Retaining & slopes · Embedded walls & sheeting
Secant pile wall calculator
Embedment and bending from the embedded-wall analysis, overlap and interlock thickness at the toe allowing for verticality, the reinforced-pile moment check and concrete and steel quantities per metre of wall.
Standard: Embedded wall (Rankine) · overlap with verticality · AS 3600 circular section
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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 |
|---|---|---|
| Pile diameter | 750 | mm |
| Centre spacing of adjacent piles | 600 | mm |
| Verticality tolerance 1 in N | 200 | |
| Wall type | Cantilever | |
| Retained height H | 4 | m |
| Prop / anchor depth | 1 | m |
| Soil γ | 19 | kN/m³ |
| φ′ | 32 | ° |
| Surcharge q | 10 | kPa |
| Factor on Kp | 1.5 | |
| Embedment increase factor | 1.2 | |
| Action factor on M | 1.35 | |
| Reinforced piles | Every second pile (secondary) | |
| Bars per reinforced pile | 12 | |
| Bar diameter | 28 | mm |
| Cover to bar centre | 85 | mm |
| f'c | 40 | MPa |
| fsy | 500 | MPa |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Embedment D | 5.88 | m |
| Pile length L | 9.88 | m |
| Mmax (analysis) | 226.4 | kNm/m |
| Design M* per reinforced pile | 366.7 | kNm |
| φMu reinforced pile | 831.1 | kNm |
| Utilisation | 44 | % |
| ku / φ | 0.270 / 0.85 | |
| Overlap at top | 150 | mm |
| Interlock thickness at top | 450 | mm |
| Deviation per pile at toe | 49 | mm |
| Overlap at toe (worst case) | 51 | mm |
| Interlock thickness at toe | 272 | mm |
| Piles per metre | 1.67 | |
| Net concrete | 6.52 | m³/m |
| Reinforcement | 477 | kg/m |
- ✓ φMu ≥ M* (reinforced pile) — 44 %
- ✓ Piles still overlap at the toe — 51 mm
- ✓ Toe overlap ≥ 50 mm (water-tightness)
- ✓ Ductile section ku ≤ 0.36
Method, formulas and assumptions
- Embedment, Mmax and prop force from the embedded-wall analysis (Rankine, Kp/1.5, embedment × 1.2)
- Interlock thickness t = 2√(R² − (s/2)²)
- Worst case: adjacent piles lean apart, s(toe) = s + 2L/N
- M* per reinforced pile = γ × Mmax × spacing of reinforced piles (1.20 m)
- φMu by strain compatibility for a circular section: rectangular stress block α2 f′c over γ·dn, 12 bars on a circle, φ = 1.24 − 13ku/12 (0.65–0.85)
- Unreinforced (primary) piles must arch between the secondary piles; check shear and arching for the soft/firm mix
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.