1. Draw a plan of a typical strip mine showing all operational features and equipment.
2. Answer the following:
a. Provide a sketch to show the difference between the final and the working slopes.
b. Why do operators try to steepen the final slope to an allowable safe maximum angle?
3. Define the following a. Swell factor
b. Struck Capacity
c. Heaped Capacity d. Fill Factor
e. Bank cubic metre
f. Loose Cubic metre g. Working slope
h. Final pit wall i. Ramp
j. Windrow
4. A dragline is to be selected to remove overburden at a rate of 395,000 bank cubic metres per month. If the dragline is scheduled to operate
720 hours per month which an operating efficiency of 0.8, the bucket fill factor is 0.8 and its cycle time is 50 seconds, what should be the size of its bucket?
5. The Maximum Usefulness factor (MUF) is equal to the product of the nominal bucket size multiplied by the machines functional reach. It can be used to relate two similar machines with different reaches or different bucket sizes. If the dumping radius of a 18 cubic metre dragline is 52 m, the tub diameter is 12 m and normal operations require the machine to be offset a distance of three-quarters of the tub diameter from the highwall, determine the potential effective reach of the machine if it is retrofitted with a new boom and a bucket of 15 cubic metres.
6. Discuss the following:
a. Summarise the steps in the development of an open pit mine. b. What are the purposes of safety benches?
c. What is the width of a safety bench?
d. Discuss some of the aspects that enter into bench height selection?
e. What is meant by the term push-back?
7. Answer the following
a. Define materials handling in surface mining
b. Name the different types of operations in materials handling
c. Name the different types of machine used in these operations
d. Name and discuss the major factors that determine the selection of excavation equipment.
e. Define the idealised output of a power shovel
8. For the following data for a shovel-truck operation calculate the idealised output in m3/hr.
i. Required production per bench = 7,000 tonnes/shift ii. Operating period = 2 shift/day (10 hours per shift)
iii. Material = well blasted rock iv. Working time = 55 mins/hr v. Operating factor = 80%
vi. Specific weight of rock = 2.0 tonne/m3
Calculate the actual shovel production in tonnes/hr given the following:
i. Material weight (bank) = 2 tonnes/m3
ii. Swell factor = 35%
iii. Bucket size = 10.5 m3
iv. Fill factor = 0.85
v. Cycle time = 30 sec vi. Availability = 83 %
9. Answer the following:
a. Discuss the factors that are considered in the selection of a truck as a haulage unit.
b. In determining the cycle time of a haulage unit name the factors in relation to the haulage road that need to be considered
c. Define the following
i. Grade resistance ii. Rolling resistance iii. Total resistance
d. Define traction
10. A 90 tonne rear dump truck travels on an 5% grade loose gravel road.
Determine the traction and total resistance
i. On the way up when the truck is loaded ii. On the way up if the truck is empty
For the following conditions:
- Rolling resistance factor = 50 kg/tonne
- Coefficient of friction = 0.35
- Vehicle weight empty = 700 kg/tonne of rated capacity
- Gross vehicle weight = dead weight + capacity
- Grade resistance factor = 10 kg/tonne
- Load distribution = 33 % on front tyres and 67% on rear tyres.
11. Answer the following:
a. Define stripping ratio and give three examples of the units it may be expressed in.
b. Define maximum stripping ratio.
c. Draw a section through an open pit showing the following:
i. Pit slope
ii. Bench slope iii. Bench crest iv. Pit floor
v. Bench toe
vi. Bench width
12. Draw a plan and cross-section of a dragline casting overburden from a new strip to an old strip in a coal mining stripping situation for a single seam and for a two seam operation.
13. Define the following terms:
a. Availability
b. Operational availability c. Mechanical availability d. Physical availability
e. Utilization
f. Working efficiency g. Job efficiency
14. The total cost of ore mining at an open pit is $ 35per tonne and that for waste is $ 25 per tonne. If the value of the ore is $ 110 per tonne and the company requires a 20% profit margin, what is the maximum stripping ratio?
15. Differentiate between the following:
a. Scheduled hours b. Annual hours
c. Total hours
d. Working hours e. Shift hours
f. Operating hours
16. What are the advantages of trolley assist for a truck haulage system?
17. Why is the mechanical availability always less than the operational availability? How does mechanical availability vary with the life of the machine?
18. Why is knowing the coefficient of traction important?
19. Answer the following:
i. In general, a road consists of several layers. Draw and label different layers and discuss their functionality.
ii. How is the load from the tyres distributed in the different layers of a road foundation? Discuss.
iii. Draw a typical stress envelope for dual rear wheel tyres for a truck. iv. Point out, on the drawing, the most affected area on the sub-grade.
20. For a 77t truck with Gross Vehicle Weight (GVW) of 136078 kg with dual rear tyres and a tyre inflation pressure is 120 psi (or 8.43 kg/cm2). Use the equivalent single tyre loading.
i. Determine the contact surface area
ii. If the sub-grade material is a firm or stiff clay, then determine the minimum required distance between the wearing surface and the top of the sub-grade.
iii. With the same truck specifications, design an acceptable haul road (ie determine different thicknesses of different layers) using CBR method. Choose your own material for different layers with proper justifications. (Use the required conversion factors)
21. Dragline Output
i. A dragline with a 2½ cu yd bucket working in wet, sticky clay, with a swell factor of 20%, handles an average loose volume of 1.8 cu yd. It can complete 3 cycles per 2 minutes. Calculate ideal output, based on digging at optimum depth with a 90°angle of swing, and no delays.
ii. Using the tables provided, calculate the probable output if the angle of swing is actually 140°and the depth of cut is 10ft.
Table 5.2: Ideal Output of Short-boom Draglines in Cubic Yards per
Hour Bank Measure
|
Class of material
|
Size of bucket (cu yd)
|
|
3/8
|
1/2
|
3/4
|
1
|
1¼
|
1½
|
1¾
|
2
|
2½
|
|
Moist loam or light sandy
Clay
|
5.0
|
5.5
|
6.0
|
6.6
|
7.0
|
7.4
|
7.7
|
8.0
|
8.5
|
|
|
70
|
95
|
130
|
160
|
195
|
220
|
245
|
265
|
305
|
|
Sand and gravel
|
5.0
|
5.5
|
6.0
|
6.6
|
7.0
|
7.4
|
7.7
|
8.0
|
8.5
|
|
|
65
|
90
|
125
|
155
|
185
|
210
|
235
|
255
|
295
|
|
Good common earth
|
6.0
|
6.7
|
7.4
|
8.0
|
8.5
|
9.0
|
9.5
|
9.9
|
10.5
|
|
|
55
|
75
|
105
|
135
|
165
|
190
|
210
|
230
|
265
|
|
Hard ,tough clay
|
7.3
|
8.0
|
8.7
|
9.3
|
10.0
|
10.7
|
11.3
|
11.8
|
12.3
|
|
|
35
|
55
|
90
|
110
|
135
|
160
|
150
|
195
|
230
|
|
Wet, sticky clay
|
7.3
|
8.0
|
8.7
|
9.3
|
10.0
|
10.7
|
11.3
|
11.8
|
12.3
|
|
|
20
|
30
|
55
|
75
|
95
|
110
|
130
|
145
|
175
|
Table 5.3:The Effect of the Depth of Cut and Angle of Swing on the
|
Per cent of
optimum
depth
|
Angle of swing (deg.)
|
|
30
|
45
|
60
|
75
|
90
|
120
|
150
|
180
|
|
20
|
1.06
|
0.99
|
0.94
|
0.90
|
0.87
|
0.81
|
0.75
|
0.70
|
|
40
|
1.17
|
1.08
|
1.02
|
0.97
|
0.93
|
0.85
|
0.78
|
0.72
|
|
60
|
1.24
|
1.13
|
1.06
|
1.01
|
0.97
|
0.88
|
0.80
|
0.74
|
|
80
|
1.29
|
1.17
|
1.09
|
1.04
|
0.99
|
0.90
|
0.82
|
0.76
|
|
100
|
1.32
|
1.19
|
1.11
|
1.05
|
1.00
|
0.91
|
0.83
|
0.77
|
|
120
|
1.29
|
1.17
|
1.09
|
1.03
|
0.985
|
0.90
|
0.82
|
0.76
|
|
140
|
1.25
|
1.14
|
1.06
|
1.00
|
0.96
|
0.88
|
0.81
|
0.75
|
|
160
|
1.20
|
1.10
|
1.02
|
0.97
|
0.93
|
0.85
|
0.79
|
0.73
|
|
180
|
1.15
|
1.05
|
0.98
|
0.94
|
0.90
|
0.82
|
0.76
|
0.71
|
|
200
|
1.10
|
1.00
|
0.94
|
0.90
|
0.87
|
0.79
|
0.73
|
0.69
|
|
|
Output of Draglines
Track-Type Tractors Dozing
Determine average hourly production of a D8N/8SU (Hydraulic with tilt cylinder) coal, an average distance of 400m down a 15% grade, using a slot dozing technique. Estimated material weight is 1600 kg/Lm3. Material density =1392 kg/Lm3. Operator is average. Job efficiency is 50 min/hr (check the notes for production curve, table for correction factors).
Uncorrected maximum production 458 Lm3/hr
23. Track-Type Tractors Ripping
Determine the loosening costs in the following situation: Machine D11R Tractor with No. 11 single shank ripper in coal Rip spacing 1600mm
Ripper penetration 500mm
Rip distance 150m
Rip time 4.32 minutes
Manoeuvre time 0.35 minutes
Seismic velocity 2500 m/s (assume this is a realistic value for coal, graphs available to check).
Working rate per hour $ 120
What is the effect of the seismic velocity of rock on dozer ripping operations?
24. Motor Grader
A Motor grader will travel at an average speed of 8km/hr along a haul road to clear the shoulder for a distance of 20km on one side. It is expected that proper clearing will require three passes, and that the machine has the usual efficiency factor of 0.6. Calculate the production expected from this grader performing this task.
25. Dragline
Rated Capacity of a Dragline Bucket
Calculate the rated capacity of a dragline bucket, given the following information:
Height at front = 2m Height at rear = 2.25m Length at top = 5.9m Length at bottom = 5.4m Width of front top = 3m Width of rear top = 3m Width of front base = 3m Width of rear base = 3m
Factor for capacity loss due to bucket design = 0.20
26. Wheel Loader
Application Dozer pile less than 3m high dump to hopper Production
Required 232.05 metric ton per hour Material poorly fragmented rock
Density 1700kg/m3
Loading is constant with a hard level surface for loader manoeuvring. Show calculations and procedure to select an appropriate loader for this task.
27. Determine the maximum production for a Caterpillar D10T Dozer fitted with a Semi -Universal Blade using the diagram below for a dozing distance of 30m.
Determine the corrected production for the dozer for downhill dozing on a 5% slope, with a 50 minute working hour and an average operator as per the correction factors below.
28. Normally the height of windrow is?
29. Which of the following has the highest power consumption in kwh/m3
a. BWE
b. Electric Face shovel c. Walking dragline
d. BCE
30. Which of these would be considered an excessively steep a grade for a normal rear dump truck?
a. 4% b. 6% c. 10% d. 12%
31. Draw and label in detail an excavator
32. What is the difference between a shovel and an excavator?
33. Sketch and label the four most common slope failure types.
34. Calculate the efficiency of a 24H Caterpillar grader maintaining a 40m wide haul road, given the following:
- road length is 20,500m
- machine takes 8 hours to complete the task
- average speed of the machine is 22km/hr
- task completion requires making 8 passes
35. Given are the following data for a shovel-truck surface mine operation:
required production/bench = 16,000 tonnes/shift
operating period = 1 shift/day
material = well blasted rock
working time = 51 min/hr and 10.5 hrs/shift
operating factor = 83%
specific weight of rock = 2.35 t/m3
Calculate the idealised output (m3/hr) of the shovel.
36. Pit Slope Angles.
Define, with a neat sketch, the different types of slope angles in a surface mine
Given:
- No. of benches = 9
- Bench face angle =65°
- Safety bench width = 10m
Based on the above data determine the following:
1. the overall slope angle
2. the overall slope angle if you introduce a ramp of 30 m width on the 5th bench
3. the inter-ramp angles
4. on the initial design, the overall slope angle if you introduce a working bench only on the 2nd bench of width 50m
5. on the initial design, the overall slope angle if you introduce a ramp of 30 m width on the 7th bench
6. the inter-ramp angles
7. final slope angle at the end of pit limit
Assume bench height of 15m.
37. If the width of a haul unit is 15m, determine the minimum width of a haul road for:
o Single lane haul road operation
o Two lane operation
o Three lane operation
Assume in each case the road width includes a safety windrow and a ditch.
38. Describe the various methods of truck loading using either a shovel or excavator fitted as a backhoe
39. Estimate the cycle time and production of a Caterpillar 777D flat floor off highway truck operating on a level haul road of 2600m length. The road is a rutted dirt roadway with no maintenance and no stabilisation, tyre penetration is 4 cm. The following can be assumed;
o Loading time 1.4 min
o Manoeuvre and dump time 0.8 min
o Truck hauls 80 tonnes of ore each trip
o Job efficiency of 0.8
40. For the situation in question 39, determine the cycle time if road conditions were improved to a rolling resistance of 30 kg/tonne.
41. For the problem in question 39 and 40 the engineer at the site is considering the use of a shorter, 1000m, haul road that has a slope of 6% adverse. If all other factors remain the same which haul route should be selected on the basis of shortest cycle times? What are the cycle times and hourly productions?
42) An off highway truck weighs 23 t empty and carts a payload of 35 t up an 7% grade. The RR factor is 50 kg/tonne. Calculate:
a) The total resistance (kg)
b) The effective grade (%)
43)A rubber tyred scraper unit weighing 50 t is towed by a crawler tractor weighing 40t up a 5% grade. The RR factor is 40kg/t. Calculate:
a) The rolling resistance (kg) b) The grade resistance (kg) c) The total resistance (kg)
44)A Caterpillar D30D articulated dump truck has the rim pull curve in figure
1. (Gross weight 21.9 t empty, 49.117 t loaded). If the truck ascends a 8% grade with a rolling resistance of 40kg/t, find the following:
a) Total resistance (kg)
b) The required rim pull (kg) when loaded
c) The maximum speed of the truck when loaded (km/h)
Figure 1: CAT D30D Rimpull, Speed, Gradeability (Caterpillar Performance
Handbook version 31 (2000)).
45)The average speed of an 18m3 scraper is 40 km/hr and its return speed uphill is 22 km/hr over a 400 m haul distance and a 450m return distance. Using a fixed time of 4 minutes, calculate the cycle time (min).
46) What are the advantages and disadvantages of in-pit crushing
47) Continuous surface miners such as the Wirtgen surface miners are used at a number of operations worldwide. Describe such a machine and detail the type of operation where such a machine has advantages over traditional surface mining techniques.