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.Draw sketches to explain:
a. Declining stripping ratio
b. Increasing stripping ratio
c. Constant stripping ratio
14.The total cost of ore mining at an open pit is $ 2.60 per tonne and that for waste is $ 1.90 per tonne. If the value of the ore is $ 14.90 per tonne and the company requires a 20% profit margin, what is the maximum stripping ratio?
15.What are the advantages and disadvantages of wheeled loaders? 16.What are the advantages of trolley assist for a truck haulage system?
17.What are the advantages and disadvantages of open pit mining?
18.What are the advantages and disadvantages of open cast mining?
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.Dragline Output
i. A dragline with a 1½ 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 120°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 Output of Draglines
|
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
|