Isothermal Response of Geosynthetics to Different Loading Regimes
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ISOTHERMAL RESPONSE OF GEOSYNTHETICS TO DIFFERENT LOADING REGIMES BlRENDRA MAHASETH A thesis suhmitted in partial fulfillment for the degree of Master of Engineering Department of Civil Engineering Bangladesh University of Engineering and Technology Dhaka, Bangladesh 1111111111111111111111111111111111 #96965# ISOTHERMAL RESPONSE OF GEOSYNTHETICS TO DIFFERENT LOADING R£GIMES by BIRENDRA MAHASETH Approved as to style and content by: -----ft.~"-- Dr. Abdul Jabbar Khan Chairman Assistant Professor (Supervisor) Department ofCE, BOOT, Dhaka ----~--- Dr. Saiful Alam Siddiquee Member Associate Professor Department ofCE, BUET, Dhaka rp1g1_~jLjA~ Dr. Mehedi Ahmed Ansary Member Associate Professor Department ofCE, BUET, Dhaka June 2002 o DECLARATION I hereby declare that the research work reported in this thesis has been performed by me and this work has not been submitted elsewhere for any other purposes except for publication. June 2002 ---~--- Birendra Mahaseth ACKNOWLEDGEMENTS I wish to express the deepest of my gratitude to Dr. Abdul Jabbar Khan for being fully contributive throughout this work. Without his supportive and friendly nature this thesis would not have come to an end in time. It was his encouragement that kept me working on computer. In this regard, I would also take the opportunity to express my appreciation to Professor Dr. M. H. Kabir for arousing my interest in the topic of study. Besides my parents, I am indebted to my wife and son who supported me morally to stay out of home for the study. I would also like to pay my appreciation to my colleagues and seniors for their encouragement and moral support to pursue the study. I am thankful to all my Nepalese friends in Rashid Hall and Intemation Hostel for their company and help. My due thanks goes to the inmates of Shahid Smrity Hall, especially to Ashish, Tapan and the floor mates who comforted me with the hospitality and their company. Finally I must thank the members of the dining in The Shahid Smrity Hall for providing their services. ABSTRACT This study is undertaken to show the conservatism inherent in the existing design methods after observing the satisfactory performance of geosynthetic reinforced soil structures (GRSSs) during the 1995 Kobe and 1994 Northridge, California earthquakes, since these structures were designed according to these methods for lesser seismic shocks than what they experienced. In fact, neither any test data pertaining to, nor any general approach to the understanding of the behaviour of geosynthetics under MSA (multi stage action) was existent. The geosynthetics being elasto-visco-plastic (EVP) in nature, the same geosynthetic is likely to show different load-strain-time responses under various loading regimes at isothermal conditions. The Isochronous Strain Energy (ISE) approach, although capable of pronouncing the behaviour of geosynthetics under different loading regimes, seems quite complex for the practicing engineers. For this reason, a simpler approach to the understanding of the behaviour of geosynthetics under sustained-short-term loading regime has been attempted to show the conservatism of the present design methods. It is identified that the total strain in an EVP material consists of two components namely 'Recoverable' strain and 'Locked-in' strain and these two strain components may combine in many different ways resulting in a strain envelope for a particular total strain, geosynthetic and loading regime. Identification of the strain components shows the likely behaviour of a geosynthetic under any single-stage and multi-stage loading regimes. To this end, a range of single-stage and multi-stage (sustained-short term) data are analyzed and presented to show the conservatism inherent in the current design codes/methods and the validity of the strain envelope approach in understanding the behaviour of geosynthetics subjected to combined sustained plus short-term seismic loading regime. Eventually, a approach to design GRSSs under this regime is suggested. 11 Contents Acknowledgements Abstract II Contents iii Notations viii List of Tables xii List of Figures xiii Chapter 1 INTRODUCTION 1.1 General 1 1.2 Development of Geosynthetic Reinforced Soil Structures 1 1.3 Design Approaches and Computer Programs 2 1.4 Actions and Design input parameters 4 1.4.1 Soil Properties for Single-Stage Actions 4 1.4.2 Soil Properties for Multi.Stage Actions 5 1.4.3 Geosynthetic Properties for Single-Stage Actions 5 1.4.4 Geosynthetic Properties for Multi-Stage Actions 6 1.5 Background of the present study 8 1.6 Objectives of the Present Study 9 1.7 Layout of the Thesis 9 Chapter 2 LITERATURE REVIEW 2.1 General 12 iii 2.2 Components ofGRSSs 12 2.2.1 Reinforced Fill 13 2.2.2 Retained Fill 13 2.2.3 Foundation Soil 14 2.2.4 Facing Units 14 2.2.5 Connections 15 2.2.6 Reinforcements 15 2.2.6.1 Inextensible Reinforcements 16 2.2.6.2 Extensible Reinforcements 17 2.3 Geosynthetics 18 2.3.1 Elasto-Visco-Plastic Nature ofGeosynthetics 18 2.3.2 Rheological and Mathematical Modelling of Geosynthetics Behaviour 21 2.3.2.1 Maxwell Model 22 2.3.2.2 Kelvin or Voigt Model 22 2.3.2.3 Maxwell and Kelvin Model 22 2.3.2.4 Zener (Standard Linear Solid) Model 23 2.3.2.5 Esteve's Method 23 2.3.2.6 Boltzmann Superposition Principle 24 2.4 Strength tests for geosynthetics 24 2.4.1 Constant rate of strain test 25 2.4.2 Sustained load creep test 25 2.4.2.1 Isochronous load-strain curves 26 2.5 Design strength of geosynthetics in GRSSs 27 2.5.1 Reference Strength 27 IV 2.5.I.1 Reference Strength for Single-Stage Actions 27 2.5.1.2 Reference Strength for Multi-Stage Actions 28 2.5.2 Partial Factors and Design Strength 30 2.6 Design approaches for GRSSs 31 2.6.1 Limit Equilibrium Approach 32 2.6.1.1 AASHTO Standard Specifications for Highway Bridges (1997) 33 2.6.1.2 The Deutsches Institut fllr Bautechnik (Dmt) Method (1998) 34 2.6.1.3 HA 68/94 Method (1997) 36 2.6.2 Hybrid Approach 37 2.6.2.1 BS8006 (1995) Method 37 2.6.2.2 Tensar Tie-back Wedge (TBW) Design Method (1998) 42 2.6.3 Limit State Approach 44 2.6.3.1 A Model for Internal Ultimate Limit State Mechanism. 45 2.6.3.2 A Model for Internal Serviceability Limit State Mechanism 46 2.7 Research outputsl Case studies related to Multi-stage actions 47 2.7.1 Sustained plus Cyclic loading 47 2,7.2 Combined Sustained plus Earthquake loading 48 2.7.2.1 Duration of Earthquake 48 2.7.2.2 Available test results 49 2.7.2.3 Case studies 49 Chapter 3 BEHAVIOUR OF MATERIALS UNDER DIFFERENT LOADING REGIMES 3.1 General 80 3.2 Types of Actions 80 v 3.2.1 Single-stage actions 82 3.2.2 Multi-stage actions 83 3.3 Strain response of materials under Single-stage Action (SSA) 83 3.3.1 Perfectly Elastic material 84 3.3.2 Perfectly plastic material 85 3.3.3 Elasto-plastic material 85 3.3.4 Elasto-visco-plastic material 86 3.4 Development of &R - EL plot and strain envelope for elasto-visco-plastic (EVP) material 88 3.5 ER - EL plots for EVP material under different single-stage action (SSA) 89 3.6 Strain response of materials under multi-stage actions (MSA) 90 3.6.1 Perfectly elastic material 91 3.6.2 Perfectly plastic material 91 3.6.3 Elasto-plastic material 92 3.6.4 Elasto-visco-plastic (EVP) material 93 3.7 ER - EL plots for EVP materials subjected to different Multi-stage actions (MSA) 94 Chapter 4 ISOTHERMAL REBA VIOUR OF SOME GEOSYNTHETICS SUBJECTED TO SINGLE STAGE LOADING 4.1 General Il2 4.2 Test set up and Procedure 112 4.2.1 Single-stage action (SSA) tests 113 4.2.1.1 Constant rate of strain (CRS) test ",/ 113 4.2.1.2 Long-term sustained CREEP test 113 VI 4.3 Extrapolation of CREEP test Data 1I4 4.4 Isochronous load-strain curves and strain envelopes lIS 4.5 Discussion on test results 1I6 4.6 Summary 1I7 Chapter 5 ISOTHERMAL BEHAVIOUR OF SOME GEOSYNTHETICS SUBJECTED TO MULTI STAGE LOADING 5.1 General 133 5.2 Test set up and Procedure 133 5.2.1 Multi-stage action (MSA) tests 134 5.2.2.1 Combined sustained-short-term loading test 135 5.3 Discussion on test results 137 5.4 Interpretation ofMSA (sustained-short term) test results on ER - EL plot 139 5.5 Summary 141 5.6 Suggested approach of designing GRSS for MSA 142 Chapter 6 DISCUSSION AND CONCLUSIONS 6.1 Discussion 164 6.2 Conclusions 168 RECOMMENDATIONS FOR FUTURE RESEARCH 170 REFERENCES 171 VII NOTATIONS Y Calculated Factor of Safety ).! Coefficient of Friction between Soil and the Reinforcements cr'vi Total Vertical Stress in the ith Layer of Reinforcement Yl Density of the Reinforced Fill I3r Slope Angle ofthe Face of the Structure Ym Partial Factor Vertical Stress on Reinforcing Element [4>~] True Angle of Friction [4>'cv] Constant Volume Angle of Friction [4>'m] Mobilised Angle of Friction [4>'p] Peak Angle of Friction [Ed Limiting Strain [Ed 'Locked-in' Strain [ Edes,eq] Factored Limiting Strain [Ep] Performance Limit Strain [ &pel Actual Post-Construction Strain [M's] Additional Short Term Load [ER] Recoverable Strain [Esoo] Strain in the Soil, Sufficient to Mobilise the Large Strain Constant Volume Angle of Friction [4>'ev] [Et] Lateral Tensile Strain [Pal Earth Pressure on the Wall [PRed Reference Strength [Ps] Sustained Load [P,] Additional Transient (traffic) Loading [t] Time [T] Temperature [to] Equivalent Instantaneous Loading Time [T Ipcs] Force Required in Order to Mobilise 1% Post-Construction Strain V11l [Tall Long-tenn Strength of the Reinforcing Element [tep1 Construction Period [Tdl Design Strength of the Reinforcing Elements for Single-Stage Actions [1&1 Design Lifetime [tEDd Time at the End of Design Life [T81 Glass Transition Temperature [tRLl Reinforcement