Physical and semi analytical modelling for geosynthetic reinforced piled embankment

PHYSICAL AND SEMI-ANALYTICAL MODELLING FOR GEOSYNTHETIC REINFORCED PILED EMBANKMENT PHOON HUNG LEONG NATIONAL UNIVERSITY OF SINGAPORE 2006 PHYSICAL AND SEMI-ANALYTICAL MODELLING FOR GEOSYNTHETIC REINFORCED PILED EMBANKMENT PHOON HUNG LEONG (B.Eng (Hons), UTM) A THESIS SUBMITTED FOR THE DEGREE OF DOCTORATE OF PHILOSOPHY DEPARTMENT OF CIVIL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2006 Acknowledgements I would like to convey my heartfelt gratitude to my supervisor, Dr. Chew Soon Hoe, for his advice, guidance, encouragement and patience. His valuable effort and time dedicated to this research are deeply appreciated. Besides that, I would like to thank my parents and sisters for their never-ending love, support and sacrifice in encouraging me to complete this research. A special acknowledgement is dedicated to Ms. Angel Yong for her support and kind assistance in the compilation of this thesis. Special thanks are also extended to the family members of Geotechnical Group: Mr. Shen Rui Fu, Mr. Loo Leong Huat, Mr. Wong Chew Yuen, Mr. Tan Lye Heng, Mr. Choy Moon Nien, Mr. Shaja Khan and Mdm. Jamilah bte Mohd., Dr. Leong Kam Weng, Dr. He Zhiwei, Dr. Chen Xi, Mr. Cheng Yonggang, Dr. Zhang Xiying, Mr. Ong Chee Wee, Ms. Zhou Yuqian, Mr. Tan Hong Wei Andy, Mr. Desmond Leong, Mr. Tan Chzia Yheaw, Mr. Ma Rui and Dr. Zhou Xiaoxian for their kind assistance and advice. I would also like to thank Polyfelt Ges.m.b.H. for the financial support in conducting the whole series of large-scale physical model tests. Sincere thanks are also extended to Prof. Pascal Villard and Mr. Bastien Le Hello from the Univeristé Joseph Fourrier, France for their help and guidance in conducting the large-scale physical model tests. Next, I would like to extend my sincere gratitude to the final year students that I had the privilege of working with. Finally, I would also like to thank all the lecturers and postgraduates that have directly or indirectly contribute to my memorable experience in the National University of Singapore. i Table of Contents Page Acknowledgements i Table of Contents ii Summary vii List of Tables x List of Figures xiii Nomenclature xxvi Chapter 1: Introduction 1.1 Overview of Embankment Constructed Over Soft Foundation Soil 1.2 Ground Improvement Methods For Embankment Constructed Over Soft Foundation Soil 1.3 Geosynthetic Reinforced Piled Embankment (GRPE) System 1.4 Scope and Objectives of Research 1.5 Outline of Thesis 10 Chapter 2: Literature Review 2.1 Introduction 12 2.2 Soil Arching Effect 12 2.2.1 Different Models of Soil Arching 13 2.2.2 Classification of Soil Arching Effect 23 2.2.3 Evaluation of Degree of Soil Arching 26 2.3 Tensioned Membrane Effect 27 2.4 Current Design Methods and Guidelines 30 2.5 Small-Scale Physical Model Test 31 2.6 Field Studies 33 2.6.1 Failure of Conventional Piled Embankment at Bridge Approach 33 2.6.2 Field Behaviour of GRPE System 35 2.7 Concluding Remarks 37 ii Chapter 3: Large-Scale Model Tests in the Field 3.1 Overview of Large-Scale Model Testing Program 48 3.2 The Configuration of Tests 49 3.3 Characteristics of Fill Soil and Simulated Subsoil Used in Large-scale Model Tests 53 3.3.1 Sandy Soil 54 3.3.2 Residual Soil 54 3.3.3 Polystyrene Beads as Simulated High Compressibility Soft Soil 55 3.4 Characteristics of Geosynthetics Used in Large-scale Model Tests 56 3.5 The Orientation of Main Reinforcement Direction 57 3.6 Instrumentation Scheme 59 3.6.1 Measurement of Surface Settlement 60 3.6.2 Measurement of Soil Stresses 60 3.6.3 Measurement of Geosynthetic Strain 63 3.6.4 Measurement of Vertical Displacement of Geosynthetic 65 3.6.5 Measurement of Vertical Load Exerted on Pile Cap 66 3.6.6 Data Logging System 66 3.7 Procedures of Conducting Large-Scale Model Tests 66 Chapter 4: Evaluation of Boundary Effect on Large-scale Model Using FEM 4.1 Introduction 80 4.2 Mesh Generation 80 4.3 Finite Element Models 81 4.4 Material Properties 82 4.5 Construction 85 4.6 Results and Discussions 86 4.7 Correction of Conceptual Tributary Area 89 4.8 Concluding Remarks 90 iii Chapter 5: Centrifuge Model Tests 5.1 Introduction 107 5.2 Centrifuge Model Principles and Scaling Relationships 107 5.2.1 Basic Scaling Law 108 5.2.2 Non-uniform Acceleration 109 5.3 NUS Geotechnical Centrifuge 110 5.4 The Configuration of Tests 111 5.5 Centrifuge Model 113 5.5.1 Model Container 113 5.5.2 Model Cavity 113 5.5.3 Geotextile 114 5.5.4 Sand 114 5.5.5 Model Pile and Model Pile Cap 116 5.5.6 Model Soft Ground 120 5.5.7 Particle Size Effect 122 5.6 Instrumentation Scheme 123 5.6.1 Measurement of Surface Settlement 123 5.6.2 Measurement of Soil Stress 124 5.6.3 Measurement of Geotextile Strain 124 5.6.4 Measurement of Pile Head Settlement and Geotextile Deformation 126 5.6.5 Measurement of Geotextile Deformation 126 5.6.6 Measurement of Pore Water Pressure 127 5.7 Experimental Procedures 128 5.7.1 Procedures of Series 128 5.7.2 Procedures of Series 129 Chapter 6: Mechanisms of Geosynthetic Reinforced Piled Embankment 6.1 Strain Development in Geosynthetic Reinforcement 150 6.2 Vertical Displacement of Geosynthetic Reinforcement 152 6.3 Effect of Arrangement of Piles and Orientation of Reinforcement Direction 154 6.4 Surface Settlement and Settled Volume 155 iv 6.5 Effect of Additional Surface Static Load 157 6.6 The Observed “Soil Arch” in Embankment Fill 160 6.7 Stress Distribution and Development of Soil Arching in Embankment Fill 161 6.7.1 Low Compressibility Subsoil 162 6.7.2 High Compressibility Subsoil 166 6.8 Effect of Embankment Fill Height 171 6.8.1 Settlement Observation in Large-Scale Model Tests 171 6.8.2 Settlement Observation in Centrifuge Model Tests 172 6.9 Effect of Fill Material 174 6.10 Effect of Thin Separation Sand Layer Between Geosynthetic Sheets 176 6.11 Effect of Stiffness of Geosynthetic 177 6.12 Effect of Pile Design 179 6.12.1 Surface Settlement, Pile Head Settlement and Geotextile Deformation 179 6.12.2 Pile Axial Force 180 6.12.3 Soil Stresses in Embankment Fill 181 6.12.4 Strain Development in Geotextile 182 6.13 The Importance of Geosynthetic Reinforcement in GRPE System 184 6.14 Concluding Remarks 186 Chapter 7: Semi- Analytical Solution and Design for GRPE 7.1 Degree of Arching with respect to Vertical Load Transfer 222 7.2 Derivation of Radial Equilibrium Equation To Predict Vertical Stress Acting On Geosynthetic 227 7.2.1 Height of Dome 227 7.2.2 Height of “Infilling Zone” 228 7.2.3 Derivation of Radial Equilibrium Equation for the Estimation of Soil Stress within and below Arched Zone 231 7.3 Verification of Vertical Soil Stress Profile from Prediction by Large-Scale Model Tests Results 233 7.4 Catenary Deformation Concept and Tensioned Membrane Theory for the Prediction of Maximum Deflection and Geosynthetic Tension 235 7.4.1 Predictions for One Geosynthetic Sheet Running in Single Direction 235 7.4.2 Predictions for Two Geosynthetic Sheets Running in Two Perpendicular Directions 240 v 7.5 Verification of Prediction of Maximum Deflection and Tension Using Large-scale Model Tests Results 243 7.5.1 Geosynthetic Deflection 243 7.5.2 Geosynthetic Tensile Force 244 7.6 Design of GRPE System 246 7.6.1 Estimation of Vertical Stress on Geosynthetic 247 7.6.2 Estimation of Geosynthetic Tension and Maximum Deflection 248 7.6.3 Verification of Newly Developed Design Charts 250 7.7 Concluding Remarks 251 Chapter 8: Full-scale Field Test 8.1 Back Ground of Project 265 8.2 Introduction of Full-scale Field Test 266 8.3 Ground Conditions 267 8.4 Proposed GRPE System 267 8.5 Instrumentations and Monitoring Program 268 8.6 Results and Discussions 270 8.6.1 Soil Stresses in Embankment Fill 270 8.6.2 Geotextile Strain 273 8.6.3 Settlement of Reinforcement Sheets 274 8.6.4 Pore Water Pressure 275 8.7 Concluding Remarks 276 Chapter 9: Conclusions 9.1 Introduction 294 9.2 Concluding Remarks of Mechanisms of GRPE 295 9.3 Concluding Remarks of Semi-Analytical Model 301 9.4 Concluding Remarks of Full-Scale Field Test 303 9.5 Practical Design of GRPE 306 9.6 Recommendations for future works 308 References 310 Appendices 317 vi Summary Summary In Southeast Asia region, soft soils such as marine clay and peaty soil can be easily found. These soft foundation soils are compressible and therefore result in large consolidation settlement. As a result, soil subsidence is a major problem for road or rail road embankment constructed over soft foundation soil. This may lead to embankment failure, or sometimes restricting the height of the embankment, or limiting the rate of construction. In addition, especially in Malaysia, these soft soils may be underlain by limestone formation. The limestone dissolution by acidic water will cause the occurrence of subsurface cavity that lead to the formation of sinkholes in the fill material of these embankments. The use of geosynthetic reinforced piled embankment (GRPE) system has gained popularity recently to overcome the problems arising from the construction of embankment over soft foundation soil. The objective of this research is to focus on the clarification of the key mechanisms and the development of suitable design methodology, in designing a cost-effective geosynthetic reinforced piled embankment (GRPE) system. This research encompasses two main goals. The first goal is to study some possible mechanisms of GRPE system. This will lead to the formulation of the design philosophy and design consideration. To achieve this goal, large-scale physical model tests and centrifuge model tests were carried out to study some key mechanisms of GRPE subjected to soil subsidence. The second goal is to translate this knowledge to useful design charts for engineers to select the geosynthetic based on the suitable design parameters. To achieve this goal, semianalytical model was developed by incorporating the load transfer mechanisms of GRPE system that were identified earlier into the equilibrium equation. In addition, a mathematical model that coupled the catenary deformation profile and load-extension characteristics of the geosynthetic was also developed. vii Summary Some of the key components related to the mechanisms of GRPE system have been investigated from the large-scale physical model tests and centrifuge model tests. The results show that the stability of piled embankment with large piles spacing or/and small pile caps can be improved with the use of geosynthetic reinforcement. In addition, the results of vertical soil stresses show that the compressibility of subsoil and the embankment fill height have significant effect on the development of soil arching in embankment fill. The results also indicate that the orientation of main reinforcement direction with respect to the arrangement of piles has certain effect on the geosynthetic strain and maximum deflection of geosynthetic. Other components related to the mechanisms of GRPE system being investigated include: the surface settlement of embankment, the effect of additional surface static load, the effect of fill material, the effect of thin separation sand layer between two geosynthetic layers, the effect of the stiffness of geosynthetic as well as the effect of pile design. These findings were then incorporated into the development of the semianalytical model. A two-part semi-analytical model is developed for the design of GRPE system. The predictions of vertical stress acting on geosynthetic reinforcement sheet, using the newly developed semi-analytical model, show reasonable agreement with the measured vertical soil stresses from large-scale model physical tests. In addition, the comparison shows that the vertical displacement of geosynthetic reinforcement at the centre of piles as well as the tension in geosynthetic reinforcement can be predicted reasonably well using this semi-analytical model. A full-scale field test was carried out in conjunction with the development of a new major expressway in Singapore. The aims are to study the actual field behaviour of GRPE system, and to allow the validation and confirmation of the proposed design viii Appendix E 5000 1040 1040 STEEL DOOR A 1460 STEEL DOOR Y B 900 P2 P5 P6 TPC1,4,7,10 P1 X 150 150 TPC2,5,8 TPC3,6,13 TPC11,12,14 300 P3 X 300 300 P4 P8 D P7 C Y 250 TPC13 250 TPC12 TPC6 250 TPC11 TPC3 250 TPC14 Compacted Soil Geotextile (TS60) 50 1040 520 520 1040 1040 Section x-x 300 300 TPC10 250 250 TPC7 TPC8 TPC4 TPC5 TPC6 250 TPC1 TPC2 TPC3 200 Compacted Soil Geotextile (TS60) TPC13 50 600 600 Section y-y Figure E8. Plan and cross-sections of locations of total pressure cells used in Test 345 Appendix E 520 1040 Y STEEL DOOR STEEL DOOR 900 PILE5 PILE6 PILE2 TPC4,5,6 PILE1 X 300 PILE3 TPC7,8,9,10 TPC11,12,13,14,15,16,17 TPC1,2,3 300 X 300 HTPC1 300 HTPC2 PILE7 PILE4 PILE8 900 Y Locations of total pressure cells 1600 Surcharge Layer 250 Surcharge Layer 500 1350 1100 1100 975 850 725 600 475 350 200 100 250 TPC10 TPC3 Compacted Sandy Soil TPC17 TPC16 TPC15 TPC14 TPC13 TPC12 TPC11 TPC2 TPC9 TPC1 TPC8 TPC7 Geotextile PEC75-2 Sandy Soil 250 250 HTPC1 100 250 100 250 Geotextile PEC75-1 1000 260 1040 520 520 1040 1040 Section X-X 1600 Surcharge Layer 250 Surcharge Layer 1350 1100 1100 975 850 725 600 475 350 200 100 250 TPC17 TPC16 TPC15 TPC14 TPC13 TPC12 TPC11 TPC6 TPC5 Compacted Sandy Soil Geotextile PEC75-2 Sandy Soil 500 TPC4 250 250 HTPC2 250 250 Geotextile PEC75-1 100 1000 600 600 Section y-y Figure E9. Plan and cross-sections of locations of total pressure cells used in Test 346 Appendix E 520 1040 Y STEEL DOOR STEEL DOOR 900 PILE5 PILE6 PILE2 TPC4,5,6 PILE1 X 300 PILE3 TPC7,8,9,10 TPC11,12,13,14,15,16,17,18 TPC1,2,3 300 X 300 HTPC1 300 HTPC2 PILE7 PILE4 PILE8 900 Y Locations of total pressure cells 1500 Surcharge Layer 250 500 Surcharge Layer 1250 250 Compacted Sandy Soil TPC3 TPC10 TPC2 TPC9 TPC15 TPC8 TPC7 TPC1 Geotextile PEC75-2 TPC18 TPC17 TPC16 TPC14 TPC13 TPC12 TPC11 1000 875 750 687.5 625 250 250 1000 100 HTPC1 250 250 500 375 250 100 Geotextile PEC75-1 1000 260 1040 520 780 520 1040 1040 Section X-X 1500 Surcharge Layer 250 500 Surcharge Layer TPC6 Compacted Sandy Soil Geotextile PEC75-2 1250 250 TPC5 TPC15 TPC4 TPC18 TPC17 TPC16 TPC14 TPC13 TPC12 TPC11 1000 875 750 687.5 625 250 250 1000 250 HTPC2 250 500 375 250 100 Geotextile PEC75-1 100 1000 600 600 Section y-y Figure E10. Plan and cross-sections of locations of total pressure cells used in Test 347 Appendix E 260 1040 Y STEEL DOOR STEEL DOOR 900 PILE5 PILE2 PILE6 TPC4,5,6 PILE1 X TPC11,12,13,14,15,16,17,18 TPC1,2,3 300 PILE3 TPC7,8,9,10 300 X 300 HTPC 300 PILE8 PILE7 PILE4 900 Y Locations of total pressure cells 250 Surcharge Layer 1750 mm 250 Surcharge Layer 1500 mm 250 1250 mm Surcharge Layer TPC3 Compacted Sandy Soil Microgrid MG 100/100-2 Microgrid MG 100/100-1 TPC18 TPC17 TPC16 TPC15 TPC14 TPC13 TPC12 TPC11 TPC10 TPC2 TPC9 TPC1 TPC8 TPC7 1000 mm 875 mm 750 mm 687.5 mm 625 mm 500 mm 375 mm 250 mm 100 mm LEVEL mm 1000 HTPC1 1000 1040 260 780 1040 1040 Section X-X 250 Surcharge Layer 250 Surcharge Layer 250 Surcharge Layer TPC18 TPC17 TPC16 TPC15 TPC14 TPC13 TPC12 TPC11 TPC6 Compacted Sandy Soil Microgrid MG 100/100-2 Microgrid MG 100/100-1 TPC5 TPC4 1000 1750 mm 1500 mm 1250 mm 1000 mm 875 mm 750 mm 687.5 mm 625 mm 500 mm 375 mm 250 mm 100 mm LEVEL mm 1000 600 600 Section y-y Figure E11. Plan and cross-sections of locations of total pressure cells used in Test 348 Appendix E 260 780 Y STEEL DOOR STEEL DOOR PILE PILE 10 PILE PILE PILE 300 PILE 300 TPC7,8,9,10 TPC11,12,13,14,15,16,17,18 TPC1,2,3 300 PILE PILE X 1200 PILE 3000 TPC4,5,6 PILE 1200 EXISTING FRAME 1200 300 EXISTING FRAME X 900 EXISTING FRAME 900 PILE 11 PILE 12 EXISTING FRAME 1385 2080 1385 4850 Y LOCATIONS OF TOTAL PRESSURE CELLS 250 1750 mm 250 1500 mm 250 Compacted Sandy Soil TPC10 TPC2 TPC9 TPC1 TPC8 TPC7 TPC18 TPC17 TPC16 TPC15 TPC14 TPC13 TPC12 TPC11 1000 TPC3 1250 mm 1000 mm 875 mm 750 mm 687.5 mm 625 mm 500 mm 375 mm 250 mm 100 mm LEVEL mm 1000 Microgrid MG 100/100 1040 260 1040 780 1040 Section X-X 250 250 250 Compacted Sandy Soil TPC5 TPC4 1000 TPC18 TPC17 TPC16 TPC15 TPC14 TPC13 TPC12 TPC11 TPC6 1500 mm 1250 mm 1000 mm 875 mm 750 mm 687.5 mm 625 mm 500 mm 375 mm 250 mm 100 mm LEVEL mm 1000 Microgrid MG 100/100 1750 mm 600 600 600 600 Section y-y Figure E12. Plan and cross-sections of locations of total pressure cells used in Test 349 Appendix E d) Locations of Strain Gauges Test - Upper Geotextile 5000 Reinfocement Direction 1040 2080 STEEL DOOR A STEEL DOOR B 620 T21 P5 580 P2 T31 P6 T22 T11 300 P1 1200 P3 T23 3000 300 T32 580 T24 T12 P4 P8 P7 T25 900 620 D C 500 500 Figure E13. Plan of locations of strain gauges on upper geotextile used in Test Test - Lower Geotextile 5000 Reinfocement Direction 1040 2080 STEEL DOOR A P5 STEEL DOOR P2 L12 B P6 L11 300 L25 150 150 150 150 L24 L35 P1 L34 L22 L21 L33 L32 L43 L42 L41 L52 L51 P3 1200 L31 3000 LP2 LP4 L45 L23 LP1 LP3 L44 300 P8 L53 P4 P7 900 D C 500 520 520 520 520 500 Figure E14. Plan of locations of strain gauges on lower geotextile used in Test 350 Appendix E Test - Upper Geotextile 5000 Reinfocement Direction 1040 2080 STEEL DOOR A STEEL DOOR B 450 L16 L5 L12 450 P5 P2 P6 L10 300 L4 L15 150 150 150 150 L9 TT2 P1 L3 L14 L11 TT4 P3 L8 TT1 L2 1200 L13 3000 TT3 L7 300 P4 P8 P7 L6 450 900 L1 D C 520 520 520 520 Figure E15. Plan of locations of strain gauges on upper geotextile used in Test Test - Lower Geotextile 5000 Reinfocement Direction 1040 2080 STEEL DOOR A STEEL DOOR P5 150 150 150 150 150 150 150 P2 BT4 B11 B10 BT7 B9 BT3 P1 B6 BT10 BT9 B8 B P6 B7 BT6 B5 BT2 B4 P3 1200 B3 3000 BT5 B2 B1 BT1 P4 P8 P7 600 900 BT8 450 D C 520 520 520 260 260 520 Figure E16. Plan of locations of strain gauges on lower geotextile used in Test 351 Appendix E Test - Upper Geotextile 5000 Reinfocement Direction 1040 2080 STEEL DOOR A STEEL DOOR P5 P2 150 150 150 150 TL6 P1 TL1 TT4 TL7 TT3 TL2 TT2 TT6 TL8 TT5 TL3 B P6 TL9 TL10 TL4 TL5 P3 1200 3000 300 TT1 P4 P8 P7 1050 900 D C 347 347 347 347 Figure E17. Plan of locations of strain gauges on upper geotextile used in Test Test 5000 1040 2080 STEEL DOOR A 300 TT1 TL1 300 TT2 TL2 300 P5 300 300 300 TT6 TL6 TT7 TL7 STEEL DOOR TT3 TL3 TT4 TL4 TL5 TT10 TL10 P2 TT5 TT8 TT9 TL8 TL9 TT14 TT12 TL12 TT13 TL14 TL15 TT17 TL13 TT15 TL17 TT18 TT19 TT20 TT21 TL18 TL20 TL21 P1 TL19 TL23 TT24 TT25 TT23 TL24 TL25 300 TT27 TL27 P8 TT11 TL11 B 205 205 P6 TT16 TL16 TT22 TL22 P3 3000 TT26 TL26 TT28 TL28 P4 P7 900 D 205 C 205 520 520 520 520 520 Figure E18. Plan of locations of strain gauges used in Test 352 Appendix E Test - Upper geotextile 5000 Reinforcement Direction 2080 STEEL DOOR A STEEL DOOR B 205 LC5 LC2 20 TL10 TT1 TT7 TT8 TT2 TL9 LC1 900 TL1 TL8 TL2 TL3 TL4 TL5 TT3 TL6 1200 LC3 TL7 3000 TT4 TT5 TT6 LC4 225 150 D 130 260 260 C 260 260 260 260 390 2080 Figure E19. Plan of locations of strain gauges on upper geotextile used in Test Test - Lower geotextile 5000 Reinforcement Direction 2080 A STEEL DOOR STEEL DOOR B 20 LC5 LC2 BL9 20 BT6 BT1 BT7 BT2 BL8 LC1 900 BL1 BL2 BL3 BL4 BT3 BL5 BL6 BL7 LC3 1200 3000 BT4 BT5 LC4 225 130 D 150 260 260 370 370 260 260 150 C Figure E20. Plan of locations of strain gauges on lower geotextile used in Test 353 Appendix E Test - Upper Geotextile Reinforcement Direction 5000 STEEL DOOR A 12 LC5 200 STEEL DOOR 00 20 20 LC2 20 200 20 200 TM6 TM5 20 TC1 TM4 TC2 TM3 TC3 TC4 TM7 TL1 255 200 TT1 TM2 TM1 LC1 1200 B 100 3000 LC3 TL2 TM7a TT2 255 TM9 LC4 TM8 200 D C 255 507 255 2080 Figure E21. Plan of locations of strain gauges on upper geotextile used in Test Test - Lower geotextile Reinforcement Direction 5000 STEEL DOOR A STEEL DOOR LC5 20 200 200 LC2 BC4 300 200 20 200 BM1 BC3 BM2 BC2 LC1 255 20 BM4 BC1 1200 20 BM3 BT1 B BM5 BM6 BC5 BL1 BL2 BM6a BC6 3000 LC3 BT2 255 BM7 BM8 200 200 LC4 D C 255 507 255 2080 Figure E22. Plan of locations of strain gauges on lower geotextile used in Test 354 Appendix E Test - Upper microgrid 5000 1250 Reinforcement Direction 2500 1250 STEEL DOOR STEEL DOOR G2 G1 G3 30 PILE5 PILE2 205 PILE6 TL8 225 205 225 150 300 150 TT1 TT8 TT7 TL7 TT3 TL1 TL2 PILE1 TL3 TT9 PILE3 TT2 TL4 TT4 TL5 1200 TL6 3000 TT5 TT6 PILE4 PILE8 130 PILE7 260 260 1040 520 1040 2080 Figure E23. Plan of locations of strain gauges on upper microgrid used in Test Test - Lower microgrid 5000 1250 Reinforcement Direction 2500 1250 STEEL DOOR STEEL DOOR G4 30 G5 PILE5 205 BL7 225 205 PILE6 520 BT1 BT5 BT6 BL6 225 PILE2 BL8 BL9 BT2 BL1 BL2 BL3 BL4 PILE3 1200 BL5 3000 BT3 PILE1 150 BT4 PILE8 PILE7 PILE4 G6 260 260 1040 350 350 1040 2080 Figure E24. Plan of locations of strain gauges on lower microgrid used in Test 355 Appendix E STEEL DOOR STEEL DOOR P9 P10 P2 L8 L2 L1 LX1 LX4 LX5 LX6 P7 P4 T7 T8 TX5 P12 P3 T5 T6 TX3 TX4 LX2 L6 T3 T4 TX2 LX3 L10 L5 L4 L3 TX1 P8 T12 T2 3000 P1 1200 T1 T11 T10 L7 TX6 900 EXISTING FRAME 150 225 P6 L9 EXISTING FRAME 225 150 P5 150 300 900 EXISTING FRAME P11 T9 EXISTING FRAME 130 1385 260 650 260 2080 260 520 1385 4850 Figure E25. Plan of locations of strain gauges on microgrid used in Test 356 Appendix F Appendix F: Calibration of Strain Gauges Used in Large-scale Model Tests by Wide-Width Tensile Test The wide-width tensile test was conducted in order to calibrate strain gauges that attached on geotextile for the experiments of series 1. The test was conducted by referring to the procedures that mentioned in ISO 10319. In this section, the graphical plots for the test results will be presented as listed below. 1) The relationship between global strain measured by video extensometer and local strain measured by attached strain gauge for machine direction of PEC75. 2) The relationship between applied tensile force and local strain measured by attached strain gauge for machine direction of PEC75. 3) The relationship between global strain measured by video extensometer and the local strain measured by attached strain gauge for cross-machine direction of PEC75. 4) The relationship between applied tensile force and local strain measured by attached strain gauge for cross-machine direction of PEC75. 357 Appendix F 14 Average CF = 0.9743 Global Strain,εG (%) 12 10 Sample 1: y=1.0010x Sample 2: y=0.9919x Sample 3: y=0.9300x 0 10 12 14 Local Strain, εL (% ) Tensile Force (kN) Figure F1. The relationship between global strain and local strain for machine direction of PEC75 17 16 15 14 13 12 11 10 Sample Sample Sample 10 11 Local Strain, εL (% ) Figure F2. The relationship between tensile force and local strain for machine direction of PEC75 358 Appendix F 14 Global Strain,εG (%) 12 Average CF = 0.7765 10 Sample 1: y=0.8050x Sample 2: y=0.7562x Sample 3: y=0.7684x 0 10 12 14 16 Local Strain, εL (% ) Figure F3. The relationship between global strain and local strain for cross-machine direction of PEC75 3.5 Sample Sample Sample Tensile Force (kN) 3.0 2.5 2.0 1.5 1.0 0.5 0.0 10 11 12 13 14 15 16 Local Strain, εL (% ) Figure F4. The relationship between tensile force and local strain for cross-machine direction of PEC75 359 Appendix G Appendix G: MATLAB Program for Geosynthetic Selection Design Chart MATLAB program: Relations between T, fmax/s, σs and J for a horizontal geosynthetic reinforcement span function [fc,minval,idx,fmx]=setfunc(fmax) S=1.2 ; a=0.21 ; gamma=19 ; Tu=89 ; epsilon=13 ; Sc=S-a; Hmin=S/sqrt(2); Cc=1.95*(Hmin/a)-0.18; Ab=S^2-a^2; Wt=((Hmin*Sc*Sc*gamma)-(((Cc*a/Hmin)^2)*a*a*Hmin*gamma))/Ab; n=size(fmax,1); fc=zeros(n,1); for i=1:n ft = Sc/(4*fmax(i)) ; fs = ft^2 ; fct=Wt*Sc*sqrt(1 + fs )*(epsilon/Tu)-((sqrt(1+1/fs)+ft*log(1/ft+sqrt(1+1/fs))2)*100); fc(i)=abs(fct); end [minval,idx]=min(fc); fmx=fmax(idx)*1000; Tmax=0.5*Wt*Sc*sqrt(1+(Sc^2/(16*((fmx/1000)^2)))) emax=Tmax*epsilon/Tu WtSc=Wt*Sc format short g A=[100,7]; A(:,1)=S(:);A(:,2)=Sc(:);A(:,3)=Wt(:);A(:,4)=WtSc(:);A(:,5)=fmx(:);A(:,6)=Tmax(:);A (:,7)=emax(:); save('n:\Hung Leong IV\Matlab\A.asc','A','-ASCII') 360 [...]... piled embankment system This thesis will discuss the mechanisms of this geosynthetic reinforced piled embankment system Large-scale physical modelling, centrifuge modelling, numerical modelling as well as simple closed form solution of this system will be presented 1.1 Overview of Embankment Constructed Over Soft Foundation Soil It is becoming increasingly necessary to construct road or rail embankment. .. to conventional piled embankment system without geosynthetic Three design approaches were used for this evaluation: (1) GRPE system, (2) convention piled embankment system with small pile cap and closed pile spacing, and (3) convention piled embankment system with large pile cap The fixed parameters for this cost comparison are: (a) the total area of site (i.e 100mx100m) and (b) the embankment fill... elaborated 1.3 Geosynthetic Reinforced Piled Embankment (GRPE) System A recent development of the piled embankment method is to incorporate geosynthetic sheet as basal reinforcement The use of basal reinforcement can increase the stability of the whole system (Jones et al., 1990), but may or may not have significant further improvement in settlement as compared to conventional piled embankment In addition,... The overall maximum vertical displacement point of perpendicularly cross-laid geosynthetic reinforcements in piled embankment Figure 6.6 Deformation of lower geosynthetic reinforcement in E-W direction in Test 1, Test 2 and Test 8 Figure 6.7 Deformation of lower geosynthetic reinforcement in N-S direction in Test 1, Test 2 and Test 8 Figure 6.8 Vertical displacement of lower geotextile measured by LVDTs... Figure 6.51 Vertical loads exerted on piles in Test 3 Figure 6.52 Deformation of lower geotextile reinforcement spinning between Pile 1 and Pile 3 in Test 2 and Test 6 Figure 6.53 Deformation of lower geotextile reinforcement spinning between Pile 1 and Pile 2 in Test 2 and Test 6 Figure 6.54 The sinkholes and tension cracks formed in embankment fill when removing the subsoil in Test 5 Figure 6.55 Geotextile... in tensile force in geosynthetic span ΔTx The change in tensile force in x-x direction geosynthetic span ΔTy The change in tensile force in y-y direction geosynthetic span xxvii Nomenclature Tg-x Tensile force of geosynthetic span in x-x direction after considering restraining effect Tg-y Tensile force of geosynthetic span in y-y direction after considering restraining effect Tstrip Tensile force of... prototype scale) Table 5.3 Physical properties of River Sand (after Chowdhury, 2003) Table 5.4 Scaling relationship between model pile and prototype pile Chapter 6 : Mechanisms of Geosynthetic Reinforced Piled Embankment Table 6.1 Recorded strains along machine direction (MD) on upper and lower geosynthetics after removal of subsoil Table 6.2 Vertical displacements of perpendicularly reinforcements at two different... (after Terzaghi, 1936 and Terzaghi, 1943) Figure 2.2 Basal reinforced piled embankment system (BS8006, 1995) Figure 2.3 The soil wedge influencing the reinforcement after Carlsson (obtained from Rogbeck et al., 1998) Figure 2.4 Load distribution to estimate the forces in the three-dimensional case (Rogbeck et al., 1998) Figure 2.5 Section through a piled embankment (after Hewlett and Randolph, 1988) Figure... between the deformation of geosynthetic reinforcement and the fill material in the “arched region” may cause further complication in the soil arching mechanism Although BS8006 (1995) has attempted to include the basal reinforcement in piled embankment design, the soil arching coefficient is still obtained from Marston’s formula, which may not be suitable for the formation of soil arching when geosynthetic. .. well and yielded reliable data for the evaluation of the performance of this GRPE system The results of the strain gauges show the proper function of geosynthetic reinforcement The settlement results show that the use of GRPE system has reduced the settlement to a satisfactory level Keywords: Geosynthetic reinforced piled embankment, Soil arching effect, Tensioned membrane effect, Large-scale physical . PHYSICAL AND SEMI-ANALYTICAL MODELLING FOR GEOSYNTHETIC REINFORCED PILED EMBANKMENT PHOON HUNG LEONG NATIONAL UNIVERSITY OF SINGAPORE 2006 PHYSICAL AND SEMI-ANALYTICAL. Chapter 6: Mechanisms of Geosynthetic Reinforced Piled Embankment 6.1 Strain Development in Geosynthetic Reinforcement 150 6.2 Vertical Displacement of Geosynthetic Reinforcement 152 6.3. : Mechanisms of Geosynthetic Reinforced Piled Embankment Figure 6.1 The critical strain zones and non-critical strain zones of cross-laid geotextiles reinforcement in piled embankment Figure