This document contains lecture slides about the design of earth-retaining structures. It provides examples of calculating the coefficient of active earth pressure (Ka) using Rankine's formula for different ground surface conditions. It also discusses designing earth-retaining structures according to Australian standard AS5100.3, including considering limit states, design loads, and design factors that account for load uncertainties and importance categories. Key steps in the design process include checking if the factored geotechnical resistance effect is greater than or equal to the design action effect.

1. The Design of
Earth-retaining Structures
ENB485
Chris Bridges
The Design of
Earth-retaining Structures
ENB485
Chris Bridges
May 2016
Lecture 5
Design of Earth-retaining Structures

2. Example –
Rankine Coeffcient of Active/Passive Earth Pressure
Ka = {1- sin (f)}/ {1+ sin (f)} = tan2(45 - f/2)
for horizontal ground surface and smooth wall
and
Kp = 1/ Ka = tan2(45 + f/2)

3. Ref.: Geoguide 1
However, for sloping ground surface and
wall friction

4. 1. Calculate Ka
Assume:
f’ = 27°
= 0°
= f’/2 = 13.5°
= 25°
2. Calculate Ka if
Fuf = 0.75 (AS4678)
Remember:
f* = tan-1(Fuf (tan27°)
 = f*/2

5. Ref.: Geoguide 1
Example 1 -
Calcualte Ka
phi 27 0.75 20.91338
d 13.5
a 90
b 25
Active soil pressure
coefficient: where
Ka = [cos(f'-a-90)]^2 / [cos(a-90)^2*cos(d1+a-
90)*{1+sqrt(sin(f'+d1)* A = cos^2(f' - a-90) = 0.79
sin(f'-b)/cos(d1+a-90)/cos(b-a-90))}^2] B = cos^2(a-90)*cos(d1+a-90) = 0.97
=
A/B/C
= 0.61 C = {see above bracket}^2 = 1.33
Example 2 -
Calcualte Ka
phi 27 0.75 20.91338
d 13.5
a 90
b 25
Active soil pressure
coefficient: where
Ka = [cos(f'-a-90)]^2 / [cos(a-90)^2*cos(d1+a-
90)*{1+sqrt(sin(f'+d1)* A = cos^2(f' - a-90) = 0.87
sin(f'-b)/cos(d1+a-90)/cos(b-a-90))}^2] B = cos^2(a-90)*cos(d1+a-90) = 0.97
=
A/B/C
= #NUM! C = {see above bracket}^2 = #NUM!
Does not work as slope angle is greater than f'

6. 16
Design to AS5100.3

7. Design to AS5100.3
• Does not cover RSS
• Design Considerations – Limit States
• Design Loads – AS5100-2
• Loads should be combined with a load factor = 1.0
• Design Factors – factors on uncertainty
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8. Retaining walls
Design Resistance Effect R*  Design Action Effect S
FgRug*  S
Geotechnical reduction
factor
Takes account of load factors = 1
Ultimate geotechnical strength
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10. Ground anchors
Design Resistance Effect R*  Design Action Effect S
FnFgRug*  S
Importance category factor
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