Retaining wall pressure inputs
Example data table
Example assumptions: H = 6 m, γ = 18 kN/m³, φ = 30°, c = 0, q = 10 kPa, level dry backfill.
| Case | Coefficient | Top pressure (kPa) | Base pressure (kPa) | Total force (kN/m) | Resultant height above base (m) |
|---|---|---|---|---|---|
| Active | 0.3333 | 3.333 | 39.333 | 128.000 | 2.156 |
| At-rest | 0.5000 | 5.000 | 59.000 | 192.000 | 2.156 |
| Passive | 3.0000 | 30.000 | 354.000 | 1152.000 | 2.156 |
Formula used
1) Earth pressure coefficients
Active, level backfill: Ka = (1 − sinφ) / (1 + sinφ)
Passive, level backfill: Kp = (1 + sinφ) / (1 − sinφ)
At-rest: K0 = (1 − sinφ) × OCRsinφ for preliminary use.
2) Sloping-backfill active coefficient
For the selected smooth-wall active model, the calculator uses
Ka = cosβ × (cosβ − √(cos²β − cos²φ)) / (cosβ + √(cos²β − cos²φ)).
3) Pressure at depth
The total lateral pressure combines soil, surcharge, cohesion, and water:
σh = K(σ'v + q) ± 2c√K + u.
Use the minus sign for active pressure and the plus sign for passive pressure.
4) Resultant force and location
P = ∫ σh dz
Mbase = ∫ σh(H − z) dz
ȳ = Mbase / P, measured above the base.
This tool is intended for preliminary engineering checks. Final design should also review drainage, wall friction, compaction, seismic loading, bearing, sliding, and overturning safety.
How to use this calculator
- Select the pressure state: active, passive, or at-rest.
- Enter the retained height, friction angle, and soil unit weights.
- Add backfill slope when the retained surface is not level.
- Enter cohesion only when a reliable design value exists.
- Add surcharge for traffic, storage, or nearby imposed loads.
- Enter groundwater depth if water stands behind the wall.
- Keep OCR above 1 only for overconsolidated at-rest conditions.
- Press the calculation button to show the result above the form.
- Review the total force, moment, pressure profile, and warnings.
- Use CSV or PDF export for documentation and checking notes.
FAQs
What does this calculator estimate?
It estimates lateral earth pressure on a retaining wall, including soil thrust, surcharge effect, hydrostatic pressure, resultant force, and moment about the base.
When should I use active pressure?
Use active pressure when the wall can move slightly away from the retained soil. That movement allows the backfill to reach the active state.
When is at-rest pressure more appropriate?
Use at-rest pressure when wall movement is very limited, such as basement walls, stiff abutments, or heavily restrained retaining systems.
Does groundwater change the result much?
Yes. Water increases lateral load and can shift the resultant. Poor drainage often controls retaining wall performance, so groundwater should not be ignored.
Why is passive pressure so large?
Passive resistance develops only after the wall pushes into soil. It is much larger theoretically, but many designs reduce it because full mobilization may not occur.
Can I rely on cohesion in design?
Be careful. Apparent cohesion may reduce with weather, cracking, wetting, or long-term movement. Many permanent wall designs use little or no cohesion benefit.
Is this enough for final wall design?
No. Final design also needs structural checks, bearing, sliding, overturning, drainage, settlement, construction staging, and any seismic or surcharge details.
Why does the tool show design notes?
The notes flag modeling limits, such as simplified sloping-backfill passive pressure or cohesive active behavior. They help you identify when a more detailed analysis is needed.