Geotechnical Civil & Structural Calculation guide Calculate a value

How much earth pressure a retaining wall actually faces

Active versus at-rest pressure, and why a wall that cannot move needs a substantially larger design thrust.

The engineering question

How much horizontal pressure does the retained soil exert, and why does it change so much depending on whether the wall is allowed to move?

Worked example

The figures below were produced by running the Earth Pressure Calculator with the same inputs — during the build, from its authoritative engine.

Results
Active coefficient Ka	0.3333 –
At-rest coefficient K₀	0.5 –
Active pressure at the base	21.3333 kPa
At-rest pressure at the base	32 kPa
Active resultant	37 kN/m
Height of the resultant above the base	1.1351 m
Assessment	Active resultant 37.0 kN/m acting at 1.14 m above the base (Coulomb sediment-free, vertical wall, dry backfill).

Active coefficient Ka = (1−sinφ)/(1+sinφ); at 30° that is 1/3.
At-rest coefficient K₀ = 1−sinφ, which at 30° is 0.5 — half again as much thrust.
Add the surcharge as a uniform rectangular pressure on top of the triangular soil pressure.

Sanity check

A propped basement wall cannot deflect, so design it for K₀. Using Ka on a stiff wall under-estimates the thrust by roughly half.

Tools for this problem

These are the EngiMetric calculators that compute the numbers in this topic. Each one shows its formula, its units and its limits rather than returning a bare result.

Engineering review required

This topic supports professional engineering work; it does not replace a sealed design. The result depends on site data, the governing standard and engineering judgement, and should be confirmed by a competent engineer before it is built.

References & standards

BS EN 1997-1 — earth pressures on retaining structures
GECP 7 — design of embedded retaining walls
Rankine (1857) — stability of loose and cohesive earth