Calculator
Choose a unit system, enter hammer and set data, then calculate. The form is optimized for 3 columns on large screens, 2 on smaller, and 1 on mobile.
Example Data Table
A simple driving log example showing depth and blows per 250 mm. Use it to compare field patterns while monitoring set changes.
| Depth (m) | Penetration Interval | Blows | Computed Set (mm/blow) | Blows per 250 mm |
|---|---|---|---|---|
| 6.0 | 250 mm | 60 | 4.167 | 60.00 |
| 8.0 | 250 mm | 85 | 2.941 | 85.00 |
| 10.0 | 250 mm | 120 | 2.083 | 120.00 |
| 12.0 | 250 mm | 165 | 1.515 | 165.00 |
Formulas Used
Set per blow is the average penetration for one hammer blow. If you enter penetration over multiple blows, then: S = Penetration / Blows.
Blow count for an interval is: N = Interval / S, where Interval is 25 mm, 100 mm, 250 mm, 1 m, or 1 ft (converted).
Delivered energy per blow (metric) is: E = η · W · H, where W is ram weight in kN, H is drop height in m, and η is efficiency. Since kN·m = kJ, E is reported in kJ.
ENR-style capacity check (metric adaptation) is: Qu = (η · W · H) / (S + C). Here S is set per blow (m) and C is a small constant (m) representing losses. Allowable capacity is Qa = Qu / FS.
How to Use This Calculator
- Select your unit system and hammer type.
- Enter ram weight, drop height, and efficiency.
- Choose a set method and provide the set inputs.
- Click Calculate to view results above the form.
- Use CSV or PDF to archive the calculation for site records.
- If you have a target capacity, enter it to back-calc set.
- Review checks and confirm values match field measurements.
Blow count and set
Blow count is the number of hammer impacts needed to advance the pile a chosen interval. Field crews often record blows per 250 mm to track resistance with depth. This calculator converts measured set to comparable counts for 25 mm, 100 mm, 250 mm, 1 m, and 1 ft, helping you standardize daily driving logs across shifts and rigs.
Delivered energy per blow
Driving performance depends on delivered energy, not the rated hammer energy. The tool estimates delivered energy using E = η·W·H, where η is efficiency, W is ram weight, and H is drop height. For example, W = 35 kN, H = 1.2 m, and η = 60% gives E = 25.2 kJ per blow (about 18,600 ft·lbf).
Capacity check using an ENR-style method
An ENR-style check links energy and set to an estimated ultimate capacity: Qu = (η·W·H)/(S + C). S is set per blow in meters and C is a small loss constant that reflects compressibility and system losses. With S = 2.5 mm/blow and C = 2.5 mm, the example above yields Qu ≈ 5,040 kN. Using FS = 2.5 gives Qa ≈ 2,016 kN.
Back-calculating required set
If your specification states a target ultimate capacity, the calculator can estimate the set needed to reach it by rearranging the capacity equation. This is useful for planning refusal criteria, setting inspector expectations, and checking whether observed blow counts are consistent with the intended driving criterion.
Practical QA/QC tips
Use consistent measurement intervals, verify stroke or drop height, and document cushions, caps, and leads condition. Very small sets may be within reading error; repeat measurements over multiple blows. Record cushion thickness at each splice daily. Treat the capacity check as screening only and confirm with project geotechnical recommendations and dynamic testing where required.
FAQs
1) How do I measure set accurately on site?
Mark the pile, measure penetration over 10–20 blows, then divide by blows. Use a consistent interval and a fixed reference point. Avoid reading single-blow movement when the set is very small.
2) Why is efficiency important in the energy calculation?
Efficiency accounts for losses in the hammer, cap, cushions, and leads. Using a realistic efficiency helps the delivered energy reflect field performance, which improves comparisons between rigs and supports better capacity screening.
3) What does the constant C represent?
C is a small allowance for compressibility and other losses not captured by set alone. It stabilizes the capacity estimate at low sets. Use the suggested value or your specification’s recommended constant.
4) Can I use this instead of dynamic testing or PDA?
No. The capacity output is an ENR-style screening check. Use it for quick field consistency and reporting. Final acceptance should follow the project geotechnical recommendations, driving criteria, and any required dynamic or static testing.
5) What if my blow count suddenly increases with depth?
First verify drop height, cushion condition, and hammer performance. Check for pile damage, splices, obstructions, or a soil layer change. Record observations and compare with expected stratigraphy and driving criteria.
6) How is blows per 250 mm computed?
The calculator converts set to blows using N = Interval / S. If you enter 250 mm penetration over a number of blows, it computes S first and then reports the equivalent blows for standard intervals.
7) Which units should I choose for reporting?
Use the unit system required by your specification and inspection forms. Metric is common for kN and mm set, while imperial is common for kips and inches. The tool converts internally to keep results consistent.