Page 263 - Civil Engineering Formulas

SOIL AND EARTHWORK FORMULAS 197

Additional power is required to overcome rolling resistance on a slope.
Grade resistance also is proportional to weight:
G R g sW (8.44)
where G grade resistance, lb (N)
R grade-resistance factor 20 lb/ton (86.3 N/t) 1% lb/lb (N/N)
g
s percent grade, positive for uphill motion, negative for downhill
Thus, the total road resistance is the algebraic sum of the rolling and grade resis-
tances, or the total pull, lb (N), required:
T (R R g s)W (2% 1.5%p 1%s)W (8.45)
In addition, an allowance may have to be made for loss of power with altitude.
If so, allow 3 percent pull loss for each 1000 ft (305 m) above 2500 ft (762 m).
Usable pull P depends on the weight W on the drivers:
P fW (8.46)
where f coefficient of traction.

Earth Quantities Hauled
When soils are excavated, they increase in volume, or swell, because of an
increase in voids:
100
V b V L L V L (8.47)
100 % swell
3
3
where V original volume, yd (m ), or bank yards
b
3
3
V loaded volume, yd (m ), or loose yards
L
L load factor
When soils are compacted, they decrease in volume:
V c V b S (8.48)
3
3
where V compacted volume, yd (m ); and S shrinkage factor.
c
Bank yards moved by a hauling unit equals weight of load, lb (kg), divided by
3
density of the material in place, lb (kg), per bank yard (m ).
SCRAPER PRODUCTION
Production is measured in terms of tons or bank cubic yards (cubic meters) of
material a machine excavates and discharges, under given job conditions, in 1 h.
3
3
3
3
Production, bank yd /h (m /h) load, yd (m ) trips per hour
working time, min/h
Trips per hour (8.49)
cycle time, min