Chapter 4
Loading and Hauling
Part 2
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4-2 DOZERS
• This section includes:
– Tractors and Dozers
– Dozer Blades
– Estimating Dozer Production
– Job Management
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Tractors and Dozers
• A tractor equipped with a front-mounted
earthmoving blade is known as a dozer or
bulldozer.
• A dozer moves earth:
– by lowering the blade and cutting until a full blade
load of material is obtained.
– It then pushes the material across the ground
surface to the required location.
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Tractors and Dozers
• Both rubber-tired (or wheel) dozers and crawler (or
track) dozers are available.
• crawler (or track) dozers
– Because of their excellent traction and low ground
pressure (typically 6 to 9 lb/sq in.; 0.4 to 0.6 bar),
crawler dozers (Figure 4-6) are well suited for use
in rough terrain or areas of low trafficability.
– Low-ground-pressure models with extra-wide
tracks are available having ground pressures as
low as 3 lb/sq in. (0.2 bar).
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– Crawler dozers can operate on steeper side slopes
and climb greater grades than can wheel dozers.
– Wheel dozers can operate at higher speed than do
crawler dozers.
– Wheel dozers are also capable of operating on
paved roads without damaging the surface.
• Crawler dozers cause damage.
– While the wheel tractor's dozing ability is limited
somewhat by its lower traction and high ground
pressure (25 to 35 lb/sq in.; 1.7 to 2.4 bars), its
high ground pressure makes it an effective soil
compactor.
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Tractors and Dozers
• Either rubber-tired or crawler tractors may be
equipped with attachments other than dozer blades.
• These include rakes used for gathering up brush and
small fallen trees, and plows, rippers, and scarifiers,
which are used to break up hard surfaces.
• Tractors are also used to tow many items of
construction equipment, such as:
– compactors,
– scrapers, and
– wagons.
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• Dozers may be equipped with:
– direct-drive,
– power-shift, or
– hydrostatic transmissions.
• Hydrostatic transmissions utilize individual hydraulic
motors to drive each track. Therefore,
– the speed of each track may be infinitely varied,
forward or reverse.
– it is possible for a dozer equipped with a
hydrostatic drive to turn in its own length by
moving one track forward while the other track
moves in reverse.
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Dozer Blades
• There are a number of types of dozer blades available, and the
four most common types are illustrated in Figure 4-7.
Figure 4-7: Common types of dozer blades
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Dozer Blades Adjustments
The three types of adjustments that maybe made to dozer
blades are illustrated in Figure 4-8.
- Tilting the blade is useful for ditching and breaking up frozen
or crusty soils.
- Pitching the blade forward reduces blade penetration and
causes the loosened material to roll in front of the blade,
whereas pitching the blade backward increases penetration.
FIGURE 4-8: Dozer blade adjustments.
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Dozer Blades
• Angling the blade is helpful in 3 purposes:
– side-hill cutting,
– ditching, and
– moving material laterally.
• All the blades shown in Figure 4-7 may be
tilted except the cushion blade.
• However, only the angle blade may be angled.
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Dozer Blades
• The wings on the universal blade (Figure 4-7)
enable it to push a large volume of material over
long distances.
– However, its low horsepower per foot of cutting edge
and per cubic yard limit its ability to penetrate hard
soils or to move heavy materials.
• The straight blade is considered the most
versatile dozer blade.
– Its smaller size gives it good penetrating and load
pushing ability.
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Dozer Blades
• Angle Blades
– Have the ability of angle blades to angle
approximately 25° to either side makes them very
effective in:
• side hill cutting,
• ditching, and
• backfilling.
– They may also be used for rough grading and for
moving material laterally.
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Dozer Blades
• The cushion blade :
– is reinforced and equipped with shock absorbers
to enable it to push-load scrapers.
– It may also be used for cleanup of the loading or
dumping areas and for general dozing when not
push-loading scrapers.
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Dozer Blades
• Other available types of dozer blades include:
– light-material U-blades,
– special clearing blades, and
– rip dozer blades (blades equipped with ripper
shanks on each end).
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Dozer Blades
• The two indicators of potential dozer
performance are based on the ratio of tractor
power to blade size.
• These indicators are :
– 1. horsepower per foot of cutting edge: provides a
measure of the blade's ability to penetrate hard
soils and
– 2. horsepower per loose cubic yard rating:
provides an indication of the blade's ability to
push material once the blade is loaded..
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Estimating Dozer Production
• The basic earthmoving production equation
(Equation 2-1) may be applied in estimating dozer
production.
– This method requires an estimate of the average
blade load and the dozer cycle time.
• There are several methods available for
estimating average blade load, including:
– the blade manufacturer's capacity rating,
– previous experience under similar conditions, and
– actual measurement of several typical loads.
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Estimating Dozer Production
• A suggested method for calculating blade
volume by measuring blade load is as follows:
– Doze a full blade load, then lift the blade while
moving forward on a
– level surface until an even pile is formed.
– Measure the width of the pile (W) perpendicular
to the blade and in line with the inside of each
track or wheel. Average the two measurements.
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Estimating Dozer Production
– Measure the height (H) of the pile in a similar
manner.
– Measure the length of the pile parallel to the
blade.
– Calculate blade volume using Equation 4-10.
• Blade load (LCY) = 0.0139 × H (ft) × W(ft) × L (ft)
• Blade load (LCM) = 0.375 × H (m) × W (m) × L (m)
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Estimating Dozer Production
• Total dozer cycle time is the sum of its:
– fixed cycle time and
– variable cycle time.
• Fixed cycle time (Table 4-4 ) represents the time
required to:
– maneuver, change gears, start loading, and dump.
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Estimating Dozer Production
• Variable cycle time is the time required to
doze and return (Table 4-5 ).
– Since the haul distance is relatively short, a dozer
usually returns in reverse gear.
– Some manufacturers provide dozer production
estimating charts for their equipment.
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EXAMPLE 4-6
• Estimate the production of the dozer that has the
following information:
– A power-shift crawler tractor has a rated blade
capacity of 7.65 LCM.
– The dozer is excavating loose common earth and
pushing it a distance of 61 m.
– Maximum reverse speed in third range is 8 km/h.
– job efficiency is 50 min/h.
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EXAMPLE 4-6
Solution
Fixed time =0.05 min (Table 4-4)
Dozing speed =4.0 km/h (Table 4-5)
Dozing time = 61/(4 ×16.7) = 0.91 min
Note: 1 km/h =16.7 m/min.
Return time = 61/(8 × 16.7) = 0.45 min
Cycle time = 0.05+ 0.91+ 0.45= 1.41 min
Production= 7.65 × 50/60 x 60/1.41= 271 LCM/h
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Job Management
• Some techniques used to increase dozer
production include:
– downhill dozing,
– slot dozing, and
– blade-to-blade dozing.
• By taking advantage of the force of gravity,
downhill dozing enables blade load to be
increased or cycle time to be reduced
compared to dozing on the level.
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Job Management
• Slot dozing utilizes a shallow trench (or slot)
cut between the loading and dumping areas
to increase the blade capacity that can be
carried on each cycle.
– Under favorable conditions, slot dozing may
increase dozer production as much as 50%.
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Job Management
• Blade-to-blade dozing involves two dozers
operating together with their blades almost
touching.
– This technique results in a combined blade capacity
considerably greater than that of two single blades.
– However, the technique is not efficient for use over
short dozing distances because of the extra
maneuvering time required.
• Mechanically coupled side by-side (S × S) dozers
equipped with a single large blade are available
and are more productive than are blade-to-blade
dozers.
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4-3 LOADERS
• A tractor equipped with a front-end bucket is
called a loader, front-end loader, or bucket
loader.
• Both wheel loaders (Figure 4-9) and track
loaders (Figure 4-10) are available.
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FIGURE4-9: Articulated wheel loader with articulated hauler. (Courtesy of Volvo
Construction Equipment North America, Inc.)
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FIGURE4-10: Track loader.
(Courtesy of John Deere Construction & Forestry Company)
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• Loaders are used for:
– excavating soft to medium-hard material,
– loading hoppers and haul units,
– stockpiling material,
– backfilling ditches, and
– moving concrete and other construction materials.
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• Wheel loaders:
– possess excellent job mobility and are capable of
over-the road movement between jobs at speeds
of 25 mi/h or higher.
– While their ground pressure is relatively low and
may be varied by the use of different size tires and
by changing inflation pressures, they do not have
the all-terrain capability of track loaders.
– Most modern wheel loaders are articulated.
• That is, they are hinged between the front and rear axles
to provide greater maneuverability.
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• Track loaders :
– are capable of overcoming steeper grades and
side slopes than are wheel loaders.
– Their low ground pressure and high tractive effort
enable them to operate in all but the lowest
trafficability soils.
– Because of their lower speed, their production is
less than that of a wheel loader over longer haul
distances.
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Estimating Loader Production
• Loader production may be estimated as the
product of average bucket load multiplied by
cycles per hour (Equation 2-1).
• Basic cycle time for a loader, wheel or track
loader, (Table4-6) includes the time required
for loading, dumping, making four reversals of
direction, and traveling a minimum distance
(15 ft or less for track loaders).
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making four reversals of direction
TABLE 4-6: Basic loader cycle time
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FIGURE 4-15: Travel time, wheel loader (haul + return).
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Estimating Loader Production
• Federal Highway Administration (FHWA) studies
have shown little variation in basic cycle time for
wheel loaders up to a distance of 80 ft (25 m)
between loading and dumping position.
– Therefore, travel time should not be added until one-
way distance exceeds this distance.
• Loader bucket capacity is rated in heaped (loose)
volume, as shown in Table 3-1.
– Bucket capacity should be adjusted by a bucket fill
factor (Table 3-2) to obtain the best estimate of actual
bucket volume.
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EXAMPLE 4-7
• Estimate the hourly production in loose
volume (LCM) of :
– a 2.68-m3 wheel loader excavating sand and gravel
(average material) from a pit and moving it to a
stockpile.
– The average haul distance is 61 m,
– the effective grade is 6%,
– the bucket fill factor is 1.00, and
– job efficiency is 50 min/h.
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EXAMPLE 4-7
• Solution
Bucket volume = 2.68 × 1 =2.68 LCM
Basic cycle time = 0.50 min (Table 4-6)
Travel time =0.30 min (Figure 4-14)
Cycle time =0.50 + 0.30 =0.80 min
Production = 2.68 × 50/60 x 60/0.80 =168 LCM/h
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Job Management
• Cutting of tires is a major problem when
loading shot rock with a wheel loader.
• Type L-5 tires (rock, extra deep tread) should
be used to increase tire life when loading rock.
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Job Management
• In selection of a loader, consideration must also
be given to the following:
– (1) the weight of the material being handled may
limit the size of the bucket that may be used on a
loader.
• Because of tipping load limitations,
– (2) clearances required during loading and dumping.
– (3) optimum positioning of the loader and haul units
• to minimize loading, maneuver, and dump times.
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Job Management
• Multisegment buckets, also called 4-in-1 buckets
and multipurpose buckets (Figure 4-16), are
capable of performing as a clamshell, dozer, or
scraper, as well as a conventional loader.
– Such buckets are often more effective than are
conventional buckets in handling wet, sticky materials.
• Blasting or ripping hard materials before
attempting to load them will often increase
loader production in such materials.
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Figure 4-16:
Multisegment loader bucket.
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