11. Development Blasting

Question 1

Advantage of cut close to sidewall?

Answer 1

better exploitation of drilling pattern with less holes/round

Question 2

Advantage of cut in the middle and low?

Answer 2

less throw and less explosives

Question 3

Advantage of cut in the middle and high?

Answer 3

easier muckpile loading but more explosives and drilling required

Question 4

When is stemming used underground?

Answer 4

if airblast is an issue

Question 5

Why is stemming typically not used underground?

Answer 5

needs air loader, no cost benefit, can’t clean out misfires, must drill another hole if misfire

Question 6

What is the purpose of cut?

Answer 6

initial expansion area for blast holes to break towards

Question 7

What is the purpose of perimeter holes?

Answer 7

protect the perimeter area of the drift

Question 8

What is the purpose of lifters?

Answer 8

break to grade and smooth working floor

Question 9

What is the purpose of shoulders and erasers?

Answer 9

fragmentation and advance

Question 10

What are the 4 parameters for good advance?

Answer 10

1. large empty holes
2. distance between the blast hole and empty hole < 1.5 x diameter of empty hole
3. charge concentration
4. drilling precision

Question 11

15% rule of thumb?

Answer 11

a minimum 15% of open area for expansion factor of rock (the more the better)

Question 12

What are 4 limiting factors to good advance?

Answer 12

1. time
2. tunnel space
3. diameter of holes must be compatible with equipment
4. parallel holes permit deeper rounds

Question 13

Normal Profile Blasting

Answer 13

• typical of mines

- rough/irregular/cracked profile

Question 14

Smooth Profile Blasting

Answer 14

• typical for road and rail tunnels

- close drill holes + weaker explosives

Question 15

What are the 4 development design requirements?

Answer 15

1. accurate drilling
2. proper burden and hole spacing
3. proper initiation sequencing
4. proper charge concentration