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Earth Pressures

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Coulomb‟s Theory

The method allows consideration of

• friction between retaining walls and backfill

• sloping wall back

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Coulomb‟s Theory

The following assumptions are made:• Planar failure surfaces

 – For rough walls, actual failure surface is curved, but

for the active case the error is small

 – For passive resistance, the error (overestimation) is

large when the angle of wall friction (d) is greater than

1/3 f„

• Mohr-Coulomb failure criterion is satisfied on

the assumed failure planes

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Coulomb‟s Theory

• For concrete walls, – the angle of friction (d) can be assumed to be 2/3 f'

for the active case and ½ f' for the passive case

 – for undrained analysis, wall adhesion (cw) can be

assumed to be ½ cu.

•  A search is made to determine the critical failure

plane that gives the maximum value of activeforce. This approach is known as the “limit

equilibrium method”.

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Charts for Ka and Kp

Refer to BS 8002:1994 or BS EN 1997-1:2004

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Charts for Ka and Kp

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Charts for Ka and Kp

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Effect of compaction on earth pressures

Refer to CIRIA C516 Pages 88 – 91

Note that, in the equations quoted below, Whitlow (2001) uses Ka(wall is assumed to deflect) in lieu of K0 (wall does not deflect).

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