Haul road design


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Haul road design

  1. 1. Venkat
  2. 2. Haul Road Design• HAUL ROADS: During the life of the pit a haul road must be maintained for access.• HAUL ROAD - SPIRAL SYSTEM: Haul road is arranged spirally along the perimeter walls of the pit. 2
  3. 3. Haul Road Design• HAUL ROAD – SWITCH BACK SYSTEM: Zigzag pattern on one side of the pit.• HAUL ROAD WIDTH: Function of capacity of the road and the size of the equipment. Haul road width must be considered in the overall pit design. 3
  4. 4. Haul Road Effect on Pit Limits 4
  5. 5. Considerations for Haul Road Design• Visibility• Stopping distances• Vertical alignment• Horizontal alignment• Cross section• Runaway-vehicle safety provisions 5
  6. 6. Sight Distances and Stopping Distances• Vertical and horizontal curves designed considering sight distance and stopping distance• Sight distance is the extent of peripheral area visible to the vehicle operator• Sight distance must be sufficient to enable vehicle traveling at a given speed to stop before reaching a hazard 6
  7. 7. Sight Distances and Stopping Distances• On vertical curves, road surface limits sight distance• Unsafe conditions remedied by lengthening curve• On horizontal curves, sight distance limited by adjacent berm dike, rock cuts, trees, etc;• Unsafe conditions remedied by laying back bank or removing obstacles 7
  8. 8. Sight Distance DiagramsSight distance diagrams for horizontal and vertical curves 8
  9. 9. Stopping Distances• Stopping distances depend on truck breaking capabilities, road slope and vehicle velocity• Stopping distance curves can be derived based on SAE service break maximum stopping distances 9
  10. 10. Stopping Distance CharacteristicsFor example,stoppingdistancecharacteristicsof vehicles of200,000 to400,000 poundsGVW 10
  11. 11. Stopping Distances• Prior to final road layout, manufacturers of vehicles that will use the road should be contacted to verify the service brake performance capabilities 11
  12. 12. Vertical Alignment• Establishment of grades and vertical curves that allow adequate stopping distances on all segments of the haul road • Maximum sustained grades • Reduction in grade significantly increases vehicle uphill speed • Reduction in grade decreases cycle time, fuel consumption, stress on mechanical components and operating costs • Reduction in grade increases safe descent speeds, increasing cycle time • The benefits of low grades offset by construction costs associated with low grades 12
  13. 13. Vehicle Performance Chart 13
  14. 14. Vehicle Retarder Chart 14
  15. 15. Vertical Alignment• Maximum sustained grades • Some states limit maximum grades to 15 to 20% and sustained grades of 10% • Most authorities suggest 10% as the maximum safe sustained grade limitation • Manufacturer studies show 8% grades result in the lowest cycle time exclusive of construction consideration 15
  16. 16. Vertical Alignment• Maximum sustained grades • Property boundaries, geology, topography, climate must be considered on a case by case basis. • Lower operating costs must be balanced against higher capital costs of low grades. • Truck simulators and mine planning studies over the life of mine should be used to make the determination of the appropriate grades 16
  17. 17. Vertical Curves• Vertical curves smooth transitions from one grade to another• Minimum vertical curve lengths are based on eye height, object height, and algebraic difference in grade 17
  18. 18. Stopping Distance vs. Vertical Curve For example, vertical curve controls 9 ft eye height (usually minimum height for articulated haulage trucks of 200,000 to 400,000 pound of GVW) 18
  19. 19. Horizontal Alignment• Deals primarily with design of curves and considers previously discussed radius, width, and sight distance in addition to superelevation• Cross slopes also should be considered in the design 19
  20. 20. Curves, Superelevation, and Speed Limits• Superelevation grade recommendations vary but should be limited to 10% or less because of traction limitations• Depending on magnitude of the side friction forces at low speed, different values are suggested for small radius curves• Kaufman and Ault suggest .04-.06 fpf (basically the normal cross slope) 20
  21. 21. Curves, Superelevation, and Speed Limits• CAT suggests higher slopes with traction cautions and 10% maximum caution• Again, where ice, snow, and mud are a problem, there is a practical limit on the degree of superelevation 21
  22. 22. Curve Superelevation 22
  23. 23. Recommended Superelevation RatesIf superelevation is not used, speed limits should be set on curves. 23
  24. 24. Curves, Superelevation, and Speed Limits• Centrifugal forces of vehicles on curves are counteracted by friction between tire an road and vehicle weight as a result of superelevation• Theoretically, with superelevation, side friction factors would be zero and centrifugal force is balanced by the vehicle weight component• To reduce tire wear, superelevation or speed limits on curves are required 24
  25. 25. Combinations of Alignments• Avoid sharp horizontal curvature at or near the crest of a hill• Avoid sharp horizontal curves near the bottom of sustained downgrades• Avoid intersections near crest verticals and sharp horizontal curvatures• Intersections should be made flat as possible• If passing allowed, grades should be constant and long enough 25
  26. 26. Cross Section• A stable road base is very important• Sufficiently rigid bearing material should be used beneath the surface• Define the bearing capacity of the material using the California Bearing Ratio (CBR) 26
  27. 27. California Bearing Ratio 27
  28. 28. Subbase Construction 28
  29. 29. Cross Slopes• Cross slopes provide adequate drainage and range from ¼ to ½ inch drop per foot of width (approximately .02 to .04 foot per foot)• Lower cross slopes used on smooth surfaces that dissipate water quickly and when ice or mud is a constant problem 29
  30. 30. Cross Slopes• Higher cross slopes permit rapid drainage, reduce puddles and saturated sub-base, and are used on rough surfaces (gravel and crushed rock) or where mud and snow are not a problem• High cross slopes can be particularly problematic with ice or snow on high grades (+5%) 30
  31. 31. Recommended Rate of Cross- Slope ChangeSlope change should be gradual. 31
  32. 32. Width• On straight or tangent segments, width depends on • Vehicle width • Number of lanes • Recommended vehicle clearance, which ranges from 44 to 50% of vehicle width 32
  33. 33. Minimum Road Design Widthsfor Various Size Dump Trucks 33
  34. 34. Typical Design Haul Road Width Typical design haul- road width for two-way traffic using 77.11-t (85- st) trucks 34
  35. 35. Typical Haulageway Sections 35
  36. 36. Width• Berm height and width as a function of vehicle size and material type• Ditch(es) added to basic recommendations• Runaway provisions may also add to width• Road wider on curves because of overhang• Minimum turning radius considered on curves (should be exceeded) 36
  37. 37. Haulageway Widths on Curves 37
  38. 38. Safety Provisions - Berms• Triangular or trapezoidal made by using local material • Stands at natural angle of repose of construction material • Redirects vehicle onto roadway • Minimum height at rolling radius of tire 38
  39. 39. Berms• Larger boulders backed with earthen material • Near vertical face deflects vehicle for slight angles of incidence • Problems with damage and injury and availability of boulders • Minimum height of boulder at height of tire allowing chassis impact 39
  40. 40. Runaway Provisions• With adverse grades some safety provision should be integrated to prevent runaway vehicles• Primary design consideration is required spacing between protective provisions• Driver must reach a safety provision before truck traveling too fast to maneuver• Maximum permissible speed depends on truck design conditions and operator 40
  41. 41. Runaway Provisions• Maximum permissible speed, equivalent downgrade, and speed at break failure determine distance between runaway truck safety provisions• For example, at an equivalent downgrade of 5% and a maximum speed of 40 mph, Speed at Failure 10 mph 20 mph Provision Spacing 1,000 ft 800 ft (Kaufman and Ault) 41
  42. 42. Runaway Precautions 42
  43. 43. Median Runaway-Vehicle Provision Berms• Vehicle straddles collision berm and rides vehicle to stop• Made of unconsolidated-screened fines• Critical design aspects spacing between berms and height of berm• Height governed by height of undercarriage and wheel track governed by largest vehicle 43
  44. 44. Median Runaway-Vehicle Provision Berms• Requires maintenance in freezing conditions• Agitation to prevent damage to vehicle• May cover berm in high rainfall areas 44
  45. 45. Escape Lanes• Good tool for stopping runaway but expensive to construct• Entrance from road is important; spacing, horizontal, vertical curve and superelevation are all considered in design• Deceleration mainly by adverse grade and high rolling resistance material 45
  46. 46. Escape Lanes• Length a function of grade and speed at entrance and rolling resistance• Stopping by level section median berm, sand or gravel or mud pits, road bumps or manual steering 46
  47. 47. Escape Lanes 47
  48. 48. Maintenance• The road surface is deformed by the constant pounding of haulage vehicles.• A good road maintenance program is necessary for safety and economics. 48
  49. 49. Safety Considerations• Dust, potholes, ruts, depressions, bumps, and other conditions can impede vehicular control. 49
  50. 50. Economic Considerations• The wear on every component is increased when a vehicle travels over a rough surface.• If the vehicle brakes constantly, unnecessary lining wear occurs as well. 50
  51. 51. Dust Control• Dust may infiltrate brakes, air filters, hydraulic lifts, and other components of machinery.• The abrasive effect of dust will result in costly cleaning or replacement of these items. 51
  52. 52. Deterioration Factors• Weather• Vehicles follow a similar path• Spillage 52
  53. 53. Motor Graders• A motor grader should be used to maintain cross slopes, remove spills, and to fill and smooth surface depressions as they occur. 53
  54. 54. Road Drainage• To avoid overflow, roadside ditches and culverts should be periodically cleaned.• Avoid erosion or saturation of subbase materials. 54
  55. 55. Thanks