Retaining & slopes · Gravity & cantilever walls
Prefabricated (segmental block) gravity wall calculator
Dry-stacked concrete blocks set back at each course, as in GEO5 Prefab Wall and the Redi-Rock module. 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.