It's all about Pit Expansion process.

1. Geometric Considerations
Pit Expansion Process

2. Lecture outline
 Parallel cuts – turn and back
Minimum operating room for parallel cuts
 Cut sequencing

3. Minimum operating room
 Space required to accommodate the large trucks and
shovels
 Width of the working bench
 Distance from the crest of the bench providing floor for the
loading operations to the toe of bench being created as parallel cut
advances
 Dependent upon single and double spotting of the trucks
 Minimum width (WB) is equal to the width of minimum
required safety bench (SB) plus the width of cut (WC)
 WB = SB + WC

4. Hypothetical Example
 Bench height = 40 ft.
 A safety berm is required
 Minimum clearance between outer truck tire and the safety
berm = 5 ft.
 Single spotting is used
 Bench face angle = 70°
 Loading equipment
 9 yd3 BE 155 shovel
 Haulage equipment
 85 ton trucks, truck width = 16 ft. and tire rolling radius = 4 ft.

5. Section and plan view of working
bench

6. Example
 Step 1: safety berm
 Height
 Depends upon the rolling radius of the truck
 4 ft.
 Assuming angle of repose of the material = 45°
 Width
 8 ft.
 Berm is located at the outer edge at the crest

7. Example
 Step 2: distance from the crest to the truck
centerline (TC)
Clearance distance between safety berm and truck
is 5 ft.
Since truck is 16 ft. wide, the centerline to crest
distance is 21 ft.

8. Example
 Step 3: shovel dimensions from the
specification sheet
Maximum dumping height (A) = 28 ft.
 More than sufficient to clear the truck
Radius of level floor (G) = 35.25 ft.
 Maximum shovel centerline to toe distance
Dumping radius at maximum height (B) = 45.5 ft.

9. Example
 Step 4:desired working bench dimension
WB = TC + B + G = 102 ft.
 Step 5: width of cut
Shovel moves along single path to the crest
 WC = 0.90 × 2 × G = 63.5 ft.
 Allowance for swell and throw of material during
blasting
 Design cut width is reduced to 60 ft.

10. Example
 Step 6: width of safety bench
 SB = 102 – 60 = 42 ft.
 Step 7: check calculations
 Maximum cutting height of the shovel (D) = 43.5 ft.
 Shovel can reach to the top of the bench for scaling
 Maximum cutting radius (E) = 54.5 ft.
 Since maximum radius of level floor (G) = 35.25 ft.
 The flattest bench face angle which could be scaled:
 Shovel can easily scale the 70° bench face
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64
25
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35
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54
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tan 1

12. Example
 Step 8: comparison of cut dimensions to the
drilling and blasting pattern
Blasthole diameter = 12 ¼ in.
Explosive = ANFO
 Burden = 25 ft.
 Blasthole spacing = 25 ft.
Two rows of blastholes are appropriate for this cut
width

13. Cut sequencing

14. Cut sequencing - mining from bench 1

15. Cut sequencing - mining from bench 2