Geoscience Reference
In-Depth Information
Table 19.9 Wall types when the at rest condition applies instead of the active condition.
Earth pressure condition
Movement
Wall type
Active
Wall movement occurs
Sheet piles
At rest
No/Negligible wall
Cantilever with stiff basal stems
movement
Rigid counterfort walls
Founded on rigid bases eg founded on strong
rock or on piles
Culvert wing walls
Bridge abutments
Basement walls
Tanks
19.10 Application of passive pressure
The passive pressure can provide a significant resisting force based on Rankine and
Coulomb theories. However this pressure should be applied with consideration
shown in the table below.
Table 19.10 Approaches to consider in application of the passive state.
Issue
Approach
Typical details
Comments
Wall movement
Reduction factor
Reduction factor of 1/3
Approximately ½ of the passive
incompatibility
applied to the
stress would apply for ¼ of the
between the active
passive pressure
strain.
and passive state
Desiccation cracks
Passive resistance
0.5 m cracked zone
Cracked zone as a proportion of
ion front of wall
starts below the
minimum (typical alpine
Active zone (H a ) varies from
depth of the
temperate and coastal
1/3 of in temperate areas
crackled zone
areas) to 3.0 m in arid
½H a in wet coastal areas
regions
¾H a in arid regions
Non triangular
Passive embedment Wall is unlikely to move The passive pressure is
distribution for
10% H
in sliding or about the
approximately 10 times the
rotation about the
base. Therefore a
active pressure. Hence 10% H.
top and sliding
triangular active
Similar factors of safety (or
condition now applies
partial factors) may then be used
with rotation about
for both sliding and overturning.
the base
Refer Table 19.8 & Fig 19.2
Excavation or
Reduce passive
No passive resistance
A heel below the middle or back
erosion in front
resistance to that
for the top 0.5 m
third of wall can use the full
of wall
depth
typically used
passive resistance
19.11 Use of wall friction
Coulomb theory considers the effect of wall friction, which reduces the pressure
in the active state and increases the passive resistance.
Application of wall friction to the design should have the following due
considerations.
 
 
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