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196 CHAPTER EIGHT
TABLE 8.3 Average Speeds of Rollers
Type mi/h (km/h)
Grid rollers 12 (19.3)
Sheepsfoot rollers 3 (4.8)
Tamping rollers 10 (16.1)
Pneumatic rollers 8 (12.8)
Compaction production can be computed from
16WSLFE
3
3
yd /h (m /h) (8.41)
P
where W width of roller, ft (m)
S roller speed, mi/h (km/h)
L lift thickness, in (mm)
3
3
3
3
F ratio of pay yd (m ) to loose yd (m )
E efficiency factor (allows for time losses, such as those due to turns):
0.90, excellent; 0.80, average; 0.75, poor
P number of passes
FORMULAS FOR EARTHMOVING
External forces offer rolling resistance to the motion of wheeled vehicles, such
as tractors and scrapers. The engine has to supply power to overcome this resis-
tance; the greater the resistance is, the more power needed to move a load.
Rolling resistance depends on the weight on the wheels and the tire penetration
into the ground:
R R f W R p pW (8.42)
where R rolling resistance, lb (N)
R rolling-resistance factor, lb/ton (N/tonne)
f
W weight on wheels, ton (tonne)
R tire-penetration factor, lb/ton in (N/tonne mm) penetration
p
p tire penetration, in (mm)
R usually is taken as 40 lb/ton (or 2 percent lb/lb) (173 N/t) and R as 30 lb/
f
p
ton in (1.5% lb/lb in) (3288 N/t mm). Hence, Eq. (8.42) can be written as
R (2% 1.5%p) W R W (8.43)
where W weight on wheels, lb (N); and R 2% 1.5%p.