Question 1: When a confined explosive charge is detonated in a blasthole, four events occur very rapidly but sequentially. Describe each of the four events briefly.
Question 2: An open pit blast consists of 120 vertical blastholes. Bench height is 10m and 1m of subdrilling is undertaken. The holes have 2.5m of stemming. Blasthole diameter is 200 mm, the burden is 6 m and spacing is 7 m. An emulsion explosive of specific gravity 1.1 is used. What is the powder factor? (Note consider the emulsion only, ie. do not consider primers)
Question 3: What is the importance of stemming in relation to blasting?
Question 4: Find the voltage required to detonate 40 electric detonators connected in series joined to 250m of firing cable with 50m of connecting wire. Resistances are as follows: average 2.2 ohms per detonator, 0.11 ohm per m of connecting wire and 0.04 ohms per m there and back for the twin core firing cable. Assume a DC supply is available.
Question 5: Determine the voltage and power input for a parallel firing circuit consisting of 25 detonators of resistance 1.6 ohms. The circuit is connected to 350m of firing cable of resistance 0.001 ohms.
Question 6: A new coal mining operation is to be worked employing surface mining using blasting to clear an overburden of Shale using 120mm holes and 13m benches. Dry rock conditions are anticipated and the decision is to use bulk ANFO with emulsion cartridges as a primer. A staggered drilling pattern with S = 1.15B is to be employed. If density of compacted ANFO = 0.85 g/cm3 and PF = 0.6 kg/m3, calculate the burden and spacing.
Question 7: Describe the methods available for secondary blasting.
Question 8: For a schist orebody determine a ring drilling pattern assuming pneumatically loaded ANFO is used of density 0.9, in 56mm diameter blastholes of average length 11m. Detail any assumptions you make.
Question 9: Flyrock, airblast and ground vibrations are common problems in blasting, what methods can be used to minimise their impact both within the mine and to the population living in the area around a mine?
Question 10: Describe the construction of a typical electric detonator. Electric initiation of charges can be problematic in certain ore body types, why is this? What other methods of initiation of explosive initiation are available.