DRILL & BLAST
TO THE POWER OF SIX: PROMOTING A TEAM-ORIENTED APPROACH TO DRILLING, BLASTING Anthony Konya discusses a steady management approach to drill and blast that encourages employee buy-in and a dedication to improved techniques and efficiency. This can assist operators with reducing expenses and achieving better fragmentation.
A
common problem for quarrying engineers and consultants is the critical challenge of achieving proper blasting. Many of the problems faced come from operational inefficiencies in the drilling and blasting program. Most operators believe that better blast design will help save costs, improve fragmentation and decrease vibration, and while this is all true, none of it can occur if the design cannot be achieved with reasonable accuracy. By achieving this accuracy, before implementing better blast designs and processes, most quarries save upwards of 15 to 30 per cent on their blasting costs. There are many ways to achieve accuracy, such as designing for inaccuracies, automating jobs and blasting management.
DESIGNING FOR INACCURACIES How does one design for inaccuracies in blasting? This is a common question when inaccuracies are encountered, because engineering out these inaccuracies is one of the easiest options with the least capital cost. 14
Quarry February 2019
However, this approach is extremely costly in the hidden costs of drilling and blasting. One of the first people to study drill deviation on a large scale was Ulf Langefors, who documented his extensive results from dozens of mines in his book The modern technique of rock blasting and discussed ways to “engineer out” drilling inefficiencies.1 He did this by analysing the average errors in drilling from: Collaring location – the drill setting up in the wrong place, causing the hole to begin in the wrong location. Alignment inaccuracies – including drilling improper angles and the deviation inside of the borehole when drilling. When Langefors studied a multitude of blasts in Sweden, he concluded that, on average, improper collaring locations accounted for 101 millimetres (or four inches) of deviation, and alignment inaccuracies were about one millimetre for every 30 centimetres (or 0.04 inches per foot) in bench blasting. To most, this may seem insignificant, but this is almost ±15cm (or ±6 inches) on a 12m
P10
P50
P80
No deviation 40mm
No deviation 302mm
No deviation 448mm
Langefors 101mm
Langefors 302mm
Langefors 498mm
Forsyth 51mm
Forsyth 302mm
Forsyth 701mm
Table 1. Fragmentation comparison.
P10
P50
P80
No deviation 40mm
No deviation 302mm
No deviation 448mm
Langefors 61mm
Langefors 190mm
Langefors 335mm
Forsyth
Forsyth 101mm
Forsyth 0.8mm
Not within accurate modeling
Table 3. Engineered fragmentation.
(40-foot) bench. This means the spacing between the two holes may be reduced by 300mm (one foot) and the burden increased by 152mm (0.5 feet).
