Retaining & slopes · Gravity & cantilever walls
Prefabricated (segmental block) gravity wall calculator
Dry-stacked concrete blocks set back at each course, as in proprietary segmental block wall systems. Coulomb active pressure with the wall batter acts on the back of the blocks. At every joint between courses the tool checks shear (interface capacity a + N·tanλ from the block manufacturer) and overturning about the front of the course below; at the base it checks sliding on the levelling pad, eccentricity and bearing.
Standard: Coulomb earth pressure with wall batter · NCMA / AS 4678 segmental wall checks: interface shear a + N·tanλ, overturning at every course, base sliding, eccentricity, bearing
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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 |
|---|---|---|
| Number of courses | 5 | |
| Course height | 0.46 | m |
| Block depth (front to back) | 1.03 | m |
| Base course depth | 1.03 | m |
| Setback per course | 0.04 | m |
| Block unit weight (solid) | 23 | kN/m³ |
| Interface shear intercept a | 20 | kN/m |
| Interface friction angle λ | 30 | ° |
| Backfill φ′ | 32 | ° |
| Backfill γ | 19 | kN/m³ |
| Surcharge | 5 | kPa |
| Backslope | 0 | ° |
| Base friction coefficient | 0.55 | |
| Allowable bearing | 200 | kPa |
| Required FS sliding / joints | 1.5 | |
| Required FS overturning | 2 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Wall height | 2.30 | m |
| Batter angle | 5.0 | ° |
| Coulomb Ka (δ = 2φ/3, batter) | 0.241 | |
| Base: thrust / weight | 14.3 / 54.5 | kN/m |
| Base sliding FS | 2.10 | |
| Base overturning FS | 2.71 | |
| Base eccentricity (B/6 = 0.172) | 0.140 | m |
| Bearing pressure | 96 | kPa |
| Weakest joint: shear FS | 4.72 | |
| Weakest joint: overturning FS | 3.84 |
- ✓ Base sliding — 2.10
- ✓ Base overturning — 2.71
- ✓ Joint shear at every course
- ✓ Joint overturning at every course
- ✓ Bearing ≤ allowable — 96 kPa
- ✓ Resultant within the middle third
Method, formulas and assumptions
- Coulomb Ka with wall batter ω = atan(setback/course height), δ = 2φ/3, horizontal component × cos(δ − ω).
- Joint at course k: shear capacity a + W·tanλ (manufacturer's interface test, ASTM D6916) vs thrust above; overturning about the front of the course below with each course set back by the setback.
- Base on a compacted granular levelling pad: sliding μW, eccentricity and Meyerhof bearing pressure. Walls taller than the gravity limit need geogrid reinforcement (MSE tool).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.