Design and Analysis of Construction Operations

Problem 1 A contractor wants to investigate the production and cost differences of using a 7S blade on a D7H) dozer or an S blade on an 824 dozer. The material is a dry sand, and it is to be moved a distance of 250 ft from the beginning of the cut. The dozing is uphill on a 5% grade. The operator will have average skill, the dozers have power-shift transmissions, and traction is assumed to be satisfactory. The operating technique is slot dozing. The site will be dusty with some visibility loss. The material weighs 103 pcf in the bank state and has a swell percent of 15%. Job efficiency is assumed to be equivalent to a 50-min hour. Calculate the direct cost of the proposed earthmoving operation in dollars per bcy. Assume that the O&O cost for the D7 dozer is $116.00 per hour and $127.00 per hour for the 824. The operator’s wage is $45.00 per hour plus 35% for fringes, workman’s compensation, and other benefits.

Complete the following for each dozer. Round all numbers to the nearest TWO decimals unless otherwise specified. If a number starts with 0, for example 0.45, do not omit the 0, write it as 0.45.

To calculate field production rates, the curve values must be adjusted by
the expected job conditions. Table 7.2 lists the correction factors to use with
the Caterpillar dozer production curves. The formula for production calculation
is
[7.6]
DOZER PRODUCTION ESTIMATING FORMAT
Following is a format that can be used to analyze dozer production. The calculations
are based on using a Caterpillar D7G crawler dozer with a straight blade
for which the specification information is given in Table 7.2 and the performance
chart is shown in Figure 7.13. This will be a slot-dozing operation. The
material is a dry, noncohesive silty sand, and it is to be moved a distance of 300
ft from the beginning of the cut. Dozing is downhill on a 10% grade. The operator
will have average skill, the dozer will have a power-shift transmission, and
both visibility and traction should be satisfactory. The material weighs 108 pcf
Production 1lcy per hour2 
ideal production
from curve 
product of the
correction factors
190 Construction Planning, Equipment, and Methods
1,000
900
800
700
600
500
400
300
200
100
0
100 200 300 400 500 600
J
H
G
F
E
C
D
A B
B
AE
D
C
GH
F
J
lm3/hr lcy/hr
700
600
500
400
300
200
100
0
0 15 30 45 60 75 90 105 120 135 150 165 180
ft
m
Average dozing distance
Key:
A
B
C
D
E
F
G
H
J
— 824S
— 834S
— D7G-7S
— D7H-7S
— 814S
— D6H-6S
— D5H-5S
— D4H-4S
— D3CLGP-3SLGP
FIGURE 7.13 Dozing production estimating curves for straight blade Caterpillar D3,
D4, D5, D6, D7, 814, 824, and 834 dozers equipped with straight blades.
Reprinted courtesy of Caterpillar, Inc.
(lb per cf) in the bank state and is estimated to swell 12% when excavated
(bank to loose state). Job efficiency is assumed to be equivalent to a 50-min
hour. Calculate the direct cost of the proposed earthmoving operation in dollars
per bcy. Assume that the owning and operating (O&O) cost for the dozer is
$32.50 per hour and the operator’s wage is $14.85 per hour.
Step 1: Ideal Maximum Production
Determine the ideal maximum production from the appropriate curve based on
the particular dozer model and type of blade. Find the dozing distance on the
bottom horizontal scale of the proper figure. Draw a vertical line upward until
Chapter 7 Dozers 191
A
2,400
2,000
1,800
1,600
1,400
1,200
1,000
800
600
400
200
0
3,000
2,800
2,600
2,400
2,200
2,000
1,800
1,600
1,400
1,200
1,000
800
600
400
200
0
Key:
A—D11N-11U
B—D10N-10U
C—D9N-9U
D—D8N-8U
E—D7H-7U
F—D7G-7U
F E
C B
A
100 200 300 400 500 600
0 15 30 45 60 75 90 105 120 135 150 165 180 195
Average dozing distance
lm3/hr lcy/hr
ft
m
B
C
D
E
F
D
FIGURE 7.14 Dozing production estimating curves for Caterpillar D7 through D11
dozers equipped with universal blades
Reprinted courtesy of Caterpillar, Inc.
192
TABLE 7.2 Caterpillar job condition correction factors for estimating dozer production
Track-type tractor Wheel-type tractor
Operator
Excellent 1.00 1.00
Average 0.75 0.60
Poor 0.60 0.50
Material
Loose stockpile 1.20 1.20
Hard to cut; frozen
with tilt cylinder 0.80 0.75
without tilt cylinder 0.70 —
cable-controlled blade 0.60 —
Hard to drift; “dead” (dry, noncohesive 0.80 0.80
material) or very sticky material
Rock, ripped or blasted 0.60–0.80 —
Slot dozing 1.20 1.20
Side-by-side dozing 1.15–1.25 1.15–1.25
Visibility
Dust, rain, snow, fog, or darkness 0.80 0.70
Job efficiency
50 min/hr 0.83 0.83
40 min/hr 0.67 0.67
Direct-drive transmission
(0.1-min fixed time) 0.80 —
Bulldozer*
Adjust based on SAE capacity relative
to the base blade used in the estimated
dozing production graphs
Grades—see the graph
*Note: Angling blades and cushion blades are not considered production-dozing tools. Depending on job
conditions, the A blade and C blade will average 50–75% of straight-blade production.
Reprinted courtesy of Caterpillar, Inc.
% Grade vs. Dozing Factor
(–) Downhill
(+) Uphill
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
–30 –20 –10 0 +10 +20 +30