Effects of Geosynthetic Reinforcement Spacing on the Behavior of Mechanically Stabilized Earth Walls
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Technical Report Documentation Page
| 1. Report No.
FHWA-RD-03-048 |
2. Government Accession No. |
3 Recipient's Catalog No. |
| 4. Title and Subtitle
EFFECTS OF GEOSYNTHETIC REINFORCEMENT SPACING ON THE PERFORMANCE OF MECHANICALLY STABILIZED EARTH WALLS |
5. Report Date
September 2003
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6. Performing Organization Code
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| 7. Author(s)
Christina Vulova and Dov Leshchinsky |
8. Performing Organization Report No.
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9. Performing Organization Name and Address
Department of Civil and Environmental Engineering
University of Delaware
Newark, DE 19711
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10. Work Unit No. (TRAIS)
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| 11. Contract or Grant No.
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| 12. Sponsoring Agency Name and Address
Office of Infrastructure Research and Development
Federal Highway Administration (FHWA)
6300 Georgetown Pike
McLean, Virginia 22101-2296 |
13. Type of Report and Period Covered
Final Report, Feb. 1999-August 2000 |
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14. Sponsoring Agency Code
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15. Supplementary Notes
Contracting Officer's Technical Representative (COTR): M. T. Adams, HRDI-06
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| 16. Abstract
The behavior of mechanically stabilized earth walls (MSEW) with modular block facing and geosynthetic reinforcement was investigated with numerical models that simulate construction of the wall, layer by layer, until it fails under gravity loading. The two-dimensional finite difference program Fast Lagrangian Analysis of Continua (FLAC), version 3.4, Itasca 1998, was used to carry out the numerical analysis. The material properties were based on data reported in the literature, which represent typical values used in design practice. Failure mechanisms of MSEW's were identified as a function of geosynthetic spacing considering the effects of soil strength, reinforcement stiffness, connection strength, secondary reinforcement layers, and foundation stiffness. The effects of reinforcement length on reinfrocement stresses and wall stability were also investigated. FLAC predictions were compared with the American Association of State Highway
and Transportation Officials (AASHTO) design method. Additional numerical experiments were carried out to investigate the effects of some modeling parameters on wall response.Four failure modes of MSEW were identified: external, deep-seated, compound, and connection. The reinforcement spacing
was identified as a major factor controlling the behavior of MSEWs. Two types of spacing were considered in studying the effects of spacing: small (less than or eequal to 0.4 m) and large (larger than 0.4m). Increasing reinforcement spacing decreased the wall stability and changed the predominant failure mode from external or deep-seated to compound and connection mode. Similar effects were identified when the soil strength, reinforcement stiffness, or foundation stiffness were decreased. Connection strength appeared to affect only the behavior of walls with large reinforcement spacing, i.e., increased strength, decreased wall displacements, improved wall stability, and changed failure mode. Similar effects were identified when secondary reinforcement layers were introduced in a model with large reinforcement spacing. Increased reinforcement length improved wall stability and decreased wall displacements and reinforcement forces.A comparison
between FLAC predictions and AASHTO calculations demonstrated a good agreement. The comparisons indicated that the existing design method could distinguish the modes of failure identified by FLAC analysis, especially those due to external stability. However, AASHTO disregards the effect of reinforcement spacing and thus, considers an external wedge always to develop internally.
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| 17. Key Words
block walls, external stability, failure mechanism, FLAC, geosynthetic reinforcement, interface effects, internal stability, MSE walls |
18. Distribution Statement
No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161. |
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19. Security Classification
(of this report)
Unclassified
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20. Security Classification
(of this page)
Unclassified
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21. No. of Pages
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22. Price |
| Form DOT F 1700.7 |
Reproduction of completed page authorized |
Metric Conversion Chart
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
Chapter
- INTRODUCTION
- BACKGROUND
- NUMERICAL ANALYSIS
- RESULTS
- COMPARISON WITH EXISTING DESIGN PRACTICE
- IMPLICATIONS TO DESIGN
- CONCLUSIONS AND RECOMMENDATIONS
LIST OF FIGURES
Figure
- 3.1 Numerical Model Components.
- 3.2 Schematic of Modeling of Construction Sequence of Wall with Reinforcement Spacing Equal to 0.4 m.
- 3.3 Definition of: (a) Failure State; (b) Critical State; (c) Stable State
- 3.4 Typical Numerical Grid.
- 3.5 Grid Definition: (a) Model Zones with Respect to Grid Generation; (b) Grid of Modular Blocks in the Current Model; (c) Grid of Modular Blocks in Early Versions of the Model.
- 3.6 Boundary Effects on Model Response: Horizontal Displacements along Vertical Section A Located 0.1 m behind the Facing.
- 3.7 Boundary Effects on Model Response: Stress Distributions along Vertical Section A Located 0.15 m behind the Facing.
- 3.8 Types of Interfaces at the Blocks.
- 3.9 Baseline Cases: (a) Number of Calculation Steps Necessary to Equilibrate Each Layer; (b) Maximum Cumulative Displacement during Wall Construction
- 3.10 Effects of FLAC Equilibrium Ratio Limit on Model Response of Case 1 (s=0.2 m, l=1.5 m): (a) Number of Calculation Steps; (b) Maximum Cumulative Displacement.
- 3.11 Effects of FLAC Step Limit on Model Response of Case 12 (s=0.2 m, l=1.5 m): (a) Number of Calculation Steps; (b) Maximum Cumulative Displacement.
- 3.12 Reinforcement Layout with Primary and Secondary Layers for Case 7 (s=0.6/0.2 m).
- 3.13 Some of the Executed Numerical Runs.
- 4.1 Critical Wall Height and Prevailing Mode of Failure: (a) Cases with Very Stiff Foundation; (b) Cases with Baseline Foundation.
- 4.2 Change of Critical Wall Height with Respect to Soil Strength: (a) Cases with Very Stiff Foundation; (b) Cases with Baseline Foundation.
- 4.3 Slip Surface Types: (a) External Slip Surface; (b) Deep-Seated Slip Surface; (c) Compound Slip Surface; (d) Internal Slip Surface
- 4.4 Definition of Vertical Sections A, B, and C along which Stress and Displacement Distributions Were Investigated.
- 4.5 State of Soil for Case 1 (s=0.2 m, l=1.5 m): (a) Failure State (h=8.6 m, l/h=0.17); (b) Critical State (h=6.6 m, l/h=0.23).
- 4.6 Displacement Vectors for Case 1 (s=0.2 m, l=1.5 m): (a) Failure State (h=8.6 m, l/h=0.17); (b) Critical State (h=6.6 m, l/h=0.23).
- 4.7 Distorted Grid for Case 1 (s=0.2 m, l=1.5 m): (a) Failure State (h=8.6 m, l/h=0.17); (b) Critical State (h=6.6 m, l/h=0.23).
- 4.8 Cumulative Horizontal Displacements for Case 1 (s=0.2 m, l=1.5 m): (a) Failure State (h=8.6 m, l/h=0.17); (b) Critical State (h=6.6 m, l/h=0.23).
- 4.9 Axial Force Distribution in Reinforcement for Case 1 (s=0.2 m, l=1.5 m): (a) Failure State (h=8.6 m, l/h=0.17); (b) Critical State (h=6.6 m, l/h=0.23).
- 4.10 State of Soil for Case 1 (s=0.4 m, l=1.5 m): (a) Failure State (h=8.2 m, l/h=0.18); (b) Critical State (h=6.0 m, l/h=0.25).
- 4.11 State of Soil for Case 4 (s=0.2 m, l=1.5 m): (a) Failure State (h=7.0 m, l/h=0.21); (b) Critical State (h=5.6 m, l/h=0.27).
- 4.12 State of Soil for Case 9 (s=0.2 m, l=1.5 m): (a) Failure State (h=8.2 m, l/h=0.18); (b) Critical State (h=6.6 m, l/h=0.23).
- 4.13 State of Soil for Case 11 (s=0.2 m, l=1.5 m): (a) Failure State (h=7.2 m, l/h=0.21); (b) Critical State (h=6.0 m, l/h=0.25).
- 4.14 State of Soil for Case 12 (s=0.2 m, l=1.5 m): (a) Failure State (h=9.4 m, l/h=0.16); (b) Critical State (h=6.6 m, l/h=0.23).
- 4.15 State of Soil for Case 10 (s=0.2 m, l=1.5 m): (a) Failure State (h=4.4 m, l/h=0.34); (b) Critical State (h=3.2 m, l/h=0.47).
- 4.16 Displacement Vectors for Case 10 (s=0.2 m, l=1.5 m): (a) Failure State (h=4.4 m, l/h=0.34); (b) Critical State (h=3.2 m, l/h=0.47).
- 4.17 Distorted Grid for Case 10 (s=0.2 m, l=1.5 m): (a) Failure State (h=4.4 m, l/h=0.34); (b) Critical State (h=3.2 m, l/h=0.47).
- 4.18 Horizontal Displacements for Case 10 (s=0.2 m, l=1.5 m) at Failure State (h=4.4 m, l/h=0.34) and Critical State (h=3.2 m, l/h=0.47).
- 4.19 Axial Force Distribution in Reinforcement for Case 10 (s=0.2 m, l=1.5 m): (a) Failure State (h=4.4 m, l/h=0.34); (b) Critical State (h=3.2 m, l/h=0.47).
- 4.20 State of Soil for Case 5 (s=0.2 m, l=1.5 m): (a) Failure State (h=5.4 m, l/h=0.28); (b) Critical State (h=4.2 m, l/h=0.36).
- 4.21 State of Soil for Case 8–1 (s=0.4 m, l=1.5 m): (a) Failure State (h=8.0 m, l/h=0.19); (b) Critical State (h=5.0 m, l/h=0.30).
- 4.22 Displacement Vectors for Case 8–1 (s=0.4 m, l=1.5 m): (a) Failure State (h=8.0 m, l/h=0.19); (b) Critical State (h=5.0 m, l/h=0.30).
- 4.23 Distorted Grid for Case 8–1 (s=0.4 m, l=1.5 m): (a) Failure State (h=8.0 m, l/h=0.19); (b) Critical State (h=5.0 m, l/h=0.30).
- 4.24 Horizontal Displacements for Case 8–1 (s=0.4 m, l=1.5 m) at Failure (h=8.0 m, l/h=0.19) and Critical State (h=5.0 m, l/h=0.30).
- 4.25 Axial Force Distribution in Reinforcement for Case 8–1 (s=0.4 m, l=1.5 m): (a) Failure State (h=8.0 m, l/h=0.19); (b) Critical State (h=5.0 m, l/h=0.30).
- 4.26 State of Soil for Case 2 (s=0.4 m, l=1.5 m): (a) Failure State (h=6.0 m, l/h=0.25); (b) Critical State (h=4.4 m, l/h=0.34).
- 4.27 State of Soil for Case 3 (s=0.2 m, l=1.5 m): (a) Failure State (h=4.2 m, l/h=0.36); (b) Critical State (h=4.0 m, l/h=0.38).
- 4.28 State of Soil for Case 7 (s=0.6/0.2 m, l=1.5 m): (a) Failure State (h=6.0 m, l/h=0.25); (b) Critical State (h=5.0 m, l/h=0.30).
- 4.29 State of Soil for Case 8–2 (s=0.4 m, l=1.5 m): (a) Failure State (h=5.4 m, l/h=0.28); (b) Critical State (h=3.2 m, l/h=0.47).
- 4.30 State of Soil for Case 8–3 (s=0.2 m, l=1.5 m): (a) Failure State (h=5.0 m, l/h=0.30); (b) Critical State (h=2.2 m, l/h=0.68).
- 4.31 State of Soil for Case 12 (s=0.6 m, l=1.5 m): (a) Failure State (h=6.0 m, l/h=0.25); (b) Critical State (h=4.6 m, l/h=0.33).
- 4.32 State of Soil for Case 2 (s=0.6 m, l=1.5 m): (a) Failure State (h=4.6 m, l/h=0.33); (b) Critical State (h=2.6 m, l/h=0.58).
- 4.33 Displacement Vectors for Case 2 (s=0.6 m, l=1.5 m): (a) Failure State (h=4.6 m, l/h=0.33); (b) Critical State (h=2.6 m, l/h=0.58).
- 4.34 Distorted Grid for Case 2 (s=0.6 m, l=1.5 m): (a) Failure State (h=4.6 m, l/h=0.33); (b) Critical State (h=2.6 m, l/h=0.58).
- 4.35 Horizontal Displacements for Case 2 (s=0.6 m, l=1.5 m) at Failure State (h=4.6 m, l/h=0.33) and Critical State (h=2.6 m, l/h=0.58).
- 4.36 Axial Force Distribution in Reinforcement for Case 2 (s=0.6 m, l=1.5 m): (a) Failure State (h=4.6 m, l/h=0.33); (b) Critical State (h=2.6 m, l/h=0.58).
- 4.37 State of Soil for Case 4 (s=0.6 m, l=1.5 m): (a) Failure State (h=5.4 m, l/h=0.28); (b) Critical State (h=3.8 m, l/h=0.39).
- 4.38 Case 1 (s=0.4 m, l=1.5 m, h=5.0 m): (a) State of Soil; (b) Axial Force Distribution in Reinforcement.
- 4.39 Connection Force and Maximum Force in Reinforcement for Case 1 (s=0.4 m, h=5.0 m, BR) and Case 8–1 (s=0.4 m, h=5.0 m, DR): Effects of Reinforcement Stiffness.
- 4.40 Horizontal Displacements along Section A: Comparison with Respect to Reinforcement Stiffness.
- 4.41 State of Soil for Cases 2 and 8–2 (s=0.4 m, h=3.2 m, l=1.5 m): (a) Case 2 (BR); (b) Case 8–2 (DR).
- 4.42 Axial Force Distributions in Reinforcement for Cases 2 and 8–2 (s=0.4 m, h=3.2 m, l=1.5 m): (a) Case 2 (BR); (b) Case 8–2 (DR).
- 4.43 Connection Force and Maximum Force in Reinforcement for Case 2 (s=0.4 m, h=3.2 m, BR) and Case 8–2 (s=0.4 m, h=3.2 m, DR): Effects of Reinforcement Stiffness.
- 4.44 State of Soil for Cases 3 and 8–3 (s=0.2 m, h=2.2 m, l=1.5 m): (a) Case 3 (BR); (b) Case 8–3 (DR).
- 4.45 Axial Force Distributions in Reinforcement for Cases 3 and 8–3 (s=0.2 m, h=2.2 m, l=1.5 m): (a) Case 3 (BR); (b) Case 8–3 (DR).
- 4.46 Connection Force and Maximum Force in Reinforcement for Case 3 (s=0.2 m, h=2.2 m, BR) and Case 8–3 (s=0.2 m, h=2.2 m, DR): Effects of Reinforcement Stiffness.
- 4.47 Effects of Connection Strength on Connection Force for Cases with Small Reinforcement Spacing (s=0.2 m).
- 4.48 Effects of Connection Strength on Maximum Force in Reinforcement for Cases with Small Reinforcement Spacing (s=0.2 m).
- 4.49 Effects of Connection Strength on Horizontal Displacements along Section A for Cases with Small Reinforcement Spacing (s=0.2 m).
- 4.50 Effects of Connection Strength on Connection Force and Maximum Force in Reinforcement for Cases with Large Reinforcement Spacing (s=0.6 m).
- 4.51 Axial Force Distribution in Reinforcement for Case 12 (l=1.5 m): (a) s=0.2 m, h=6.6 m; (b) s=0.6 m, h=2.6 m.
- 4.52 Effects of Connection Strength on Horizontal Displacements along Section A for Cases with Large Reinforcement Spacing (s=0.6 m).
- 4.53 Effects of Foundation Strength on Critical Wall Height.
- 4.54 Effects of Foundation Strength for Cases 1, 4, and 10 (s=0.2 m, l=1.5 m h=3.2 m) on: (a) Horizontal Displacements along Section A; (b) Connection Force and Maximum Axial Force in Reinforcement; (c) Stresses along Section A.
- 4.55 Stress Distributions along Section A for Critical and Stable States of Case 1 (s=0.2 m, h=6.6 m, l/h=0.23–0.5).
- 4.56 Stress Distributions along Section C for Critical and Stable States of Case 1 (s=0.2 m, h=6.6 m, l/h=0.23–0.5).
- 4.57 Horizontal Displacements along Sections A and B for Critical and Stable States of Case 1 (s=0.2 m, h=6.6 m, l/h=0.23–0.5).
- 4.58 Maximum Axial Force in Reinforcement for Critical and Stable States of Case 1 (s=0.2 m, h=6.6 m, l/h=0.23–0.5).
- 4.59 Connection Force for Critical and Stable States of Case 1 (s=0.2 m, h=6.6 m, l/h=0.23–0.5).
- 4.60 Stress Distributions along Section A for Critical and Stable States of Case 8–1 (s=0.4 m, h=5.0 m, l/h=0.3–0.5).
- 4.61 Stress Distributions along Section C for Critical and Stable States of Case 8–1 (s=0.4 m, h=5.0 m, l/h=0.3–0.5).
- 4.62 Horizontal Displacements along Sections A and B for Critical and Stable States of Case 8–1 (s=0.4 m, h=5.0 m, l/h=0.3–0.5).
- 4.63 Connection Force and Maximum Axial Force in Reinforcement for Critical and Stable States of Case 8–1 (s=0.4 m, h=5.0 m, l/h=0.3–0.5)
- 4.64 Stress Distributions along Section A for Critical and Stable States of Case 10 (s=0.2 m, h=3.2 m, l/h=0.47–0.7).
- 4.65 Stress Distributions along Section C for Critical and Stable States of Case 10 (s=0.2 m, h=3.2 m, l/h=0.47–0.7).
- 4.66 Horizontal Displacements along Sections A and B for Critical and Stable States of Case 10 (s=0.2 m, h=3.2 m, l/h=0.47–0.7).
- 4.67 Connection Force and Maximum Axial Force in Reinforcement for Critical and Stable States of Case 10 (s=0.2 m, h=3.2 m, l/h=0.47–.7).
- 4.68 Effects of Secondary Reinforcement: Axial Force Distribution in Reinforcement for Case 7 (s=0.6/0.2 m), (a) h=2.6 m; (b) h=5.0 m.
- 4.69 Effects of Secondary Reinforcement: State of Soil for Case 7 (h=2.6 m, s=0.6/0.2 m).
- 4.70 Effects of Secondary Reinforcement: Horizontal Displacements along Section A for Cases 2 and 7 (h=2.6 m).
- 4.71 Effects of Secondary Reinforcement: Connection Force and Maximum Axial Force in Reinforcement for Cases 2 and 7 (h=2.6 m).
- 5.1 Maximum Force in Reinforcement: Comparison of FLAC and AASHTO Results for Case 1 (s=0.4 m) and Case 2 (s=0.6 m).
- 5.2 Maximum Force in Reinforcement: Comparison of FLAC and AASHTO Results for Case 8–1 (s=0.4 m) and Case 10 (s=0.2 m).
- 5.3 Comparison of FLAC and AASHTO Results for Case 8–1 (s=0.4 m, h=5.0 m, l=1.5 m): (a) MSEW 1.1 Analysis: Critical Slip Surface from Compound Stability Analysis; (b) FLAC Analysis: Failure Zones Distribution at the Critical State.
- 5.4 Comparison of FLAC and AASHTO Results for Case 10 (s=0.2 m, h=3.2 m, l=1.5 m): (a) MSEW 1.1 Analysis: Critical Slip Surface from Deep-Seated Stability Analysis; (b) FLAC Analysis: Failure Zones Distribution at the Critical State.
- 5.5 Stress Distributions along Sections A and C for Failure State of Case 1 (s=0.2 m, h=8.6 m, l/h=0.17).
- 5.6 Stress Distributions along Sections A and C for Critical State of Case 1 (s=0.2 m, h=8.6 m, l/h=0.17).
- 5.7 Stress Distributions along Sections A and C for Failure State of Case 2 (s=0.6 m, h=4.6 m, l/h=0.33).
- 5.8 Stress Distributions along Sections A and C for Critical State of Case 2 (s=0.6 m, h=4.6 m, l/h=0.33).
- 5.9 Stress Distributions along Sections A and C for Failure State of Case 8–1 (s=0.4 m, h=8.0 m, l/h=0.19).
- 5.10 Stress Distributions along Sections A and C for Critical State of Case 8–1 (s=0.4 m, h=8.0 m, l/h=0.19).
- 5.11 Stress Distributions along Sections A and C for Failure State of Case 10 (s=0.2 m, h=4.4 m, l/h=0.34).
- 5.12 Stress Distributions along Sections A and C for Critical State of Case 10 (s=0.2 m, h=4.4 m, l/h=0.34).
LIST OF TABLES
Table
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