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

Flexibility of Wall Systems

External Stability Sliding

Sliding Failure

External Stability Overturning

External Stability Overall Stability

Surcharge Water Pressure Earth Pressure Forces Earthquake

Forces Back Slope Surcharge

Forces Surcharge

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 !!

Drainage System Installation

Why Care about Drainage? An example…

20’ 20’ 5’

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

Design Concepts Topic 2 Internal Stability Design of MSE Walls

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

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

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

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

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!

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

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

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

MSE Facing Durability

MSE Wall Design

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