Calculator Inputs
Example Data Table
| Scenario | Diameter (mm) | Bench (m) | Pattern | Burden (m) | Spacing (m) | Charge (kg/hole) |
|---|---|---|---|---|---|---|
| Typical quarry face | 115 | 10 | Staggered | ≈ 3.3 | ≈ 4.1 | ≈ 75 |
| Harder rock, tighter design | 102 | 9 | Staggered | ≈ 2.7 | ≈ 3.4 | ≈ 55 |
| Lower bench, square pattern | 76 | 6 | Square | ≈ 1.9 | ≈ 2.4 | ≈ 20 |
Formula Used
- Diameter method: Burden B = kD × D, where D is hole diameter in meters.
- Bench method: Burden B = kH × H, where H is bench height in meters.
- Adjustments: B is modified by rock, fragmentation, energy, and angle factors, then bounded to practical ranges.
- Spacing: S = (S/B) × B.
- Subdrill: J = (J/B) × B.
- Stemming: T = (T/B) × B and capped below the bench height.
- Charge per hole (column): W = A × Lc × ρ, with A = πD²/4, Lc = (H+J) − T, and ρ in kg/m³.
- Powder factor: PF = W / V, where V is rock volume per hole.
How to Use This Calculator
- Enter your hole diameter, bench height, and drilling angle.
- Select rock condition and your fragmentation target.
- Choose explosive type, then confirm density and energy factor.
- Pick a design method, adjust coefficients if your site requires.
- Set spacing ratio and the stemming/subdrill ratios you follow.
- Press Calculate to view results above the form.
- Export CSV or PDF for sharing and record keeping.
Technical Article
Design Variables That Drive Burden
Burden controls how much rock confines the explosive before it breaks free. Hole diameter, bench height, and drilling angle set the geometric starting point. Rock condition and the fragmentation target then refine burden using practical factors, because hard, massive rock usually needs tighter burden for consistent breakage. Higher energy products can tolerate slightly larger burden, but only within safe bounds.
Spacing Strategy and Pattern Effects
Spacing works with burden to distribute energy evenly across the face. A spacing ratio near 1.15 to 1.50 is common, while very wide spacing can leave toe and back-break. Pattern choice matters: staggered layouts generally improve uniformity by reducing straight-line relief gaps, while square patterns simplify drilling. This calculator reflects that difference through the area-per-hole assumption.
Stemming, Subdrill, and Floor Control
Stemming length is the primary control on venting and airblast. Too little stemming wastes energy and increases flyrock risk; too much reduces breakage at the collar. Subdrill supports floor grade and prevents a hard toe when burden and spacing are optimized. Using ratios tied to burden keeps these elements proportional as hole size and bench height change.
Charge Weight, Powder Factor, and Efficiency
Charge weight per hole depends on hole diameter, charge length, and explosive density. Once volume per hole is estimated from burden, spacing, and bench height, powder factor summarizes energy intensity in kg per cubic meter. A low powder factor often signals poor breakage or boulders, while a high value can raise vibration, overbreak, and cost. Use it to compare scenarios, not to replace site trials.
Field Validation and Reporting Workflow
Treat calculator outputs as a first-pass design. Validate with drilling accuracy, burden checks at the face, and feedback from fragmentation, dig rate, and back-break observations. Record the chosen coefficients, ratios, and explosive properties so designs are repeatable. The CSV and PDF exports support shift handovers, compliance documentation, and quick comparison between benches and lithology changes.
FAQs
1) Which design method should I pick?
Use the diameter method when hole size is your main driver and you have historical k values. Use the bench method when bench height and face geometry dominate. Compare both and choose what matches your site data.
2) Why does staggered pattern change the powder factor?
Staggered patterns typically increase effective coverage per hole because rows interlock. That changes the area assigned to each hole, which changes the estimated rock volume per hole. Powder factor shifts because it is charge divided by volume.
3) How do I set stemming and subdrill ratios?
Start with common ranges: stemming about 0.6–0.9 times burden and subdrill about 0.15–0.30 times burden. Adjust using toe condition, flyrock history, and collar breakout observations, then document the final ratios.
4) What does a warning message mean?
Warnings flag values outside typical planning ranges, such as very tight burden for the hole size or unusually high powder factor. They are prompts to review assumptions, not definitive failures. Confirm with local standards and field measurements.
5) Can I use this for vibration compliance?
It can estimate charge per hole and a simple holes-per-delay limit if you enter a maximum charge per delay. For compliance, you still need a vibration model, monitoring, delay timing verification, and a qualified blasting plan.
6) Why do my charge estimates differ from actual loading?
Actual loading varies with decking, primers, water, cuttings, stemming practices, and product bulk density. Hole deviation also changes true charge length. Use the calculator as a consistent baseline, then calibrate with measured loading records.
Technical Article
Design Variables That Drive Burden
Burden controls how much rock confines the explosive before it breaks free. Hole diameter, bench height, and drilling angle set the geometric starting point. Rock condition and the fragmentation target then refine burden using practical factors, because hard, massive rock usually needs tighter burden for consistent breakage. Higher energy products can tolerate slightly larger burden, but only within safe bounds.
Spacing Strategy and Pattern Effects
Spacing works with burden to distribute energy evenly across the face. A spacing ratio near 1.15 to 1.50 is common, while very wide spacing can leave toe and back-break. Pattern choice matters: staggered layouts generally improve uniformity by reducing straight-line relief gaps, while square patterns simplify drilling. This calculator reflects that difference through the area-per-hole assumption.
Stemming, Subdrill, and Floor Control
Stemming length is the primary control on venting and airblast. Too little stemming wastes energy and increases flyrock risk; too much reduces breakage at the collar. Subdrill supports floor grade and prevents a hard toe when burden and spacing are optimized. Using ratios tied to burden keeps these elements proportional as hole size and bench height change.
Charge Weight, Powder Factor, and Efficiency
Charge weight per hole depends on hole diameter, charge length, and explosive density. Once volume per hole is estimated from burden, spacing, and bench height, powder factor summarizes energy intensity in kg per cubic meter. A low powder factor often signals poor breakage or boulders, while a high value can raise vibration, overbreak, and cost. Use it to compare scenarios, not to replace site trials.
Field Validation and Reporting Workflow
Treat calculator outputs as a first-pass design. Validate with drilling accuracy, burden checks at the face, and feedback from fragmentation, dig rate, and back-break observations. Record the chosen coefficients, ratios, and explosive properties so designs are repeatable. The CSV and PDF exports support shift handovers, compliance documentation, and quick comparison between benches and lithology changes. Keep a revision log whenever geology or products change.
FAQs
1) Which design method should I pick?
Use the diameter method when hole size is your main driver and you have historical k values. Use the bench method when bench height and face geometry dominate. Compare both and choose what matches your site data.
2) Why does staggered pattern change the powder factor?
Staggered patterns typically increase effective coverage per hole because rows interlock. That changes the area assigned to each hole, which changes the estimated rock volume per hole. Powder factor shifts because it is charge divided by volume.
3) How do I set stemming and subdrill ratios?
Start with common ranges: stemming about 0.6–0.9 times burden and subdrill about 0.15–0.30 times burden. Adjust using toe condition, flyrock history, and collar breakout observations, then document the final ratios.
4) What does a warning message mean?
Warnings flag values outside typical planning ranges, such as very tight burden for the hole size or unusually high powder factor. They are prompts to review assumptions, not definitive failures. Confirm with local standards and field measurements.
5) Can I use this for vibration compliance?
It can estimate charge per hole and a simple holes-per-delay limit if you enter a maximum charge per delay. For compliance, you still need a vibration model, monitoring, delay timing verification, and a qualified blasting plan.
6) Why do my charge estimates differ from actual loading?
Actual loading varies with decking, primers, water, cuttings, stemming practices, and product bulk density. Hole deviation also changes true charge length. Use the calculator as a consistent baseline, then calibrate with measured loading records.