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DBS721S - Drilling and Blasting 324 - 2ndt Opp - Nov 2022 |
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nAmlBIA unlVERSITY
OF SCIEnCE Ano TECHnOLOGY
FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
DEPARTMENT OF MINING AND PROCESSENGINEERING
QUALIFICATION : BACHELORS OF ENGINEERING IN MINING ENGINEERING
QUALIFICATION CODE: 08BMIN
LEVEL: 7
COURSE CODE: DBS721S
COURSE NAME: DRILLING AND BLASTING 323
SESSION: NOV 2022
DURATION: 3 HOURS
PAPER: THEORY
MARKS: 100
EXAMINER{S)
MODERATOR:
SECOND OPPORTUNITY EXAM PAPER
Mr L. Madziwa
Mr P. Shava
INSTRUCTIONS
1. Answer all questions.
2. Read all the questions carefully before answering.
3. Marks for each questions are indicated at the end of each question.
4. Please ensure that your writing is legible, neat and presentable.
PERMISSIBLEMATERIALS
1. Examination paper.
2. Scientific calculator.
THIS QUESTION PAPER CONSISTS OF 5 PAGES (Including this front page)
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Question 1 [13 marks]
In blasting operations, the quantity of explosives used is one of the major factors that control
fragmentation size. Differentiate between the following:
i. Low explosive and high explosive
[2]
ii. Dry Blasting agent and wet blasting agent
[2]
iii. Safety fuse and detonating fuse
[2]
iv. Detonation and Deflagration
[2]
v. Primary and Secondary blasting
[2]
vi. Plaster shooting and Pop shooting
[3]
Question 2 [10 marks]
(a} Explain briefly the following properties of explosive:
i. Water resistance
[2]
ii. Fumes characteristics
[2]
iii. Sensitiveness
[2]
iv. Flammability
[2]
(b} Explain the role of detonation pressure in rock breakage
[2]
Question 3 [17 marks]
a} The specific gravity of commercial product ranges from 0.8 - 1.6. Determine the
loading density of an explosive which has a charge diameter of 45mm and a specific
gravity of 1.2
[ 4]
b} In a quarry, rock is extracted with a uniaxial compressive strength of 200MPa, in
benches 10m high. Drilling carried out with rotary percussive to hammer rig and a
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diameter of 105mm. The explosives used are composed of cartridge slurry of 75mm
in diameter and bulk ANFO with respective densities of 1.2 and 0.8g/l. The drilling
pattern and charge distribution are to be determined, maintaining the blasthole
inclination at 20°. Determine the following parameters, given that Qc =26.57 kg, Qb
= 24.63 kg
a. the sub drill (J),
[1]
b. blasthole length (L),
[4]
C. burden,
[1]
d. spacing,
[1]
e. volume of broken rock (VR),
[2]
f. yield of broken rock (RA),
[1]
g. blasthole charge (Q), and
[1]
h. the Powder Factor CE.
[1]
Question 4 [20 marks]
A new zinc and lead deposit is to be worked by surface mining methods with 12m benches
using 250mm diameter blast holes. The prevailing condition is dry rock, it has been decided
to use bulk AN FO with emulsion cartridges as primer. Assume that the overall density of
compacted ANFO and the primer as 0.85 g/cm 3 and the powder factor of 0.6 kg/m 3 • Find the
following parameters, by assuming that the drilled blast holes are staggered pattern forming
equilateral triangle, Rock Factor (A} = 11, Fly rock must be controlled (Z) = 1.25, The mass of
explosive (Q) in 8-hole diameter= 25 kg :
a. Burden
b. Spacing for vertical and inclined holes
C. Optimum Stemming (T)
d. Subdrilling (J)
e. Blasthole length (L}
f. Charge length (Le}
g. Explosive mass per meter (Qe)
h. Mass of Explosive (Qm)
i. Volume of rock blasted (Vr}
j. Charge length of incline holes 20°
k. Volume of rock blasted (VR)
[1]
[1]
[4]
[1]
[1]
[1]
[2]
[2]
[2]
[3]
[2]
Question 5 [20 marks]
Given the following information design a blast using the formulae in Surface Blast Design, in
a competent dolomite using the following parameters.
• Hole Diameter= 98mm
• Bench height= 15.0 m
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• Hole angle = goo
• Explosive = Magnum Buster Gel
• Density of magnum cartridge P = 1.21kg/m 3
• Cartridge diameter= ¾*98
• K,ech= 0.45 kg/m3
• Spacing to Burden S = B
The mine is close to a residential area, so fly rock must be controlled. The conditions are dry
with little or no water in the holes. Loading equipment in use is front-end loader. Determine
the following;
a. Burden,
[1]
b. Sub-drill,
[2]
c. Stemming height,
[2]
d. explosive column,
[5]
e. number of cartridges and
[5]
f. the powder factor.
[5]
Question 6 [15 marks]
The open pit mine has massive fine-grained lava with a skarn gold mineralization. Blast holes
drilling is to be carried out in this rock formation with UCS of 200MPa by using two TC
inserted tricone bits of 320 mm and 300mm diameter from different manufacturers, with a
feed force including the drill head weight of 30 000 kg at a rotary speed of 80 rpm and rock
penetration factor of 65.
a. Determine which bit size will yield a faster penetration rate if both bits operate
with the same feed force and speed?
[5]
b. Calculate the drilling rates for both bit sizes?
[5]
c. Draw your conclusion on the answers in (a) and (b)?
[5]
Question 7 [5 marks]
An explosive is a material that undergoes rapid exothermic oxidation reaction (combustion),
producing immense quantities of gas when it detonates.
a) Calculate the detonation pressure of explosive ANFO if its density is 0.85g/cc
and the velocity of detonation is 3000 m/sec.
[4]
b) A percussion drill working on a granite bearing uranium mine with a
penetrating rate of 50m/h including non-productive times and mechanical
availability of the machine which is usually 80%. Calculate the average drilling
rate per hour.
[1]
End of Examination
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Important formulae for DLB 721S - 2022
1.
K act
2.
3.
=-"" \\J
C' p •)C 1-
··(i
- ' 100 1273
4.
B=
5.
=2
V rrD xRD
4
6.
= rr d
Q 4 1000P
7.
P = 5.7 x 10-5 x {RF - 28 x log {0.145 x Sc))W/(/J x RPM
P = (6] - 28loE:1()
H
,-)¢
•
1p1n
300
7.a.
Where:
d = diameterof the chip in inches
p = density of chip in Ib/ft3
8.
9.
°· VM
=
2
*
VP
0 65
·
= 2 * 50
= 65
10.
RDI = 25*RD-50=25*2.8-50 = 20
11. HF= UCS/5 =500/5=100
12. Rock Factor {A)= 0.06{RMD+JF+RDl+HF) =0.06(50+ 20+100) =10.2
13.
p = 2.5 X pv 2 X 10-6
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