Calculator Inputs
Example Data Table
| Scenario | Advance (m) | Net time (h) | Delays (h) | RPM | Net rate (m/h) | Gross rate (m/h) | mm/rev |
|---|---|---|---|---|---|---|---|
| Shift A (steady ground) | 14.0 | 3.5 | 0.8 | 4.0 | 4.000 | 3.256 | 1.6667 |
| Shift B (more stops) | 10.5 | 3.0 | 1.5 | 3.8 | 3.500 | 2.333 | 1.5351 |
| Shift C (no RPM recorded) | 12.0 | 4.0 | 0.5 | — | 3.000 | 2.667 | — |
Formula Used
- PRnet = L / Tnet, where L is advance length (m) and Tnet is cutting time (h).
- PRgross = L / (Tnet + Tdelay), where Tdelay includes downtime and stoppages (h).
- Advance/day = 24 × PR, for continuous operation comparison.
- If RPM is entered: total revolutions N = RPM × 60 × Tnet, and mm/rev = (L × 1000) / N.
How to Use This Calculator
- Enter the measured advance length for the period (meters).
- Enter net boring time that the cutterhead was actively excavating.
- Add delays to estimate realistic production including stops and interventions.
- Optionally enter RPM to estimate penetration per revolution (mm/rev).
- Press Calculate to show results above the form.
- Use Download CSV for spreadsheets and Download PDF for sharing.
Practical Guide to TBM Penetration Rate
Penetration rate is a core production metric for tunnel boring machines because it converts raw shift activity into a comparable performance value. When measured consistently, it helps engineers separate cutting capability from operational interruptions. This calculator reports a net penetration rate, based only on active boring time, and a gross penetration rate, which includes delays such as segment build, inspections, tool checks, mucking constraints, or unplanned stoppages. Using both values supports realistic scheduling while still tracking how the ground and cutterhead are behaving.
Net rate is best for technical comparisons: geology changes, cutter wear, thrust and torque settings, conditioning quality, and face stability. Gross rate is best for program management: crew efficiency, logistics, downtime trends, and the impact of maintenance windows. If gross rate collapses while net rate stays stable, the issue is rarely the ground; it is usually workflow, availability, or planned activities. If both rates fall together, investigate face conditions, tool condition, operating parameters, or blockages.
Worked example: assume the TBM advances 14.0 m during 3.5 h of active cutting. The net penetration rate is 14.0 / 3.5 = 4.000 m/h. If the same period includes 0.8 h of delays, gross time becomes 4.3 h, giving 14.0 / 4.3 = 3.256 m/h. Multiplying by 24 provides an equivalent daily advance for comparison across different shift patterns.
The example table above shows three typical cases. “Shift A” represents steady cutting with modest downtime, producing strong gross performance. “Shift B” demonstrates how additional stops can reduce gross rate even when net cutting remains acceptable. “Shift C” shows that RPM is optional; when it is recorded, the calculator also estimates penetration per revolution in mm/rev, which is useful when comparing cutterhead speed strategies under similar ground conditions.
For reporting, consider calculating rates over a consistent window such as a full shift, a ring, or a fixed chainage interval. Use rolling averages to smooth short interruptions and highlight true trends. Remember that penetration rate alone does not describe overall utilization or cost. Pair it with availability, tool change frequency, intervention time, and key consumables. Together, these measures provide a clearer basis for benchmarking, forecasting, and improving performance.
For best results, define time categories at the project level and train crews to log them the same way every shift. Record advance length from surveyed chainage, keep boring time limited to active excavation, and capture delays with simple, repeatable codes. Consistent data improves trend analysis, supports maintenance planning, and strengthens production forecasts.
FAQs
1) What is the difference between penetration rate and advance rate?
Penetration rate is distance bored per unit time for a chosen time definition. Advance rate is often used broadly for overall progress. This tool reports net and gross penetration rates to separate cutting performance from delays.
2) What should be included in net boring time?
Include only periods when the cutterhead is actively excavating and the machine is producing forward movement. Exclude ring building, planned inspections, belt or slurry interruptions, and any stoppage where excavation is not occurring.
3) Where do segment erection and grouting belong?
Treat segment erection, gasket checks, grouting, and related activities as delays when computing gross rate. Keeping them separate from net cutting time makes comparisons between ground types and tooling changes more meaningful.
4) Why is RPM optional, and what does mm/rev tell me?
RPM is not always recorded reliably. When provided, the calculator estimates millimeters advanced per cutterhead revolution. This can help compare operating strategies, especially when torque limits or conditioning affect optimal cutterhead speed.
5) Can I use this for EPB and slurry machines?
Yes. The formulas depend on advance and time, not the mucking system. Just keep time definitions consistent, and classify interruptions like conditioning, chamber interventions, slurry treatment limits, or conveyor issues as delays.
6) How should I compare two headings or drives?
Compare net rates to understand ground and cutter performance, then compare gross rates to understand operational efficiency. Use the same measurement window, logging rules, and chainage method. Avoid mixing partial shifts with full shifts.
7) What if my gross penetration rate is much lower than net?
Large gaps indicate significant downtime. Review the top delay categories, check availability of segments and logistics, and assess maintenance planning. Improving workflow may raise gross output without changing cutting parameters or tooling.