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MSE Wall Design

MSE Wall Design. MSE Wall as a Gravity Wall. An MSE wall is a gravity wall. Heavy walls are good. External Stability. Bearing resistance Settlement Sliding Overturning Overall Stability. External Stability. Bearing. Bearing Failure. External Stability. Settlement.

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MSE Wall Design

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  1. MSE Wall Design

  2. MSE Wall as a Gravity Wall • An MSE wall is a gravity wall. Heavy walls are good

  3. External Stability • Bearing resistance • Settlement • Sliding • Overturning • Overall Stability

  4. External Stability Bearing

  5. Bearing Failure

  6. External Stability Settlement

  7. Flexibility of Wall Systems

  8. External Stability Sliding

  9. Sliding Failure

  10. External Stability Overturning

  11. External Stability Overall Stability

  12. Surcharge Water Pressure Earth Pressure Forces Earthquake

  13. Forces Back Slope Surcharge

  14. Forces Surcharge

  15. Drainage • If the wall backfill “fills” with water …. • Weight of soil increases • Shear strength of backfill decreases • Pressures on the wall increase • Greater tendency for fill to settle • Potential for movement of soils as water exits wall or slope. • Buoyancy needs to be considered • Appropriate drainage systems are critical !!

  16. Drainage System Installation

  17. Why Care about Drainage? An example…

  18. 20’ 20’ 5’

  19. 20’ H=25’ Hw=20’ 5’ LATERAL EARTH PRESSURES

  20. Design Concepts Topic 2 Internal Stability Design of MSE Walls

  21. What is a Failure Surface ?? Geosynthetic Reinforced Wall Potential Failure Surface Resistant Zone Active Zone Metal Reinforced Wall H Soil Reinforcement Reinforced Soil Mass L

  22. How do Reinforcements Hold Up the Wall ? “Active” Force Resistant Length, Le Active Length, La Soil Reinforcement L

  23. Internal Stability Reinforcement Failure Modes • Pull out • Reinforcement tensile strength • Connection

  24. Internal Stability Reinforcement Failure Modes – CORROSION/DEGRADATION • STEEL REINFORCEMENT • Area of steel is increased to account for the anticipated corrosion loss over the design life • GEOSYNTHETIC REINFORCEMENT • Ultimate tensile strength increased to account for strength loss due to installation damage, creep, and durability

  25. Design Checks Class Exercise • Compare the internal stability of the Design MSE wall and the As-Built MSE Wall The internal stability of this wall seems OK!

  26. Design Turf reinforcement mat, topsoil, and seed 1 2 Backfill Medium sand with 15% (max) non-plastic fines at 95% compaction H = 20 ft Spacing 18” Continuous Geogrid Reinforcement Chimney Drain 3 ft 1 3 4 ft L = 20 ft Section

  27. 1 1.5 Note: Geogrid Coverage = 50% Backfill Medium sand with 35% plastic fines at 95% compaction H = 25 ft Geogrid Reinforcement Spacing 36” L = 15 ft 2 ft L = 20 ft 1 2 2 ft Plan Section As-Built

  28. Durability • MSE Walls • Corrosion of steel reinforcement • Degradation of geosynthetic reinforcement • Durability of the facing

  29. MSE Facing Durability

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