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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

1.2-7

Flexibility of Wall Systems

TYPE OF FACING LIMIT OF DIFFERENTIAL SETTLEMENT

CIP Gravity Wall 1/500 2 In. in 100 Ft.

Welded Wire Facing 1/50 2 Ft. in 100 Ft.5’ x 5’ Panels with ¾” Joints 1/100 1 Ft. in 100 Ft.5’ x 10’ Panels with ¾” Joints 1/200 6 In. in 100 Ft.Modular Block Walls 1/200 6 In. in 100 Ft.Full Height Facing Panels 1/500 2 In. in 100 Ft.

External Stability

Sliding

Sliding Failure

External Stability

Overturning

External Stability

Overall Stability

Forces

Water Pressure

Earth Pressure

Surcharge

Earthquake

ForcesBack Slope Surcharge

ForcesSurcharge

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’

5’

20’

20’

5’

Hw=

20’

LATERAL EARTH PRESSURES

H=25’

Design Concepts

Topic 2

Internal Stability Design of MSE Walls

What is a Failure Surface ??

Geosynthetic Reinforced Wall

H

L

Active

Zone

Resistant

Zone

Potential

Failure

Surface

Soil ReinforcementReinforced

Soil Mass

Metal Reinforced Wall

How do Reinforcements Hold Up the Wall ?

L

Soil

Reinforcement

“Active” Force

Resistant Length, LeActive

Length, La

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

The internal stability of this wall seems OK!

• Compare the internal stability of the Design MSE wall and the As-Built MSE Wall

Design Checks

Continuous Geogrid Reinforcement

H =

20

ft

L = 20 ft

2

1

Section

Backfill

Medium sand with 15% (max) non-plastic fines at

95% compaction

Spacing

18”

Chimney Drain

4 ft

3 ft

31

Turf reinforcement mat, topsoil, and seed

Design

H =

25

ft

L = 20 ft

1.5

1

Plan Section

L = 15 ft

Backfill

Medium sand with 35% plastic fines at 95% compaction

Spacing 36”

Geogrid

Reinforcement

Note: Geogrid Coverage = 50%

2 ft

2 ft

21

As-Built

Durability

• MSE Walls• Corrosion of steel reinforcement• Degradation of geosynthetic

reinforcement• Durability of the facing

1.2-29

MSE Facing Durability