haul road design
Post on 19-Oct-2014
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TRANSCRIPT
Venkat
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• 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.
Haul Road Design
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• 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.
Haul Road Design
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Haul Road Effect on Pit Limits
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Considerations for Haul Road Design
• Visibility
• Stopping distances
• Vertical alignment
• Horizontal alignment
• Cross section
• Runaway-vehicle safetyprovisions
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Sight Distances and StoppingDistances
• Vertical and horizontal curves designedconsidering sight distance and stoppingdistance
•
•
Sight distance is the extent of peripheral areavisible to the vehicle operator
Sight distance must be sufficient to enablevehicle traveling at a given speed to stopbefore reaching a hazard
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Sight Distances and StoppingDistances
• 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
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Sight Distance Diagrams
Sight distance diagrams for horizontal and vertical curves
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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
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Stopping DistanceCharacteristics
For example,stoppingdistance
characteristicsof vehicles of200,000 to400,000 poundsGVW
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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
Vertical Alignment
• Establishment of grades and vertical curves thatallow adequate stopping distances on all segmentsof the haul road
• Maximum sustained grades• Reduction in grade significantly increases vehicle uphill speed
• Reduction in grade decreases cycle time, fuel consumption, stresson mechanical components and operating costs
•
•
Reduction in grade increases safe descent speeds, increasingcycle time
The benefits of low grades offset by construction costs associatedwith low grades
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Vehicle Performance Chart
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Vehicle Retarder Chart
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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 constructionconsideration
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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 determinationof the appropriate grades
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
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Stopping Distance vs. Vertical Curve
For example,
vertical curve
controls 9 ft eyeheight (usually
minimum height
for articulated
haulage trucks of
200,000 to
400,000 pound ofGVW)
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 thedesign
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Curves, Superelevation, andSpeed Limits
• Superelevation grade recommendations varybut should be limited to 10% or less becauseof traction limitations
•
•
Depending on magnitude of the side frictionforces at low speed, different values aresuggested for small radius curves
Kaufman and Ault suggest .04-.06 fpf(basically the normal cross slope)
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Curves, Superelevation, andSpeed 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
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Curve Superelevation
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Recommended Superelevation Rates
If superelevation is not used, speed limits should be set on curves.
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Curves, Superelevation, andSpeed 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
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Combinations of Alignments
• Avoid sharp horizontal curvature at or near the crestof a hill
•
•
••
Avoid sharp horizontal curves near the bottom ofsustained downgrades
Avoid intersections near crest verticals and sharphorizontal curvatures
Intersections should be made flat as possible
If passing allowed, grades should be constant andlong enough
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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 materialusing the California Bearing Ratio (CBR)
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California Bearing Ratio
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Subbase Construction
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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
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Cross Slopes
• Higher cross slopes permit rapid drainage,reduce puddles and saturated sub-base, andare used on rough surfaces (gravel andcrushed rock) or where mud and snow arenot a problem
• High cross slopes can be particularlyproblematic with ice or snow on high grades(+5%)
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Recommended Rate ofCross- Slope Change
Slope change should be gradual.
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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
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Minimum Road Design Widthsfor Various Size Dump Trucks
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Typical Design Haul Road Width
Typical
design haul-
road width
for two-way
traffic using
77.11-t (85-
st) trucks
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Typical Haulageway Sections
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Width
• Berm height and width as a function ofvehicle 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 oncurves (should be exceeded)
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Haulageway Widths on Curves
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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
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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
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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
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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
Provision Spacing
10 mph
1,000 ft
20 mph
800 ft
(Kaufman and Ault)
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Runaway Precautions
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Median Runaway-VehicleProvision 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
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Median Runaway-VehicleProvision Berms
• Requires maintenance in freezing conditions
•Agitation to prevent damage to vehicle
• May cover berm in high rainfall areas
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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
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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
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Escape Lanes
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Maintenance
• The road surface is
deformed by the constant
pounding of haulage
vehicles.
• A good road maintenanceprogram is necessary for
safety and economics.
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Safety Considerations
• Dust, potholes, ruts, depressions, bumps, and
other conditions can impede vehicular
control.
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Economic Considerations
• The wear on every component is increased when avehicle travels over a rough surface.
• If the vehicle brakes constantly, unnecessary liningwear occurs as well.
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Dust Control
• Dust may infiltrate brakes, air filters,hydraulic lifts, and other components ofmachinery.
• The abrasive effect of dust will result incostly cleaning or replacement of theseitems.
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Deterioration Factors
• Weather
• Vehicles follow a
similar path
• Spillage
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Motor Graders
•A motor grader
should be used to
maintain cross slopes,
remove spills, and to
fill and smooth
surface depressions asthey occur.
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Road Drainage
• To avoid overflow, roadside ditches and
culverts should be periodically cleaned.
• Avoid erosion or saturation of subbase
materials.
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