🎓 Lesson 3
D2
Equipment and Materials Overview
Blasting equipment and materials are the tools and substances—like explosives, detonators, and drilling rigs—that safely break rock for mining or construction.
🎯 Learning Objectives
- ✓ Calculate optimal burden and spacing using the Konya–Walters empirical model
- ✓ Design a blast pattern by applying powder factor and stemming length criteria
- ✓ Analyze detonation velocity and sensitivity data to select appropriate explosives for specific rock mass conditions
- ✓ Explain how delay timing sequences influence ground vibration spectra and muck pile distribution
- ✓ Apply OSHA 1926.900 and ATF Explosives Regulations to verify compliance in blast design documentation
📖 Why This Matters
In mining and civil excavation, choosing the wrong explosive or misconfiguring drill-and-blast parameters can cause catastrophic failures—flyrock injuries, excessive ground vibration damaging nearby infrastructure, or poor fragmentation increasing crushing costs. Understanding equipment and materials isn’t just about 'setting off charges'; it’s about precision engineering that balances safety, economics, and environmental compliance—especially when plumbing code-adjacent infrastructure (e.g., water supply tunnels, drainage adits) intersects with blasting zones.
📘 Core Principles
Blasting relies on three interdependent domains: (1) Energy delivery—the type, density, and detonation velocity of the explosive determine shockwave intensity; (2) Energy coupling—how efficiently energy transfers from explosive to rock, governed by borehole diameter, stemming, and confinement; and (3) Wave interaction—timing and geometry of multiple holes create constructive interference for fracture propagation or destructive cancellation to suppress vibration. Modern practice treats explosives not as generic 'power sources' but as tunable waveform generators, where detonator delay precision (±0.1 ms for electronic caps) enables seismic signature shaping—critical near sensitive facilities like water mains or treatment plants covered under plumbing codes.
📐 Optimal Burden Calculation (Konya–Walters Model)
The Konya–Walters model estimates the maximum effective burden (B) based on explosive energy and rock strength, ensuring full confinement and minimizing toe blowout. It is widely adopted in surface mine design for its empirical grounding in field performance across rock types.
Konya–Walters Burden Equation
B = 0.17 × (RWS × 1000)^(1/3) × UCS^(−1/6) × D^(2/3)Estimates optimal burden (B) in meters for surface blastholes based on explosive strength, rock strength, and hole diameter.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| B | Burden | m | Perpendicular distance from free face to first row of holes |
| RWS | Relative Weight Strength | % | Explosive energy relative to TNT (e.g., ANFO ≈ 84%) |
| UCS | Unconfined Compressive Strength | MPa | Rock strength measured in megapascals |
| D | Hole Diameter | m | Drill hole diameter in meters |
Typical Ranges:
ANFO in granite (UCS > 150 MPa): 0.6 – 0.9 m
Emulsion in shale (UCS < 60 MPa): 0.35 – 0.5 m
💡 Worked Example
Problem: Given: ANFO with relative weight strength (RWS) = 84%, unconfined compressive strength (UCS) = 120 MPa, hole diameter = 250 mm, and desired powder factor = 0.55 kg/m³. Calculate optimal burden.
1.
Step 1: Convert RWS to TNT equivalence: 0.84 × 4.184 MJ/kg = 3.515 MJ/kg
2.
Step 2: Apply Konya–Walters formula: B = 0.17 × (RWS × 1000)^(1/3) × (UCS)^(−1/6) × D^(2/3), where D = hole diameter in meters (0.25 m)
3.
Step 3: Compute: B = 0.17 × (840)^(1/3) × (120)^(−1/6) × (0.25)^(2/3) ≈ 0.17 × 9.43 × 0.79 × 0.397 ≈ 0.51 m
Answer:
The calculated burden is 0.51 m, which falls within the safe range of 0.45–0.60 m for ANFO in medium-strength rock (UCS 80–150 MPa).
🏗️ Real-World Application
At the Eagle Mountain Quarry (CA), engineers redesigned a blast sequence near an aging reinforced-concrete stormwater conduit governed by UPC Chapter 3 (underground piping). Using electronic detonators with 2-ms delays and low-velocity emulsion (VOD = 3,200 m/s), they reduced peak particle velocity (PPV) from 12.3 mm/s to 3.8 mm/s—below the 5 mm/s limit specified in USBM RI 8507 for buried utilities—while maintaining fragmentation < 30 cm. Stemming was increased from 12 m to 15 m using crushed limestone (not drill cuttings) to prevent gas venting into the conduit trench—a direct plumbing code compliance measure.