Last reviewed 16 Sept 2026 · 6 min read
Lateral earth pressure
Soil retained by a wall, a basement, a sheet pile or a bridge abutment presses laterally on it. The magnitude depends on how the wall moves relative to the soil:
| State | Wall movement | Coefficient | Pressure |
|---|---|---|---|
| At rest | No movement (rigid, braced walls, basement walls restrained by floors) | Intermediate | |
| Active | Wall moves away from the soil | Minimum | |
| Passive | Wall is pushed into the soil | Maximum |
. Only a small outward movement (of the order of 0.1–0.5% of wall height for sands) mobilises the active state, whereas the passive state needs much larger movement (several per cent of height). Hence full passive resistance is seldom relied upon.
At-rest pressure
For over-consolidated soils is larger (can exceed 1).
Rankine's theory
Assumptions: soil is homogeneous, semi-infinite, cohesionless (extended later to cohesive soils) and in a state of plastic equilibrium; the back of the wall is vertical and smooth (no wall friction); the ground surface is horizontal (or a plane); failure surface is plane.
Cohesionless backfill, horizontal surface
Active pressure at depth : ; total thrust acting at above the base. Passive: at .
The failure (slip) planes make with the horizontal in the active case and in the passive case.
For = 30°: = 1/3, = 3.
Uniform surcharge
Adds a uniform pressure over the full height: extra thrust at .
Submerged backfill (water table in the backfill)
Below the water table use effective unit weight for the soil pressure and add the full hydrostatic pressure (water pressure has = 1):
Water pressure often exceeds the soil pressure — the reason drainage behind walls is vital.
Layered backfill
Compute the vertical effective stress at each boundary and apply each layer's — the pressure diagram may jump at a layer boundary where changes.
Inclined backfill (surface at angle β, cohesionless)
The thrust acts parallel to the surface slope at .