Wall Friction Angle in Sheet Piling Structures

Generally, the wall is not completely smooth, which means that a wall friction angle δ ≠0 between the wall and the soil is established. This is mobilised when the wall and soil move in relation to each other (as the follow picture shows). Here, δ is the angle between the direction of application of the active or passive earth pressure and a line perpendicular to the surface of the wall.

Assuming a straight slip plane, the wall friction angle in sheet piling structures may be assumed to lie within the limits δ a/p = ±2/3ϕ on the active and passive sides. If a curved slip plane is assumed for the passive earth pressure, the wall friction angle must be increased to δ p = ±ϕ according to EAU 2004 section 8.2.4.2 . Normally, δ a ≥ 0 and δ p ≤ 0 because the active wedge of soil moves downwards with respect to the wall and the passive wedge of soil upwards.

It is easy to see that the wall friction angle can change the forces in the polygon of forces considerably. In particular, the passive earth pressure increases drastically in the case of a negative wall friction angle δ p ≤ 0.

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