Estimating Retaining Wall Concrete, Rebar, and Backfill
A cantilever retaining wall is a repeating cross-section. Estimate one metre of wall completely, then multiply along the length with adjustments for height changes.
Concrete per metre of wall
Base = base thickness × base width (heel + toe + stem)
Key (if any) = key depth × key width
Total m³/m = stem + base + key
Stems often taper — use the average thickness. Break the wall into height bands and estimate each band’s cross-section.
Reinforcement
- Stem: vertical bars on the earth face (main), horizontal distribution bars, and lighter bars on the exposed face.
- Base: top bars over the heel, bottom bars under the toe, plus distribution both ways.
- Dowels from base into stem, lapped 40d.
Convert to kg/m of wall by bar diameter, then multiply by length and add splice and wastage allowances.
Formwork
Stem: both faces × height. Base: edge forms only if cast in open excavation. Key: two faces × depth.
Backfill and drainage
| Item | Basis |
|---|---|
| Granular backfill behind stem | wedge area behind wall × length |
| Subsoil drain (perforated pipe + gravel) | per metre along the heel |
| Weep holes | 1 per 1.5–3 m of wall |
| Geotextile filter / drainage composite | back-of-wall area |
| Excavation & disposal | to founding level + working space, minus backfill |
EngEst Pro’s Structural and Civil calculators handle the retaining wall together — stem and base concrete, two-face rebar, formwork, granular backfill, subsoil drainage, and excavation — as one BOQ section priced per metre of wall.
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