# Bored Pile Calculator Concrete, overbreak and rebar cage weight for bored piles in one go. - Page: https://jianzhujisuan.com/en/bored-pile - Category: Construction (https://jianzhujisuan.com/en/c/construction) - Chinese version: https://jianzhujisuan.com/zh/bored-pile.md - Data checked: 2026-10-25 ## Quick result With the default inputs (Pile diameter 800 mm, Pile length 30 m, Number of piles 10 pcs, Overbreak allowance 10%, Main bar diameter 20 mm, Bars per pile 12 pcs): **Total concrete 165.9 m³** ## Inputs | Parameter | Type | Default | Unit | Note | |---|---|---|---|---| | Pile diameter | number | 800 | mm | | | Pile length | number | 30 | m | | | Number of piles | number | 10 | pcs | | | Overbreak allowance | number | 10 | % | Laitance to trim, usually 5-15% | | Main bar diameter | number | 20 | mm | | | Bars per pile | number | 12 | pcs | | ## Formula - **Section area**: A = πD²/4 - **Concrete per pile**: V₁ = A·L·(1+overbreak%) - **Total concrete**: V = V₁·n - **Main bar unit weight**: m = d²×0.00617 (kg/m) - **Cage weight**: W = m·L·bars·piles / 1000 (t) ## Worked example 800 mm × 30 m, 10 piles, 10% overbreak: 16.6 m³ per pile, 166 m³ total; Φ20 × 12 bars at 2.468 kg/m gives about 8.9 t of cage, ~54 kg/m³. ### Quantities per metre by diameter (from this page's formulas, 10% overbreak, 12 × 20 mm bars) | Diameter (mm) | Section area (m²) | Concrete (m³/m) | Cage (kg/m) | 30 m pile (m³) | |---|---|---|---|---| | 600 | 0.283 | 0.311 | 29.6 | 9.33 | | 800 | 0.503 | 0.553 | 29.6 | 16.59 | | 1000 | 0.785 | 0.864 | 29.6 | 25.92 | | 1200 | 1.131 | 1.244 | 29.6 | 37.32 | | 1500 | 1.767 | 1.944 | 29.6 | 58.32 | | 2000 | 3.142 | 3.456 | 29.6 | 103.67 | ### Choosing the drilling method (typical conditions, not code limits) | Method | Ground it suits | Below water table | Support | Typical diameter (mm) | Main cost | |---|---|---|---|---|---| | Rotary auger (spin rig) | Cohesive soils, silt, sand, gravel at moderate N | Yes, with slurry or casing | Slurry / full casing | 600-2000 | Large spoil volume, needs a hard standing | | Rotary drilling (direct / reverse circulation) | Clay, silt, fine to medium sand | Yes | Slurry | 600-1600 | Slow; reverse circulation cleans the base better | | Percussion / chisel | Cobbles, boulders, weathered rock | Yes | Slurry | 600-1500 | Good rock penetration but slow | | Continuous flight auger (dry) | Cohesive soils and silt above the water table | Not suitable (fails below water) | None | 400-800 | No slurry and fast, but fails the moment water appears | | Full casing (oscillator / rotator) | Unstable ground, collapse-prone holes, next to existing buildings | Yes (dry inside the casing) | Steel casing | 800-1500 | Expensive and heavy, but no slurry and no vibration | ## Questions ### What overbreak allowance should I use? The laitance at the pile top is trimmed, usually 0.5-1.0 m, i.e. a factor of 1.05-1.15. Longer piles and longer hole-open times mean more settlement and a higher allowance. Tremie concrete has its own overbreak on top. Default is 10%; allow 15% for poor ground or deep piles. ### Why does the cage weight only count main bars? Main bars make up over 85% of the cage and dominate material and pricing. Stirrups, stiffening rings and spacers are small-diameter, distributed items - add 8-12% of the main bars. If the reinforcement ratio falls outside 60-120 kg/m³, recheck bar count and diameter. ### Why overpour bored piles, and by how much? The hole is held open with slurry and the concrete is poured from the bottom up, so the top of the column mixes with slurry and laitance and has to be broken off. Practice is to overpour 0.5-1.0 m, or to apply a 1.05-1.15 factor to the concrete volume. That overpour is sunk cost and must be in the quote, otherwise it comes out of your margin at settlement. The actual height is set by the trial pile and the local code - this tool only leaves you the factor to fill in. ### What reinforcement ratio is normal for a bored pile? Typically 60-120 kg/m³ of pile volume. Small friction piles sit at the low end; large diameters and piles taking lateral load or seismic detailing sit high. If your figure is well under 60, check the bar count and diameter first; well over 120, check whether you have counted stiffening rings and sonic logging tubes. This tool counts main bars only - stirrups, rings and spacers add roughly 8-12%. ### Can this tool work out the pile capacity? No, and it should not be used for that. It totals materials only: concrete volume and cage weight. Capacity depends on the ground investigation parameters, the bearing stratum, shaft friction, the construction method and the trial pile results; the designer must calculate it to JGJ 94 or the local code and prove it with a static load test. Treating a take-off as a capacity figure is how structural failures happen. ### How do I reconcile concrete against the client after trimming the pile top? Keep two figures. The design volume (drawing length times section area) is what you bill. The poured volume, including overpour and overbreak, is what you reconcile against the ready-mix supplier and what the concrete actually costs. The gap is the overpour loss, usually 5-15%. Never bill the poured volume and never cost the design volume - the two are different measurements and mixing them loses money on one side or the other. ## Related tools - [Plaster and Render Calculator](https://jianzhujisuan.com/en/plaster-coat): Mortar, cement and sand by layer for internal plastering. - [Mortar Mix Design Calculator](https://jianzhujisuan.com/en/mortar-strength): Trial strength, cement, water and sand, and the mix by mass. - [Labour Days and Crew Calculator](https://jianzhujisuan.com/en/labor-productivity): Man-days, crew size and labour cost from output rates. - [Line-of-Balance Duration Calculator](https://jianzhujisuan.com/en/schedule-flow): Rhythmic flow duration with overlap and break adjustments. - [Material Storage Area Calculator](https://jianzhujisuan.com/en/material-storage): Net footprint, total area and a suggested bay size. - [Dewatering Calculator](https://jianzhujisuan.com/en/dewatering): Pit inflow by the equivalent-well method, then well count. --- Generated by BuildCalc. All calculations run in your browser; no data is uploaded. Formulas follow national standards and common trade practice; local codes govern.