🎓 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 in mining and construction.
🎯 Learning Objectives
- ✓ Calculate optimal burden and spacing for a given bench height and rock type using empirical relationships
- ✓ Analyze blast design parameters (powder factor, stemming length, delay timing) to predict fragmentation and ground vibration outcomes
- ✓ Design a basic perimeter blast pattern for a limestone quarry using industry-standard spacing ratios and delay sequencing
- ✓ Explain how explosive energy distribution (e.g., relative weight strength, VOD) influences cratering and backbreak in open-pit applications
- ✓ Apply USBM and DIN 4150-3 criteria to evaluate whether predicted peak particle velocity complies with site-specific vibration limits
📖 Why This Matters
In open-pit mining, over 90% of ore and waste movement begins with blasting—and poor equipment or material choices cause flyrock, excessive vibrations, oversized boulders, or unplanned wall damage. Understanding how drills, explosives, and initiators interact with geology isn’t just theoretical—it directly impacts production cost, safety record, regulatory approvals, and downstream crushing efficiency. A single misapplied powder factor can increase haulage costs by 12% due to secondary breaking.
📘 Core Principles
Blast design rests on three interdependent pillars: (1) Energy delivery—governed by explosive type (ANFO, emulsion, dynamite), density, detonation velocity (VOD), and confinement; (2) Geometry control—burden (distance from hole to free face), spacing, stemming, and subdrilling determine fracture propagation direction and confinement; (3) Timing precision—millisecond delays enable stress wave interaction and improved fragmentation. Rock mass rating (RMR), joint spacing, and elastic modulus dictate how energy couples into the formation; low RMR rock requires reduced burden and tighter spacing to avoid excessive throw and cratering.
📐 Burden Calculation (Langefors–Kihlström Empirical Method)
This widely adopted empirical formula estimates initial burden based on rock strength and explosive energy. It balances confinement and throw, forming the foundation for all subsequent pattern design.
Langefors Burden Formula
B = K × (ρₑ / ρᵣ)^0.5 × (VODₑ / 3000)^0.25Empirical estimation of burden (B) in meters based on rock factor (K), explosive and rock densities, and explosive detonation velocity.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| B | Burden | m | Shortest distance from blasthole to free face |
| K | Rock Factor | dimensionless | Function of UCS and rock type; K ≈ 1.25 × √UCS (MPa) |
| ρₑ | Explosive Density | g/cm³ | Loaded density of explosive column |
| ρᵣ | Rock Density | g/cm³ | In-situ bulk density of rock |
| VODₑ | Explosive Detonation Velocity | m/s | Measured detonation speed of the explosive |
Typical Ranges:
Hard rock (granite, quartzite): 6.0 – 9.0 m
Medium rock (limestone, sandstone): 5.0 – 7.5 m
Soft rock (shale, claystone): 3.0 – 5.0 m
💡 Worked Example
Problem: Given: unconfined compressive strength (UCS) = 120 MPa, specific gravity of rock = 2.65, ANFO density = 0.85 g/cm³, ANFO VOD = 4000 m/s, desired fragmentation index = 0.85.
1.
Step 1: Calculate rock factor K = 1.25 × UCS^0.5 = 1.25 × √120 ≈ 13.7
2.
Step 2: Compute burden B = K × (ρₑ / ρᵣ)^0.5 × (VODₑ / 3000)^0.25 = 13.7 × (0.85/2.65)^0.5 × (4000/3000)^0.25 ≈ 13.7 × 0.566 × 1.072 ≈ 8.3 m
3.
Step 3: Apply practical constraint: for 12-m bench, maximum burden should not exceed 0.7 × bench height = 8.4 m → result (8.3 m) is acceptable and within safe range.
Answer:
The calculated burden is 8.3 m, which falls within the safe range of 7.0–8.4 m for a 12-m bench in competent limestone.
🏗️ Real-World Application
At the Boliden Aitik copper mine (Sweden), engineers replaced traditional 25-ms non-electric delays with programmable electronic detonators (i-kon™) and switched from straight ANFO to water-resistant emulsion in wet benches. This reduced oversize (>75 cm) from 18% to 4.2%, cut secondary breaking costs by €1.3M/year, and lowered PPV at the nearest village (1.2 km away) from 12.7 mm/s to 5.1 mm/s—meeting the Swedish Environmental Protection Agency’s limit of 5 mm/s for residential areas (Naturvårdsverket, 2021).
✏️ Design Exercise
You are tasked with designing a production blast for a granite quarry (UCS = 220 MPa, RQD = 75%, joint spacing = 0.45 m). Bench height = 15 m. Use ANFO (ρₑ = 0.8 g/cm³, VOD = 4000 m/s). Calculate: (a) Langefors burden, (b) recommended spacing (using S/B = 1.15), (c) powder factor if hole diameter = 127 mm and subdrill = 1.2 m, and (d) verify stemming length per DIN 62115.