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:

(8.44)

whereGgrade resistance, lb (N)
Rggrade-resistance factor 20 lb/ton (86.3 N/t) 1% lb/lb (N/N)
spercent 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:

(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 Pdepends on the weight Won the drivers:
(8.46)

wherefcoefficient of traction.

Earth Quantities Hauled

When soils are excavated, they increase in volume, or swell, because of an
increase in voids:

(8.47)

whereVboriginal volume, yd^3 (m^3 ), or bank yards
VLloaded volume, yd^3 (m^3 ), or loose yards
Lload factor

When soils are compacted, they decrease in volume:

(8.48)

whereVccompacted volume, yd^3 (m^3 ); and Sshrinkage factor.
Bank yards moved by a hauling unit equals weight of load, lb (kg), divided by
density of the material in place, lb (kg), per bank yard (m^3 ).

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.

Production, bank yd^3 /h (m^3 /h)load, yd^3 (m^3 )trips per hour

Trips per hour (8.49)

working time, min/h

cycle time, min

VcVbS

VbVLL

100

100 % swell

VL

PfW

T(RRgs)W(2%1.5%p1%s)W

GRgsW