Blasting: Design

Question 1

ease fragmentation

Answer 1

break the rock to make it easier to dig, load, haul and crush

Question 2

ease stripping

Answer 2

mover overburden or waste rock overlying seam/ore by explosive means

Question 3

well fragmented

Answer 3

rock has to be closely fractured and jumbled up by the associated movement of a blast

Question 4

movement is essential

Answer 4

bulking occurs as the chunks or rock are randomly reoriented so that void spaces are developed

Question 5

3 keys to blast efficiency

Answer 5

energy distribution
energy confinement
energy levels

Question 6

stemming length

Answer 6

too shallow: excessive airblast and fly rock
middle: good breakage and displacement
too deep: poor fragmentation

Question 7

blasthole diameter

Answer 7

controls the energy distribution

Question 8

stemming length

Answer 8

depends on the fragmentation required and type of stemming

Question 9

burden distance

Answer 9

with stemming length, it ensures burden relieft upwards and forwards

Question 10

blasthole spacing

Answer 10

determines horizontal energy distribution

Question 11

subdrilling

Answer 11

only used where appropriate, 0-10 times blasthole diameter

Question 12

blasthole inclination

Answer 12

remedy poor energy distribution

Question 13

flyrock

Answer 13

• overload blast holes
• inadequate face burden-excessive powder factor
• blasting misfire