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
6.3.2. Standard compaction test results................................................................... 119
6.3.3. California Bearing Ratio (CBR) test results ................................................. 122
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
6.3.8. Hydraulic conductivity test results ............................................................... 131
6.4 Geotechnical Characteristics of Biosolids Stabilised with Fly-ash......................... 135
6.4.1. Index properties ............................................................................................ 135
6.4.1. Standard compaction test results................................................................... 137
6.4.2. California Bearing Ratio (CBR) test results ................................................. 140
6.4.3. Hydraulic conductivity test results ............................................................... 142
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
7.5 Finite Element Analysis of Embankments using Biosolids Stabilised with
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 5.11. Consolidated drained triaxial test results for biosolids in stockpile 2 ........ 70
Figure 5.12. Consolidated drained triaxial test results for biosolids in stockpile 3 ........ 71
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
Figure 6.3. Atterberg limits variation with percentage of lime added to biosolids in
stockpile 2 ....................................................................................................... 81
Figure 6.4. Atterberg limits variation with percentage of lime added to biosolids in
stockpile 3 ....................................................................................................... 82
Figure 6.5. Particle size distribution of biosolids samples stabilised with lime in
Stockpile 1....................................................................................................... 83
Figure 6.6. Particle size distribution of biosolids samples stabilised with lime in
Stockpile 2....................................................................................................... 83
Figure 6.7. Particle size distribution of biosolids samples stabilised with lime in
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
Figure 6.14. Consolidated drained triaxial test results for stabilised biosolids with 5%
lime.................................................................................................................. 89
Figure 6.15. Variation of void ratio with vertical stress for biosolids in stockpile 1 ...... 90
Figure 6.16. Variation of void ratio with vertical stress for biosolids in stockpile 2 ...... 91
Figure 6.17. Variation of void ratio with vertical stress for biosolids in stockpile 3 ...... 91
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
Figure 6.23. Atterberg limits with percentage of cement added to biosolids in
stockpile 2 ....................................................................................................... 99
xvi
Figure 6.24. Atterberg limits with percentage of cement added to biosolids in
stockpile 3 ..................................................................................................... 100
Figure 6.25. Particle size distribution of biosolids stabilised with cement in Stockpile 1
....................................................................................................................... 101
Figure 6.26. Particle size distribution of biosolids stabilised with cement in Stockpile 2
....................................................................................................................... 101
Figure 6.27. Particle size distribution of biosolids stabilised with cement in Stockpile 3
....................................................................................................................... 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
Figure 6.33. Consolidated drained triaxial test results for stabilised biosolids with 3%
cement ........................................................................................................... 107
Figure 6.34. Consolidated drained triaxial test results for stabilised biosolids with 5%
cement ........................................................................................................... 107
Figure 6.35. Variation of void ratio with vertical stress for biosolids in stockpile 1 .... 108
Figure 6.36. Variation of void ratio with vertical stress for biosolids in stockpile 2 .... 109
Figure 6.37. Variation of void ratio with vertical stress for biosolids in stockpile 3 .... 109
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
Figure 6.40. Variation of secondary consolidation for biosolids stabilised with 5%
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
Figure 6.44. Atterberg limits with percentage of bauxsol added to biosolids in
stockpile 2 ..................................................................................................... 118
xvii
Figure 6.45. Atterberg limits with percentage of bauxsol added to biosolids in
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
Figure 6.51. Consolidated drained triaxial test results for stabilised biosolids with 3%
bauxsol .......................................................................................................... 124
Figure 6.52. Consolidated drained triaxial test results for stabilised biosolids with 5%
bauxsol .......................................................................................................... 125
Figure 6.53. Variation of void ratio with vertical stress for biosolids in stockpile 1 .... 126
Figure 6.54. Variation of void ratio with vertical stress for biosolids in stockpile 2 .... 126
Figure 6.55. Variation of void ratio with vertical stress for biosolids in stockpile 3 .... 127
Figure 6.56. Rowe Cell test results for stabilised biosolids with 3% bauxsol .............. 128
Figure 6.57. Variation of secondary consolidation for biosolids stabilised with 3%
bauxsol .......................................................................................................... 130
Figure 6.58. Variation of secondary consolidation for biosolids stabilised with 5%
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
Figure 6.62. Atterberg limits with percentage of fly ash added to biosolids in stockpile 2
....................................................................................................................... 136
Figure 6.63. Atterberg limits with percentage of fly ash added to biosolids in stockpile 3
....................................................................................................................... 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
Figure 7.14. Deformation mesh of 5 m embankment using biosolids stabilised with 3%
cement. .......................................................................................................... 171
Figure 7.15. Vertical settlement of 5m embankment using biosolids stabilised with 3%
cement. .......................................................................................................... 171
Figure 7.16. Variation of vertical settlement of 5 m embankment using biosolids
stabilised with 3% and 5% cement. ............................................................ 172
Figure 7.17. Variation of vertical settlement of various embankments using biosolids
stabilised with 3% cement............................................................................. 173
Figure 7.18. Variation of vertical settlement of various embankments using biosolids
stabilised with 5% cement............................................................................. 173
Figure 7.19. Typical geometry for embankment using biosolids stabilised with bauxsol.
....................................................................................................................... 177
Figure 7.20. Deformation mesh of 5 m embankment using biosolids stabilised with 3%
bauxsol. ......................................................................................................... 178
Figure 7.21. Vertical settlement of 5 m embankment using biosolids stabilised with 3%
bauxsol. ......................................................................................................... 178
Figure 7.22. Variation of vertical settlement of 5 m embankment using biosolids
stabilised with 3% and 5% bauxsol. ............................................................ 179
Figure 7.23. Variation of vertical settlement of various embankments using biosolids
stabilised with 3% bauxsol. ........................................................................... 180
Figure 7.24. Variation of vertical settlement of various embankments using biosolids
stabilised with 5% 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
Figure 8.4. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% lime. ................................................................................. 205
Figure 8.5. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% lime. ................................................................................. 205
Figure 8.6. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% lime. ................................................................................. 206
Figure 8.7. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 208
Figure 8.8. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 210
Figure 8.9. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 210
Figure 8.10. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 211
Figure 8.11. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 214
Figure 8.12. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 215
Figure 8.13. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 216
Figure 8.14. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 216
Figure 8.15. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 219
Figure 8.16. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 220
Figure 8.17. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 220
Figure 8.18. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 221
Figure 8.19. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 224
Figure 8.20. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 225
xxi
Figure 8.21. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 226
Figure 8.22. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 226
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
Victoria, (Golders Associates, 2006). ............................................................. 22
Table 2.15. Summary of triaxial undrained compression testing on treated biosolids in
Victoria, (Golders Associates, 2006). ............................................................. 23
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
Table 6.3. Summary of geotechnical characteristics of biosolids stabilised with 3% lime
......................................................................................................................... 96
Table 6.4. Summary of geotechnical characteristics of biosolids stabilised with 5% lime
......................................................................................................................... 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
Table 6.7. Summary of geotechnical characteristics of biosolids stabilised with 3%
cement ........................................................................................................... 115
Table 6.8. Summary of geotechnical characteristics of biosolids stabilised with 5%
cement ........................................................................................................... 116
Table 6.9. Consolidation (creep) values for the biosolids stabilised with bauxsol. ...... 129
Table 6.10. Summary of geotechnical characteristics of biosolids stabilised with 1%
bauxsol .......................................................................................................... 132
Table 6.11. Summary of geotechnical characteristics of biosolids stabilised with 3%
bauxsol .......................................................................................................... 133
Table 6.12. Summary of geotechnical characteristics of biosolids stabilised with 5%
bauxsol .......................................................................................................... 134
Table 6.13. Summary of geotechnical characteristics of biosolids stabilised with 10%
fly ash ............................................................................................................ 143
Table 6.14. Summary of geotechnical characteristics of biosolids stabilised with 20%
fly ash ............................................................................................................ 144
xxiv
Table 6.15. Summary of geotechnical characteristics of biosolids stabilised with 30%
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 7.5. Summary of total and residual settlement of embankments using biosolids
stabilised with 3% cement............................................................................. 174
Table 7.6. Summary of total and residual settlement of embankments using biosolids
stabilised with 5% cement............................................................................. 174
Table 7.7. Material properties of biosolids stabilised with 3% and 5% bauxsol. ......... 177
Table 7.8. Summary of total and residual settlement of embankments using biosolids
stabilised with 3% bauxsol. ........................................................................... 181
Table 7.9. Summary of total and residual settlement of embankments using biosolids
stabilised with 5% bauxsol. ........................................................................... 181
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
biosolids with 5% lime. ................................................................................. 204
Table 8.14. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% lime. ................................................................................. 206
Table 8.15. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% lime. ................................................................................. 206
Table 8.16. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% lime. ................................................................................. 207
Table 8.17. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 209
Table 8.18. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 211
Table 8.19. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 211
Table 8.20. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 3% cement. ............................................................................ 212
Table 8.21. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 214
Table 8.22. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 217
Table 8.23. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 217
Table 8.24. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% cement. ............................................................................ 217
Table 8.25. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 219
Table 8.26. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 221
xxvi
Table 8.27. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 221
Table 8.28. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 3% bauxsol. ........................................................................... 222
Table 8.29. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 224
Table 8.30. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 227
Table 8.31. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 227
Table 8.32. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% bauxsol. ........................................................................... 227
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
BH5 2 3.0 Biosolids 8 80 Firm
BH7 2 4.0 Biosolids 23 230 Very Stiff
BH11 3 2.0 Biosolids 8 80 Firm
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
Stockpile 2- Sample 1
Stockpile 2- Sample 2
Stockpile 3- Sample 1
Stockpile 3- 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
Stockpile 1-Sample 2
Stockpile 2-Sample 1
Stockpile 2-Sample 2
Stockpile 3-Sample 1
Stockpile 3-Sample 2
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
Figure 5.11 presents the Mohr coulomb circle for consolidated drained triaxial test on
the compacted untreated biosolids in stockpile 2. From the consolidated drained triaxial
test of the compacted untreated biosolids, the effective friction angle was 10.9 degrees
while the effective cohesion was 0 kPa.
Figure 5.11. Consolidated drained triaxial test results for biosolids in stockpile 2
71
Figure 5.12 presents the Mohr coulomb circle for consolidated drained triaxial test on
the compacted untreated biosolids in stockpile 3. From the consolidated drained triaxial
test of the compacted untreated biosolids, the effective friction angle was 16.8 degrees
while the effective cohesion was 0 kPa.
Figure 5.12. Consolidated drained triaxial test results for biosolids in stockpile 3
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
Figure 5.19 presents the behaviour of the displacement with the vertical stress of
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
untreated biosolids in stockpile 2.
Figure 5.19. Rowe Cell test results for biosolids in stockpile 2
77
Figure 5.20 presents the behaviour of the displacement with the vertical stress of
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
untreated biosolids in stockpile 3.
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
Stablised biosolids with 3%Lime
Stablised biosolids with 5%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
0 1 3 5Percentage of lime added to biosolids (%)
Moi
stur
e co
nten
t (%
)
Liquid Limit
Plastic Limit
Plastic Index
Figure 6.3. Atterberg limits variation with percentage of lime added to biosolids in stockpile 2
82
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 6.4. Atterberg limits variation with percentage of lime added to biosolids in stockpile 3
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
Sample 1- 1% Lime Sample 2- 1% Lime
Sample 1- 3% Lime Sample 2- 3% Lime
Sample 1- 5% Lime Sample 2- 5% 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
(%
)
Sample 1- 0% Lime Sample 2- 0% Lime
Sample 1- 1% Lime Sample 2- 1% Lime
Sample 1- 3% Lime Sample 2- 3% Lime
Sample 1- 5% Lime Sample 2- 5% Lime
0.060.002 2 60
Clay Silt Sand Gravel Cobbles & Boulders
Figure 6.6. Particle size distribution of biosolids samples stabilised with lime in Stockpile 2
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
(%
)
Sample 1- 0% Lime Sample 2- 0% Lime
Sample 1- 1% Lime Sample 2- 1% Lime
Sample 1- 3% Lime Sample 2- 3% Lime
Sample 1- 5% Lime Sample 2- 5% Lime
0.060.002 2 60
Clay Silt Sand Gravel Cobbles & Boulders
Figure 6.7. Particle size distribution of biosolids samples stabilised with lime in Stockpile 3
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
Percentage of lime added to biosolids (%)
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
Percentage of lime added to biosolids (%)
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
Percentage of lime added to biosolids (%)
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
Percentage of lime added to biosolids (%)
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
Figure 6.13 presents the Mohr coulomb circle for consolidated drained triaxial test on
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
Figure 6.14 presents the Mohr coulomb circle for consolidated drained triaxial test on
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.
Figure 6.16 presents the behaviour of the void ratio with the vertical stress of biosolids
stabilised with 3% and 5% lime at stockpile 2 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 2 stabilised with 3% lime was 250 kN/m2 and 300 kN/m2 for
biosolids stabilised with 5% lime.
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
10 100 1000Vertical Stress (kN/m2)
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
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Lime
3% Lime
5% Lime
Figure 6.16. Variation of void ratio with vertical stress for biosolids in stockpile 2
Figure 6.17 presents the behaviour of the void ratio with the vertical stress of biosolids
stabilised with 3% and 5% lime at stockpile 3 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 3 stabilised with 3% lime was 280 kN/m2 and 300 kN/m2 for
biosolids stabilised with 5% lime.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Lime
3% Lime
5% Lime
Figure 6.17. Variation of void ratio with vertical stress for biosolids in stockpile 3
92
6.1.6. Rowe Cell consolidation test results
Figure 6.18 presents the behaviour of the displacement with the vertical stress of
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
Percentage of lime added to biosolids (%)
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.
Table 6.2. Summary of geotechnical characteristics of biosolids stabilised with 1% lime
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
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
Liquid Limit % 88 92 94
Plastic Limit % 75 71 75
Plasticity Index % 13 21 19
Compaction
Type of Compaction effort Standard Standard Standard
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
* - CBR swell after load applied at the end of soak period
96
Table 6.3. Summary of geotechnical characteristics of biosolids stabilised with 3% lime
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 45.4 40.5 45.0 47.3 35.3 41.7
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
Liquid Limit % 82 83 80
Plastic Limit % 70 64 60
Plasticity Index % 12 19 20
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.93 0.92 0.90 0.93
Optimum Moisture Content % 42 41 42 38
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
Preconsolidation Pressure kN/m2 200 250 280
Compression Index 0.513 0.522 0.537
Recompression Index 0.031 0.034 0.040
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
Permeability Permeability m/s 1.23 x 10-7 1.21 x 10-7 1.34 x 10-7
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
97
Table 6.4. Summary of geotechnical characteristics of biosolids stabilised with 5% lime
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 45.4 41.6 43.1 48.4 32.3 42.0
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
Liquid Limit % 76 80 77
Plastic Limit % 60 67 61
Plasticity Index % 16 13 16
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.91 0.90 0.89 0.90
Optimum Moisture Content % 40 42 39 41
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
Coefficient of Consolidation m2/year 0.7 0.2 0.3
Coefficient of Permeability m/s 7.0 x 10-11 2.2 x 10-11 4.1 x 10-11
Preconsolidation Pressure kN/m2 250 300 300
Compression Index 0.475 0.458 0.467
Recompression Index 0.027 0.024 0.029
Triaxial
Compression
Type of Test CD - -
Cohesion kN/m2 0 - -
Phi Angle Degree 45.4 - -
Falling Head
Permeability Permeability m/s 1.13 x 10-7 1.36 x 10-7 1.27 x 10-7
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
98
6.2 Geotechnical Characteristics of Biosolids Stabilised with Cement
6.2.1. Index properties
Moisture content tests were undertaken on samples of biosolids stabilised with 1%, 3%,
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
Stablised biosolids with 3%Cement
Stablised biosolids with 5%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
0 1 3 5Percentage of cement added to biosolids (%)
Moi
stur
e co
nten
t (%
)
Liquid Limit
Plastic Limit
Plastic Index
Figure 6.23. Atterberg limits with percentage of cement added to biosolids in stockpile 2
100
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 6.24. Atterberg limits with percentage of cement added to biosolids in stockpile 3
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
Sample 1- 1% Cement Sample 2- 1% Cement
Sample 1- 3% Cement Sample 2- 3% Cement
Sample 1- 5% Cement Sample 2- 5% Cement
0.060.002 2 60
Clay Silt Sand Gravel Cobbles & Boulders
Figure 6.25. Particle size distribution of biosolids stabilised with cement 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
(%
)
Sample 1- 0% Cement Sample 2- 0% Cement
Sample 1- 1% Cement Sample 2- 1% Cement
Sample 1- 3% Cement Sample 2- 3% Cement
Sample 1- 5% Cement Sample 2- 5% Cement
0.060.002 2 60
Clay Silt Sand Gravel Cobbles & Boulders
Figure 6.26. Particle size distribution of biosolids stabilised with cement in Stockpile 2
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
(%
)
Sample 1- 0% Cement Sample 2- 0% Cement
Sample 1- 1% Cement Sample 2- 1% Cement
Sample 1- 3% Cement Sample 2- 3% Cement
Sample 1- 5% Cement Sample 2- 5% Cement
0.060.002 2 60
Clay Silt Sand Gravel Cobbles & Boulders
Figure 6.27. Particle size distribution of biosolids stabilised with cement in Stockpile 3
6.2.2. 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 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.
Figure 6.29 presents the maximum dry density of biosolids stabilised with various
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
Moisture Content (%)
Dry
Den
sity
(t/m
3)
Biosolids + 1% Cement
Biosolids + 3% Cement
Biosolids + 5% 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
Percentage of cement added to biosolids (%)
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
Percentage of cement added to biosolids (%)
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
6.2.3. California Bearing Ratio (CBR) test results
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
Figure 6.32 shows the CBR swell results after 4 days for biosolids stabilised with 1%,
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
Percentage of cement added to biosolids (%)
Sw
ell (
%)
0% Cement 1% Cement 3% Cement 5% Cement
Figure 6.32. Swell results after 4 days for biosolids stabilised with cement
6.2.4. Triaxial (Consolidated Drained) test results
Figure 6.33 presents the Mohr coulomb circle for consolidated drained triaxial test on
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
while the effective cohesion was 0 kPa.
107
Figure 6.33. Consolidated drained triaxial test results for stabilised biosolids with 3% cement
Figure 6.34 presents the Mohr coulomb circle for consolidated drained triaxial test on
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
while the effective cohesion was 0 kPa.
Figure 6.34. Consolidated drained triaxial test results for stabilised biosolids with 5% cement
108
6.2.5. One dimensional consolidation test results
Figure 6.35 presents the behaviour of the void ratio with the vertical stress of biosolids
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
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Cement
3% Cement
5% Cement
Figure 6.35. Variation of void ratio with vertical stress for biosolids in stockpile 1
Figure 6.36 presents the behaviour of the void ratio with the vertical stress of biosolids
stabilised with 3% and 5% cement at stockpile 2 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 2 stabilised with 3% cement was 230 kN/m2 and 300 kN/m2 for
biosolids stabilised with 5% cement.
109
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Cement
3% Cement
5% Cement
Figure 6.36. Variation of void ratio with vertical stress for biosolids in stockpile 2
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Cement3% Cement5% Cement
Figure 6.37. Variation of void ratio with vertical stress for biosolids in stockpile 3
110
Figure 6.37 presents the behaviour of the void ratio with the vertical stress of biosolids
stabilised with 3% and 5% cement at stockpile 3 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 3 stabilised with 3% cement was 280 kN/m2 and 320 kN/m2 for
biosolids stabilised with 5% cement.
6.2.6. Rowe Cell consolidation test results
Figure 6.38 presents the behaviour of the displacement with the vertical stress of
stabilised biosolid sample with 3% cement 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 180 kN/m2 was obtained for
stabilised biosolids with 3% cement.
Figure 6.38. Rowe Cell test results for stabilised biosolids with 3% cement
111
6.2.7. 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 3% cement and 5% cement.
Table 6.5 summarises the creep consolidation test results of biosolids stabilised with 3%
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
biosolids stabilised with 5% cement.
Table 6.5. Secondary consolidation (creep) values for biosolids stabilised with cement.
Secondary consolidation value- Cα (% of strain per log cycle)
Stabilised biosolids Applied vertical stress (kPa)
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
0 200 400 600 800 1000Applied vertical stress (kPa)
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
0 200 400 600 800 1000Applied vertical stress (kPa)
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
6.2.8. Hydraulic conductivity test results
Figure 6.41 presents the hydraulic conductivity of biosolids stabilised with 3% and 5%
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
Percentage of cement added to biosolids (%)
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
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 49.9 51.1 42.2 54.8 39.9 45.5
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
Liquid Limit % 97 95 89
Plastic Limit % 78 73 71
Plasticity Index % 19 22 18
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.85 0.84 0.85 0.85
Optimum Moisture Content % 39 38 40 40
CBR CBR Swell* % 0.15 0.34 0.52 0.40
CBR Value % 1.8 2.0 1.9 1.7
* - CBR swell after load applied at the end of soak period
115
Table 6.7. Summary of geotechnical characteristics of biosolids stabilised with 3% cement
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 48.4 44.3 39.7 48.7 36.2 38.9
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
Liquid Limit % 80 77 81
Plastic Limit % 65 60 62
Plasticity Index % 15 17 19
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.87 0.88 0.87 0.86
Optimum Moisture Content % 40 40 40 38
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
Coefficient of Consolidation m2/year 0.5 0.2 0.5
Coefficient of Permeability m/s 9.7 x 10-11 4.7 x 10-11 5.0 x 10-11
Preconsolidation Pressure kN/m2 220 230 280
Compression Index 0.410 0.395 0.409
Recompression Index 0.029 0.022 0.032
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
Permeability Permeability m/s 1.17 x 10-7 1.32 x 10-7 1.10 x 10-7
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
116
Table 6.8. Summary of geotechnical characteristics of biosolids stabilised with 5% cement
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 45.7 43.2 38.6 47.0 31.5 36.5
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
Liquid Limit % 74 82 75
Plastic Limit % 60 65 60
Plasticity Index % 14 17 15
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.87 0.88 0.87 0.88
Optimum Moisture Content % 37 40 37 36
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
Coefficient of Consolidation m2/year 0.5 0.5 0.4
Coefficient of Permeability m/s 8.1 x 10-11 4.9 x 10-11 2.9 x 10-11
Preconsolidation Pressure kN/m2 220 300 320
Compression Index 0.275 0.325 0.295
Recompression Index 0.021 0.028 0.025
Triaxial
Compression
Type of Test - CD -
Cohesion kN/m2 - 0 -
Phi Angle Degree - 39.5 -
Falling Head
Permeability Permeability m/s 9.31 x 10-8 1.05 x 10-7 8.54 x 10-8
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
117
6.3 Geotechnical Characteristics of Biosolids Stabilised with Bauxsol
6.3.1. Index properties
Moisture content tests were undertaken on samples of biosolids stabilised with 1%, 3%,
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
Liquid limit, plastic limit and plastic index tests were undertaken on biosolids stabilised
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
0 1 3 5Percentage of bauxsol added to biosolids (%)
Moi
stur
e co
nten
t (%
)
Liquid Limit
Plastic Limit
Plastic Index
Figure 6.44. Atterberg limits with percentage of bauxsol added to biosolids in stockpile 2
119
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 6.45. Atterberg limits with percentage of bauxsol added to biosolids in stockpile 3
6.3.2. 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 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.
Figure 6.47 presents the maximum dry density of biosolids stabilised with various
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
Moisture Content (%)
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
Figure 6.48 presents the optimum moisture content of biosolids stabilised with various
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
Percentage of bauxsol added to biosolids (%)
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
Percentage of bauxsol added to biosolids (%)
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
6.3.3. California Bearing Ratio (CBR) test results
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
Percentage of bauxsol added to biosolids (%)
CB
R V
alue
(%
)
0% Bauxsol 1% Bauxsol 3% Bauxsol 5% Bauxsol
Figure 6.49. CBR results of biosolids stabilised with bauxsol
123
Figure 6.50 shows the CBR swell results after 4 days for biosolids stabilised with 1%,
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
Percentage of bauxsol added to biosolids (%)
Sw
ell (
%)
0% Bauxsol 1% Bauxsol 3% Bauxsol 5% Bauxsol
Figure 6.50. Swell results after 4 days for biosolids stabilised with bauxsol.
124
6.3.4. Triaxial (Consolidated Drained) test results
Figure 6.51 presents the Mohr coulomb circle for consolidated drained triaxial test on
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
while the effective cohesion was 0 kPa.
Figure 6.51. Consolidated drained triaxial test results for stabilised biosolids with 3% bauxsol
Figure 6.52 presents the Mohr coulomb circle for consolidated drained triaxial test on
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
while the effective cohesion was 0 kPa.
125
Figure 6.52. Consolidated drained triaxial test results for stabilised biosolids with 5% bauxsol
6.3.5. One dimensional consolidation test results
Figure 6.53 presents the behaviour of the void ratio with the vertical stress of biosolids
stabilised with 3% and 5% bauxsol 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% bauxsol was 300 kN/m2 and 300 kN/m2 for
biosolids stabilised with 5% bauxsol.
Figure 6.54 presents the behaviour of the void ratio with the vertical stress of biosolids
stabilised with 3% and 5% bauxsol at stockpile 2 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 2 stabilised with 3% bauxsol was 280 kN/m2 and 230 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
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Bauxsol3% Bauxsol5% Bauxsol
Figure 6.53. Variation of void ratio with vertical stress for biosolids in stockpile 1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Bauxsol3% Bauxsol5% Bauxsol
Figure 6.54. Variation of void ratio with vertical stress for biosolids in stockpile 2
127
Figure 6.55 presents the behaviour of the void ratio with the vertical stress of biosolids
stabilised with 3% and 5% bauxsol at stockpile 3 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 3 stabilised with 3% bauxsol was 280 kN/m2 and 220 kN/m2 for
biosolids stabilised with 5% bauxsol.
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
10 100 1000Vertical Stress (kN/m2)
Voi
d R
atio
(e)
0% Bauxsol3% Bauxsol5% Bauxsol
Figure 6.55. Variation of void ratio with vertical stress for biosolids in stockpile 3
128
6.3.6. Rowe Cell consolidation test results
Figure 6.56 presents the behaviour of the displacement with the vertical stress of
stabilised biosolid sample with 3% bauxsol 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 170 kN/m2 was obtained for
stabilised biosolids with 3% bauxsol.
Figure 6.56. Rowe Cell test results for stabilised biosolids with 3% bauxsol
129
6.3.7. 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 3% bauxsol and 5% bauxsol.
Table 6.9 summarises the creep consolidation test results of biosolids stabilised with 3%
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.
Secondary consolidation value- Cα (% of strain per log cycle)
Stabilised biosolids Applied vertical stress (kPa)
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
0 200 400 600 800 1000Applied vertical stress (kPa)
Cα
(% o
f stra
in p
er l
og c
ycle
)
Figure 6.57. Variation of secondary consolidation for biosolids stabilised with 3%
bauxsol
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 200 400 600 800 1000Applied vertical stress (kPa)
Cα
(%
of s
tra
in p
er
log
cy
cle
)
Figure 6.58. Variation of secondary consolidation for biosolids stabilised with 5% bauxsol
131
6.3.8. Hydraulic conductivity test results
Figure 6.59 presents the hydraulic conductivity of biosolids stabilised with 3% and 5%
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
Percentage of bauxsol added to biosolids (%)
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
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 54.6 52.1 50.9 54.6 44.3 45.7
Atterberg
Limit
Liquid Limit % 89 92 91
Plastic Limit % 71 78 75
Plasticity Index % 18 14 16
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.88 0.86 0.91 0.89
Optimum Moisture Content % 48 44 44 45
CBR CBR Swell* % 0.50 0.38 0.52 0.25
CBR Value % 1.7 2.1 1.9 2.0
* - CBR swell after load applied at the end of soak period
133
Table 6.11. Summary of geotechnical characteristics of biosolids stabilised with 3% bauxsol
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 53.8 49.1 49.5 55.5 44.0 43.2
Atterberg
Limit
Liquid Limit % 76 77 74
Plastic Limit % 62 60 61
Plasticity Index % 14 17 13
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.90 0.90 0.89 0.91
Optimum Moisture Content % 46 45 43 44
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
Coefficient of Consolidation m2/year 0.3 0.6 0.3
Coefficient of Permeability m/s 6.2 x 10-11 14.6 x 10-11 3.1 x 10-11
Preconsolidation Pressure kN/m2 300 280 280
Compression Index 0.501 0.472 0.487
Recompression Index 0.032 0.029 0.034
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
Permeability Permeability m/s 1.24 x 10-7 1.33 x 10-7 9.59 x 10-8
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
134
Table 6.12. Summary of geotechnical characteristics of biosolids stabilised with 5% bauxsol
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 50.3 50.7 48.4 53.2 43.6 43.9
Atterberg
Limit
Liquid Limit % 75 72 76
Plastic Limit % 60 57 60
Plasticity Index % 15 15 16
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.88 0.90 0.89 0.89
Optimum Moisture Content % 41 40 38 40
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
Coefficient of Consolidation m2/year 0.5 0.4 0.5
Coefficient of Permeability m/s 3.2 x 10-11 4.2 x 10-11 7.0 x 10-11
Preconsolidation Pressure kN/m2 300 230 220
Compression Index 0.412 0.409 0.389
Recompression Index 0.032 0.023 0.019
Triaxial
Compression
Type of Test - - CD
Cohesion kN/m2 - - 0
Phi Angle Degree - - 43.0
Falling Head
Permeability Permeability m/s 1.09 x 10-7 1.08 x 10-7 9.01 x 10-8
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
135
6.4 Geotechnical Characteristics of Biosolids Stabilised with Fly-ash
6.4.1. Index properties
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
Stablised biosolids with 20% Fly ash
Stablised biosolids with 30% Fly ash
Figure 6.60. Moisture content variation with percentage of fly ash added to biosolids
Liquid limit, plastic limit and plastic index tests were undertaken on biosolids stabilised
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
Figure 6.61. Atterberg limits with percentage of fly ash added to biosolids in stockpile 1
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
Figure 6.62. Atterberg limits with percentage of fly ash added to biosolids in stockpile 2
137
0
20
40
60
80
100
120
0 10 20 30Percentage of fly ash added to biosolids (%)
Moi
stur
e co
nten
t (%
)Liquid LimitPlastic LimitPlastic Index
Figure 6.63. Atterberg limits with percentage of fly ash added to biosolids in stockpile 3
6.4.1. 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 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.
Figure 6.65 presents the maximum dry density of biosolids stabilised with various
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
Figure 6.66 presents the optimum moisture content of biosolids stabilised with various
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
Percentage of fly ash added to biosolids (%)
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
Percentage of fly ash added to biosolids (%)
Opt
imum
Moi
stur
e C
onte
nt (
%)
0% Fly ash10% Fly ash20% Fly ash30% Fly ash
Figure 6.66. Variation of Optimum Moisture Content (OMC) with percentage of fly ash
140
6.4.2. California Bearing Ratio (CBR) test results
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
Percentage of fly ash added to biosolids (%)
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
Percentage of fly ash added to biosolids (%)
Opt
imum
Moi
stur
e C
onte
nt (
%)
0% Fly ash10% Fly ash20% Fly ash30% Fly ash
Figure 6.68. Swell results after 4 days for biosolids stabilised with fly ash.
Figure 6.68 shows the CBR swell results after 4 days for biosolids stabilised with 10%,
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
6.4.3. Hydraulic conductivity test results
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
Percentage of fly ash added to biosolids (%)
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
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 46.3 45.3 50.4 48.3 48.0 50.8
Atterberg
Limit
Liquid Limit % 93 85 91
Plastic Limit % 70 68 69
Plasticity Index % 23 17 22
Compaction
Type of Compaction effort Standard Standard Standard
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
Coefficient of Consolidation m2/year 0.4 0.35 0.3
Coefficient of Permeability m/s 3.2 x 10-11 4.1 x 10-12 4.5 x 10-13
Preconsolidation Pressure kN/m2 210 240 250
Compression Index 0.475 0.515 0.483
Recompression Index 0.034 0.041 0.038
Falling Head
Permeability Permeability m/s 10.3 x 10-8 8.6 x 10-8 1.36 x 10-8
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
144
Table 6.14. Summary of geotechnical characteristics of biosolids stabilised with 20% fly ash
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 42.4 38.6 40.3 40.9 41.7 40.1
Atterberg
Limit
Liquid Limit % 87 83 80
Plastic Limit % 69 67 65
Plasticity Index % 18 16 15
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.91 0.87 0.88
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
Coefficient of Consolidation m2/year 0.5 0.4 0.6
Coefficient of Permeability m/s 3.5 x 10-11 7.2 x 10-12 5.3 x 10-13
Preconsolidation Pressure kN/m2 270 250 280
Compression Index 0.375 0.412 0.395
Recompression Index 0.021 0.031 0.028
Falling Head
Permeability Permeability m/s 2.64 x 10-8 1.51 x 10-8 6.31 x 10-8
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
145
Table 6.15. Summary of geotechnical characteristics of biosolids stabilised with 30% fly ash
Geotechnical Characteristics Unit Stockpile 1 Stockpile 2 Stockpile 3
Moisture Content % 33.46 31.36 35.87 36.2 34.64 35.25
Atterberg
Limit
Liquid Limit % 79 81 75
Plastic Limit % 62 68 61
Plasticity Index % 17 13 14
Compaction
Type of Compaction effort Standard Standard Standard
Maximum Dry Density t/m3 0.88 0.9 0.92
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
Coefficient of Consolidation m2/year 0.5 0.58 0.6
Coefficient of Permeability m/s 2.8 x 10-11 10.4 x 10-12 3.2 x 10-13
Preconsolidation Pressure kN/m2 280 290 310
Compression Index 0.42 0.234 0.365
Recompression Index 0.025 0.042 0.036
Falling Head
Permeability Permeability m/s 5.62 x 10-8 4.21 x 10-8 6.54 x 10-8
* - CBR swell after load applied at the end of soak period
UU – Unconsolidated Undrained Triaxial test
CD –Consolidated Drained Triaxial test
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
Percentage of fly ash added to biosolids (%)
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
Percentage of lime added to biosolids (%)
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
Percentage of cement added to biosolids (%)
Wat
er c
onte
nt (
%)
Liquid Limit (LL)
Plastic Limit (PL)
Plasticity Index (PI)
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
Percentage of bauxsol added to biosolids (%)
Wat
er c
onte
nt (
%)
Liquid Limit (LL)
Plastic Limit (PL)
Plasticity Index (PI)
Figure 6.74. Correlation of atterberg limits with percentage of bauxsol added to the biosolids
The proposed trend of liquid limits, plastic limits and plasticity indexes with the
percentage of bauxsol in the mixture is presented in Figure 6.74 and is found to follow
the exponential function as presented in equation 6.11 for the correlation of liquid limit,
equation 6.12 for the correlation of plastic limit and equation 6.13 for correlation of
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
Percentage of fly ash added to biosolids (%)
Wat
er c
onte
nt(%
)
Liquid Limit (LL)
Plastic Limit (PL)
Plasticity Index (PI)
Expon. (Liquid Limit
Figure 6.75. Correlation of atterberg limits with percentage of fly ash added to the biosolids
The proposed trend of liquid limits, plastic limits and plasticity indexes with the
percentage of fly ash in the mixture is presented in Figure 6.75 and is found to follow
the exponential function as presented in equation 6.14 for the correlation of liquid limit,
equation 6.15 for the correlation of plastic limit and equation 6.16 for correlation of
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
7.3 Finite Element Analysis of Embankments using Biosolids Stabilised with
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.
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.
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.
The Mohr-coulomb model was specified for the subsoil comprising basalt and the
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
biosolids stabilised with 5% lime.
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
6 months preloading period
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
7.4 Finite Element Analysis of Embankments using Biosolids Stabilised with
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.
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.
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 3% and 5% cement is presented in Figure 7.13.
The Mohr-coulomb model was specified for the subsoil comprising basalt and the
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 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
Figure 7.14 presents the finite element deformation mesh for the 5 m embankment using
biosolids stabilised with 3% cement. Figure 7.15 presents the vertical settlement of the 5
m embankment using biosolids stabilised with 3% cement.
Biosolids + 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
Impermeable geomembrane separator or0.5 m impermeable clay layer
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.
Figure 7.16 presents the variation of total vertical settlement as well as the residual
settlement with time for the finite element analysis of the 5 m high embankment using
biosolids stabilised with 3% and 5% cement.
A residual settlement of 30 mm was obtained after 6 months of preloading for the 5 m
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
6 months preloading period
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.
Figure 7.17 compares the variation of total vertical settlement with time for the 2 to 5 m
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
)
5m Embankment 4m Embankment 3m Embankment 2m Embankment
6 months preloading period
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
)
5m Embankment 4m Embankment 3m Embankment 2m Embankment
6 months preloading period
Figure 7.18. Variation of vertical settlement of various embankments using biosolids stabilised with 5% cement.
174
Table 7.5 summarises the total and residual settlement and time taken to complete the
settlement after 6 months of preloading of embankments using biosolids stabilised with
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
Table 7.6 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% cement. In total, 356 days were taken to complete total settlement for the 5 m high
embankment using biosolids stabilised with 5% cement.
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).
176
7.5 Finite Element Analysis of Embankments using Biosolids Stabilised with
Bauxsol
This section discuss the results of finite element analysis of embankment using
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.
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.
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 3% and 5% bauxsol is presented in Figure 7.19.
The Mohr-coulomb model was specified for the subsoil comprising basalt and the
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 20kPa 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 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
Figure 7.20 presents the finite element deformation mesh for the 5 m embankment using
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
Impermeable geomembrane separator or0.5 m impermeable clay layer
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.
Figure 7.22 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
biosolids stabilised with 3% and 5% bauxsol.
A residual settlement of 17 mm was obtained after 6 months of preloading for the 5 m
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
6 months preloading period
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.
Figure 7.23 compares the variation of total vertical settlement with time for the 2 to 5 m
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
)
5m Embankment 4m Embankment 3m Embankment 2m Embankment
6 months preloading period
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
)
5m Embankment 4m Embankment 3m Embankment 2m Embankment
6 months preloading period
Figure 7.24. Variation of vertical settlement of various embankments using biosolids stabilised with 5% bauxsol.
181
Table 7.8 summarises the total and residual settlement and time taken to complete the
settlement after 6 months of preloading of embankments using biosolids stabilised with
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
Table 7.9 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% 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.
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).
183
7.6 Finite Element Analysis of Embankments using Untreated Biosolids
This section discuss the results of finite element analysis of embankment using
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.
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 untreated biosolids is presented in Figure 7.25.
The Mohr-coulomb model was specified for the subsoil comprising basalt and the
engineered fill (Type B and C). The soft soil creep model was specified for the
untreated 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 20kPa was specified in
the analyses prior to the preloading period.
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
Biosolids + 3% Cement
Settlement in Biosolids layer 278 310 332 348 Residual Thickness of the biosolids layer 222 190 168 152
Biosolids + 5% Cement
Settlement in Biosolids layer 212 226 242 254 Residual Thickness of the biosolids layer 288 275 258 246
Biosolids + 3% Bauxsol
Settlement in Biosolids layer 263 279 300 318 Residual Thickness of the biosolids layer 237 221 200 182
Biosolids + 5% Bauxsol
Settlement in Biosolids layer 216 229 250 264 Residual Thickness of the biosolids layer 284 271 250 236
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 Identification Sample 1
Sample 2
Sample 3
Sample 4
Average Standard deviation
Biosolids + 1% Lime
Temperature (degreeC)
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
Conductivity (µS/cm)
2060 2095 2098 2054 2077 22.97
Biosolids + 3% Lime
Temperature (degreeC)
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
Conductivity (µS/cm)
1803 1771 1865 1829 1817 39.83
Biosolids + 5% Lime
Temperature (degreeC)
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
Conductivity (µS/cm)
1684 1751 1692 1745 1718 34.88
195
Table 8.6. pH and electrical conductivity test results of biosolids stabilised with cement.
Sample Identification Sample 1
Sample 2
Sample 3
Sample 4
Average Standard deviation
Biosolids + 1% Cement
Temperature (degreeC)
20.4 20.7 21 21.4 20.88 0.43
pH 6.98 6.63 6.69 6.96 6.8 0.18
Conductivity (µS/cm)
2070 1937 2058 1930 1999 75.56
Biosolids + 3% Cement
Temperature (degreeC)
20.3 20.5 20.5 20.6 20.48 0.13
pH 8.95 9 9 9.01 9 0.026
Conductivity (µS/cm)
1803 2029 1979 1838 1912 108.83
Biosolids + 5% Cement
Temperature (degreeC)
20.3 20.4 20.5 20.5 20.43 0.10
pH 10 10.07 10.04 10.01 10.0 0.03
Conductivity (µS/cm)
1870 1939 1951 1944 1926 37.66
Table 8.7. pH and electrical conductivity test results of biosolids stabilised with bauxsol.
Sample Identification Sample 1
Sample 2
Sample 3
Sample 4
Average Standard deviation
Biosolids + 1% Bauxsol
Temperature (degreeC)
21 21 21.1 21.1 21.05 0.06
pH 5.25 5.14 5.14 5.13 5.2 0.06
Conductivity (µS/cm)
1718 1650 1694 1734 1699 36.57
Biosolids + 3% Bauxsol
Temperature (degreeC)
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
Conductivity (µS/cm)
1721 1734 1728 1756 1735 15.13
Biosolids + 5% Bauxsol
Temperature (degreeC)
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
Conductivity (µS/cm)
1737 1755 1680 1732 1726 32.22
196
Table 8.8. pH and electrical conductivity test results of biosolids stabilised with fly-ash.
Sample Identification Sample 1
Sample 2
Sample 3
Sample 4
Average Standard deviation
Biosolids + 10% Fly-ash
Temperature (degreeC)
20.7 31 21 21.1 23.45 5.04
pH 5.58 5.44 5.37 5.32 5.4 0.11
Conductivity (µS/cm)
1916 1876 1892 1940 1906 28.00
Biosolids + 20% Fly-ash
Temperature (degreeC)
20.9 21.1 21 20.8 20.95 0.13
pH 5.1 5.07 5.12 5.15 5.1 0.03
Conductivity (µS/cm)
1888 1780 1834 1855 1839 45.32
Biosolids + 30% Fly-ash
Temperature (degreeC)
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
0.00
0.10
0.20
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.
The effect of pH value in the biodegradation settlement was analysed by reducing the
pH value to 8 and 9 and also increasing the pH value to 11. The prediction of
biodegradation settlements in the 5m height embankment using layer of 0.5m thick
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.
The biodegradation settlement 25 years after the construction of 5m height embankment
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
0.00
0.05
0.10
0.15
0.20
0.25
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
Figure 8.3. Biodegradation settlement of 5m height embankment using stabilised
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
0.05
0.10
0.15
0.20
0.25
0 100 200 300 400 500 600 700 800 900 1000
Time (years)
Set
tlem
ent (
m)
Biosolids+5% Lime : Actual pH=10.40 Biosolids+5%Lime : pH=8Biosolids+5%Lime : pH=9 Biosolids+5%Lime : pH=11
Figure 8.4. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% lime.
0.00
0.05
0.10
0.15
0.20
0.25
0 100 200 300 400 500 600 700 800 900 1000
Time (years)
Set
tlem
ent (
m)
Biosolids+5% Lime : Actual pH=10.40 Biosolids+5% Lime : pH=8Biosolids+5% Lime : pH=9 Biosolids+5% Lime : pH=11
Figure 8.5. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% lime.
206
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% Lime : Actual pH=10.40 Biosolids+5% Lime : pH=8Biosolids+5% Lime : pH=9 Biosolids+5% Lime : pH=11
Figure 8.6. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% lime.
Table 8.14. Biodegradation settlement of 4m height embankment using stabilised biosolids with 5% lime.
Settlement of 4m Height embankment using stabilised biosolids with 5% lime (mm) pH 8 9 10.4 11
25 Years 230 215 50 10 50 Years - 230 100 30
100 Years - - 150 60 200 Years - - 220 105 350 Years - - 230 150
1000 Years - - - 220
Table 8.15. Biodegradation settlement of 3m height embankment using stabilised biosolids with 5% lime.
Settlement of 3m Height embankment using stabilised biosolids with 5% lime (mm) pH 8 9 10.4 11
25 Years 240 210 50 10 50 Years - 240 100 30
100 Years - - 150 60 200 Years - - 210 110 350 Years - - 240 160
1000 Years - - - 230
207
Table 8.16. Biodegradation settlement of 2m height embankment using stabilised biosolids with 5% lime.
Settlement of 2m Height embankment using stabilised biosolids with 5% lime (mm) pH 8 9 10.4 11
25 Years 250 230 60 10 50 Years - 250 100 30
100 Years - - 160 65 200 Years - - 210 115 350 Years - - 250 165
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.
The effect of pH value in the biodegradation settlement was analysed by reducing the
pH values to 7 and 8 and also increasing the pH value to 10. The prediction of
biodegradation settlements in the 5m height embankment using layer of 0.5m thick
stabilised biosolids with 3% cement are presented in Figure 8.7.
The assumed residual biosolids layer thickness of 0.21m 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 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
Figure 8.7. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 3% cement.
209
The biodegradation settlement 25 years after the construction of 5m height embankment
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
The prediction of biodegradation settlements in the 4m, 3m and 2m heights
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
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 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
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% Cement : Actual pH=8.99 Biosolids+3% Cement : pH=7Biosolids+3% Cement : pH=8 Biosolids+3% Cement : pH=10
Figure 8.8. Biodegradation settlement of 4m height embankment using 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
Figure 8.9. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 3% cement.
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
)
Biosolids+3% Cement : Actual pH=8.99 Biosolids+3% Cement : pH=7Biosolids+3% Cement : pH=8 Biosolids+3% Cement : pH=10
Figure 8.10. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 3% cement.
Table 8.18. Biodegradation settlement of 4m height embankment using stabilised biosolids with 3% cement.
Settlement of 4m Height embankment using stabilised biosolids with 3% cement (mm)
pH 7 8 9 10
25 Years 220 220 200 95 50 Years - - 220 150
100 Years - - - 200 200 Years - - - 215 350 Years - - - 220
Table 8.19. Biodegradation settlement of 3m height embankment using stabilised biosolids with 3% cement.
Settlement of 3m Height embankment using stabilised biosolids with 3% cement (mm)
pH 7 8 9 10
25 Years 220 220 200 95 50 Years - - 220 150
100 Years - - - 200 200 Years - - - 215 350 Years - - - 220
212
Table 8.20. Biodegradation settlement of 2m height embankment using stabilised biosolids with 3% cement.
Settlement of 2m Height embankment using stabilised biosolids with 3% cement (mm)
pH 7 8 9 10
25 Years 230 230 210 100 50 Years - - 230 155
100 Years - - - 210 200 Years - - - 225 350 Years - - - 230
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
The biodegradation settlement of 5m height embankment using stabilised biosolids with
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.
The effect of pH value in the biodegradation settlement was analysed by reducing the
pH values to 8 and 9 and also increasing the pH value to 11. The prediction of
biodegradation settlements in the 5m height embankment using layer of 0.5m thick
stabilised biosolids with 5% cement are presented in Figure 8.11.
The assumed residual biosolids layer thickness of 0.25m 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% cement.
The biodegradation settlement 25 years after the construction of 5m height embankment
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
Figure 8.11. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 5% cement.
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.
Table 8.21. Biodegradation settlement of 5m height embankment using stabilised biosolids with 5% cement.
Settlement of 5m Height embankment using stabilised biosolids with 5% cement (mm)
pH 8 9 10 11
25 Years 250 230 100 20 50 Years - 250 165 30
100 Years - - 215 60 200 Years - - 245 110 350 Years - - 250 160
1000 Years - - - 240
The prediction of biodegradation settlements in the 4m, 3m and 2m heights
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.
The assumed residual biosolids layer thickness of 0.26m, 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% 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
tlem
ent (
m)
Biosolids+5% Cement : Actual pH=10.03 Biosolids+5% Cement : pH=8Biosolids+5% Cement : pH=9 Biosolids+5% Cement : pH=11
Figure 8.12. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% cement.
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
)
Biosolids+5% Cement : Actual pH=10.03 Biosolids+5% Cement : pH=8Biosolids+5% Cement : pH=9 Biosolids+5% Cement : pH=11
Figure 8.13. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% cement.
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)
Biosolids+5% Cement : Actual pH=10.03 Biosolids+5% Cement : pH=8Biosolids+5% Cement : pH=9 Biosolids+5% Cement : pH=11
Figure 8.14. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% cement.
217
Table 8.22. Biodegradation settlement of 4m height embankment using stabilised biosolids with 5% cement.
Settlement of 4m Height embankment using stabilised biosolids with 5% cement (mm)
pH 8 9 10 11
25 Years 260 230 65 20 50 Years - 260 110 35
100 Years - - 180 65 200 Years - - 235 115 350 Years - - 260 170
1000 Years - - - 255
Table 8.23. Biodegradation settlement of 3m height embankment using stabilised biosolids with 5% cement.
Settlement of 3m Height embankment using stabilised biosolids with 5% cement (mm)
pH 8 9 10 11
25 Years 280 250 100 20 50 Years - 280 180 40
100 Years - - 245 70 200 Years - - 275 120 350 Years - - 280 180
1000 Years - - - 270
Table 8.24. Biodegradation settlement of 2m height embankment using stabilised biosolids with 5% cement.
Settlement of 2m Height embankment using stabilised biosolids with 5% cement (mm)
pH 8 9 10 11
25 Years 290 255 110 20 50 Years - 290 190 40
100 Years - - 250 70 200 Years - - 285 130 350 Years - - 290 190
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
The biodegradation settlement of 5m height embankment using stabilised biosolids with
3% bauxsol is presented in Figure 8.15 and also the results are summarised in Table
8.25. The average pH value from the four samples of stabilised biosolids with 3%
bauxsol is 5.5 from the pH test.
The effect of pH value in the biodegradation settlement was analysed by reducing the
pH value to 4 and 5 and also increasing the pH value to 6. The prediction of
biodegradation settlements in the 5m height embankment using layer of 0.5m thick
stabilised biosolids with 3% bauxsol are presented in Figure 8.15.
The assumed residual biosolids layer thickness of 0.2m 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 3% bauxsol.
The biodegradation settlement 25 years after the construction of 5m height embankment
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.
The biodegradation settlement in embankment using stabilised biosolids with 3%
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
Figure 8.15. Biodegradation settlement of 5m height embankment using stabilised
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
change in pH value are presented in Figure 8.16, Figure 8.17 and Figure 8.18
respectively and also the results are summarised in Table 8.26, Table 8.27 and Table
8.28 respectively.
The assumed residual biosolids layer thickness of 0.2m, 0.22m and 0.24m 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 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)
Biosolids+3% Bauxsol : Actual pH=5.54 Biosolids+3% Bauxsol : pH=4Biosolids+3% Bauxsol : pH=5 Biosolids+3% Bauxsol : pH=6
Figure 8.16. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 3% bauxsol.
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% Bauxsol : Actual pH=5.54 Biosolids+3% Bauxsol : pH=4Biosolids+3% Bauxsol : pH=5 Biosolids+3% Bauxsol : pH=6
Figure 8.17. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 3% bauxsol.
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
)
Biosolids+3% Bauxsol : Actual pH=5.54 Biosolids+3% Bauxsol : pH=4Biosolids+3% Bauxsol : pH=5 Biosolids+3% Bauxsol : pH=6
Figure 8.18. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 3% bauxsol.
Table 8.26. Biodegradation settlement of 4m height embankment using stabilised biosolids with 3% bauxsol.
Settlement of 4m 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 - - -
Table 8.27. Biodegradation settlement of 3m height embankment using stabilised biosolids with 3% bauxsol.
Settlement of 3m Height embankment using stabilised biosolids with 3% bauxsol (mm)
pH 4 5 5.5 6
25 Years 110 210 220 220 50 Years 165 220 - -
100 Years 205 - - - 150 Years 215 - - - 200 Years 220 - - -
222
Table 8.28. Biodegradation settlement of 2m height embankment using stabilised biosolids with 3% bauxsol.
Settlement of 2m Height embankment using stabilised biosolids with 3% bauxsol (mm)
pH 4 5 5.5 6
25 Years 120 225 240 240 50 Years 175 240 - -
100 Years 225 - - - 150 Years 235 - - - 200 Years 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
The biodegradation settlement of 5m height embankment using stabilised biosolids with
5% bauxsol is presented in Figure 8.19 and also the results are summarised in Table
8.29. The average pH value from the four samples of stabilised biosolids with 5%
bauxsol is 5.7 from the pH test.
The effect of pH value in the biodegradation settlement was analysed by reducing the
pH value to 4 and 5 and also increasing a pH value to 6. The prediction of
biodegradation settlements in the 5m height embankment using layer of 0.5m thick
stabilised biosolids with 5% bauxsol are presented in Figure 8.19.
The assumed residual biosolids layer thickness of 0.24m 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% 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
)
Biosolids+5% Bauxsol : Actual pH=5.66 Biosolids+5% Bauxsol : pH=4Biosolids+5% Bauxsol : pH=5 Biosolids+5% Bauxsol : pH=6
Figure 8.19. Biodegradation settlement of 5m height embankment using stabilised
biosolids with 5% bauxsol.
The biodegradation settlement in embankment using stabilised biosolids with 5%
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).
Table 8.29. Biodegradation settlement of 5m height embankment using stabilised biosolids with 5% bauxsol.
Settlement of 5m Height embankment using stabilised biosolids with 5% bauxsol (mm)
pH 4 5 5.7 6
25 Years 80 160 170 170 50 Years 125 170 - -
100 Years 160 - - - 150 Years 165 - - - 200 Years 170 - - -
The prediction of biodegradation settlements in the 4m, 3m and 2m heights
embankment using layer of 0.5m thick stabilised biosolids with 5% bauxsol with the
225
change in pH value are presented in Figure 8.20, Figure 8.21 and Figure 8.22
respectively and also the results are summarised in Table 8.30, Table 8.31 and Table
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
0.15
0.20
0.25
0.30
0 50 100 150 200 250 300 350 400 450 500
Time (years)
Set
tlem
ent (
m)
Biosolids+5% Bauxsol : Actual pH=5.66 Biosolids+5% Bauxsol : pH=4Biosolids+5% Bauxsol : pH=5 Biosolids+5% Bauxsol : pH=6
Figure 8.20. Biodegradation settlement of 4m height embankment using stabilised
biosolids with 5% bauxsol.
226
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
)
Biosolids+5% Bauxsol : Actual pH=5.66 Biosolids+5%Bauxsol : pH=4Biosolids+5%Bauxsol : pH=5 Biosolids+5%Bauxsol : pH=6
Figure 8.21. Biodegradation settlement of 3m height embankment using stabilised
biosolids with 5% bauxsol.
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
tlem
ent (
m)
Biosolids+5% Bauxsol : Actual pH=5.66 Biosolids+5% Bauxsol : pH=4Biosolids+5% Bauxsol : pH=5 Biosolids+5% Bauxsol : pH=6
Figure 8.22. Biodegradation settlement of 2m height embankment using stabilised
biosolids with 5% bauxsol.
227
Table 8.30. Biodegradation settlement of 4m height embankment using stabilised biosolids with 5% bauxsol.
Settlement of 4m Height embankment using stabilised biosolids with 5% bauxsol (mm)
pH 4 5 5.7 6
25 Years 115 230 250 250 50 Years 185 250 - -
100 Years 230 - - - 150 Years 245 - - - 200 Years 250 - - -
Table 8.31. Biodegradation settlement of 3m height embankment using stabilised biosolids with 5% bauxsol.
Settlement of 3m Height embankment using stabilised biosolids with 5% bauxsol (mm)
pH 4 5 5.7 6
25 Years 130 250 270 270 50 Years 200 270 - -
100 Years 250 - - - 150 Years 265 - - - 200 Years 270 - - -
Table 8.32. Biodegradation settlement of 2m height embankment using stabilised biosolids with 5% bauxsol.
Settlement of 2m Height embankment using stabilised biosolids with 5% bauxsol (mm)
pH 4 5 5.7 6
25 Years 140 270 290 290 50 Years 210 290 - -
100 Years 270 - - - 150 Years 280 - - - 200 Years 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
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.