Active and passive earth pressure on a retaining wall using Rankine theory — vertical wall, horizontal backfill, no wall friction. Optional cohesion.
Standard method — stated scope limits apply
Soil & Depth
Enter soil properties and depth.
About This Calculation
Rankine earth pressure theory (1857) gives the lateral pressure soil exerts on a retaining wall — active pressure, which pushes the wall outward as the retained soil tries to slide, and passive pressure, the much larger resistance available on the other side if the wall is pushed into the soil. Both come from the same friction-angle-based coefficients, and both scale directly with depth and soil unit weight. It’s the standard starting point for retaining wall design, though real designs also need to check Coulomb theory (which accounts for wall friction) and overall stability, not lateral pressure alone.
Frequently Asked Questions
Why is passive pressure so much larger than active pressure for the same soil?
The active and passive coefficients (Ka and Kp) are reciprocals of each other by the Rankine formula — at a typical friction angle of 30°, Ka ≈ 0.33 while Kp = 3, a nine-fold difference. Physically, soil resists being compressed (passive case) far more than it resists relaxing as a wall moves away from it (active case).
What does cohesion do to the active pressure calculation?
Cohesion REDUCES active pressure (by a term proportional to −c√Ka) because cohesive soil can partly support itself without relying on friction alone — enough cohesion can theoretically make the calculated active pressure negative near the surface, which is why the calculator also reports a tension-crack depth for cohesive soils.
Does this account for water pressure behind the wall?
Not directly — this calculates lateral EARTH pressure using the soil’s unit weight. If the backfill is saturated or has a water table behind the wall, hydrostatic water pressure adds a separate, often very significant, additional lateral load that must be calculated and added on top of this result.
Why does the calculator only handle a horizontal backfill with no wall friction?
That’s the scope of classical Rankine theory itself — sloped backfill and wall friction genuinely change the pressure coefficients, and are handled by Coulomb theory instead, which uses a more complex (and more broadly applicable) set of equations.