Bored Pile Concrete and Rebar Calculator
Concrete volume, overbreak factor and reinforcement for bored piles.
Quick answer
With the default inputs: Pile diameter 800 · Pile length 20 · Number of piles 20 pcs etc.Total concrete 231.22 m³
Edit the inputs below to recalculate.Inputs
Result
Total concrete
231.22m³
| Volume per pile (theoretical) | 10.053m³ |
| Concrete per pile | 11.561m³ |
| Overbreak volume | 30.16m³ |
| Cage diameter | 700mm |
| Main bars per pile | 592.3kg |
| Spiral length per pile | 219.9m |
| Stirrups per pile | 86.8kg |
| Steel per pile | 679.2kg |
| Total steel | 13.583t |
| Steel ratio | 58.7kg/m³ |
The overbreak factor is actual concrete placed over design volume, covering over-excavation and side collapse, typically 1.1-1.25. Ordering to theoretical volume always runs short, and stopping mid-pour creates a discontinuity. Reinforcement here excludes stiffening rings, anchorage and laps — add 5-8% for actual cutting.
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Formula
| Theoretical volume | π r² L with r = d ÷ 2 |
| With overbreak | volume × K |
| Main bars | 0.00617 × d² × count × length |
| Spiral length | π(D − 2c) × (length ÷ pitch) |
| Stirrup mass | 0.00617 × d² × spiral length |
| Steel ratio | steel ÷ actual volume |
Φ800, 20 m long, 20 piles, 1.15 overbreak, 12Φ20 main bars and Φ8 spiral at 200 mm: 10.053 m³ per pile theoretical, 11.561 m³ actual, 231.22 m³ in total, 679.2 kg of steel per pile at 58.8 kg/m³.
How to work it out
- Theoretical volume per pile = π/4 × D² × L, with D the diameter and L the design length.
- Multiply by the overbreak factor: bored piles run 1.1-1.3 (1.1 in clay, 1.2 in sand, 1.3 in gravel), never 1.0.
- Add the overpour: 0.5-1.0 m above cut-off is laitance and must be broken off, more on long piles; it is paid for but is not pile length.
- Main steel: total length = bars × (pile length + embedment into the pile cap), times unit weight. Embedment is normally 35d-40d.
- Links: spiral length = π(D − 2c + d) × turns × √(1 + (pitch/(π × diameter))²), plus stiffening rings every 2 m.
Where it goes wrong
- Taking the overbreak factor as 1.0 — bored holes enlarge, so 10-30% more concrete goes in than the theoretical volume; at 1.0 the supply runs out mid-pour and the pile breaks.
- Omitting the overpour — 0.5-1.0 m at the head is laitance and contamination that must be broken out; the concrete is wasted but still paid for.
- Measuring links as circumference × turns — a spiral is longer than the circles by 1-3%, and the tightened zones at head and toe need separate treatment.
- Not embedding the main bars in the cap — the pile-to-cap connection is that anchorage, and short embedment wastes the pile.
Material and cost
Bored piles with drilling, cage and concrete 800-1500 CNY/m³, or 600-1200 CNY/m for a φ800. Underwater C30 concrete 480-580 CNY/m³, 15% above normal because of admixtures and higher cement content.
On site
- Underwater concrete needs 180-220 mm slump; stiffer mixes block the tremie, and poor blockage handling breaks the pile.
- Keep tremie embedment between 2 and 6 m — shallower lets water in, deeper and the pipe cannot be withdrawn.
- Do integrity testing at the code frequency and add cross-hole testing on important work; remediation is very expensive.
Basis
- GB 50202-2018 Code for acceptance of foundation construction, Chapter 5 (piles)
- JGJ 94-2008 Technical code for building pile foundations, Chapter 6
- GB 50666-2011 Code for construction of concrete structures, Chapter 7
FAQ
Why can't the overbreak factor be 1.0?
Because drilling always over-excavates: bit wear, uneven walls and local collapse in sand all make the hole bigger than design, so more concrete goes in than theory allows. Ordering at 1.0 leaves every pile half a cube short, the last one waits for the next truck, and a stopped pour risks a discontinuity. Settlement also measures against the overbreak factor.
What steel ratio is reasonable for a bored pile?
Friction piles usually run 50-80 kg/m³, end-bearing 60-100, and piles taking lateral load or uplift can exceed 120. Below 40 suggests under-reinforcement and needs a crack and bending check; above 150 is usually uneconomic and a precast or steel pile may be the better answer. Steel ratio is a core comparison between pile options.
How does underwater concreting differ?
Underwater work needs the tremie method with a highly workable mix — 180-220 mm slump, aggregate no larger than 40 mm and no more than a quarter of the clear bar spacing, plus a retarder to keep the pour continuous. In a dry hole the slump can drop to 100-140 mm and cement content falls. The wrong mix blocks the pipe, segregates or traps mud in the shaft.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Bored Pile Concrete and Rebar Calculator. 2026-10-25. https://jianzhujisuan.com/en/pile-concrete
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.