Earth pressures - Geotechnical Investigation and Design Tables - page 242

σ v .
- Water pressures can have a significant effect on the design of the walls.

= σ h /

-K o

Table 19.1 Earth pressures.

Type Movement Earth pressure Stresses Comment

coefficient

Active Soil Wall K a K o σ h < σ v K a 1/K p → < =

At rest None K o

σ h , σ v

Fixed and unyielding

Passive Wall Soil K p K o σ h > σ v Large strains required to

mobilise passive resistance

→ >

19.2 Earth pressure distributions
•

The earth pressure depends primarily on the soil type.

•

The shape of the pressure distribution depends on the surcharge, type of wall,
restraint and its movement.

Table 19.2 Types of earth pressure distribution.

Type of wall No. of Example Pressure Comments

props distribution

Braced Multi 2 Open strutted trench Trapezoidal/ Fully restrained system

>

Rectangular H 5m

>

Semi flexible Two Soldier pile with two Trapezoidal/ Partially restrained

anchors Rectangular/ system H 5m

<

Triangular

Flexible One Soldier pile with one Triangular Shape changes depends

system - no None anchor Sheet piling, on type of wall

bracing Gravity wall movement

Any with uniform Any Concrete platform at Rectangular Added to triangular or

surcharge load at top of wall with other pressure

top of wall 20 kPa traffic distribution

Any with load Any Point load - pad footing Irregular with Based on the theory of

offset at Line load - narrow strip maximum near elasticity. This is added

top of wall footing top half of wall to the other loads

Strip load - strip footing

During wall Any Compaction induced Passive line at Applies when a heavy

construction pressure distribution the top with static or dynamic

vertical drop to construction load is

the active line within 1/2 height of wall

•

A triangular distributionwhile used for the analysis of any non-bracedwall, strictly
applies only to walls with no movement (at rest condition) and free to rotate about
the base.

•

When rotation occurs about the top and/or sliding (translating) occurs, then the
shape of the triangular distribution changes with arching near the top.