Retaining & slopes · Gravity & cantilever walls
Cantilever retaining wall: L, inverted-T or counterfort, with reinforcement calculator
Reinforced concrete retaining wall as an L-shape (no toe), inverted-T or counterfort wall. Stability by Rankine active pressure on the vertical plane through the heel: sliding, overturning, eccentricity and bearing. Reinforcement from the AS 3600 rectangular stress block for the stem (cantilever, or spanning horizontally between counterforts), the heel and the toe, plus the counterfort tie.
Standard: AS 4678 earth-retaining structures · AS 3600 · Rankine active pressure · GEO5 Cantilever Wall style
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Wall type | Inverted-T (toe and heel) | |
| Total height, underside of base to top of fill | 4.5 | m |
| Base thickness | 0.4 | m |
| Stem thickness at base | 0.35 | m |
| Stem thickness at top | 0.25 | m |
| Toe length | 0.8 | m |
| Heel length (behind the stem) | 2.3 | m |
| Counterfort spacing (counterfort wall) | 3 | m |
| Counterfort thickness | 0.3 | m |
| Backfill γ | 19 | kN/m³ |
| Backfill φ′ | 32 | ° |
| Surcharge on the fill | 10 | kPa |
| Base friction coefficient tan δb | 0.5 | |
| Allowable bearing pressure | 200 | kPa |
| Concrete f′c | 32 | MPa |
| Reinforcement fsy | 500 | MPa |
| Cover | 50 | mm |
| Bar diameter | 16 | mm |
| Required FS sliding | 1.5 | |
| Required FS overturning | 2 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Ka (Rankine) | 0.307 | |
| Active thrust Pa | 72.9 | kN/m |
| Vertical load ΣV (excl. surcharge) | 241.8 | kN/m |
| FS sliding | 1.66 | |
| FS overturning | 4.16 | |
| Eccentricity e (B/6 = 0.58) | 0.094 | m |
| Bearing qmax / qmin | 89 / 64 | kPa |
| Stem base M* | 139.3 | kNm/m |
| Stem steel (vertical, back face) | 1,168 mm²/m → N16 @ 150 | |
| Heel M* (top steel) | 98.9 | kNm/m |
| Heel steel | 762 mm²/m → N16 @ 250 | |
| Toe M* (bottom steel) | 36.9 | kNm/m |
| Toe steel | 762 mm²/m → N16 @ 250 |
- ✓ Sliding FS ≥ 1.5 — 1.66
- ✓ Overturning FS ≥ 2 — 4.16
- ✓ Resultant in the middle third — 0.094 m
- ✓ Bearing ≤ allowable — 89 kPa
- ✓ Stem section adequate (no compression failure)
Method, formulas and assumptions
- Rankine Ka on the vertical plane through the heel; Pa = ½Kaγ H² + Ka q H. Surcharge excluded from resisting forces for sliding and overturning, included for bearing.
- Structural actions with load factor 1.5 on earth pressure; As from the AS 3600 rectangular stress block (φ = 0.85, α2 = 0.85 − 0.0015f′c), not less than 0.24(D/d)² f′ct,f/fsy·bd.
- Counterfort wall: the stem spans horizontally between counterforts, M* = p*·S²/10 at the base; each counterfort is a cantilever T-beam taking S × the cantilever moment, tie steel along the sloping back (lever arm ≈ 0.9 × (heel + stem)).
- Heel moment: soil + surcharge + base weight less the average bearing under the heel; toe: bearing less base weight.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.