 0.31% to 0.84%

with the addition of 1% of lime; 0.14% to 0.95% with the addition of 3% of lime and

0.17% and 0.52% with the addition of 5% of lime.

88

0.05

0.25

0.45

0.65

0.85

1.05

1.25

1.45

0 1 2 3 4 5


Sw

ell (

%)

0% Lime 1% Lime 3% Lime 5% Lime

Figure 6.12. Swell results after 4 days for biosolids stabilised with lime

89

6.1.4. Triaxial (Consolidated Drained) test results


the stabilised biosolids with 3% lime. From the consolidated drained triaxial test of the

stabilised biosolids with 3% lime, the effective friction angle was 45.4 degrees while the

effective cohesion was 0 kPa.

Figure 6.13. Consolidated drained triaxial test results for stabilised biosolids with 3% lime


the stabilised biosolids with 5% lime. From the consolidated drained triaxial test of the

stabilised biosolids with 5% lime, the effective friction angle was 44.5 degrees while the

effective cohesion was 0 kPa.

Figure 6.14. Consolidated drained triaxial test results for stabilised biosolids with 5% lime

90

6.1.5. One dimensional consolidation test results

Figure 6.15 presents the behaviour of the void ratio with the vertical stress of biosolids

stabilised with 3% and 5% lime at stockpile 1 as compared to untreated biosolids from

the one dimensional consolidation test. Standard compaction effort was applied to the

biosolids prior to commencing the consolidation test. Pre-consolidation pressure for

biosolids in stockpile 1 stabilised with 3% lime was 250 kN/m2 and 250 kN/m2 for

biosolids stabilised with 5% lime.







0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Voi

d R

atio

(e)

0% Lime

3% Lime

5% Lime

Figure 6.15. Variation of void ratio with vertical stress for biosolids in stockpile 1

91

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Voi

d R

atio

(e)

0% Lime

3% Lime

5% Lime








0.0

0.2

0.4

0.6

0.8

1.0

1.2


Voi

d R

atio

(e)

0% Lime

3% Lime

5% Lime


92

6.1.6. Rowe Cell consolidation test results


stabilised biosolid sample with 3% lime from the Rowe consolidation test. Standard

compaction effort was applied to the stabilised sample prior to commencing the

consolidation test. A pre-consolidation pressure of 120 kN/m2 was obtained for

stabilised biosolids with 3% lime.

Figure 6.18. Rowe Cell test results for stabilised biosolids with 3% lime

93

6.1.7. Creep consolidation test results

The creep consolidation tests were conducted to determine the secondary compression

index for the finite element analysis. The long-term creep consolidation tests were

undertaken by applying each load increment for seven days (as compared to the

traditional 1 day load increment). The results from these creep consolidation test results

were used as input parameters in the finite element analysis of embankments using

stabilised biosolids with 5% lime.

0.0

0.1

0.2

0.3

0.4

0.5

0 200 400 600 800 1000Applied vertical stress (kPa)

Cα

(%

of

stra

in p

er lo

g cy

cle)

Figure 6.19. Variation of secondary consolidation for biosolids stabilised with 5% lime

Table 6.1 summarises the creep consolidation test results of biosolids stabilised with 5%

lime and also Figure 6.19 presents the variation of secondary consolidation (creep) with

applied stress for the biosolids stabilised with 5% lime.

Table 6.1. Secondary consolidation (creep) values for biosolids stabilised with lime.

Secondary consolidation value- Cα (% of strain per log cycle)

Stabilised biosolids Applied vertical stress (kPa)

50 100 200 400 800

Biosolids + 5% Lime 0.013 0.031 0.134 0.108 0.223

94

6.1.8. Hydraulic conductivity test results

Figure 6.20 presents the hydraulic conductivity of biosolids stabilised with 3% and 5%

of lime compared to untreated biosolids. Standard compaction effort was applied to the

stabilised biosolids before undertaken falling head permeability test. The permeability

of untreated compacted biosolids ranges between 1.24 x 10-7 m/s to 1.60 x 10-7 m/s. The

permeability of stabilised biosolids with 3% lime varied from 1.23 x 10-7 m/s to 1.34 x

10-7 m/s and the permeability of stabilised biosolids with 5% lime varied from 1.13 x

10-7 m/s to 1.36 x 10-7 m/s. In general there is little difference in the hydraulic

conductivity value between biosolids stabilised with the addition of 3% and 5% lime as

compared to the untreated biosolids.

0.5

1.0

1.5

0 1 2 3 4 5


Per

mea

bilit

y (

x10-

7 m

/s)

0% Lime 3% Lime 5% Lime

Figure 6.20. Permeability of stabilised biosolids with lime

95

Table 6.2 to 6.4 summaries the geotechnical characteristics of biosolids stabilised with

1%, 3% and 5% lime respectively.



Moisture Content % 47.9 42.7 49.5 51.0 37.5 44.9

Particle Size

Analysis

60.0mm to 2.0mm % 6 4 5 4 5 4

2.0mm to 0.06mm % 56 45 53 46 56 48

0.06mm to 0.002mm % 38 51 40 48 39 46

<0.002mm % 0 0 2 2 0 2

Atterberg

Limit




Compaction


Maximum Dry Density t/m3 0.91 0.89 0.88 0.89

Optimum Moisture Content % 43 41 40 40

CBR CBR Swell* % 0.84 0.31 0.45 0.54

CBR Value % 1.2 1.6 1.6 1.3


96




Particle Size

Analysis

60.0mm to 2.0mm % 6 4 5 4 5 4

2.0mm to 0.06mm % 55 45 52 46 55 48

0.06mm to 0.002mm % 39 51 41 48 40 46

<0.002mm % 0 0 2 2 0 2

Atterberg

Limit




Compaction




CBR CBR Swell* % 0.14 0.56 0.52 0.95

CBR Value % 1.6 1.4 1.7 1.7

Consolidation

- Oedometer

e0 0.808 0.863 0.909

Coefficient of Consolidation m2/year 0.4 0.3 0.2

Coefficient of Permeability m/s 5.4 x 10-11 2.8 x 10-11 2.9 x 10-11




Consolidation

- Rowe Cell Preconsolidation Pressure kN/m2 - 120 -

Triaxial

Compression

Type of Test CD - -

Cohesion kN/m2 0 - -

Phi Angle Degree 44.5 - -

Falling Head





97




Particle Size

Analysis

60.0mm to 2.0mm % 6 4 5 4 5 4

2.0mm to 0.06mm % 54 44 49 46 54 48

0.06mm to 0.002mm % 40 52 44 48 40 46

<0.002mm % 0 0 2 2 1 2

Atterberg

Limit




Compaction




CBR CBR Swell* % 0.46 0.52 0.17 0.35

CBR Value % 4.2 3.3 4.0 4.7

Consolidation

- Oedometer

e0 0.853 0.872 0.699






Triaxial

Compression

Type of Test CD - -

Cohesion kN/m2 0 - -

Phi Angle Degree 45.4 - -

Falling Head





98

6.2 Geotechnical Characteristics of Biosolids Stabilised with Cement



and 5% of cement. The results as shown in Figure 6.21 indicate variation in moisture

content between biosolids stabilised with cement and the untreated biosolids. Moisture

content was noted to decrease with increasing percentages of cement.

0

10

20

30

40

50

60

70

0 1 2 3 4 5

Percentage of cement added to biosolids (%)

Moi

stur

e C

onte

nt (

%)

Untreated biosolids

Stablised biosolids with 1%Cement



Figure 6.21. Moisture content variation with percentage of cement added to biosolids

Liquid limit, plastic limit and plastic index tests were undertaken on biosolids stabilised

with various percentages of cement. Figure 6.22 to 6.23 presents the atterberg limits

results of biosolids from stockpiles 1 to 3 after stabilisation with 1%, 3% and 5% of

cement. It was noted that the liquid limit, plastic limit and plastic index in all three

stockpiles decreased with the addition of increasing amounts of cement.

99

0

20

40

60

80

100

120

0 1 3 5Percentage of cement added to biosolids (%)

Moi

stur

e co

nten

t (%

)Liquid Limit

Plastic Limit

Plastic Index

Figure 6.22. Atterberg limits with percentage of cement added to biosolids in stockpile 1

0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)

Liquid Limit

Plastic Limit

Plastic Index


100

0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)Liquid Limit

Plastic Limit

Plastic Index


Figure 6.25 to 6.26 shows a combined grained-size distribution plot for the untreated

and stabilised biosolids with cement in stockpile 1, stockpile 2 and stockpile 3

respectively. All three figures indicate that there are only little changes in the percentage

of sand and silt particles when cement added to the biosolids.

The biosolids samples stabilised with 1% cement contain 2% to 4% of gravel sized

particles; 46% to 59% sand sized particles; 37% to 50% silt sized particles and up to 2%

clay sized particles respectively. The biosolids samples stabilised with 3% cement

contain 2% to 6% of gravel sized particles; 44% to 56% sand sized particles; 35% to

51% silt sized particles and 1% to 5% clay sized particles respectively. The biosolids

samples stabilised with 5% cement contain 4% to 5% of gravel sized particles; 43% to

56% sand sized particles; 35% to 52% silt sized particles and 1% to 5% clay sized

particles respectively.

101

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10 100 1000

Particle Size (mm)

Per

cen

tag

e P

assi

ng

(%

)

Sample 1- 0% Cement Sample 2- 0% Cement




0.060.002 2 60



0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10 100 1000

Particle Size (mm)

Per

cen

tag

e P

assi

ng

(%

)





0.060.002 2 60



102

0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10 100 1000

Particle Size (mm)

Per

cen

tag

e P

assi

ng

(%

)





0.060.002 2 60






and 5% of cement. The compaction curves for the biosolids stabilised with 1%, 3% and

5% of cement are presented in Figure 6.28. The compaction test results are summarised

in Table 6.6 to 6.8 and also the variation of the maximum dry density and optimum

moisture content with the percentage of cement added for the stabilisation is presented

in Figure 6.29 and Figure 6.30 respectively.


percentages of cement as compared to untreated biosolids. The maximum dry density of

stabilised biosolids varied from 0.84t/m3 to 0.85t/m3 with the addition of 1% of cement,

0.86t/m3 to 0.88t/m3 with the addition of 3% of cement and between 0.87t/m3 to

0.88t/m3 with the addition of 5% of cement. In general, increasing the proportion of

cement had little effect on the maximum dry density of the biosolids.

103

0.80

0.85

0.90

0.95

1.00

1.05

20 25 30 35 40 45 50 55 60


Dry

Den

sity

(t/m

3)

Biosolids + 1% Cement



ZAV (G=1.5)

ZAV (G=1.75)

Figure 6.28. Compaction curves for the stabilised biosolids with cement

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0 1 2 3 4 5


Max

imum

Dry

Den

sity

(t/m

3)

0% Cement1% Cement3% Cement5% Cement

Figure 6.29. Variation of Maximum Dry Density (MDD) with percentage of cement

104

Figure 6.30 presents the optimum moisture content of biosolids stabilised with various

percentages of cement as compared to untreated biosolids. The optimum moisture

content of stabilised biosolids was 38% to 40% with 1 % of cement; 38% to 40% with 3

% of cement and 37% to 40% with 5% of cement. The addition of cement had little

effect on the optimum moisture content of the biosolids as compared with the untreated

biosolids.

10

20

30

40

50

60

70

0 1 2 3 4 5


Opt

imum

Moi

stur

e C

onte

nt (

%)

0% Cement1% Cement3% Cement5% Cement

Figure 6.30. Variation of Optimum Moisture Content (OMC) with percentage of cement


Figure 6.31 presents the CBR results for biosolids stabilised with 1%, 3% and 5% of

cement as compared to untreated biosolids. The CBR value of stabilised biosolids varies

from 1.7% to 2.0% with the addition of 1% of cement; 2.0% to 2.4% with the addition

of 3% of cement, 3.8%, and 4.6% with the addition of 5% of cement. In general, the

stabilisation of biosolids with cement increases the CBR value of biosolids.

105

From the results in Figure 6.31, it is apparent that biosolids stabilised with 3% and 5%

cement satisfies the VicRoads minimum requirement of 2% CBR for Type B fill

material

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 1 2 3 4 5Percentage of cement added to biosolids (%)

CB

R V

alue

(%

)

0% Cement 1% Cement 3% Cement 5% Cement

Figure 6.31. CBR results for biosolids stabilised with cement


3% and 5% of cement. The swell value of stabilised biosolids varied from 0.15% to

0.52% with the addition of 1% of cement, 0.12% to 0.77% with the addition of 3% of

cement and 0.28% and 1.29% with the addition of 5% of cement.

106

0.05

0.25

0.45

0.65

0.85

1.05

1.25

1.45

0 1 2 3 4 5


Sw

ell (

%)

0% Cement 1% Cement 3% Cement 5% Cement

Figure 6.32. Swell results after 4 days for biosolids stabilised with cement



the stabilised biosolids with 3% cement. From the consolidated drained triaxial test of

the stabilised biosolids with 3% cement, the effective friction angle was 45.1 degrees


107

Figure 6.33. Consolidated drained triaxial test results for stabilised biosolids with 3% cement


the stabilised biosolids with 5% cement. From the consolidated drained triaxial test of

the stabilised biosolids with 5% cement, the effective friction angle was 39.5 degrees


Figure 6.34. Consolidated drained triaxial test results for stabilised biosolids with 5% cement

108



stabilised with 3% and 5% cement at stockpile 1 as compared to untreated biosolids

from the one dimensional consolidation test. Standard compaction effort was applied to

the biosolids prior to commencing the consolidation test. Pre-consolidation pressure for

biosolids in stockpile 1 stabilised with 3% cement was 220 kN/m2 and 220 kN/m2 for

biosolids stabilised with 5% cement.

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Voi

d R

atio

(e)

0% Cement

3% Cement

5% Cement








109

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Voi

d R

atio

(e)

0% Cement

3% Cement

5% Cement


0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1


Voi

d R

atio

(e)

0% Cement3% Cement5% Cement


110









stabilised biosolid sample with 3% cement from the Rowe consolidation test. Standard



stabilised biosolids with 3% cement.

Figure 6.38. Rowe Cell test results for stabilised biosolids with 3% cement

111







stabilised biosolids with 3% cement and 5% cement.


cement and 5% cement. Figure 6.39 presents the variation of secondary consolidation

(creep) with applied stress for the biosolids stabilised with 3% cement and Figure 6.40

presents the variation of secondary consolidation (creep) with applied stress for the


Table 6.5. Secondary consolidation (creep) values for biosolids stabilised with cement.



50 100 200 400 800

Biosolids + 3% Cement 0.043 0.037 0.1 0.1 0.239

Biosolids + 5% Cement 0.001 0.053 0.072 0.085 0.194

112

0.0

0.1

0.2

0.3

0.4

0.5


Cα

(%

of

stra

in p

er lo

g cy

cle)

Figure 6.39. Variation of secondary consolidation for biosolids stabilised with 3% cement

0.00

0.05

0.10

0.15

0.20

0.25

0.30


Cα

(%

of s

tra

in p

er lo

g cy

cle)

Figure 6.40. Variation of secondary consolidation for biosolids stabilised with 5% cement

113



of cement as compared to untreated biosolids. Standard compaction effort was applied

to the stabilised biosolids before undertaken falling head permeability test. The

permeability of untreated compacted biosolids ranges between 1.24 x 10-7 m/s to 1.60 x

10-7 m/s. The permeability of stabilised biosolids with 3% cement varied from 1.10 x

10-7 m/s to 1.32 x 10-7 m/s and the permeability of stabilised biosolids with 5% cement

varied from 0.85 x 10-7 m/s to 1.05 x 10-7 m/s. In general, the hydraulic conductivity of

stabilised biosolids with cement decreases slightly with increasing cement percentage.

0.5

1.0

1.5

0 1 2 3 4 5


Per

mea

bilit

y (

x10-

7 m

/s)

0% Cement 3% Cement 5% Cement

Figure 6.41. Permeability of biosolids stabilised with cement

114

Table 6.6 to 6.8 summaries the geotechnical characteristics of biosolids stabilised with

1%, 3% and 5% cement respectively.

Table 6.6. Summary of geotechnical characteristics of biosolids stabilised with 1% cement



Particle

Size

Analysis

60.0mm to 2.0mm % 4 4 4 2 4 2

2.0mm to 0.06mm % 58 46 52 48 59 51

0.06mm to 0.002mm % 38 50 42 48 37 45

<0.002mm % 0 0 2 2 0 2

Atterberg

Limit




Compaction




CBR CBR Swell* % 0.15 0.34 0.52 0.40

CBR Value % 1.8 2.0 1.9 1.7


115




Particle Size

Analysis

60.0mm to 2.0mm % 4 4 4 2 6 4

2.0mm to 0.06mm % 56 44 51 48 54 47

0.06mm to 0.002mm % 35 51 42 47 40 46

<0.002mm % 5 1 3 3 0 3

Atterberg

Limit




Compaction




CBR CBR Swell* % 0.24 0.12 0.51 0.77

CBR Value % 2.0 2.4 2.2 2.1

Consolidation

- Oedometer

e0 0.851 0.667 0.638






Consolidation

- Rowe Cell Preconsolidation Pressure kN/m2 180 - -

Triaxial

Compression

Type of Test - CD -

Cohesion kN/m2 - 0 -

Phi Angle Degree - 45.1 -

Falling Head





116




Particle Size

Analysis

60.0mm to 2.0mm % 4 4 5 4 5 4

2.0mm to 0.06mm % 56 43 49 45 54 47

0.06mm to 0.002mm % 35 52 43 48 40 46

<0.002mm % 5 1 3 3 1 3

Atterberg

Limit




Compaction




CBR CBR Swell* % 0.59 1.29 0.52 0.28

CBR Value % 4.1 4.6 3.8 4.5

Consolidation

- Oedometer

e0 0.789 0.809 0.785






Triaxial

Compression

Type of Test - CD -

Cohesion kN/m2 - 0 -

Phi Angle Degree - 39.5 -

Falling Head





117

6.3 Geotechnical Characteristics of Biosolids Stabilised with Bauxsol



and 5% of bauxsol. The results as shown in Figure 6.42 indicate variation in moisture

content between biosolids stabilised with bauxsol and the untreated biosolids. Moisture

content was noted to decrease marginally with increasing percentages of bauxsol.

0

10

20

30

40

50

60

70

0 1 2 3 4 5

Percentage of bauxsol added to biosolids (%)

Moi

stur

e C

onte

nt (

%)

Untreated biosolidsStablised biosolids with 1%BauxsolStablised biosolids with 3%BauxsolStablised biosolids with 5%Bauxsol

Figure 6.42. Moisture content variation with percentage of bauxsol added to biosolids


with various percentages of bauxsol. Figure 6.43 to 6.43 presents the atterberg limits

results of biosolids from stockpiles 1 to 3 after stabilisation with 1%, 3%, and 5% of

bauxsol as compared to the untreated biosolids. It was noted that the liquid limit, plastic

limit and plastic index in all three stockpiles generally decreases with the addition of

increasing amounts of bauxsol.

118

0

20

40

60

80

100

120

0 1 3 5Percentage of bauxsol added to biosolids (%)

Moi

stur

e co

nten

t (%

)Liquid Limit

Plastic Limit

Plastic Index

Figure 6.43. Atterberg limits with percentage of bauxsol added to biosolids in stockpile 1

0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)

Liquid Limit

Plastic Limit

Plastic Index


119

0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)Liquid Limit

Plastic Limit

Plastic Index





and 5% of bauxsol. The compaction curves for the biosolids stabilised with 1%, 3% and

5% of bauxsol are presented in Figure 6.46. The compaction test results are summarised

in Table 6.10 to 6.12 and also the variation of the maximum dry density and optimum

moisture content with the percentage of bauxsol added for the stabilisation is presented

in Figure 6.47 and Figure 6.48 respectively.


percentages of bauxsol as compared to untreated biosolids. The maximum dry density

of stabilised biosolids varied from 0.86t/m3 to 0.91t/m3 with the addition of 1% bauxsol;

0.89t/m3 to 0.91t/m3 with the addition of 3% bauxsol and 0.88t/m3 to 0.90t/m3 with the

addition of 5% bauxsol. In general, increasing the proportion of bauxsol had little effect

on the maximum dry density of the biosolids.

120

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

30 35 40 45 50 55 60 65


Dry

Den

sity

(t/m

3)

Biosolids + 1% BauxsolBiosolids + 3% BauxsolBiosolids + 5% BauxsolZAV (G=1.5)ZAV (G=1.75)

Figure 6.46. Compaction curves for the stabilised biosolids with bauxsol


percentages of bauxsol as compared to the untreated biosolids. The optimum moisture

content of stabilised biosolids was 44% to 48% with 1% bauxsol, 43% to 46% with 3%

bauxsol and 38% to 41% with 5% bauxsol respectively. The addition of bauxsol was

found to slightly decrease the optimum moisture content of the biosolids as compared

with the untreated biosolids.

121

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0 1 2 3 4 5


Max

imum

Dry

Den

sity

(t/m

3)

0% Bauxsol1% Bauxsol3% Bauxsol5% Bauxsol

Figure 6.47. Variation of Maximum Dry Density (MDD) with percentage of bauxsol

10

20

30

40

50

60

70

0 1 2 3 4 5


Opt

imum

Moi

stur

e C

onte

nt (

%)

0% Bauxsol1% Bauxsol3% Bauxsol5% Bauxsol

Figure 6.48. Variation of Optimum Moisture Content (OMC) with percentage of bauxsol

122


Figure 6.49 presents the CBR value results for biosolids stabilised with 1%, 3% and 5%

of bauxsol as compared to untreated biosolids. The CBR value of stabilised biosolids

varies from 1.7% to 2.1% with the addition of 1% of bauxsol; 2.0% to 2.7% with the

addition of 3% of bauxsol and 3.1% to 3.7% with the addition of 5% of bauxsol. In

general, the stabilisation of biosolids with bauxsol increases the CBR value of biosolids.

From the results in Figure 6.49, it is apparent that biosolids stabilised with 3% and 5%

bauxsol satisfies the VicRoads minimum requirement of 2% CBR for Type B fill

material.

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 1 2 3 4 5


CB

R V

alue

(%

)

0% Bauxsol 1% Bauxsol 3% Bauxsol 5% Bauxsol

Figure 6.49. CBR results of biosolids stabilised with bauxsol

123


3% and 5% of bauxsol. The swell value of stabilised biosolids varied from 0.25% to

0.50% with the addition of 1% of bauxsol; 0.34% to 1.11% with the addition of 3% of

bauxsol and 0.47% and 1.23% with the addition of 5% of bauxsol.

0.05

0.25

0.45

0.65

0.85

1.05

1.25

1.45

0 1 2 3 4 5


Sw

ell (

%)

0% Bauxsol 1% Bauxsol 3% Bauxsol 5% Bauxsol

Figure 6.50. Swell results after 4 days for biosolids stabilised with bauxsol.

124



the stabilised biosolids with 3% bauxsol. From the consolidated drained triaxial test of

the stabilised biosolids with 3% bauxsol, the effective friction angle was 43.1 degrees


Figure 6.51. Consolidated drained triaxial test results for stabilised biosolids with 3% bauxsol


the stabilised biosolids with 5% bauxsol. From the consolidated drained triaxial test of

the stabilised biosolids with 5% bauxsol, the effective friction angle was 43.0 degrees


125

Figure 6.52. Consolidated drained triaxial test results for stabilised biosolids with 5% bauxsol



stabilised with 3% and 5% bauxsol at stockpile 1 as compared to untreated biosolids



biosolids in stockpile 1 stabilised with 3% bauxsol was 300 kN/m2 and 300 kN/m2 for

biosolids stabilised with 5% bauxsol.







126

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0


Voi

d R

atio

(e)

0% Bauxsol3% Bauxsol5% Bauxsol


0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9


Voi

d R

atio

(e)



127







0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2


Voi

d R

atio

(e)



128



stabilised biosolid sample with 3% bauxsol from the Rowe consolidation test. Standard



stabilised biosolids with 3% bauxsol.

Figure 6.56. Rowe Cell test results for stabilised biosolids with 3% bauxsol

129







stabilised biosolids with 3% bauxsol and 5% bauxsol.


bauxsol and 5% bauxsol.

Figure 6.57 presents the variation of secondary consolidation (creep) with applied stress

for the biosolids stabilised with 3% bauxsol. Figure 6.58 presents the variation of

secondary consolidation (creep) with applied stress for the biosolids stabilised with 5%

bauxsol.

Table 6.9. Consolidation (creep) values for the biosolids stabilised with bauxsol.



50 100 200 400 800

Biosolids + 3% Bauxsol 0.088 0.061 0.02 0.048 0.190

Biosolids + 5% Bauxsol 0.055 0.046 0.069 0.06 0.143

130

0.00

0.05

0.10

0.15

0.20

0.25

0.30


Cα

(% o

f stra

in p

er l

og c

ycle

)


bauxsol

0.00

0.05

0.10

0.15

0.20

0.25

0.30


Cα

(%

of s

tra

in p

er

log

cy

cle

)

Figure 6.58. Variation of secondary consolidation for biosolids stabilised with 5% bauxsol

131



of bauxsol as compared to untreated biosolids. Standard compaction effort was applied

to untreated and stabilised biosolids before undertaken falling head permeability test.

The permeability of untreated compacted biosolids ranges between 1.24 x 10-7 m/s to

1.60 x 10-7 m/s. The permeability of stabilised biosolids with 3% bauxsol varied from

0.96 x 10-7 m/s to 1.33 x 10-7 m/s and the permeability of stabilised biosolids with 5%

bauxsol varied from 0.90 x 10-7 m/s to 1.09 x 10-7 m/s. In general there is little

difference in the hydraulic conductivity value of biosolids stabilised with 3% and 5% of

bauxsol as compared to the untreated biosolids.

0.5

1.0

1.5

0 1 2 3 4 5


Per

mea

bilit

y (

x10-

7 m

/s)

0% Bauxsol 3% Bauxsol 5% Bauxsol

Figure 6.59. Permeability of untreated and stabilised biosolids with bauxsol

132

Table 6.10 to 6.12 summaries the engineering properties of biosolids stabilised with 1%,

3% and 5% bauxsol respectively.

Table 6.10. Summary of geotechnical characteristics of biosolids stabilised with 1% bauxsol



Atterberg

Limit




Compaction




CBR CBR Swell* % 0.50 0.38 0.52 0.25

CBR Value % 1.7 2.1 1.9 2.0


133




Atterberg

Limit




Compaction




CBR CBR Swell* % 0.56 0.97 0.34 1.11

CBR Value % 2.0 2.1 2.5 2.7

Consolidation

- Oedometer

e0 0.817 0.810 0.752






Consolidation

- Rowe Cell Preconsolidation Pressure kN/m2 - - 170

Triaxial

Compression

Type of Test - - CD

Cohesion kN/m2 - - 0

Phi Angle Degree - - 43.1

Falling Head





134




Atterberg

Limit




Compaction




CBR CBR Swell* % 0.50 1.23 0.60 0.47

CBR Value % 3.7 3.1 3.3 3.5

Consolidation

- Oedometer

e0 0.843 0.744 0.697






Triaxial

Compression

Type of Test - - CD

Cohesion kN/m2 - - 0

Phi Angle Degree - - 43.0

Falling Head





135

6.4 Geotechnical Characteristics of Biosolids Stabilised with Fly-ash


Moisture content tests were undertaken on samples of biosolids stabilised with 10%,

20%, and 30% of fly ash. The results as shown in Figure 6.60. Indicate variation in

moisture content between biosolids stabilised with fly ash and the untreated biosolids.

Moisture content was noted to decrease marginally with increasing percentages of fly

ash.

0

10

20

30

40

50

60

70

0 10 20 30 40 50

Percentage of fly ash added to biosolids (%)

Moi

stur

e C

onte

nt (

%)

Untreated biosolids

Stablised biosolids with 10% Fly ash



Figure 6.60. Moisture content variation with percentage of fly ash added to biosolids


with various percentages of fly ash. Figure 6.61 to 6.60 presents the atterberg limits

results of biosolids from stockpiles 1 to 3 after stabilisation with 10%, 20%, and 30% of

fly ash as compared to the untreated biosolids. It was noted that the liquid limit, plastic

limit and plastic index in all three stockpiles generally decreases with the addition of

increasing amounts of fly ash.

136

0

20

40

60

80

100

120

0 10 20 30Percentage of fly ash added to biosolids (%)

Moi

stur

e co

nten

t (%

)Liquid Limit

Plastic Limit

Plastic Index


0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)

Liquid Limit

Plastic Limit

Plastic Index


137

0

20

40

60

80

100

120


Moi

stur

e co

nten

t (%

)Liquid LimitPlastic LimitPlastic Index




obtained from the standard compaction test results of biosolids stabilised with 10%,

20% and 30% of fly ash. The compaction curves for the biosolids stabilised with 10%,

203% and 30% of fly ash are presented in Figure 6.64 . The compaction test results are

summarised in Table 6.13 to 6.8 and also the variation of the maximum dry density and

optimum moisture content with the percentage of fly ash added for the stabilisation is

presented in Figure 6.65 and Figure 6.66 respectively.


percentages of fly ash as compared to untreated biosolids. The maximum dry density of

stabilised biosolids varied from 0.87t/m3 to 0.88t/m3 with the addition of 10% fly ash;

0.87t/m3 to 0.91t/m3 with the addition of 20% fly ash and 0.88t/m3 to 0.92t/m3 with the

addition of 30% fly ash. In general, increasing the proportion of fly ash had little effect

on the maximum dry density of the biosolids.

138

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

20 25 30 35 40 45 50 55 60Moisture Content (%)

Dry

Den

sity

(t/m

3)

Biosolids + 10% Fly ashBiosolids + 20% Fly ashBiosolids + 30% Fly ashZAV (G=1.5)ZAV (G=1.75)

Figure 6.64. Compaction curves for the stabilised biosolids with fly ash


percentages of fly ash as compared to the untreated biosolids. The optimum moisture

content of stabilised biosolids was 45% to 46% with 10% fly ash, 40% to 43% with

20% fly ash and 37% to 42% with 30% fly ash respectively. The addition of fly ash was

found to slightly decrease the optimum moisture content of the biosolids as compared

with the untreated biosolids.

139

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0 10 20 30 40 50


Max

imum

Dry

Den

sity

(t/m

3)

0% Fly ash10% Fly ash20% Fly ash30% Fly ash

Figure 6.65. Variation of Maximum Dry Density (MDD) with percentage of fly ash

20.00

30.00

40.00

50.00

60.00

0 10 20 30 40 50


Opt

imum

Moi

stur

e C

onte

nt (

%)


Figure 6.66. Variation of Optimum Moisture Content (OMC) with percentage of fly ash

140


Figure 6.67 presents the CBR value results for biosolids stabilised with 10%, 20% and

30% of fly ash as compared to untreated biosolids. The CBR value of stabilised

biosolids varies from 3.9% to 5.2% with the addition of 10% of fly ash; 3.9% to 6.1%

with the addition of 20% of fly ash and 4.3% to 6.4% with the addition of 30% of fly

ash. In general, the stabilisation of biosolids with fly ash increases the CBR value of

biosolids.

From the results in Figure 6.67, it is apparent that biosolids stabilised with minimum of

10% fly ash satisfies the VicRoads minimum requirement of 2% CBR for Type B fill

material.

0.0

2.0

4.0

6.0

8.0

10.0

0 10 20 30 40 50


CB

R V

alue

(%

)

0% Fly ash 10% Fly ash 20% Fly ash 30% Flyash

Figure 6.67. CBR results of biosolids stabilised with fly ash

141

20.00

30.00

40.00

50.00

60.00

0 10 20 30 40 50


Opt

imum

Moi

stur

e C

onte

nt (

%)


Figure 6.68. Swell results after 4 days for biosolids stabilised with fly ash.


20% and 30% of fly ash. The swell value of stabilised biosolids varied from 0.21% to

0.45% with the addition of 10% of fly ash; 0.17% to 0.34% with the addition of 20% of

fly ash and 0.1% and 0.27% with the addition of 30% of fly ash.

142


Figure 6.69 presents the hydraulic conductivity of biosolids stabilised with 10%, 20%

and 30% of fly ash as compared to untreated biosolids. Standard compaction effort was

applied to untreated and stabilised biosolids before undertaken falling head permeability

test. The permeability of untreated compacted biosolids ranges between 1.24 x 10-7 m/s

to 1.60 x 10-7 m/s. The permeability of stabilised biosolids with 10% fly ash varied from

1.36 x 10-8 m/s to 10.3 x 10-8 m/s, permeability of stabilised biosolids with 20% fly ash

varied from 1.51x 10-8 m/s to 6.31 x 10-8 and the permeability of stabilised biosolids

with 30% fly ash varied from 4.21 x 10-8 m/s to 6.51 x 10-8 m/s. In general there is little

difference in the hydraulic conductivity value of biosolids stabilised with 10%, 20% and

30% of fly ash as compared to the untreated biosolids.

1.0

6.0

11.0

0 10 20 30 40 50


Per

mea

bilit

y (

x10-

8 m

/s)

0% Fly ash 10% Fly ash 20%Fly ash 30% Fly ash

Figure 6.69. Permeability of untreated and stabilised biosolids with fly ash

143

Table 6.13 to 6.15 summaries the engineering properties of biosolids stabilised with

10%, 20% and 30% fly ash respectively.

Table 6.13. Summary of geotechnical characteristics of biosolids stabilised with 10% fly ash



Atterberg

Limit




Compaction


Maximum Dry Density t/m3 0.87 0.87 0.88

Optimum Moisture Content % 45.3 46.1 47.2

CBR CBR Swell* % 0.21 0.45 0.31

CBR Value % 5.2 4.7 3.9

Consolidation

- Oedometer

e0 0.878 0.815 0.853






Falling Head





144




Atterberg

Limit




Compaction



Optimum Moisture Content % 40.3 41.5 43

CBR CBR Swell* % 0.34 0.22 0.17

CBR Value % 6.1 3.9 4

Consolidation

- Oedometer

e0 0.781 0.805 0.796






Falling Head





145




Atterberg

Limit




Compaction



Optimum Moisture Content % 37.5 40.2 42.6

CBR CBR Swell* % 0.1 0.19 0.27

CBR Value % 4.3 3.5 6.4

Consolidation

- Oedometer

e0 0.765 0.76 0.83






Falling Head





146

6.5 Analysis of Laboratory Test Results for Untreated and Stabilised Biosolids

6.5.1. Moisture content

The natural moisture content in the biosolids obtained from the stockpiles was found to

decrease with the increasing percentage of additives in the mixture. The proposed trend

of natural water content with the percentage of lime, cement and bauxsol in the mixture

is presented in Figure 6.70 and also the proposed trend of natural water content with the

percentage of fly ash in the mixture id presented in Figure 6.71.

0

10

20

30

40

50

60

70

0 1 2 3 4 5Percentage of addtives added to biosolids (%)

Wat

er c

onte

nt (

%)

LimeCementBauxsolBauxsolLimeCement

Figure 6.70. Correlation of natural water content with percentage of additives added to the biosolids

The relation between the natural water content and percentage of additives were found

to follow the linear variation as presented in equation 6.1 for lime, equation 6.2 for

cement, equation 6.3 for bauxsol and equation 6.4 for fly ash. A significant positive

correlation is observed between the natural moisture content and the percentage of

additives in the mixture.

147

0

10

20

30

40

50

60

70

0 10 20 30


Wat

er c

onte

nt (

%)

Figure 6.71. Correlation of natural water content with percentage of fly ash added to the biosolids

)7847.1(591.49 Lw ×−= Eq. (6.1)

)2362.2(631.50 Cw ×−= Eq. (6.2)

)6929.0(547.51 Bxw ×−= Eq. (6.3)

)6027.0(873.52 Fw ×−= Eq. (6.4)

Where w refers to the natural moisture content (%), L refers to content of lime by

weight (%), C refers to content of cement by weight (%), Bx refers to content of

bauxsol by weight (%) and F refers to content of fly ash by weight (%).

148

6.5.2. Atterberg Limits

The atterberg limits of biosolids stabilised with lime, cement, bauxsol and fly ash were

found to decrease with the increasing percentage of additives in the mixture. The

proposed trend of liquid limits, plastic limits and plasticity indexes with the percentage

of lime in the mixture is presented in Figure 6.72 and is found to follow the exponential

function as presented in equation 6.5 for the correlation of liquid limit, equation 6.6 for

the correlation of plastic limit and equation 6.7 for correlation of plasticity index with

the percentage of lime in the mixture. A significant positive correlation is observed

between the atterberg limits and the percentage of lime in the mixture.

( )LeLL ×−×= 0566.019.100 Eq. (6.5)

( )LePL ×−×= 0509.0476.78 Eq. (6.6)

( )LePI ×−×= 0788.0355.21 Eq. (6.7)

Where LL refers to the liquid limit (%), PL refers to plastic limit (%), PI refers to

plasticity index (%) and L refers to content of lime by weight (%).

0

20

40

60

80

100

120

0 1 2 3 4 5


Wat

er c

onte

nt (

%)

Liquid Limit (LL)

Plastic Limit (PL)

Plasticity Index (PI)

Figure 6.72. Correlation of atterberg limits with percentage of lime added to the biosolids

149

0

20

40

60

80

100

120

0 1 2 3 4 5


Wat

er c

onte

nt (

%)

Liquid Limit (LL)

Plastic Limit (PL)


Figure 6.73. Correlation of atterberg limits with percentage of cement added to the biosolids

The proposed trend of liquid limits, plastic limits and plasticity indexes with the

percentage of cement in the mixture is presented in Figure 6.73 and is found to follow

the exponential function as presented in equation 6.8 for the correlation of liquid limit,

equation 6.9 for the correlation of plastic limit and equation 6.10 for correlation of

plasticity index with the percentage of cement in the mixture. A significant positive

correlation is observed between the atterberg limits and the percentage of cement in the

mixture.

( )CeLL ×−×= 0619.006.101 Eq. (6.8)

( )CePL ×−×= 0559.0449.78 Eq. (6.9)

( )CePI ×−×= 0839.0526.22 Eq. (6.10)

Where C refers to content of cement by weight (%).

150

0

20

40

60

80

100

120

0 1 2 3 4 5


Wat

er c

onte

nt (

%)

Liquid Limit (LL)

Plastic Limit (PL)


Figure 6.74. Correlation of atterberg limits with percentage of bauxsol added to the biosolids


percentage of bauxsol in the mixture is presented in Figure 6.74 and is found to follow



plasticity index with the percentage of bauxsol in the mixture. A significant positive

correlation is observed between the atterberg limits and the percentage of bauxsol in the

mixture.

( )BxeLL ×−×= 0618.0588.99 Eq. (6.11)

( )BxePL ×−×= 0659.012.79 Eq. (6.12)

( )BxePI ×−×= 0734.0132.20 Eq. (6.13)

Where Bx refers to content of bauxsol by weight (%).

151

0

20

40

60

80

100

120

0 10 20 30


Wat

er c

onte

nt(%

)

Liquid Limit (LL)

Plastic Limit (PL)


Expon. (Liquid Limit

Figure 6.75. Correlation of atterberg limits with percentage of fly ash added to the biosolids


percentage of fly ash in the mixture is presented in Figure 6.75 and is found to follow



plasticity index with the percentage of fly ash in the mixture. A significant positive

correlation is observed between the atterberg limits and the percentage of fly ash in the

mixture.

( )FeLL ×−×= 0094.083.101 Eq. (6.14)

( )FePL ×−×= 0074.0994.77 Eq. (6.15)

( )FePI ×−×= 0171.0859.23 Eq. (6.16)

Where F refers to content of fly ash by weight (%).

152

6.5.3. Compaction characteristics

The correlation between dry density and the water content of the untreated biosolids is

presented in Figure 6.76 and was found to follow the power function as presented in

equation 6.17. The relation between the dry density and water content of the peat soil,

which has high content of the organics from the study by Den Haan (1997) in the

central Netherlands and also from the study by Bujang et al. (2007) in Malaysia is also

presented in Figure 6.76.

ρd = 0.9182w-0.0211

ρd = 35.075w-0.856ρd = 22.422w-0.804

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100Water content, w (%)

Dry

den

sity

, ρd

(Mg/

m3)

Dry density of untreated biosolids - from natural watercontentDen Haan (1997) - from the peat soil in the centralNetherlandBujang et al. (2007) - from peat soil in Malaysia

Figure 6.76. Correlation of dry density with water content in the biosolids

The relationship between the dry density and water content of the peat soil in above

mentioned studied was derived to follow the power functions as presented in equation

6.18 and 6.19 respectively.

0211.09182.0 −×= wdρ Eq. (6.17)

856..0075.35 −×= wdρ Eq. (6.18)

804..0422.22 −×= wdρ Eq. (6.19)

153

Where dρ refers to dry density of untreated biosolids and peat soil (Mg/m3) and w

refers to moisture content (%).

A significant positive correlation is observed between the biosolids and peat soil at the

higher amount of water content but the dry density of the biosolids lower than peat soil

at lower amount of water content below 50 percentages.

154

6.6 Conclusions: Laboratory Testing

Biosolid samples obtained from three stockpiles at Biosolids Stockpile Area, Western

Treatment Plant were tested to investigate the geotechnical characteristics of biosolids

and the suitability of biosolids as stabilised fill material. Based on the geotechnical

laboratory test results the following conclusions can be made:

The biosolid samples are classified as organic fined-grained soils of medium to high

plasticity with a group symbol of ‘OH’ as per Australian standard for the geotechnical

site investigation (AS 1276, 1993). The biosolid samples contain approximately 5%

gravel size, 50% sand size, 40% silt size and 5% clay sized particles.

The biosolids samples in the three stockpiles have high moisture content, liquid limit

and plasticity indices that are comparable to common inorganic soils. The moisture

content, liquid limit and plasticity indices decrease when biosolids stabilised with lime,

cement and bauxsol. The particle density of biosolids was found to be approximately

1.75 t/m3.

The shear strength test results from the triaxial test indicate that the biosolids stabilised

with the required proportions of additives indicate that the stabilised biosolids possess

suitable shear strength to make them suitable for use as fill material.

Consolidation test results of stabilised biosolids with additives provided coefficient of

consolidation results that need to be reviewed for the modelling of the biosolids

embankment in the next phase of this research. This is as the design input parameters

will be dependant on the imposed embankment loads.

Long-term laboratory testing of secondary consolidation settlement (creep

characteristics) of the biosolids were used as input parameters in the finite element

analysis of embankments using stabilised biosolids. The creep consolidation tests were

conducted to determine the secondary compression index for the finite element analysis.

The long-term creep consolidation tests were undertaken by applying each load

increment for seven days (as compared to the traditional 1 day load increment).

155

The coefficient of permeability from falling head permeability test results indicated that

the untreated and stabilised biosolids have low permeability similar to that of clay type

materials.

The CBR values of biosolids stabilised with a minimum of 5% lime, 3% cement, 3%

bauxsol and 30% crushed brick satisfies the VicRoads specification for Type B fill

material which requires a minimum CBR of 2%.

The composition of the biosolids will have an impact on the geotechnical testing results

as will other factors such as formation history, treatment process, drying duration,

drying method, storage methods, and storage period and handling methods.

156

7 FINITE ELEMENT MODELLING OF STABILISED BIOSOLID

EMBANKMENTS

7.1 Overview of Finite Element Modelling

Embankment design comprises of three vital design criteria: settlement, slope stability

and bearing capacity. Finite element modelling is a useful tool to simulate the in-situ

field conditions and to predict embankment behaviour. Presently, there are various finite

element softwares available for the analysis of embankments and other geotechnical

issues. For this project, Plaxis Version 8 (Plaxis, 2006) was used to analyse the

behaviour of embankments when biosolids were used with various additives as an

engineered fill in the embankments.

This report presents the results of the finite element analysis of biosolids when

stabilised with cement, lime, bauxsol and fly ash based on laboratory parameters

obtained from geotechnical laboratory testing on biosolids.

To negate the effect of long term decomposition of biosolids and after discussions with

local road works authority in Victoria, Australia (VicRoads), the thickness of the

stabilised biosolids layer was restricted to 0.5 meters for the various embankment

scenarios analysed. Finite element modelling was undertaken for embankments with

heights ranging from 2 to 5 meters.

As basalt is commonly obtained in the Western suburbs and the drained parameters for

basalt are readily available, the stabilised biosolids embankments were studied when

constructed on basalt formations.

Discussions with VicRoads indicated that their requirement for the embankment would

be for a residual settlement not exceeding 50 mm over a period of 20 years after a

maximum of 6 months of preloading.

157

7.2 Finite Element Modelling Theory

7.2.1. Geometry model

The plane strain model was used in the analysis as it is suitable for embankments with a

uniform cross section, corresponding stress state and loading scheme over a certain

length perpendicular to the cross section (z-direction as shown in Figure 7.1).

Displacement and strain in z-direction was assumed to be zero but the normal stresses in

z-direction are fully taken into account in this model.

Figure 7.1. Coordinate system of geometry.

A typical full scale geometry of a stabilised biosolids embankment on basalt formation

is illustrated in Figure 7.2. In the analysis the ground water was assumed to be at a level

of 1m below the ground surface.

Biosolids

Type C fill

Type B fill

Type C fill

X = 3H 30m X = 3H

H

Basalt

1

3 1.5

1

0.5m

Impermeable geomembrane separator or

0.5 m impermeable clay layer

Figure 7.2. Typical geometry of embankment with stabilised biosolids on basalt formation.

158

An impermeable geomembrane separator or 0.5 m impermeable clay layer is used to

encapsulate the biosolids and to prevent any seepage or leaching of biosolids into the

fill material. The geomembrane and clay layer acts as a separator and will furthermore

provide a transition between the stabilised biosolids and the engineered fill.

Due to the symmetry of the embankment, only half of the embankment was analysed

with the appropriate boundary conditions. The side boundaries of the embankment were

specified as free in the vertical direction. The bottom boundary was specified as a fixed

in the vertical and horizontal directions. To avoid any influence of the outer boundary,

the model was extended in horizontal (x-direction) a total length of 20m from the toe of

the embankment.

VicRoads defines Type B fill as material which has a minimum assigned CBR of 2 to 5

%, be free from organic and has a particle dimension not more than 150 to 450 mm

depending on the place of use. VicRoads defines Type C fill as material which has

lesser quality material than Type B and shall be capable of spreading in layers of not

more than 500mm.

The geometry model of a typical 5m embankment with 0.5m of stabilised biosolids is

presented in Figure 7.3. In the analysis, the Type B engineered fill material was

specified as being placed in three stages. Furthermore the final layer of Type B fill was

placed simultaneously as the Type C fill layer.

Figure 7.3. Typical geometry model for a 5m high embankment using stabilised biosolids.

159

7.2.2. Finite element mesh for embankment

Finite element meshes were generated by using 15 node triangular elements. More

elements were generated at the toe of the embankment as that is the critical point for

slope stability analysis. The mesh coarseness was selected as “fine” for element

distribution in the models as a finer finite element mesh gives the more accurate results

than a coarser mesh.

Figure 7.4 presents the finite element mesh for the geometry model of a typical 5m high

embankment. Figure 7.5 presents the nodal elements for the geometry model of a

typical 5 m high embankment. Figure 7.6 presents the stress points for the geometry

model of a typical 5m high embankment.

Figure 7.4. Finite element mesh for the geometry model of a 5m high embankment.

Figure 7.5. Finite element mesh with nodes for the geometry model of a 5m high embankment.

160

Figure 7.6. Finite element mesh with stress points for the geometry model of a 5m high embankment.

7.2.3. Soil models

Plaxis is capable of analysing eight different soil model types. The Mohr-coulomb

models and soft soil creep models were the appropriate models in this case and were

used in the analysis of the embankments.

The Mohr-coulomb model was specified for the subsoil comprising basalt and the

engineered fill. The soft soil creep model was specified for the stabilised biosolids in the

embankment to analyse the long-term creep behaviour of the stabilised biosolids.

A minimum pore water pressure of 0.01 kN/m2 was specified in the analysis which

enables a conservative analysis of consolidation settlement of the embankments. A

traffic load of 20kPa was specified in the analyses prior to the preloading period.

7.2.3.1. Mohr-coulomb model

The Mohr-coulomb model is known as perfect plastic model. The Mohr-coulomb model

is a constitutive model with a fixed yield surface, i.e. a yield surface that is fully defined

by model parameters and not affected by plastic straining. The Mohr-coulomb model

requires the following input parameters:

161

E : Young’s modulus (kN/m2)

ν : Poisson’s ratio

Φ : Friction angle (Degree)

с : Cohesion (kN/m2)

ψ : Dilatancy angle (Degree)

The Young’s modulus is the basic stiffness modulus in the Mohr-coulomb model.

Figure 7.7 presents the computation of the Young’s modulus in the Mohr-coulomb

model. E0 and E50 is the initial slope and the secant modulus at 50% strength

respectively in the stress versus strain variation obtained from triaxial tests. The

deviator stress is denoted as (σ1 – σ3).

Figure 7.7. Derivation of elastic modulus from triaxial tests.

7.2.3.2. Soft soil creep model

Biosolids behaviour is similar to a soft soil with a high degree of compressibility. The

compressibility and creep consolidation properties of biosolids play a vital role in

engineering behaviour of embankment. As such, the soft soil creep model was

considered the best soil model to be used to simulate the compressibility behaviour of

stabilised biosolids in actual field conditions. The soft soil creep model requires the

following input parameters:

162

Φ : Friction angle (Degree)

λ* : Modified compression index

κ* : Modified swelling index

µ* : Secondary compression index

The modified compression index (λ*), modified swelling index (κ*) and secondary

compression index (µ*) were determined from the one dimensional consolidation

(oedometer) test results.

The secondary compression index (µ*) is the important parameter in the analysis the

creep properties of biosolids. The secondary compression index was obtained from

long-term creep consolidation tests using oedometers.

The modified compression index (λ*), modified swelling index (κ*) and secondary

compression index (µ*) were subsequently derived using equations 8.1, 8.2 and 8.3

respectively.

Eq. (8.1)

Eq. (8.2)

Eq. (8.3)

where Cc is the compression index, Cr is the recompression index and Cα is the

secondary compression index which was parameters derived from the long-term creep

consolidation test results.

)1(3.2 0

*

e

C c

+=λ

)1(3.2

2

0

*

e

C r

+=κ

)1(3.2 0

*

e

C

+= αµ

163

7.2.4. Material properties of subsoil and fill material

The finite element model parameters for the basalt formation underlying the

embankment and the engineered fill (Type B and C) was obtained from various local

reports on the property of these materials in Victoria. The geotechnical parameters used

in the models for basalt and engineered fill material is presented in Table 7.1.

Table 7.1.Summary of finite element model parameters for basalt and engineered fill.

Mohr-Coulomb Unit Basalt Engineered Fill

Parameter - Drained Drained

γunsat [kN/m³] 19 19

γsat [kN/m³] 21 19

kx [m/day] 1 1

ky [m/day] 1 1

Eref [kN/m²] 35000 25000

ν [-] 0.3 0.35

Gref [kN/m²] 13450 9250

Eoed [kN/m²] 47115 40125

cref [kN/m²] 2 5

ϕ [°] 25 25

ψ [°] 0 0

164


Lime

This section discusses the results of finite element analysis of embankment using

biosolids stabilised with 5% lime. To negate the effect of long term decomposition of

biosolids, the thickness of the stabilised biosolids layer was restricted to 0.5 meters for

the various embankment scenarios analysed. VicRoads indicated that their requirement

for the embankment would be for a residual settlement not exceeding 50 mm after a

maximum of 6 months of preloading.





Finite element modelling was undertaken in the analysis for embankments of 2 to 5

meters in height. The typical geometry for the finite element analysis of embankments

using biosolids stabilised with 5% lime is presented in Figure 7.8.


engineered fill (Type B and C). The soft soil creep model was specified for the

stabilised biosolids in the embankment to analyse the creep consolidation behaviour of

the biosolids after 6 months of preloading. A minimum pore water pressure of 0.01

kN/m2 was specified in the calculation phase of the analyses to determine the residual

settlement after 6 months of preloading which enables a conservative analysis of

consolidation settlement of the embankments. A traffic load of 20 kPa was specified in

the analyses prior to the preloading period.

The material properties for engineered fill and basalt were presented previously in Table

7.1. The material properties of biosolids stabilised with 5% lime is summarised in Table

7.2. These material properties were used as input parameters for the finite element

models and were derived from the laboratory testing results.

165

Figure 7.9 presents the finite element deformation mesh for the 5 m embankment using

biosolids stabilised with 5% lime. Figure 7.10 presents the vertical settlement of the 5 m

embankment using biosolids stabilised with 5% lime.

Biosolids + 5% Lime

Type C fill

Type B fill

Type C fill

X = 3H 30m X = 3H

H

Basalt

1

3 1.5

1

0.5m

Impermeable geomembrane separator or0.5 m impermeable clay layer

Figure 7.8. Typical geometry for embankment using biosolids stabilised with 5% lime

Table 7.2. Material properties of biosolids stabilised with 5% lime.

Soft Soil Creep Unit Biosolids + 5% Lime

Parameter - Undrained

γunsat [kN/m³] 12.1

γsat [kN/m³] 13.4

kx [m/day] 0.01

ky [m/day] 0.01

λ∗ [-] 0.1

κ∗ [-] 0.01

µ∗ [-] 0.06

c [kN/m²] 1

ϕ [°] 45

ψ [°] 0

νur(nu) [-] 0.15

Κ0nc [-] 0.43

166

Figure 7.9. Deformation mesh of 5 m embankment using biosolids stabilised with 5% lime

Figure 7.10. Vertical settlement of 5 m embankment using biosolids stabilised with 5% lime.

Figure 7.11 presents the variation of total vertical settlement as well as the residual

settlement with time for the finite element analysis of the 5m high embankment using


A residual settlement of 27 mm was obtained after 6 months of preloading for the 5 m

high embankment which meets the VicRoads requirement of a maximum of 50 mm

after 6 months of preloading. A total vertical settlement of 449 mm was obtained for the

5 m high embankment.

167

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250 300 350 400 450

Time (Day)

Set

tlem

ent (

mm

)

6 months preloading period

27mm

Figure 7.11. Variation of vertical settlement of 5 m embankment using biosolids stabilised with 5% lime.

Figure 7.12 compares the variation of total vertical settlement with time for the 2 to 5 m

high embankments using biosolids stabilised with 5% lime. As expected, the magnitude

of settlement and residual settlement increases with the height of the embankment.

Table 7.3 summarises the total and residual settlement and time taken to complete the

settlement after 6 months of preloading of embankments using biosolids stabilised with

5% lime. In total, 401 days were taken to complete the total settlement for the 5 m high

embankment using biosolids stabilised with 5% lime.

168

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250 300 350 400 450Time (Day)

Set

tlem

ent (

mm

)

5m Embankment 4m Embankment 3m Embankment 2m Embankment


Figure 7.12. Variation of vertical settlement of various embankments using biosolids stabilised with 5% lime.

Table 7.3. Summary of total and residual settlement of embankments using biosolids stabilised with 5% lime.

Embankment

height (H) Total

settlement

(mm)

Total settlement

in the biosolids

layer (mm)

Residual

settlement –

after 6 months

(mm)

Total time

(days)

2 m 380 304 28 377

3 m 398 318 21 344

4 m 429 343 26 379

5 m 449 359 27 401

The residual settlement of the embankments analysed were all found to be within

VicRoad’s residual settlement requirement of a maximum of 50 mm after 6 months of

preloading. The residual settlement reported is until the completion of total settlement

based on a minimum pore water pressure of 0.01 kN/m2 that was conservatively

specified in the calculation phase of the analyses (as compared to the traditionally

recommended minimum pore water pressure of 1 kN/m2).

169


Cement

This section discuss the results of finite element analysis of embankment using

biosolids stabilised with 3% and 5% cement. To negate the effect of long term

decomposition of biosolids, the thickness of the stabilised biosolids layer was restricted

to 0.5 meters for the various embankment scenarios analysed. VicRoads indicated that

their requirement for the embankment would be for a residual settlement not exceeding

50 mm after a maximum of 6 months of preloading.







using biosolids stabilised with 3% and 5% cement is presented in Figure 7.13.







consolidation settlement of the embankments. A traffic load of 20 kPa was specified in



7.1. The material properties of biosolids stabilised with 3% and 5% cement is

summarised in Table 7.4. These material properties were used as input parameters for

the finite element models and were derived from the laboratory testing results.

170


biosolids stabilised with 3% cement. Figure 7.15 presents the vertical settlement of the 5

m embankment using biosolids stabilised with 3% cement.


Type C fill

Type B fill

Type C fill

X = 3H 30m X = 3H

H

Basalt

1

3 1.5

1

0.5m


Figure 7.13. Typical geometry for embankment using biosolids stabilised with cement.

Table 7.4. Material properties of biosolids stabilised with 3% and 5%cement.

Soft Soil Creep Unit Biosolids + 3% Cement Biosolids + 5% Cement

Parameter - Undrained Undrained

γunsat [kN/m³] 11.6 11.6

γsat [kN/m³] 13.3 13.3

kx [m/day] 0.01 0.01

ky [m/day] 0.01 0.01

λ∗ [-] 0.1 0.08

κ∗ [-] 0.02 0.01

µ∗ [-] 0.07 0.05

c [kN/m²] 1 1

ϕ [°] 45 40

ψ [°] 0 0

νur(nu) [-] 0.15 0.15

Κ0nc [-] 0.42 0.51

171

Figure 7.14. Deformation mesh of 5 m embankment using biosolids stabilised with 3% cement.

Figure 7.15. Vertical settlement of 5m embankment using biosolids stabilised with 3% cement.


settlement with time for the finite element analysis of the 5 m high embankment using

biosolids stabilised with 3% and 5% cement.


high embankment using biosolids stabilised with 3% cement. A residual settlement of

17 mm was obtained after 6 months of preloading for the 5 m high embankment using

biosolids stabilised with 5% cement. The residual settlements of 5 m embankment using

biosolids stabilised with 3% and 5% cement, as such meet the VicRoads requirement of

a maximum of 50 mm after 6 months of preloading.

172

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250 300 350 400 450 500

Time (Day)

Set

tlem

ent

(mm

)

Biosolids + 5% Cement Biosolids + 3% Cement


30mm

17mm

Figure 7.16. Variation of vertical settlement of 5 m embankment using biosolids stabilised with 3% and 5% cement.

A total vertical settlement of 435 mm was obtained for the 5 m high embankment using

biosolids stabilised with 3% cement. A total vertical settlement of 317 mm was obtained

for the 5 m high embankment using biosolids stabilised with 5% cement.


high embankments using biosolids stabilised with 3% cement. Figure 7.18 compares the

variation of total vertical settlement with time for the 2 to 5 m high embankments using

biosolids stabilised with 5% cement. As expected, the magnitude of settlement increases

with the height of the embankment.

173

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250 300 350 400 450Time (Day)

Set

tlem

ent (

mm

)



Figure 7.17. Variation of vertical settlement of various embankments using biosolids stabilised with 3% cement.

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350 400Time (Day)

Set

tlem

ent (

mm

)



Figure 7.18. Variation of vertical settlement of various embankments using biosolids stabilised with 5% cement.

174



3% cement. In total, 418 days were taken to complete total settlement for the 5 m high

embankment using biosolids stabilised with 3% cement.

Table 7.5. Summary of total and residual settlement of embankments using biosolids stabilised with 3% cement.

Embankment

height (H) Total

settlement

(mm)

Total settlement

in the biosolids

layer (mm)

Residual

settlement –

after 6 months

(mm)

Total time

(days)

2 m 348 278 26 360

3 m 388 310 24 376

4 m 415 332 27 392

5 m 435 348 30 418

Table 7.6. Summary of total and residual settlement of embankments using biosolids stabilised with 5% cement.

Embankment

height (H) Total

settlement

(mm)

Total settlement

in the biosolids

layer (mm)

Residual

settlement –

after 6 months

(mm)

Total time

(days)

2 m 265 212 17 336

3 m 282 226 15 329

4 m 303 242 17 354

5 m 317 254 17 356

175



5% cement. In total, 356 days were taken to complete total settlement for the 5 m high

embankment using biosolids stabilised with 5% cement.







176


Bauxsol


biosolids stabilised with 3% and 5% bauxsol. To negate the effect of long term

decomposition of biosolids, the thickness of the stabilised biosolids layer was restricted

to 0.5 meters for the various embankment scenarios analysed. VicRoads indicated that

their requirement for the embankment would be for a residual settlement not exceeding

50 mm after a maximum of 6 months of preloading.







using biosolids stabilised with 3% and 5% bauxsol is presented in Figure 7.19.







consolidation settlement of the embankments. A traffic load of 20kPa was specified in



7.1. The material properties of biosolids stabilised with 3% and 5% bauxsol is

summarised in Table 7.7. These material properties were used as input parameters for

the finite element models and were derived from the laboratory testing results.

177


biosolids stabilised with 3% bauxsol. Figure 7.21 presents the vertical settlement of the

5 m embankment using biosolids stabilised with 3% bauxsol.

Biosolids + 3% Bauxsol

Type C fill

Type B fill

Type C fill

X = 3H 30m X = 3H

H

Basalt

1

3 1.5

1

0.5m


Figure 7.19. Typical geometry for embankment using biosolids stabilised with bauxsol.

Table 7.7. Material properties of biosolids stabilised with 3% and 5% bauxsol.

Soft Soil Creep Unit Biosolids + 3% Bauxsol Biosolids + 5% Bauxsol

Parameter - Undrained Undrained

γunsat [kN/m³] 12.5 11.9

γsat [kN/m³] 13.4 13.4

kx [m/day] 0.01 0.01

ky [m/day] 0.01 0.01

λ∗ [-] 0.12 0.11

κ∗ [-] 0.02 0.02

µ∗ [-] 0.05 0.04

c [kN/m²] 1 1

ϕ [°] 43 43

ψ [°] 0 0

νur(nu) [-] 0.15 0.15

Κ0nc [-] 0.45 0.45

178

Figure 7.20. Deformation mesh of 5 m embankment using biosolids stabilised with 3% bauxsol.

Figure 7.21. Vertical settlement of 5 m embankment using biosolids stabilised with 3% bauxsol.


settlement with time for the finite element analysis of the 5m high embankment using

biosolids stabilised with 3% and 5% bauxsol.


high embankment using biosolids stabilised with 3% bauxsol. A residual settlement of 6

mm was obtained after 6 months of preloading for the 5 m high embankment using

biosolids stabilised with 5% bauxsol. The residual settlements of 5 m embankment

179

using biosolids stabilised with 3% and 5% bauxsol, as such meet the VicRoads

requirement of a maximum of 50 mm after 6 months of preloading.

0

50

100

150

200

250

300

350

400

450

0 50 100 150 200 250 300 350 400

Time (Day)

Set

tlem

ent

(mm

)

Biosolids + 5% Bauxsol Biosolids + 3% Bauxsol


17mm

6mm

Figure 7.22. Variation of vertical settlement of 5 m embankment using biosolids stabilised with 3% and 5% bauxsol.

A total vertical settlement of 398 mm was obtained for the 5m high embankment using

biosolids stabilised with 3% bauxsol. A total vertical settlement of 330 mm was

obtained for the 5m high embankment using biosolids stabilised with 5% bauxsol.


high embankments using biosolids stabilised with 3% bauxsol. Figure 7.24 compares

the variation of total vertical settlement with time for the 2 to 5 m high embankments

using biosolids stabilised with 5% bauxsol. As expected, the magnitude of settlement

increases with the height of the embankment.

180

0

50

100

150

200

250

300

350

400

450

0 50 100 150 200 250 300 350Time (Day)

Set

tlem

ent (

mm

)



Figure 7.23. Variation of vertical settlement of various embankments using biosolids stabilised with 3% bauxsol.

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300Time (Day)

Set

tlem

ent (

mm

)



Figure 7.24. Variation of vertical settlement of various embankments using biosolids stabilised with 5% bauxsol.

181



3% bauxsol. In total, 344 days were taken to complete total settlement for the 5 m high

embankment using biosolids stabilised with 3% bauxsol.

Table 7.8. Summary of total and residual settlement of embankments using biosolids stabilised with 3% bauxsol.

Embankment

height (H) Total

settlement

(mm)

Total settlement

in the biosolids

layer (mm)

Residual

settlement –

after 6 months

(mm)

Total time

(days)

2 m 329 263 18 334

3 m 349 279 14 312

4 m 375 300 13 301

5 m 398 318 17 344

Table 7.9. Summary of total and residual settlement of embankments using biosolids stabilised with 5% bauxsol.

Embankment

height (H) Total

settlement

(mm)

Total settlement

in the biosolids

layer (mm)

Residual

settlement –

after 6 months

(mm)

Total time

(days)

2 m 270 216 8 255

3 m 286 229 3 223

4 m 312 250 4 237

5 m 330 264 6 244

182



5% bauxsol. In total, 244 days were taken to complete total settlement and residual

settlement respectively for the 5 m high embankment using biosolids stabilised with 5%

bauxsol.







183

7.6 Finite Element Analysis of Embankments using Untreated Biosolids


untreated biosolids. To negate the effect of long term decomposition of biosolids, the

thickness of the stabilised biosolids layer was restricted to 0.5 meters for the various

embankment scenarios analysed. VicRoads indicated that their requirement for the

embankment would be for a residual settlement not exceeding 50 mm after a maximum

of 6 months of preloading.



using untreated biosolids is presented in Figure 7.25.



untreated biosolids in the embankment to analyse the creep consolidation behaviour of




consolidation settlement of the embankments. A traffic load of 20kPa was specified in


The material properties for engineered fill and basalt was presented previously in Table

7.1. The material properties of untreated biosolids is summarised in Table 7.10. These

material properties were used as input parameters for the finite element models and

were derived from the laboratory testing results obtained.

184

Untreated Biosolids

Type C fill

Type B fill

Type C fill

X = 3H 30m X = 3H

H

Basalt

1

3 1.5

1

0.5m

Impermeable geomembrane separator or

0.5 m impermeable clay layer

Figure 7.25. Typical geometry for embankment using untreated biosolids.

Table 7.10. Material properties of untreated biosolids.

Soft Soil Creep Unit Untreated Biosolids

Parameter - Undrained

γunsat [kN/m³] 12.05

γsat [kN/m³] 13.61

kx [m/day] 0.01

ky [m/day] 0.01

λ∗ [-] 0.15

κ∗ [-] 0.02

µ∗ [-] 0.2

c [kN/m²] 1

ϕ [°] 11

ψ [°] 0

νur(nu) [-] 0.15

Κ0nc [-] 0.81

185

The finite element analysis of embankment using untreated biosolids was not completed

successfully. This was because the low shear strength and friction angle of the untreated

biosolids was found to be inadequate to carry the embankment and traffic load.

Figure 7.26 presents the collapsed finite element deformation mesh for the 5m

embankment using untreated biosolids. The analysis confirms that biosolids has to be

stabilised before usage as embankment fill material and as such untreated biosolids

cannot be used in such embankment applications.

Figure 7.26. Collapsed deformation mesh of 5 m embankment using untreated biosolids.

The residual settlement of the biosolids stabilised with various additives including lime

(5%), cement (3%, 5%), bauxsol (3%, 5%) and fly ash (10%, 20%, 30%) were found to

be within VicRoad’s residual settlement requirement of a maximum of 50mm over a

period of 20 years after 6 months of preloading. The results of the analysis agree well

with the laboratory testing results and indicate that biosolids when stabilised with

additives to the required percentages can be use as stabilised fill in embankments.

The residual settlement reported for the stabilised biosolids with lime, cement and

bauxsol was until the completion of total settlement based on a minimum pore water

pressure of 0.01 kN/m2 that was conservatively specified in the calculation phase of the

analyses (as compared to the traditionally recommended minimum pore water pressure

of 1 kN/m2).

186

7.7 Conclusions: Finite Element Modelling

Finite element analysis was conducted to analyse the behaviour of embankment using

stabilised biosolids with lime, cement, bauxsol and fly ash as well as untreated

biosolids.

An analysis was undertaken for untreated biosolids but the analysis could not be

completed successfully. This was because the low shear strength and friction angle of

the untreated biosolids was found to be inadequate to carry the embankment and traffic

load. The analysis confirms that biosolids has to be stabilised before usage as

embankment fill material and as such untreated biosolids cannot be used in such

embankment applications.

An impermeable geomembrane separator or 0.5 m impermeable clay layer is

recommended to be used to encapsulate the biosolids and to prevent any seepage or

leaching of biosolids into the fill material. The geomembrane and clay layer acts as a

separator and will furthermore provide a transition between the stabilised biosolids and

the engineered fill. The cost of encapsulating the stabilised biosolids with a

geomembrane is minimal as the geomembrane has been included solely for separation

purposes. The stabilised biosolids is thus confined and encapsulated 3 dimensionally

and there is furthermore conservation of mass but not volume of stabilised biosolids as

the stabilised biosolids will still comprise of air and moisture voids.

No additional fill for surcharging of the embankment has been provided in this study.

Topping up of the embankments is required to the specified finish levels following the

completion of the 6 month preloading period. This is to compensate for the total

settlements of the embankment during construction and preloading.

The summary of the residual and total settlement in the embankment and also in the

0.5m thick biosolids layer for 2 to 5 m embankments using various additives

summarised in Table 7.11 and the unit weight of biosolids stabilised with various

additives also summarised in Table 7.11.

187

Table 7.11. Summary of residual settlement, total settlement and unit weight of biosolids.

Stabilised Biosolids

Residual

Settlement

(mm) *

Total

Settlement

(mm) *

Total

Settlement in

biosolids

layer

(mm) *

Saturated

unit weight

(kN/m3)

Biosolids + 5% Lime 21 - 28 380 - 449 304 - 359 13.4

Biosolids + 3% Cement 24 - 30 348 - 435 278 - 348 13.3

Biosolids + 5% Cement 15 - 17 265 - 317 212 - 254 13.3

Biosolids + 3% Bauxsol 13 - 18 329 – 398 263 - 318 13.4

Biosolids + 5% Bauxsol 3 - 8 270 - 330 216 - 264 13.4

* Settlement range for 2 m to 5 m embankments

The settlement results form the finite element modelling of the embankment using

stabilised biosolids with lime, cement, and bauxsol is indicate that the total settlement of

2m to 5m height embankments varied between 265mm to 449mm. The embankment

using stabilised biosolids with 5% cement indicate low total settlement of 265mm for

2m to 5m height embankments and also the embankment using stabilised biosolids with

5% lime indicate the higher total settlement of 449mm for 2m to 5m height

embankments. The total settlement in the biosolids layer in embankment using

stabilised biosolids with all admixtures indicates that the most of the settlement are in

the biosolids layer of itself. The highes total settlement in the biosolids layer was in the

embankment using 0.5m thick layer of stabilised biosolids with 5% lime.

188

8 BIODEGRADATION SETTLEMENT OF BIOSOLIDS AND

CORROSIVITY

8.1 Methodology and Approach of Biodegradation settlement of Biosolids

Prediction of waste due to biosolids was historically carried out applying the rheological

model for the long-term compression in peat (Edil et.al 1990). Yen and Scanlon (1975)

used the hyperbolic function used in settlement prediction of soft ground under

surcharge fill. Park and Lee (1997 & 2002) proposed a method of prediction for

biodegradation applying biological process. More accurate prediction of biosolids and

other waste decomposition rates in relationship with initial chemistry of waste was

studied by Rowe et.al. (2001) Melillo et.al (1982), Gower and Son (1992), Stump and

Binkley (1993), Scott and Binkley (1997) stated that the lignin to N ratio of litter is

often a good predictor of rates of decomposition.

Settlement due to biodegradation occurs over a very long period. Magnitude of

biodegradable settlement is furthermore dependent upon biodegradable fraction. This

biodegradable fraction could be estimated applying following equation described by

Shah (2000) as follow:

)28.0(83.0 LCBF ×−= Eq. (8.1)

Where BF is biodegradable fraction, LC is Lignin content as a percentage of volatile.

0.83 and 0.28 are empirical constants. Depending upon the lignin content,

biodegradable fraction could be varying between 10 to 80 %.

Depending upon the biodegradable fraction, the rate of biodegradation can be classified

as ranging between slowly degradable to rapidly degradable biosolids. The decay rate of

biodegradable wastes are categorised as 0.00001, 0.0001, 0.001 and 0 for non-

biodegradable, slowly biodegradable, moderately biodegradable and rapidly

biodegradable materials respectively (Chakma & Mathur 2007).

189

A generalized equation for biodegradation decay of waste was given by Park and Lee

(1997) as follow:

( ){ }tkEDHtS ×−−××= exp1)( 0 Eq. (8.2)

Where S(t) is settlement at time t in metre, H0 is the initial height of waste in metre, ED

is total expected strain in fraction, k is the first order kinetic constant in (day -1) and t is

time since the start of decay in day.

However, Park and Lee model did not take into consideration of variable parameters

such as moisture content, bulk density, pH and temperature for predicting settlement

due to biodegradation. Therefore in 2007 Chakma and Mathur proposed the modified

model, which takes into consideration of abovementioned parameters.

( ) ( ) ( ){ }[ ] ( )4,3,2,1:;4,3,2,1,,, ==××−= jiMpHTkdt

Mdsij

si θς Eq. (8.3)

Where, Ms1, Ms2, Ms3 and Ms4 are the masses of the slowly degradable, moderately

degradable, rapidly degradable solid waste with their respective rate constants ks1, ks2,

ks3 and ks4. The ζ is a function of temperature, pH and moisture content (θ) in fraction as

defined by following equation:

( )( )

−+

×−−××=

184

exp1

3

4ln7exp

,,

2

T

pHT

pHT

θθς Eq. (8.4)

The volume of waste at any time t (Vs,N) can be calculated applying following equation:

( ) ( ){ }tpHTkMtV

jsiiNs ××−××

=θςρ ,,exp

1)(, Eq. (8.5)

The strain due to biodegradation is estimated using following equation:

( )

−

=Ni

NsNibi V

tVVt

,

,, )()(ε Eq. (8.6)

Where Vi,N is the initial volume of waste.

190

Finally, the settlement due to biodegradation at any time (t) can be computed applying

following equation:

)()( tHtS biib ε×= Eq. (8.7)

Where , Hi is the initial thickness of waste.

In the biodegradation settlement analysis, the following assumptions were made:

• Biosolids in this study is considered as slowly degradable waste as it might have

passed the active decomposition stage.

• After completing construction, biodegradation will occur concurrently with

consolidation.

• The residual thickness of the biosolids layer with admixtures in the

biodegradation is assumed the thickness after the completion of primary,

secondary and creep consolidation settlement, which were determined from the

finite element results on different height of embankments.

• The residual thickness of the untreated biosolids was assumed as 0.2m, as the

primary, secondary and creep settlements are not determined from the finite

element modelling.

The total settlement and residual settlement after the completion of primary, secondary

and creep settlements for the stabilised biosolids with admixtures from the finite

element result is presented in Table 8.1.

Table 8.1. Settlements and residual thickness of the biosolids layer after the primary, secondary and creep consolidation.

Biosolids Mixtures

Settlement and Residual Thickness Embankment Heights

2m 3m 4m 5m

Biosolids + 5% Lime

Settlement in Biosolids layer 304 318 343 359 Residual Thickness of the biosolids layer 196 182 157 141









191

The assumed residual thickness, after the completion of primary and consolidation

settlement on the various embankment heights of 2m, 3m, 4m and 5m with the

untreated and also the stabilised biosolids with various admixtures were presented in

Table 8.2. These residual settlements were used in the biodegradation settlement

analysis.

Table 8.2. Assumed residual thickness of the biosolids layer for biodegradation settlement computation.

Biosolids Mixtures Embankment height

2m 3m 4m 5m

Untreated Biosolids 200 200 200 200

Biosolids stabilised with 5% Lime 250 240 230 220

Biosolids stabilised with 3% Cement 230 220 220 210

Biosolids stabilised with 5% Cement 290 275 255 250

Biosolids stabilised with 3% Bauxsol 235 220 200 200

Biosolids stabilised with 5% Bauxsol 285 270 250 235

The parameters which were used in the biodegradation settlement analysis, such as

temperature, moisture content and the density of untreated and stabilised biosolids with

various additives, is presented in Table 8.3. The pH value of the untreated and stabilised

biosolids with lime, cement, bauxsol and fly-ash are also one of the parameter in the

settlement analysis due to the biodegradation. The pH test results of untreated and

stabilised biosolids with lime, cement, bauxsol and fly-ash are presented and discussed

in Table 8.4 to Table 8.8.

192

Table 8.3. Assigned biosolids parameters for biodegradation settlement analysis.

Temperature, T

(Degree C)

Moisture Content, θ

(Fraction)

Density,

ρ

(kg/m3)

Untreated Biosolids 30 0.53 1617

Biosolids stabilised with 5% Lime 30 0.40 1567

Biosolids stabilised with 3% Cement 30 0.42 1673

Biosolids stabilised with 5% Cement 30 0.39 1517

Biosolids stabilised with 3% Bauxsol 30 0.49 1687

Biosolids stabilised with 5% Bauxsol 30 0.48 1657

The biodegradation settlement analysis were undertaken on untreated biosolids and also

only for those blends that satisfy the geotechnical design requirement of fill material for

the highway embankment as presented in the Chapter 6. Predictions of settlement due to

biodegradation were carried out for untreated biosolids and stabilised biosolids with

5 % lime, 3% cement, 5% cement, 3% bauxsol and 5% bauxsol.

The flow on this biodegradation settlement analysis model which approach to

biodegrade completely of some point. This biodegradation settlement model does not

cater the reduction of thickness with time, that reduction in thickness was not

considered, and also the reduction of biodegradable ability and also that reduction in

biodegradable ability were not considered. Further research work is recommended to

accurately model biodegradation accounting for the reduction of thickness and the

reduction of biodegradable ability with time.

193

8.2 pH and Electrical Conductivity Tests

For the investigation of biodegradation settlement of biosolids and the corrosion

potential of biosolids, pH test and electrical conductivity tests were performed on

untreated biosolids and stabilised biosolids with various admixtures. The pH and

electrical conductivity are two vital parameters for the biodegradation and corrosivity.

The pH is a measure of the acidity or alkalinity of the water or soil based on its

hydrogen ion concentration and is mathematically defined as the negative logarithm of

the hydrogen ion concentration, as presented in equation 8.8 below.

[ ]+−= HpH log Eq. (8.8)

where the brackets around the H+ symbolize “concentration”.

The pH of a material ranges on a logarithmic scale from 1-14, where pH 1-6 are acidic,

pH 7 is natural, and pH 8-14 are alkaline. Lower pH corresponds with higher [H+],

while higher pH is associated with lower [H+].

Electrical conductivity is a measurement of the dissolved material in and aqueous

solution, which relates to the ability of the material to conduct electrical current through

it. The electrical conductivity is a measure in units called Siemens per unit area (e.g:

mS/cm, or milli Siemens per centimetre). The higher the dissolved material in water or

soil sample, the higher the electrical conductivity present in that material. The electrical

conductivity is generally described in units of moh-cm (moh centimetre). The resistivity

is the reciprocal of conductivity, and the unit conversion between conductivity and

resistivity is presented in equation 8.9 below.

)(Re

1)(

cmohmsistivitycmmhotyConductivi

−=− Eq. (8.9)

Also the unit conversion between conductivity and Siemens is described in equation

8.10 below.

)()( SnsmicroSeimemhomicromho µµ = Eq. (8.10)

194

The pH value and the electrical conductivity test results of untreated biosolids are

presented in Table 8.4. Also the pH value and the electrical conductivity of stabilised

biosolids with lime, cement, bauxsol and fly-ash are presented in Table 8.4 to Table 8.8

respectively. The average value and standard deviation of the measurement of pH and

electrical conductivity are also presented in the tabulated test results tables respectively.

The average values of the pH were used for the settlement analysis due to the

biodegradation in untreated biosolids and biosolids stabilised with lime, cement,

bauxsol and fly-ash.

Table 8.4. pH and electrical conductivity test results of untreated biosolids.

Sample Identification Sample 1

Sample 2

Sample 3

Sample 4

Average Standard deviation

Untreated Biosolids

Temperature (degreeC)

21.4 21.5 21.6 21.8 21.58 0.17

pH 4.65 4.7 4.68 4.69 4.7 0.02

Conductivity (µS/cm)

1871 2001 2093 1935 1975 94.90

Table 8.5. pH and electrical conductivity test results of biosolids stabilised with lime.


Sample 2

Sample 3

Sample 4


Biosolids + 1% Lime


20.1 20.3 20.4 20.5 20.33 0.171

pH 7.6 7.55 7.59 7.58 7.6 0.022


2060 2095 2098 2054 2077 22.97

Biosolids + 3% Lime


20.5 20.4 20.8 20.7 20.60 0.18

pH 9.08 9.05 9.09 9.16 9.1 0.05


1803 1771 1865 1829 1817 39.83

Biosolids + 5% Lime


20.2 20.7 20.7 20.6 20.55 0.24

pH 10.36 10.38 10.41 10.44 10.4 0.04


1684 1751 1692 1745 1718 34.88

195

Table 8.6. pH and electrical conductivity test results of biosolids stabilised with cement.


Sample 2

Sample 3

Sample 4




20.4 20.7 21 21.4 20.88 0.43

pH 6.98 6.63 6.69 6.96 6.8 0.18


2070 1937 2058 1930 1999 75.56



20.3 20.5 20.5 20.6 20.48 0.13

pH 8.95 9 9 9.01 9 0.026


1803 2029 1979 1838 1912 108.83



20.3 20.4 20.5 20.5 20.43 0.10

pH 10 10.07 10.04 10.01 10.0 0.03


1870 1939 1951 1944 1926 37.66

Table 8.7. pH and electrical conductivity test results of biosolids stabilised with bauxsol.


Sample 2

Sample 3

Sample 4




21 21 21.1 21.1 21.05 0.06

pH 5.25 5.14 5.14 5.13 5.2 0.06


1718 1650 1694 1734 1699 36.57



20.8 20.6 20.6 20.6 20.65 0.10

pH 5.58 5.52 5.48 5.56 5.5 0.04


1721 1734 1728 1756 1735 15.13



20.4 20.5 20.5 20.5 20.48 0.05

pH 5.65 5.69 5.64 5.67 5.7 0.02


1737 1755 1680 1732 1726 32.22

196

Table 8.8. pH and electrical conductivity test results of biosolids stabilised with fly-ash.


Sample 2

Sample 3

Sample 4


Biosolids + 10% Fly-ash


20.7 31 21 21.1 23.45 5.04

pH 5.58 5.44 5.37 5.32 5.4 0.11


1916 1876 1892 1940 1906 28.00



20.9 21.1 21 20.8 20.95 0.13

pH 5.1 5.07 5.12 5.15 5.1 0.03


1888 1780 1834 1855 1839 45.32



20.7 20.6 20.7 20.7 20.68 0.05

pH 4.87 4.75 4.75 4.7 4.8 0.07 Conductivity (µS/cm)

1957 1820 1892 1960 1907 66.09

8.3 Corrosivity Analysis of Biosoilds

In general, the corrosivity towards a buried object in the highway embankment is

dependent on a number of parameters, including embankment fill material’s resistivity,

water content, dissolved salts, pH, presence of bacteria and the amount of oxygen

available at the buried metal surface. It is generally agreed that no one parameter can be

used to accurately forecast the corrosivity of a particular embankment fill material or

soil. Nevertheless, electrical resistivity is commonly utilised as an indicator of the

embankment fill material’s of soil’s corrosivity. Observation of soil drainage and/or

measurement of pH, supplement resistivity measurements were conducted by

researchers (Coburn 1987; Davie et al. 1996).

The general relationship that exits between soil resistivity/pH and corrosion of ferrous

metals is presented in Table 8.9. However, because of the other factors, the relationships

may not be always valid or considerable vary in the ranges tabulated values (Coburn

1987; Davie et al. 1996). Figure 8.1 shows the effect of solution pH upon the corrosion

rate of iron (Scully, 1990).

197

Table 8.9. Soil corrosivity classification.

Parameters

Classification

Little

Corrosive

Mildly

Corrosive

Moderately

Corrosive Corrosive

Very

Corrosive

Resistivity

(ohm-cm) > 10,000a,b

2,000-10,000a

5,000-10,000b

1,000-2,000a

2,000-

5,000b,c

500-1,000a

700-2,000b,c

<500a

<700b,c

pH >5.0 and

<10.0b 5.0-6.5a <5.0a

aAmerican Petroleum Institute (1991) bSTS Consultants, Inc. (1990) cCoburn, S. K. (1987)

The pH and electrical conductivity tests were performed in accordance with the

Australian Standard ( AS 1289.D3.1-1997). The standard pH and electrical conductivity

meters were used to measure the pH value and electrical conductivity of untreated and

stabilised biosolids with various amounts of lime, cement, bauxsol and fly-ash, but the

biodegradation settlement analysis were only performed for the untreated biosolids,

stabilised biosolids with 5% lime, 3% cement, 5% cement, 3% bauxsol, 5% bauxsol,

10% fly-ash, 20% fly-ash and 30% fly-ash in the highway embankment heights of 2m,

3m, 4m and 5m.

Figure 8.1. The effect of solution pH upon the corrosion rate of iron (Scully, 1990).

198

The pH and electrical conductivity tests were performed on four samples in untreated

biosolids and the stabilised biosolids with various amounts of lime, cement, bauxsol and

fly-ash. The samples were prepared in accordance with the sample preparation in AS

1289.D3.1-1997.

The average conductivity values of untreated and stabilised biosolids with lime (1%,

2%, 3%), cement (1%, 2%, 3%), bauxsol (1%, 2%, 3%) and fly ash (10%, 20%, 30%)

are summarised in Table 8.10. The resistivity values and corrosivity classifications of

untreated and stabilised biosolids with admixtures are also presented in Table 8.10.

Based on soil corrosivity classification by Coburn 1987 and Davie et al. 1996, the

conductivity measurements of untreated and stabilised biosolids with lime (1%, 2%,

3%), cement (1%, 2%, 3%), bauxsol (1%, 2%, 3%) and fly ash (10%, 20%, 30%) shows

that, the untreated and stabilised biosolids with admixtures are moderately corrosive.

Table 8.10. Soil corrosivity classification for biosolids based on conductivity values.

Sample Identification Conductivity

(µS/cm) Resistivity (ohm-cm)

Corrosivity Classification

Untreated Biosolids 1975 4534 Moderately Corrosive Biosolids + 1% Lime 2077 4768 Moderately Corrosive Biosolids + 3% Lime 1817 4171 Moderately Corrosive Biosolids + 5% Lime 1718 3944 Moderately Corrosive Biosolids + 1% Cement 1999 4589 Moderately Corrosive Biosolids + 3% Cement 1912 4390 Moderately Corrosive Biosolids + 5% Cement 1926 4422 Moderately Corrosive Biosolids + 1% Bauxsol 1699 3900 Moderately Corrosive Biosolids + 3% Bauxsol 1735 3983 Moderately Corrosive Biosolids + 5% Bauxsol 1726 3962 Moderately Corrosive Biosolids + 10% Fly-ash 1906 4376 Moderately Corrosive Biosolids + 20% Fly-ash 1839 4222 Moderately Corrosive Biosolids + 30% Fly-ash 1907 4379 Moderately Corrosive

The average pH values of untreated and stabilised biosolids with lime (1%, 2%, 3%),

cement (1%, 2%, 3%), bauxsol (1%, 2%, 3%) and fly ash (10%, 20%, 30%) are

summarised in Table 8.11. The biosolids corrosivity classifications of untreated and

stabilised biosolids with admixtures are also presented in Table 8.11. Based on pH by

Coburn 1987 and Davie et al. 1996, the pH values of untreated and stabilised biosolids

199

with admixtures indicate that, the untreated and stabilised biosolids with bauxsol and fly

ash are corrosive and stabilised biosolids with lime and cement mildly corrosive.

These biosolids corrosivity classifications based on pH values is also agreed with the

effect of pH value upon the corrosion rate of iron by Scully (Sully, 1990), as presented

in Figure 8.1. In general, the corrosivity of untreated and stabilised biosolids with

bauxsol (1%, 2%, 3%) and fly ash (10%, 20%, 30%) are classified as moderately

corrosive to corrosive. The stabilised biosolids with lime (1%, 2%, 3%) and cement

(1%, 2%, 3%) are classified as mildly to moderately corrosive.

Table 8.11. Soil corrosivity classification for biosolids based on pH values.

Sample Identification pH Corrosivity Classification

Untreated Biosolids 5 Corrosive Biosolids + 1% Lime 8 Mildly Corrosive Biosolids + 3% Lime 9 Mildly Corrosive Biosolids + 5% Lime 10 Mildly Corrosive Biosolids + 1% Cement 7 Mildly Corrosive Biosolids + 3% Cement 9 Mildly Corrosive Biosolids + 5% Cement 10 Mildly Corrosive Biosolids + 1% Bauxsol 5 Corrosive Biosolids + 3% Bauxsol 6 Corrosive Biosolids + 5% Bauxsol 6 Corrosive Biosolids + 10% Fly-ash 5 Corrosive Biosolids + 20% Fly-ash 5 Corrosive Biosolids + 30% Fly-ash 5 Corrosive

200

8.4 Sensitivity Analysis of Biodegradation Settlement

Sensitivity analysis of the biodegradation settlement on an embankment using stabilised

biosolids is vital on the one hand to assess the influence of important input parameters

and any uncertainty involved in their determination. The uncertainties in the input

parameters selection could arise due to various reasons including sample preparation

and laboratory experimental errors.

In many instances, settlement analysis has to be carried out with limited data.

Biodegradation settlement of the biosolids in highway embankment depends on factors

such as density, moisture content, temperature and pH. It is common practice for

engineers/researchers to use the available empirical relationships between soil

properties to estimate the parameters required for the analysis/design.

The density and moisture content of the untreated biosolids and the stabilized biosolids

with various amounts of admixtures were determined from the geotechnical laboratory

test results. The pH value of the untreated biosolids and also the stabilized biosolids

with various amounts of admixtures were obtained from the pH test results. Moreover,

there could be uncertainties in the measured soil parameters since they are often

obtained from laboratory testing on small samples and they are affected by factors such

as quality of the sample (i.e. sample preparation), and testing procedure. Therefore,

investigating the sensitivity of variations of such parameters on the performance of the

embankment is essential for researchers and engineers.

A parametric study has been carried out to examine the sensitivity of pH with the

settlement due to biodegradation action. The parametric study described in this chapter

consists of the sensitivity of the biodegradation settlement for various heights of

highway embankment and with varying pH values for the 0.5m thick untreated biosolids

and stabilised biosolids.

The primary consolidation and creep settlement were completed within a short period of

time from the results of finite element analysis. Therefore the biodegradation

settlements were calculated based on residual thickness for various embankment

heights, as presented in Chapter 7.

201

8.5 Biodegradation Settlement of Untreated Biosolids

The biodegradation settlement analysis was carried out on the assumed residual

thickness of 0.2m biosolids layer in 5m height embankment. The biodegradation

settlement of 5m height embankment using untreated biosolids is presented in Figure

8.2 and also the results are summarised in Table 8.12. The average pH value from the

four samples of untreated biosolids is 4.7 from the pH test.

The effect of pH value in the biodegradation settlement was analysed by reducing the

pH value to 3 and 4 and also increasing the pH value to 5. The prediction of

biodegradation settlements in the 5m height embankment using layer of 0.5m thick

untreated biosolids are presented in Figure 8.2.

The biodegradation settlement 25 years after the construction of 5m height embankment

using layer of 0.2m thick untreated biosolids was found to be 175mm for the pH value

of 4.7. The biodegradation settlement was reduced to 105mm and 20mm with reduced

pH value of 4 and 3 respectively, and increased to 190mm with a pH value of 5.

The biodegradation settlement in embankment using untreated biosolids in 5m height

embankment increases exponentially, and reached the fully biodegradation in 1000

years, 200 years, 100 years and 50 years for the pH value of 3, 4, 4.7 and 5 respectively.

The rate of biodegradation settlement is reduced with the pH value reduction of

biosolids. The time taken to fully degradation for the biosolids with the pH value of 3 is

1000 years, and reduced to 50 years with a pH value of 5.

202

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0 100 200 300 400 500 600 700 800 900 1000

Time (years)

Set

tlem

ent (

m)

Untreated : Actual pH=4.67 Untreated : pH=3 Untreated : pH=4 Untreated : pH=5

Figure 8.2. Biodegradation settlement of 5m height embankment using untreated

biosolids.

Table 8.12. Biodegradation settlement of 5m height embankment using untreated biosolids.

Settlement of 5m Height embankment using untreated biosolids (mm) pH 3 4 4.7 5

25 Years 20 105 175 190 50 Years 35 150 175 200

100 Years 65 185 200 - 200 Years 105 200 - - 350 Years 150 - - -

1000 Years 200 - - - The pH value of untreated biosolids is in acidic range in the pH scale. Even though the

untreated biosolids in the acidic range, biodegradation settlement analysis shows that,

untreated biosolids with the more acidity (ie: pH value of less than 3) takes more time

than the untreated biosolids with lesser acidic for fully biodegradation process. The time

for fully biodegradation process for the untreated biosolids in 5m embankment with a

pH value below 3 takes more than doubled than the pH value above 3.

203

8.6 Biodegradation Settlement of Stabilised Biosolids with Lime

8.6.1 Biodegradation settlement of stabilised biosolids with 5% Lime

The biodegradation settlement of a 5m height embankment using stabilised biosolids

with 5% lime is presented in Figure 8.3 and also the results are summarised in Table

8.13. The average pH value from the four samples of stabilised biosolids with 5% lime

is 10.40 from the pH test.




stabilised biosolids with 5% lime are presented in Figure 8.3.

The assumed residual biosolids layer thickness of 0.22m after the primary consolidation

and creep behaviour in the embankment was used in biodegradation calculation for the

5m height embankment using layer of 0.5m thick stabilised biosolids with 5% lime.


using layer of 0.5m thick stabilised biosolids with 5% lime was found to be 50mm for

the pH value of 10.4. The biodegradation settlement was increased to 200mm and

220mm with reduced pH value of 9 and 8 respectively, and reduced to 15mm with a pH

value of 11.

The biodegradation settlement in embankment using stabilised biosolids with 5% lime

in 5m height embankment increases exponentially, and reached the fully biodegradation

in 25 years, 50 years, 350 years and more than 1000 years for the pH value of 8, 9, 10.4

and 11 respectively. The rate of biodegradation settlement is reduced with the pH value

increment of the biosolids. The time taken to fully degradation for the biosolids with the

pH value of 11 is 1000 years, and reduced to 25 years with a pH value of 8.

204

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0 100 200 300 400 500 600 700 800 900 1000

Time (years)S

ettle

men

t (m

)

Biosolids+5% Lime : Actual pH=10.40 Biosolids+5%Lime : pH=8Biosolids+5%Lime : pH=9 Biosolids+5%Lime : pH=11


biosolids with 5% lime.

Table 8.13. Biodegradation settlement of 5m height embankment using stabilised biosolids with 5% lime.

Settlement of 5m Height embankment using stabilised biosolids with 5% lime (mm) pH 8 9 10.4 11

25 Years 220 200 50 15 50 Years - 220 90 30

100 Years - - 140 55 200 Years - - 190 100 350 Years - - 220 145

1000 Years - - - 210

The prediction of biodegradation settlements in the 4m, 3m and 2m heights

embankment using layer of 0.5m thick stabilised biosolids with 5% lime with the

change in pH value are presented in Figure 8.4, Figure 8.5 and Figure 8.6 respectively

and also the results are summarised in Table 8.14, Table 8.15 and Table 8.16

respectively.

The assumed residual biosolids layer thickness of 0.23m, 0.24m and 0.25m after the

primary consolidation and creep behaviour in the embankment was used in

biodegradation calculation for the 4m, 3m and 2m height embankments, using layer of

0.5m thick stabilised biosolids with 5% lime respectively. The biodegradation

settlement in 4m, 3m and 2m height embankments using stabilised biosolids with 5%

205

lime increases exponentially, and reached the fully biodegradation in 25 years, 50 years,

350 years and more than 1000 years for the pH value of 8, 9, 10.4 and 11 respectively.

0.00

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0 100 200 300 400 500 600 700 800 900 1000

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Set

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Biosolids+5% Lime : Actual pH=10.40 Biosolids+5%Lime : pH=8Biosolids+5%Lime : pH=9 Biosolids+5%Lime : pH=11



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0 100 200 300 400 500 600 700 800 900 1000

Time (years)

Set

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Biosolids+5% Lime : Actual pH=10.40 Biosolids+5% Lime : pH=8Biosolids+5% Lime : pH=9 Biosolids+5% Lime : pH=11



206

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0.10

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0 100 200 300 400 500 600 700 800 900 1000

Time (years)S

ettle

men

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)

Biosolids+5% Lime : Actual pH=10.40 Biosolids+5% Lime : pH=8Biosolids+5% Lime : pH=9 Biosolids+5% Lime : pH=11





25 Years 230 215 50 10 50 Years - 230 100 30


1000 Years - - - 220



25 Years 240 210 50 10 50 Years - 240 100 30


1000 Years - - - 230

207



25 Years 250 230 60 10 50 Years - 250 100 30


1000 Years - - - 240 The pH value of stabilised biosolids with 5% lime is in alkaline range in the pH scale.

Even though it is in the alkaline range, the time taken for the fully biodegradation

process with more alkaline (i.e.: pH value of higher than 11) takes more time than those

with lesser alkaline. The time for fully biodegradation process for the stabilised

biosolids with 5% lime in 2m, 3m, 4m and 5m embankment with a pH value of 11 takes

more than doubled than the pH values of 8, 9 and 10.40.

208

8.7 Biodegradation Settlement of Stabilised Biosolids with Cement

8.7.1 Biodegradation settlement of stabilised biosolids with 3% cement

The biodegradation settlement of 5m height embankment using stabilised biosolids with

3% cement is presented in Figure 8.7 and also the results are summarised in Table 8.17.

The average pH value from the four samples of stabilised biosolids with 3% cement is 9

from the pH test.


pH values to 7 and 8 and also increasing the pH value to 10. The prediction of


stabilised biosolids with 3% cement are presented in Figure 8.7.



5m height embankment using layer of 0.5m thick stabilised biosolids with 3% cement.

0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)

Set

tlem

ent (

m)

Biosolids+3% Cement : Actual pH=8.99 Biosolids+3% Cement : pH=7Biosolids+3% Cement : pH=8 Biosolids+3% Cement : pH=10


biosolids with 3% cement.

209


using layer of 0.5m thick stabilised biosolids with 3% cement was found to be 195mm

for the pH value of 9. The biodegradation settlement was increased to 210mm with

reduced the both pH value of 7 and 8 respectively, and also reduced to 100mm with a

pH value of 10.

Table 8.17. Biodegradation settlement of 5m height embankment using stabilised biosolids with 3% cement.

Settlement of 5m Height embankment using stabilised biosolids with 3% cement (mm)

pH 7 8 9 10

25 Years 210 210 195 100 50 Years - - 210 150

100 Years - - - 190 200 Years - - - 205 350 Years - - - 210


embankment using layer of 0.5m thick stabilised biosolids with 3% cement with the

change in pH value are presented in Figure 8.8, Figure 8.9 and Figure 8.10 respectively

and also the results are summarised in Table 8.18, Table 8.19, Table 8.20 and

respectively.

The assumed residual biosolids layer thickness of 0.22m, 0.22m, and 0.23m after the



0.5m thick stabilised biosolids with 3% cement respectively. The biodegradation

settlement in 4m, 3m and 2m height embankments using stabilised biosolids 3% cement

increases exponentially, and reached the fully biodegradation in 25 years, 25 years, 50

years and 350 years for a pH values of 7, 8, 9 and 10 respectively.

210

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0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)S

ettle

men

t (m

)




0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)

Set

tlem

ent (

m)




211

0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)S

ettle

men

t (m

)






pH 7 8 9 10

25 Years 220 220 200 95 50 Years - - 220 150




pH 7 8 9 10

25 Years 220 220 200 95 50 Years - - 220 150


212



pH 7 8 9 10

25 Years 230 230 210 100 50 Years - - 230 155


The pH value of stabilised biosolids with 3% cement is in alkaline range in the pH

scale. Even though this mixture in alkaline range, the time taken for the fully

biodegradation process with more alkaline (i.e.: pH value of 10) take more time than

those with lesser alkaline (i.e.: pH value of 7, 8 and 9).

213

8.7.2 Biodegradation settlement of stabilised biosolids with 5% cement


5% cement is presented in Figure 8.11 and also the results are summarised in Table

8.21. The average pH value from the four samples of stabilised biosolids with 5%

cement is 10.03 from the pH test.


pH values to 8 and 9 and also increasing the pH value to 11. The prediction of


stabilised biosolids with 5% cement are presented in Figure 8.11.



5m height embankment using layer of 0.5m thick stabilised biosolids with 5% cement.


using layer of 0.5m thick stabilised biosolids with 5% cement was found to be 100mm

for the pH value of 10. The biodegradation settlement was increased to 230 and 250mm

with reduced the both pH values of 9 and 8 respectively, and also reduced to 20mm with

a pH value of 11.

214

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500 600 700 800 900 1000

Time (years)S

ettle

men

t (m

)

Biosolids+5% Cement : Actual pH=10.03 Biosolids+5% Cement : pH=8Biosolids+5%Cement : pH=9 Biosolids+5%Cement : pH=11



The biodegradation settlement in embankment using stabilised biosolids with 5%

cement in 5m height embankment increases exponentially, and reached the fully

biodegradation in 25 years, 50 years, 350 years and more than 1000 years for the pH

value of 8, 9, 10.03 and 11 respectively. The rate of biodegradation settlement is

reduced with the pH value increment of the biosolids. The time taken to fully

degradation for the biosolids with a pH value of 11.



pH 8 9 10 11

25 Years 250 230 100 20 50 Years - 250 165 30


1000 Years - - - 240


embankment using layer of 0.5m thick stabilised biosolids with 5% cement with the

change in pH value are presented in Figure 8.12, Figure 8.13 and Figure 8.14

215

respectively and also the results are summarised in Table 8.22, Table 8.23 and Table

8.24 respectively.




0.5m thick stabilised biosolids with 5% cement respectively. The biodegradation

settlement in embankment using stabilised biosolids 5% cement in 4m, 3m and 2m

height embankments increase exponentially, and reached the fully biodegradation in 25

years, 50 years, 350 years and 1000 years for a pH value of 8, 9, 10.03 and 11

respectively.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500 600 700 800 900 1000

Time (years)

Set

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ent (

m)




216

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500 600 700 800 900 1000

Time (years)S

ettle

men

t (m

)




0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500 600 700 800 900 1000

Time (years)

Set

tlem

ent (

m)




217



pH 8 9 10 11

25 Years 260 230 65 20 50 Years - 260 110 35


1000 Years - - - 255



pH 8 9 10 11

25 Years 280 250 100 20 50 Years - 280 180 40


1000 Years - - - 270



pH 8 9 10 11

25 Years 290 255 110 20 50 Years - 290 190 40


1000 Years - - - 280 The pH value of stabilised biosolids with 5% cement is in alkaline range in the pH

scale. Even though it is in the alkaline range, the time taken for the fully biodegradation

process with more alkaline (i.e.: pH value of higher than 11) takes more time than those

with lesser alkaline. The time for fully biodegradation process for the stabilised

biosolids with 5% cement in 2m, 3m, 4m and 5m embankment with a pH value of 11

takes twenty times more than the pH value of 9.

218

8.8 Biodegradation Settlement of Stabilised Biosolids with Bauxsol

8.8.1 Biodegradation settlement of stabilised biosolids with 3% bauxsol


3% bauxsol is presented in Figure 8.15 and also the results are summarised in Table


bauxsol is 5.5 from the pH test.




stabilised biosolids with 3% bauxsol are presented in Figure 8.15.



5m height embankment using layer of 0.5m thick stabilised biosolids with 3% bauxsol.


using layer of 0.5m thick stabilised biosolids with 3% bauxsol was found to be 200mm

for the pH value of 5.54. The biodegradation settlement was decreased to 185mm and

100mm with reduced the both pH values of 5 and 4 respectively, and also 200mm with

a pH value of 6.


bauxsol in 5m height embankment increases exponentially, and reached the fully

biodegradation in 200 years, 50 years, 25 years and 25 years for the pH value of 4, 5,

5.5 and 6 respectively. The rate of biodegradation settlement is increased with the pH

value increment of the biosolids. The time taken to fully degradation for the biosolids

with a pH value of 4 is decreased from a pH value of 6 and also doubled with a scale

increment in pH value (i.e.; pH=5).

219

0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)S

ettle

men

t (m

)

Biosolids+3% Bauxsol : Actual pH=5.54 Biosolids+3% Bauxsol : pH=4Biosolids+3% Bauxsol : pH=5 Biosolids+3% Bauxsol : pH=6


biosolids with 3% bauxsol.

Table 8.25. Biodegradation settlement of 5m height embankment using stabilised biosolids with 3% bauxsol.

Settlement of 5m Height embankment using stabilised biosolids with 3% bauxsol (mm)

pH 4 5 5.5 6

25 Years 100 185 200 200 50 Years 150 200 - -

100 Years 185 - - - 150 Years 195 - - - 200 Years 200 - - -

The prediction of biodegradation settlements in the 4m, 3m and 2m height

embankments using layer of 0.5m thick stabilised biosolids with 3% bauxsol with the



8.28 respectively.




0.5m thick stabilised biosolids with 3% bauxsol. The biodegradation settlement in

220

embankment using stabilised biosolids 3% bauxsol in 4m, 3m and 2m height

embankments increase exponentially, and reached the fully biodegradation in 200 years,

50 years, 25 years and 25 years for a pH values of 4, 5, 5.5 and 6 respectively. The time

taken to fully degradation for the biosolids with a pH value of 4 is decreased from the

pH value of 6.

0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)

Set

tlem

ent (

m)




0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)

Set

tlem

ent (

m)




221

0.00

0.05

0.10

0.15

0.20

0.25

0 50 100 150 200 250 300 350 400 450 500

Time (years)S

ettle

men

t (m

)






pH 4 5 5.5 6

25 Years 100 185 200 200 50 Years 150 200 - -




pH 4 5 5.5 6

25 Years 110 210 220 220 50 Years 165 220 - -


222



pH 4 5 5.5 6

25 Years 120 225 240 240 50 Years 175 240 - -


The pH value of stabilised biosolids with 3% bauxsol is in acidic range in the pH scale.

Even though this mixture in the acidic range, the time taken for the fully biodegradation

process with higher acidic (i.e.: pH value of 4) takes more time than those with lesser

acidic.

223

8.8.2 Biodegradation settlement of stabilised biosolids with 5% bauxsol


5% bauxsol is presented in Figure 8.19 and also the results are summarised in Table


bauxsol is 5.7 from the pH test.


pH value to 4 and 5 and also increasing a pH value to 6. The prediction of


stabilised biosolids with 5% bauxsol are presented in Figure 8.19.



5m height embankment using layer of 0.5m thick stabilised biosolids with 5% bauxsol.

The biodegradation settlement 25 years the construction of 5m height embankment

using layer of 0.5m thick stabilised biosolids with 5% bauxsol was found to be 240mm

for a pH value of 5.7. The biodegradation settlement was decreased to 220mm and

110mm with reduced the both pH values of 5 and 4 respectively, and also 240mm with

a pH value of 6.

224

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 50 100 150 200 250 300 350 400 450 500

Time (years)S

ettle

men

t (m

)





bauxsol in 5m height embankment increases exponentially, and reached the fully

biodegradation in 200 years, 50 years, 25 years and 25 years for the pH value of 4, 5,

5.7 and 6 respectively. The rate of biodegradation settlement is increased with the pH

value increment of the biosolids. The time taken to fully degradation for the biosolids

with a pH values of 4 is decreased from the pH value of 6 and also double with a scale

increment in pH value (i.e.; pH=5).



pH 4 5 5.7 6

25 Years 80 160 170 170 50 Years 125 170 - -



embankment using layer of 0.5m thick stabilised biosolids with 5% bauxsol with the

225



8.32 respectively .

The residual biosolids layer thickness of 0.25m, 0.28m and 0.29m after the primary

consolidation and creep behaviour in the embankment was used in biodegradation

calculation for the 4m, 3m and 2m height embankments using layer of 0.5m thick

stabilised biosolids with 5% bauxsol. The biodegradation settlement in embankment

using stabilised biosolids 5% bauxsol in 4m, 3m and 2m height embankments increase

exponentially, and reached the fully biodegradation in 200 years, 50 years, 25 years and

25 years for a pH values of 4, 5, 5.7 and 6 respectively. The time taken to fully

degradation for the biosolids with a pH value of 4 is decreased from the pH value of 6.

0.00

0.05

0.10

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0.20

0.25

0.30

0 50 100 150 200 250 300 350 400 450 500

Time (years)

Set

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226

0.00

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0.10

0.15

0.20

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0 50 100 150 200 250 300 350 400 450 500

Time (years)S

ettle

men

t (m

)

Biosolids+5% Bauxsol : Actual pH=5.66 Biosolids+5%Bauxsol : pH=4Biosolids+5%Bauxsol : pH=5 Biosolids+5%Bauxsol : pH=6



0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 50 100 150 200 250 300 350 400 450 500

Time (years)

Set

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227



pH 4 5 5.7 6

25 Years 115 230 250 250 50 Years 185 250 - -




pH 4 5 5.7 6

25 Years 130 250 270 270 50 Years 200 270 - -




pH 4 5 5.7 6

25 Years 140 270 290 290 50 Years 210 290 - -


The pH value of stabilised biosolids with 5% bauxsol is in acidic range in the pH scale.

Even though it is in the acidic range, the time taken for the fully biodegradation process

with more acidic (i.e.: pH value of 4) takes more time than those with lesser acidic.

228

8.9 Discussion on Biodegradation Settlement of Biosolids

The total time taken for the biodegradation process was analysed on untreated biosolids

and stabilised biosolids with 5% lime, 3% and 5% cement and 3% and 5% bauxsol. The

results of the biodegradation settlement analysis are presented in Figure 8.23 with

analysed pH values of each biosolids mixture. The time taken for fully biodegradation

process decreases dramatically with pH value of the biosolids mixture between 0 and 6

and then increases exponentially with pH value of the biosolids between 8 and 14. The

trend of the time taken for the completion of the biodegradation process as presented in

Figure 8.23 clearly indicates sensitivity of pH value in biodegradation process.

0

100

200

300

400

500

600

700

800

900

1000

0 2 4 6 8 10 12 14pH

Tim

e ta

ken

for

fully

Bio

degr

adat

ion

proc

ess

(Yea

rs)

Untreated Biosolids

Stabilised Biosolids with 3% and 5%

Bauxsol

Stabilised Biosolids with 5% Cement

Stabilised Biosolids with 3% Cement

Stabilised Biosolids with 5% Lime

Neutral

Increasing Acidity

Increasing Alkalinity

Figure 8.23. Time taken for biodegradation with pH values.

The rate of biodegradation process decreases with the increasing acidity and alkalinity

of the biosolids mixture. The maximum rate of biodegradation process is expected at a

pH value of 7 (neutral). The rate of biodegradation process is presented in Figure 8.24.

229

0

50

0 2 4 6 8 10 12 14pH

Rat

e of

Bio

degr

adat

ion

Neutral

Increasing Acidity

Increasing Alkalinity

Figure 8.24. Trend of biodegradation process with pH values.

230

8.10 Conclusion: Biodegradation Settlement of Biosolids and Corrosivity

In the sensitivity analysis, it is assumed that the biosolids are not in their active stage of

biodegradation. The active stage of biodegradation is assessed to have occurred during

stockpiling. Moisture content and net thickness of biosolids were assumed to be reduced

with cement option. In addition prediction of biodegradation was only calculated for

biosolids volume in admixture option and volume change due to primary and secondary

consolidation was only occurred in biosolids and not in admixtures. It was found that

biodegradation was slightly reduced after treated with lime, cement and bauxsol.

Prediction of biosolids was carried out applying Chakma and Mathur (2007). In the

prediction biosolids was assumed to be beyond their active state of biodegradation and

active state was completed during stockpile. There is a flow on this biodegradation

settlement analysis model which approach to biodegrade completely of some point. The

biodegradable ability and biodegradable thickness of biosolids become slower with time

need to take in account to accurately model biodegradation.

Biodegradation is more sensitive with temperature, moisture content and pH. In addition

biosolids degradation is also dependent upon their initial state and composition of

biosolids. As biodegradation should not be affected by the additional stress on the

embankment, the basic assumption made in this analysis was, the biodegradation will

occur after completion of the construction and also concurrently with consolidation. The

strain due to the biodegradation was determined from the residual thickness of the

biosolids layer from the finite element analysis.

The rate of biodegradation process decreases with the increasing acidity and alkalinity

of the biosolids mixture. The maximum rate of biodegradation process is expected at a

pH value of 7 (neutral).

Electrical resistivity is an important parameter used in evaluating the corrosivity of a

material. High resistivity is associated with low corrosion potential. The pH

measurement results showed that untreated biosolids and stabilised biosolids with lime,

cement, bauxsol and fly-ash mixtures exhibit high alkalinity, indicating low corrosion

potential. Due to the complex nature of corrosion mechanism, one single parameter may

231

not be sufficient to evaluate corrosivity of a material. Based on the electrical

conductivity and pH test results, it is concluded that untreated biosolids and stabilised

biosolids with admixtures such as lime, cement, bauxsol and fly-ash are potentially

corrosive.

Biodegradation and the corrosivity characteristics of the biosolids are more important to

analysis the behaviour of any buried infrastructures in the untreated or stabilised

biosolids layer in the embankment. The maximum biodegradation rate was observed the

biosolids having pH value of 7 (natural). However, lower corrosivity rate was observed

at the same pH level (pH value of 7). To balance the both biodegradation and

corrosivity effects on the buried structure the maintain the pH in acidity or alkalinity is

need to be done by further research.

232

9 CONCLUSION AND RECOMMENDATION

9.1 Literature Review

The Literature Review for this investigation was undertaken for laboratory testing and

research studies conducted on sludge and biosolids locally and around the world and

discusses the geotechnical characteristics of the sludge and the biosolids. The

stabilisation of sludge and biosolids by using additives such as lime (1 to 5%), cement

(1 to 5%), bauxsol (1 to 5%) and fly-ash (10 to 30%) are also discussed together with

the finite element modelling and analysis conducted on sludge and soft soil in recent

decades.

9.2 Field Testing

The field testing and sampling works which were undertaken at the Western Treatment

Plant in Werribee. The following conclusions can be made based on the field testing

results:

• The standard penetration test (SPT) results indicated that the estimated

allowable bearing capacity of the biosolids in the stockpiles was found to vary

between 70 to 80 kPa at a depth of 1.5 m to 3.0 m in boreholes BH3 (Stockpile

1), BH5 (Stockpile 2) and BH11 (Stockpile 3). The allowable bearing capacity

of the biosolids in borehole BH7 (Stockpile 2) at depth of 4.0 m was found to be

230 kPa. The standard penetration test results indicate that the consistency of the

biosolids in all the stockpiles is firm to very stiff.

• The field vane shear test results indicate that the consistency of the biosolids is

very stiff to hard. The undrained shear strength of biosolids was found to

generally increase with the depth.

• In general, the estimated California Bearing Ratio (CBR) values from dynamic

cone penetrometer tests increases with the depth of the biosolids stockpile. The

CBR results indicate that the consistency of the biosolids in the stockpiles is

firm to hard.

233

• It is noted that the various field testing methods consistently indicate that the

biosolids at the stockpiles are firm to hard. The slight variability between the

various field testing methods is expected due to the various assumptions and

empirical equations used in each test methods.

9.3 Laboratory Testing on Untreated and Stabilised Biosoldis with Admixtures

Biosolid samples obtained from three stockpiles at Biosolids Stockpile Area, Western

Treatment Plant were tested to investigate the geotechnical characteristics of biosolids

and the suitability of biosolids as stabilised fill material. Based on the geotechnical

laboratory test results the following conclusions can be made:

• The biosolid samples are classified as organic fined-grained soils of medium to

high plasticity with a group symbol of ‘OH’ as per Australian standard for the

geotechnical site investigation (AS 1276, 1993). The biosolid samples contain

approximately 5% gravel size, 50% sand size, 40% silt size and 5% clay sized

particles.

• The biosolids samples in the three stockpiles have high moisture content, liquid

limit and plasticity indices that are comparable to common inorganic soils. The

moisture content, liquid limit and plasticity indices decrease when biosolids

stabilised with lime, cement and bauxsol. The particle density of biosolids was

found to be approximately 1.75 t/m3

• The shear strength test results from the triaxial test indicate that the biosolids

stabilised with the required proportions of additives indicate that the stabilised

biosolids possess suitable shear strength to make them suitable for use as fill

material.

• Consolidation test results of stabilised biosolids with additives provided

coefficient of consolidation results that need to be reviewed for the modelling of

234

the biosolids embankment in the next phase of this project. This is as the design

input parameters will be dependant on the imposed embankment loads.

• Long-term laboratory testing of secondary consolidation settlement (creep

characteristics) of the biosolids were used as input parameters in the finite

element analysis of embankments using stabilised biosolids. The creep

consolidation tests were conducted to determine the secondary compression

index for the finite element analysis. The long-term creep consolidation tests

were undertaken by applying each load increment for seven days (as compared

to the traditional 1 day load increment).

• The coefficient of permeability from falling head permeability test results

indicated that the untreated and stabilised biosolids have low permeability

similar to that of clay type materials.

• The composition of the biosolids will have an impact on the geotechnical testing

results as will other factors such as formation history, treatment process, drying

duration, drying method, storage methods, storage period and handling methods.

9.4 Finite Element Modelling of Embankment using Stabilised Biosolids with

Admixtures

Finite element analysis was conducted to analyse the behaviour of embankment using

stabilised biosolids with lime, cement, bauxsol and fly-ash as well as untreated

biosolids. The following conclusions can be made from the finite element analysis:

• The residual settlement of the biosolids stabilised with various additives

including lime (5%), cement (3%, 5%), bauxsol (3%, 5%) and fly-ash (10%,

20%, 30%) were found to be within VicRoad’s residual settlement requirement

of a maximum of 50 mm over a period of 20 years after 6 months of preloading.

235

• The results of the analysis agrees well with the laboratory testing results and

indicates that biosolids when stabilised with additives to the required

percentages can be use as stabilised fill in embankments.

• The residual settlement reported for the stabilised biosolids with lime, cement

and bauxsol was until the completion of total settlement based on a minimum

pore water pressure of 0.01 kN/m2 that was conservatively specified in the

calculation phase of the analyses (as compared to the traditionally recommended

minimum pore water pressure of 1 kN/m2).

• An analysis was undertaken for untreated biosolids but the analysis could not be

completed successfully. This was because the low shear strength and friction

angle of the untreated biosolids was found to be inadequate to carry the

embankment and traffic load.

• The analysis confirms that biosolids has to be stabilised before usage as

embankment fill material and as such untreated biosolids cannot be used in such

embankment applications.

• An impermeable geomembrane separator or 0.5 m impermeable clay layer is

recommended to be used to encapsulate the biosolids and to prevent any seepage

or leaching of biosolids into the fill material. The geomembrane and clay layer

acts as a separator and will furthermore provide a transition between the

stabilised biosolids and the engineered fill.

• The cost of encapsulating the stabilised biosolids with a geomembrane is

minimal as the geomembrane has been included solely for separation purposes.

The stabilised biosolids is thus confined and encapsulated 3 dimensionally and

there is furthermore conservation of mass but not volume of stabilised biosolids

as the stabilised biosolids will still comprise of air and moisture voids.

236

9.5 Biodegradation Settlement Analysis of Untreated and Stabilised Biosolids

with Admixtures

The biodegradation settlement analysis and corrosivity was conducted on the

embankment using stabilised biosolids with 5% lime, 3% and 5% cement, 3% and 5%

bauxsol as untreated biosolids. The following conclusions can be made from the

biodegradation settlement analysis:

• In the sensitivity analysis it is assumed that the biosolids not to be in their active

stage of biodegradation. The active stage of biodegradation is assessed to have

occurred during stockpiling. Moisture content and net thickness of biosolids

were assumed to be reduced with stabilised biosolids options.

• The flow on this biodegradation settlement analysis model which approach to

biodegrade completely of some point. The biodegradable ability and

biodegradable thickness of biosolids become slower with time need to take in

account to accurately model biodegradation.

• Biodegradation is more sensitive with temperature, moisture content and pH. In

addition biosolids degradation is also dependent upon their initial state and

composition of biosolids. As biodegradation should not affected by the

additional stress on the embankment, the basic assumption made in this analysis

was, the biodegradation will occur after completion of the construction and also

concurrently with consolidation.

• The total time taken for the biodegradation process was analysed on untreated

biosolids and stabilised biosolids with 5% lime, 3% and 5% cement and 3% and

5% bauxsol. The time taken for fully biodegradation process decreases

dramatically with pH value of the biosolids mixture between 0 and 6 and then

increases exponentially with pH value of the biosolids between 8 and 14. The

trend of the time taken for the fully biodegradation process clearly indicates

sensitivity of pH value in biodegradation process.

237

• The rate of biodegradation process decreases with the increasing acidity and

alkalinity of the biosolids mixture. The maximum rate of biodegradation process

is expected at a pH value of 7 (neutral).

9.6 Corrosivity Settlement Analysis of Untreated and Stabilised Biosolids with

Admixtures

The following conclusions can be made from the corrosivity analysis of biosolids:

• Electrical resistivity is an important parameter used in evaluating the corrosivity

of a material. High resistivity is associated with low corrosion potential.

• The pH measurement results showed that untreated biosolids and stabilised

biosolids with lime, cement, bauxsol and fly-ash mixtures exhibit high

alkalinity, indicating low corrosion potential.

• Due to the complex nature of corrosion mechanism, one single parameter may

not be sufficient to evaluate corrosivity of a material. Based on the electrical

conductivity and pH test results, it is concluded that untreated biosolids and

stabilised biosolids with admixtures such as lime, cement, bauxsol and fly-ash

are potentially corrosive.

Stabilised biosolids with lime (5%), cement (3% and 5%), bauxsol (3% and 5%) and fly

ash (10%, 20% and 30%) could be used as embankment fill material in highway

construction. However field trial embankment using untreated and stabilised biosolids

with above mentioned percentages of admixtures would be recommend to analyis the

performance of untreated and stabilised as a embankment fill material, and also it could

be used to calibrate the finite element model which used in the finite element analysis.

Further research would recommend to incorporate the geotechnical and biodegradation

settlements into single model, which could be used in the finite element analysis of

embankment using untreated and stabilised biosolids.

238

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APPENDIX 1

Copies of selected published and in print refereed journal papers

resulting from this study

PLEASE NOTE

Appendix 1 is unable to be reproduced online. Please consult print copy held in the Swinburne Library or

click on the links below.

Suthagaran V, Arulrajah A, Bo MW, Wilson, J (2009). Stabilisation of biosolids with admixtures for potential use as an embankment fill

material. Australian Geomechanics, 44 (3): 63-70 http://www.australiangeomechanics.org/journal/443.php

Suthagaran V, Arulrajah A, Bo, MW (2010). Geotechnical laboratory testing of biosolids, International Journal of Geotechnical

Engineering 4(3): 407-415 DOI: 10.3328/IJGE.2010.04.03.407-415

http://dx.doi.org/10.3328/IJGE.2010.04.03.407-415

APPENDIX 2

Copies of refereed conference papers resulting from this study

PLEASE NOTE

Appendix 2 is unable to be reproduced online. Please consult print copy held in the Swinburne Library or

click on the links below.

Suthagaran V, Arulrajah A, Wilson J, Bo MW (2007). Field testing to determine the suitability of biosolids for embankment fill. Paper

presented at the 12th European Biosolids and Organic Resources Conference, Manchester, United Kingdom, 12-14 November 2007.

Suthagaran V, Arulrajah A, Bo MW, Wilson J (2008). Biosolids as

a construction material for engineered fills. Paper presented at the 10th International Conference on Applications of Advanced Technologies in

Transportation (AATT 2008), Athens, Greece, 27-31 May 2008.

http://www.civil.ntua.gr/aatt/aatt.html

Suthagaran V, Arulrajah A, Lamborn J, Wilson J (2008). Geotechnical testing to determine the suitability of biosolids for embankment ill. Paper

presented at the Biosolids Speciality IV Conference, Adelaide, South Australia, Australia, 11-12 June.

http://hdl.handle.net/1959.3/43579

Disfani MM, Arulrajah A, Suthagaran V, Bo MW (2009). Geotechnical characteristics of recycled glass-biosolid mixtures. Paper presented at the

17th International Conference on Soil Mechanics and Geotechnical Engineering, Alexandria, Egypt, 05-09 October 2009

Disfani MM, Arulrajah A, Suthagaran V, Bo MW (2009), Shear

strength behaviour of recycled glass-biosolids mixtures. Paper presented at the 62nd Canadian Geotechnical Conference and 10th

Joint Canadian Geotechnical Society (CGS) and Canadian National Chapter of the International Association of Hydrogeologists (IAH-CNC) Ground

Water Speciality Conference (GeoHalifax2009), Halifax, Nova Scotia, Canada, 20-24 September 2009.

Suthagaran V, Arulrajah A, Bo MW (2009). Settlement behaviour of

biosolids stabilised with bauxsol in road embankment. Paper presented at the 1st International Conference on Sustainable Infrastructure and Built Environment (SIBE-2009), Bandung, Indonesia, 02-03 November 2009.

Documents

Geotechnical characteristics and admixture stabilization ......ADMIXTURE STABILIZATION OF BIOSOLIDS Visvalingam Suthagaran This thesis is submitted for the Degree of Doctor of Philosophy