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Southern Illinois University School of Engineering, Department of Civil Engineering

This doctoral dissertation proposal defense delves into the seismic behaviors of cantilever retaining walls, assessing their responses based on earth thrust and ground motion through analytical, experimental, and numerical methods. Various failure modes, seismic responses, and fragility analyses are explored to enhance understanding and develop robust solutions.

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Southern Illinois University School of Engineering, Department of Civil Engineering

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  1. Southern Illinois University School of Engineering, Department of Civil Engineering Doctoral Dissertation Proposal Defense, Sep 2016 Seismic Investigation of Cantilever Retaining Walls Based on Pressure and Motion Approaches Siavash Zamiran, Ph.D., P.E., M.ASCE Project Engineer, Marino Engineering Associates, Inc. Adjunct Faculty, St. Louis University Chair of Sustainability Committee, ASCE St. Louis Director and Lead Organizer, CreativeMornings St. Louis www.zamiran.net 2/25/2019 Exponent Oakland, CA

  2. Outline • Overview • Background • Problem Statement • Numerical Modeling Procedure & Research Methodology • Verification of the Numerical Modeling • Seismic Response Based on Earth Thrust • Seismic Response Based on Ground Motion • Fragility Analysis • Experimental Studies • Conclusions

  3. Outline • Overview • Background • Problem Statement • Numerical Modeling Procedure & Research Methodology • Verification of the Numerical Modeling • Seismic Response Based on Earth Thrust • Seismic Response Based on Ground Motion • Fragility Analysis • Experimental Studies • Conclusions

  4. Overview

  5. Cantilever Retaining Walls

  6. Failure of Retaining Walls due to Earthquakes

  7. Caused by Kobe Earthquake in 1995 (National Platform for Natural Hazards, 2005)

  8. Caused by Mid-Niigata prefecture earthquake in 2004 (Public Work Research Institute, 2008)

  9. Caused by Mid-Niigata prefecture earthquake in 2004 (Changwei et al., 2015)

  10. Failure Modes of Retaining Walls Backfill soil Governing failure modes in earthquake conditions

  11. Seismic Response of Retaining Walls • Seismic total force • Seismic load vs. earthquake intensity • Free-field acceleration • Wall displacement δ

  12. Outline • Overview • Background • Problem Statement • Numerical Modeling Procedure & Research Methodology • Verification of the Numerical Modeling • Seismic Response Based on Earth Thrust • Seismic Response Based on Ground Motion • Fragility Analysis • Experimental Studies • Conclusions

  13. Background

  14. Background : Analysis Methods Analytical Experimental Numerical + Realistic results - Time consuming - Limited number of models - Expensive - Scaling issues / calibration + Can be realistic + Reasonable cost + Can consider various features - Need of calibration and verification + Cheap and easy + Quick method - Simplification of a complex problem - Over-estimation

  15. Background:Analytical Methods

  16. Analytical Solutions Based on the Mathematical Method • Pseudo-dynamic • Pseudo-static EQ=f(time, frequency, height) EQ=k*(Static load) • Shear wave velocity • Primary wave velocity • Okabe (1924), Mononobe and Matsuo (1929), Prakash and Saran (1966), Das and Puri (1996) Steedman and Zeng (1990), Choudhury and Nimbalkar (2006), Nimbalkar and Choudhury (2007), Ghosh (2007), Lin et al. (2015)

  17. Background:Experimental Methods

  18. Background: Seismic Experimental Studies Features studied in the experimental studies: • Seismic total force and earth pressure distribution • Acceleration distribution • Wall deformation • Effects of backfill cohesion • Structural behavior of the retaining wall • Wall moment • Wall stiffness • Earthquake characteristics • PGA intensity • Effect of different earthquakes

  19. Shake Table (SIU, 2019)

  20. Centrifuge (Zhejiang University)

  21. Review of Seismic Experimental Studies • Only for cohesionless backfill • Limited number of studies • Neglecting flexibility of walls • Only sinusoidal acceleration inputs 23

  22. Review of Experimental Studies for Cohesive • Limited number of studies • Neglecting flexibility of walls

  23. Background:Numerical Methods

  24. Numerical Methods

  25. Background: Seismic Numerical Studies Features studied in the experimental studies • Seismic earth pressure Woodward and Griffiths (1996), Green and Ebeling (2002), Atik and Sitar (2010), Jung and Bobet (2008), Wilson and Elgamal (2010) • Wall displacement Woodward and Griffiths (1996), Green and Ebeling (2002), Al-Homoud and Whitman (1995) • Wall rigidity Vieira et al. (2008), Green et al. (2008), Psarropoulos et al. (2005) • Phase differences of dynamic variables Green and Ebeling (2002), Athanasopoulos -Zekkos et al. (2013), Atik and Sitar (2010) • Backfill cohesion Agusti and Sitar (2013), Madabhushi and Zeng (2007)

  26. FD: Finite difference, FE: Finite element

  27. Cohesion Feature

  28. Field Study of Kapuskar 2005 • Considered backfills of retaining walls and abutments of 20 bridges • Bridge sites considered for the study: • 22 Number of bridges on State highways

  29. Bridge Sites Investigated

  30. Field Study of Kapuskar 2005

  31. Properties Used in Dynamic Studies for Cohesive Backfill • Be conservative about the apparent cohesion! • Use a cohesion value less than that measured in the laboratory!

  32. Gap of Knowledge

  33. Gap of Knowledge on: Effects of Cohesion Feature, Analytical Studies • Many analytical solutions do not consider cohesion and wall adhesion • Cohesion-based analytical solutions contain multiple simplifications • Neglecting dynamic features: • Damping of the system • Wave propagation • Phase differences between acceleration and seismic pressure • Time history of the acceleration • Residual earth pressure Wall adhesion

  34. Gap of Knowledge on: Experimental Studies • Limited types of soil backfill • Limited numbers of dynamic experiments • Scaling issues of the experimental studies • Boundary condition problems

  35. Gap of Knowledge on: Previous Numerical Studies • Simulating soil with simplified models such as Mohr-Coulomb • Neglecting the hysteretic effects of soil • In many studies, lack of modeling calibration • Lack of thorough investigation on the effects of backfill cohesion, acceleration intensity, and different earthquake events • Lack of thorough study on motion response of retaining walls based on different earthquake events, and different acceleration intensities • Neglecting the effects of earthquake uncertainty

  36. Outline • Overview • Background • Problem Statement • Numerical Modeling Procedure & Research Methodology • Verification of the Numerical Modeling • Seismic Response Based on Earth Thrust • Seismic Response Based on Ground Motion • Fragility Analysis • Experimental Studies • Conclusions

  37. Problem Statement

  38. Problem Statement • Effect of backfill cohesion • Effects of wall rigidity • Effects of soil-wall interaction • The correlation between numerical, experimental, and analytical studies • Effects of different earthquake events • Effects of earthquake acceleration intensity • Effects of earthquake uncertainty

  39. Investigation Approaches • Pressure approach • Seismic earth pressure • Seismic total thrust • Retaining wall moment • Point of action • Motion approach • Displacement variation during earthquake • Fragility analysis δ

  40. Outline • Overview • Background • Problem Statement • Numerical Modeling Procedure & Research Methodology • Verification of the Numerical Modeling • Seismic Response Based on Earth Thrust • Seismic Response Based on Ground Motion • Fragility Analysis • Experimental Studies • Conclusions

  41. Numerical Modeling Procedure&Research Methodology

  42. Considerations for Numerical Method • Conducting complicated non-linear problems • Continuum medium • Large deformational output • Short calculation time period Finite difference method • Soil-structure interaction • Material damping • Fully dynamic analysis Software used: FLAC

  43. Retaining Wall Geometry Used for the Study

  44. Static Analysis Static analysis prior to earthquake excitation to reach static equilibrium: Construction of the wall Initial conditions of the backfill Monitoring static earth pressure

  45. Soil Constitutive Model UBCHYST (Naesgaard, 2011) • Simulating the hysteretic behavior of soil during dynamic analysis: • Soil damping • Material softening • Shear modulusreduction with an increase in strain

  46. Numerical Modeling of Cyclic Simple Shear Test • Calibration of soil properties • Determination of shear modulus reduction factor • Determination of soil damping (material damping)

  47. Retaining Wall Geometry Used for the Study

  48. Dynamic Modeling Considerations Dynamic Modeling Considerations • Constitutive model • Material damping • Dynamic boundary conditions • Baseline correction

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