P&Q University Lesson 4 - Drilling & Blasting

In quarry operations, the first step of production—drilling and blasting—significantly affects the efficiency and cost of various downstream processes such as loading, hauling, crushing, and screening. This phase also impacts the balance between high-value products and low-value byproducts. When executed accurately, drilling and blasting offer a substantial opportunity to enhance productivity and minimize costs.

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Drilling

Modern mechanized drilling, which began with the industrial age, revolutionized production costs and scales, making numerous industries economically sustainable. Drills combined with explosives enabled this transformation. Yet, this essential technology is often considered a commodity, especially as most drilling and blasting are now done by contractors.

Subsequent to the 2007 financial crisis, cost-cutting became a priority, affecting contracted services such as drilling and blasting. However, the “new normal” necessitates a reevaluation of these processes, recognizing their importance in optimizing quarry operations. This new approach requires precise placement, quantity, and timing of explosive energy, starting with the drilling phase.

Technological advancements have made drilling safer and more productive, reducing overall costs. The goal now is to master and control the process, converting blasting into a primary stage of crushing, and measuring costs in the context of the entire production cycle.

At a technical level, a blasthole must be properly placed and sized to be effective. The drilling phase, usually the costliest in the blasting cycle, has long-term impacts on the entire production cycle, affecting excavating, hauling, crushing, and screening. Thus, selecting the right drilling equipment is paramount for surface operations.

Choosing Hole Diameter

The first step is to determine the appropriate hole diameter for the project, considering future changes as the operation matures. Factors influencing drill capability include:

• Required production
• Terrain
• Material characteristics
• Type and size of excavating and hauling equipment
• Proximity to vibration-sensitive areas
• Bench or lift height
• Type and size of explosives

Production Requirements

Production requirements dictate the selection of drilling equipment. For example, choosing a medium-sized rotary drill rig for 1 million tons of annual production can be excessive if it’s capable of 3 to 5 million tons. Conversely, for greater annual production, a more efficient solution than crawler-mounted drifters may be necessary.

Terrain Considerations

Larger hole diameters require larger drilling platforms, which are less adaptable to adverse terrains. In pioneering phases, a study on the gradability and traversability of drill units is essential. Operations may start with smaller drills until the site development supports larger equipment.

Material Characteristics

Rock hardness and structure impact drill selection. Hard rock may necessitate smaller, closely spaced holes for effective fragmentation. Jointed or friable structures might permit larger, farther apart holes. Unique structural features, such as blocky cap rocks, require careful evaluation to balance cost savings against the need for secondary breakage measures.

Excavation and Hauling Equipment

Blasthole size should be cautiously determined based on the size of the excavation and hauling equipment. Larger equipment promotes economic production but doesn’t always justify larger blastholes. Smaller equipment may require a careful balance between hole size and fragmentation needs.

Vibration-Sensitive Areas

Drilling near vibration-sensitive areas restricts the explosive weight per hole, necessitating careful selection of drill sizes and vibration control measures.

Bench Height

Bench height influences drilling and explosive loading. The bench height dictates the ratio of explosives to pay volume and requires consideration of hole depth, subdrilling needs, and explosive column height for optimal results.

Type and Size of Explosives

The choice of explosive, including its type, size, and loading method, should align with the hole diameter and application. Bulk loading systems and types of explosives such as emulsions and ANFO can impact efficiency and cost.

Drilling Methods

Understanding the appropriate drilling method is essential. Two broad categories are percussion and rotary, with subcategories such as top hammer, down-the-hole drills (DHDs), and rotary blade or roller-cone bits.

Percussion Drilling

Percussion drilling, akin to the ancient hand steel and hammer method, utilizes mechanized equipment for imparting blows to the drill bit. Options include compressed air or hydraulic fluid actuated systems.

Down-the-Hole Drills

DHDs place the piston inside the hole, directly transferring blow energy to the bit. Compressed air operates DHDs, providing efficient energy transfer and reducing noise levels.

Rotary Drilling

Rotary drills cause rock to fail through down pressure and rotation speeds. Suitable for larger hole diameters, rotary drilling requires significant pull-down systems and rotation power.

Rotary Bit Considerations

Rotary bit design weight is crucial for determining appropriate pulling forces, impacting bit performance and productivity.

Drill Rigs and Mountings

Choosing the right drill rig involves evaluating mobility, simplicity, reliability, productivity, and safety. Options include truck-mounted and track-mounted configurations, each with unique advantages and limitations.

Maximizing Productivity

Effective drill rig selection considers bottom-hole time, mechanical downtime, and non-drilling time during the cycle.

Overall Cost Efficiency

A holistic view of drilling and blasting evaluates effects on fragmentation, shot control, and downstream processes, aiming for optimal economic outcomes.

Conclusion

Evaluating and selecting the appropriate blasthole drill impacts total project costs and productivity. Attentive selection supports sustainable success, highlighting the importance of comprehensive understanding and integration of technology and process.

Blasting

Blasting is strictly regulated by various agencies. It initiates the rock-fragmentation process, affecting all subsequent operations. An optimized blast is crucial for profitability, emphasizing the importance of a well-coordinated drilling and blasting strategy. Effective communication and safety measures are essential to minimize community impact.

Additional reading:
What is Water Well Drill Rod and Why Do We Use Them?

Fragmentation

Fragmentation is vital in various quarrying activities, from loading to crushing. Advances in predictive techniques and technology offer better fragmentation control, improving operation efficiency.

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Additional reading:
What is Water Well Drill Rod and Why Do We Use Them?

Explosives

Recent advancements introduced new explosive formulations such as emulsions and ANFO blends. Emulsions, either bulk-loaded or packaged, provide high detonation velocities and energy efficiency. ANFO, a mix of ammonium nitrate and fuel oil, remains widely used but performs poorly in wet conditions unless properly contained.

Heavy ANFO increases ANFO’s energy output by adding emulsion, enhancing water resistance. Proper loading techniques ensure optimal performance and safety.

Dynamite

Though largely replaced by emulsions and slurries, dynamites are still used in specific applications like small-diameter construction blasting and priming ANFO.

Detonators and Initiating Systems

Detonators, primarily electronic, electric, or non-electric delay types, are crucial for effective blasting. Accurate initiation timing minimizes scatter, ensuring proper blast sequencing and reducing vibrations.

Electronic Blasting Systems

Electronic blasting systems offer high accuracy and safety, replacing traditional pyrotechnic delays with programmable, timer-based alternatives, enhancing explosion control and minimizing environmental impact.

Summary

Delay detonators improve fragmentation, blast flexibility, vibration control, and overall blast performance. Reference materials such as the Explosives Product Guide provide extensive information.

Blast Design Factors

Effective blast design considers material type, desired fragmentation, geological structure, explosive performance, initiation systems, and regulatory constraints. Accurate hole placement and pattern ties ensure optimal results.

Blasthole Layout

Accurate hole layout and profiling are essential for consistent blasting results. Advanced profiling technologies enhance layout precision, improving safety and fragmentation quality.

Loading Techniques

Proper blasthole loading and stemming are critical for effective blasting. Modern bulk trucks aid in accurate loading, minimizing flyrock and ensuring optimal fragmentation.

Tie-Ins and Spacing

Correctly tied-in blast patterns optimize burden-to-spacing relationships and ensure efficient detonation sequencing.

Millisecond Delay Timing

Appropriate millisecond delay timing allows for synchronous hole relief and optimized blasting results, reducing the risk of cutoffs and misfires.

Choosing the Right DTH Tools

Choosing the right Down-the-Hole (DTH) tools requires considering application and operating conditions. Factors like hammer size, hole diameter, and rock type influence efficiency and cost.

Selecting Hammer Size

Hammer size selection is based on hole diameter and rock formation. Typically, DTH drilling covers holes from 3 ½ to 10 inches, with specific ranges for optimal performance.

Matching Hammer and Pipe Diameter

Correct pipe diameter ensures optimal flushing and reduced risk of getting stuck. High-quality pipes, with good construction and heat-treated threads, improve durability and performance.

Choosing the Right Bit

DTH bits must match the hammer’s shank and diameter, and be suitable for the rock type. Bit design impacts rate of penetration and bit life.

Premium vs. Economy Hammers

Premium hammers provide superior performance and longevity, suitable for high productivity applications. Economy hammers, though simpler, offer cost-efficiency for specific tasks.

Application Specifics

Different applications like quarrying, mineral exploration, geotechnical drilling, and open-pit mining have specific requirements. Choosing the right hammer impacts productivity and costs.

Prediction and Evaluation of Blast Fragmentation

Advances in predictive methods, like the Kuz-Ram approach, aid in anticipating blast fragmentation. Empirical methods combined with actual measurements enhance accuracy. Effective fragmentation reduces overall costs and improves processing efficiency.

Sources

Contributors to this chapter include:

William Hissem
Senior Mining Engineer
Sandvik Construction

Robert McClure
Blasting Consultant
R.A. McClure Inc.
r.mcclure@ramets.com

George D. Raitt
Formerly Ingersoll-Rand Co.

Lyall Workman
Vice President, Senior Mining Consultant
Barr Engineering

Lesson 4 Quiz

1. What is a cylindrical vehicle designed and strategically situated to hold and contain an explosive charge for efficient detonation?

2. What is the most expensive phase in the drilling and blasting portion of production?

3. What is the first step in the drilling process?

4. What are the two broad categories of drilling methods?

5. What aspects need to be considered regarding drill rig and mounting?

6. What does DTH stand for in drilling and blasting?

7. What commonly used product in blasting combines oxidizer and fuel?

8. In modern-day blasting, what type of detonator is virtually always used?

 

Click here for the quiz answers.

 

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