Calculator Inputs
Formula Used
- Cylinder shaft: V = π · (D²/4) · H
- Tapered shaft (frustum): V = (π · H / 12) · (D₁² + D₁·D₂ + D₂²)
- Bell base (modeled as frustum): same frustum formula using D₂ = bell diameter.
- Allowances: V_adj = V_raw · (1+Overbreak%) · (1+Waste%)
This tool reports adjusted volumes in m³ and yd³ to support ordering and logistics.
How to Use This Calculator
- Select a unit system that matches your drawings.
- Choose the caisson shape: straight, tapered, or belled.
- Enter height and diameters; add bell details if needed.
- Set overbreak and waste based on site conditions.
- Optional: enter cost rate and truck capacity for planning.
- Press Calculate to view results above the form.
- Use CSV or PDF downloads to share with your team.
Example Data Table
| Case | Unit | Shape | Height | Top Ø | Bottom Ø | Bell (h, Ø) | Overbreak | Waste | Adjusted Volume (per) |
|---|---|---|---|---|---|---|---|---|---|
| Sample A | Metric | Straight | 12.00 m | 1.20 m | 1.20 m | — | 2% | 3% | ≈ 14.96 m³ |
| Sample B | Metric | Tapered | 10.00 m | 1.10 m | 1.40 m | — | 3% | 4% | ≈ 14.10 m³ |
| Sample C | Imperial | Bell | 30.00 ft | 4.00 ft | 4.00 ft | 4.00 ft, 6.50 ft | 2% | 3% | ≈ 23.06 yd³ |
Example outputs are approximate and depend on allowances and chosen geometry.
Technical Article
1) Why volume accuracy matters
Concrete caissons are high‑volume foundation elements, so small geometric errors scale into costly over‑ordering or placement delays. A 1.20 m diameter, 12 m deep straight shaft holds about 13.57 m³ before allowances. Adding 2% overbreak and 3% waste increases order volume to roughly 14.96 m³, which often equals an extra partial truck.
2) Geometry options used here
This calculator supports three common field cases: straight shafts, tapered shafts, and belled bases. Straight shafts use the cylinder formula. Tapered shafts use a frustum model with top and bottom diameters. Belled caissons are modeled as a base frustum transitioning from shaft diameter to bell diameter over the bell height.
3) Allowances and field realities
Overbreak accounts for excavation beyond design lines from soil raveling, drilling tolerances, or casing removal. Waste covers tremie start‑up, spillage, and cleanout. Typical combined allowances range from 3% to 10% depending on groundwater control and crew experience. Apply higher values for irregular bell excavation or unstable sands.
4) Weight, logistics, and cost
Concrete density is commonly about 2400 kg/m³ (or 150 lb/ft³). With density, the tool estimates total weight to support crane planning and placement sequencing. It also converts adjusted volume to yd³ for suppliers and estimates truck loads using your entered capacity, such as 8 m³ or 10 yd³ per truck.
5) Using outputs on site
Use “per caisson” values for pour cards and “total” values for procurement. Compare results across shape options to see how taper or bell geometry changes demand. Export CSV for takeoff logs and PDF for approvals. Always reconcile with project specs, reinforcement cage volume, and any required concrete overfill above cutoff. For quality control, record actual tremie volumes, compare against planned totals, and adjust allowance settings for the next shafts to reduce variance steadily today.
FAQs
1) Which diameters should I enter?
Use design diameters from your drawings. For straight shafts, enter the same value for top and bottom. For tapered shafts, enter the diameter at the top and the diameter at the bottom of the shaft.
2) When should I choose the tapered option?
Select tapered when the drilled hole or casing is intentionally stepped or sloped between two diameters. The frustum model estimates the average cross‑section more accurately than using a single diameter.
3) How is a belled caisson represented?
The bell is modeled as a frustum transitioning from the shaft bottom diameter to the bell bottom diameter over the bell height. This provides a practical approximation for under‑reamed bases when exact profiles are unavailable.
4) What overbreak and waste values are typical?
Many projects start with 2–5% overbreak and 2–5% waste, then adjust using field measurements. Increase allowances for unstable soils, groundwater, irregular bell excavation, long tremie starts, or strict cleanup requirements.
5) Why do I see m³ and yd³ together?
Drawings may be metric while ready‑mix orders are often placed in cubic yards. Showing both units reduces conversion errors and helps confirm quantities with suppliers, batching tickets, and site pour logs.
6) Does the volume include reinforcement displacement?
No. Rebar and cage displacement is typically small versus caisson volume and is usually ignored for ordering. If required by your specification, apply a minor reduction or consult your engineer.
7) How is the truck load count calculated?
The tool divides total adjusted volume by your entered truck capacity and rounds up to the next whole load. Use conservative capacity when access is tight, slump is low, or partial loads are common on the project.
Engineering note: Always align inputs with project specifications and local placement methods.