CIVILKITengineering toolsOpen retaining-wall tool

retaining walls / field note

What does a Rankine active-pressure screen assume?

A lateral thrust estimate is useful when the pressure diagram, wall-movement assumption, and surcharge basis are visible. It becomes misleading when it is presented as a complete retaining-wall design.

Field note / retaining-wall earth pressure

Active pressure depends on movement.

Active pressure is the reduced lateral pressure associated with a wall moving sufficiently away from a cohesionless backfill to mobilise the active condition. A restrained or very stiff wall may not reach that state, so the pressure model must match the actual wall and ground behaviour.

Separate the two pressure shapes.

Rankine's coefficient for level backfill is Ka = (1 − sin φ)/(1 + sin φ). Soil self-weight creates a triangular thrust, Pγ = ½KaγH², while a uniform surcharge creates a rectangular thrust, Pq = KaqH. Their lines of action differ, so the resultant height matters for overturning calculations.

What the quick screen cannot prove

  • Sliding, overturning, bearing pressure, eccentricity, uplift, wall self-weight, or reinforced-concrete capacity.
  • Hydrostatic pressure, drainage, seepage, layered or cohesive soils, sloping backfill, wall friction, seismic loading, or compaction effects.
  • Whether active, at-rest, Coulomb, seismic, or another project-specific pressure model is required.

Run the earth-pressure screen

The Rankine coefficient and horizontal stress relationship are also shown in FHWA guidance.