Design a cantilever retaining wall — stem, heel and toe — in one pass. Enter the wall geometry, backfill soil properties and any surcharge, the allowable bearing pressure and friction coefficient, and the concrete and steel strengths, and the calculator works out the Rankine active earth pressure, checks overturning and sliding stability (factor of safety ≥ 1.5), checks the bearing pressure at the toe and heel including eccentricity, and designs the flexural steel for the stem, heel and toe.
Switch between metric and imperial units at the top of the form; every result converts with it.
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This is a preliminary design aid, not a substitute for a full geotechnical and structural analysis. Always have a licensed engineer check the final design.
What the calculator checks
- Active earth pressure. Rankine active pressure coefficient Ka from your backfill friction angle, for a level backfill with no wall friction or cohesion, plus any uniform surcharge.
- Overturning stability. Overturning moment from the active pressure versus the resisting moment from wall, base and soil self-weight, with a required factor of safety of 1.5.
- Sliding stability. Sliding force versus base friction resistance (passive resistance conservatively ignored), with a required factor of safety of 1.5.
- Bearing pressure. Resultant eccentricity, middle-third check, and maximum/minimum bearing pressure at the toe and heel against your allowable soil bearing pressure.
- Flexural design. Required steel area for the stem (cantilever under active pressure), heel (cantilever under soil and self-weight, less any upward soil reaction), and toe (cantilever under the net upward bearing pressure).
What to have ready
- Stem height, base thickness, stem thickness, and the base width split into heel and toe
- Backfill soil unit weight and friction angle, plus any surcharge load
- Allowable bearing pressure and base-to-soil friction coefficient
- Concrete strength, steel yield strength, cover and bar size
Notes and limitations
This tool assumes a level backfill with no wall friction or cohesion (Rankine theory), and conservatively ignores passive resistance in the sliding check. It does not check a shear key, seismic (pseudo-static) loading, global/slope stability, or drainage design. Final acceptance of the design rests with the responsible engineer.
Cantilever Retaining Wall Design Reference Table — ACI 318 / Rankine
| Design Parameter | Typical Value / Range | Reference | Notes |
|---|---|---|---|
| Active earth pressure coefficient (Ka) — φ = 30° | 0.333 | Rankine | Ka = (1−sin φ)/(1+sin φ) |
| Passive pressure coefficient (Kp) — φ = 30° | 3.0 | Rankine | Kp = (1+sin φ)/(1−sin φ) |
| Minimum factor of safety — overturning | 1.5 | IBC 1807.2.3 | OTM safety factor for unfactored loads |
| Minimum factor of safety — sliding | 1.5 | IBC 1807.2.3 | Sliding resistance / horizontal force |
| Concrete unit weight (normal weight) | 150 pcf | ACI 318-19 Table 19.2.4 | Standard value for design |
| Soil unit weight (moist granular) | 110–130 pcf | NAVFAC DM-7 | Verify with geotechnical report |
| Surcharge load (vehicle traffic) | 250 psf | AASHTO / IBC 1611 | H = surcharge / γ_soil (equivalent height) |
| Footing width rule of thumb | 40–60% of wall height | Engineering practice | Starting point; verify by analysis |
| Stem thickness at base | 8–12% of wall height | Engineering practice | Minimum 8 in per ACI 318 Section 11.3 |
| Min. concrete cover (soil contact) | 3 in | ACI 318-19 Table 20.6.1.3 | Cast against and permanently in contact with earth |
Source: ACI 318-19 (Building Code for Structural Concrete), IBC 2021 Section 1807, Rankine earth pressure theory.
Cantilever Retaining Wall Design FAQ
How is the active earth pressure calculated for a retaining wall?
For a cohesionless backfill with a horizontal backfill surface, the active earth pressure is calculated using Rankine’s theory: Pa = 0.5 × Ka × γ × H², where Ka = (1 − sin φ) / (1 + sin φ) is the active pressure coefficient, γ is the unit weight of the retained soil, and H is the height of the retained soil. The resultant force Pa acts at H/3 from the base. For typical granular backfill with φ = 30°, Ka = 0.333, so Pa = 0.5 × 0.333 × γ × H². For backfill with a surcharge load q (psf), add an equivalent height Hs = q/γ to H before calculating the resultant: Pa = 0.5 × Ka × γ × (H + Hs)².
What are the stability checks required for a cantilever retaining wall?
Three stability checks are required for a cantilever retaining wall per IBC Section 1807 and standard structural engineering practice: (1) Overturning — the factor of safety against overturning about the toe must be ≥ 1.5 (unfactored loads), computed as Resisting Moment / Overturning Moment; (2) Sliding — the factor of safety against horizontal translation must be ≥ 1.5, computed as Horizontal Resistance (base friction + passive pressure on key) / Active Force; (3) Bearing capacity — the maximum soil pressure under the footing must not exceed the allowable bearing capacity of the soil. A shear key on the footing base is often added to increase sliding resistance when the factor of safety is marginal.
How is the cantilever wall stem designed per ACI 318?
The stem of a cantilever retaining wall acts as a vertical cantilever beam fixed at the footing. The critical design section is at the base of the stem. The factored moment at the base is Mu = 1.6 × 0.5 × Ka × γ × H³ / 3 (using LRFD load factor of 1.6 for lateral earth pressure per ASCE 7-22). The required area of flexural reinforcement is calculated per ACI 318-19 Section 22.2 using the strength reduction factor φ = 0.90 for bending. Minimum horizontal reinforcement for temperature and shrinkage per ACI 318-19 Section 11.6 is As,min = 0.0020 × b × h for Grade 60 bars, distributed on both faces.
What is the required footing depth for a retaining wall?
The footing of a cantilever retaining wall must extend below the frost line per IBC Section 1809.5 — typically 12 to 48 inches depending on the geographic location, per ASHRAE Handbook climate data and local building codes. Beyond frost, the footing depth is governed by the need for passive resistance against sliding; the foundation should be set deep enough that the passive pressure zone in front of the toe can develop (typically the full exposed height H_p of the front face below grade, up to 3 feet). Deeper footings also reduce net bearing pressure by increasing the soil weight contributing to the resisting moment.
When should I use a retaining wall with a shear key vs. a wider footing?
A shear key is a downward projection from the bottom of the footing that engages undisturbed soil below the footing to provide additional passive resistance against sliding. It is used when the factor of safety against sliding is below 1.5 and widening the footing is not practical due to site constraints. The key is typically located at approximately one-third of the base width from the toe and sized to develop the passive pressure needed to bring FS_slide to 1.5. A wider footing is preferred when space allows — it increases both overturning stability and bearing contact area, often solving both sliding and overturning deficiencies simultaneously without the construction complexity of a key.