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Pit Expansion Process .ppt

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Pit Expansion Process .ppt

  1. 1. Geometric Considerations Pit Expansion Process
  2. 2. Lecture outline  Parallel cuts – turn and back Minimum operating room for parallel cuts  Cut sequencing
  3. 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. 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. 5. Section and plan view of working bench
  6. 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. 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. 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. 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. 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      3 . 64 25 . 35 5 . 54 40 tan 1
  11. 11. 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
  12. 12. Cut sequencing
  13. 13. Cut sequencing - mining from bench 1
  14. 14. Cut sequencing - mining from bench 2

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