CIVIL ENGINEERING FORMULAS

196 CHAPTER EIGHT

Compaction production can be computed from

(8.41)

whereWwidth of roller, ft (m)
Sroller speed, mi / h (km / h)
Llift thickness, in (mm)
Fratio of pay yd^3 (m^3 ) to loose yd^3 (m^3 )
Eefficiency factor (allows for time losses, such as those due to turns):
0.90, excellent; 0.80, average; 0.75, poor
Pnumber of passes

FORMULAS FOR EARTHMOVING

External forces offer rolling resistanceto 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:

(8.42)

where Rrolling resistance, lb (N)
Rfrolling-resistance factor, lb/ton (N/tonne)
Wweight on wheels, ton (tonne)
Rptire-penetration factor, lb/tonin (N/tonnemm) penetration
ptire penetration, in (mm)

Rfusually is taken as 40 lb/ton (or 2 percent lb/lb) (173 N/t) and Rpas 30 lb/
tonin (1.5% lb/lbin) (3288 N/tmm). Hence, Eq. (8.42) can be written as

(8.43)

whereWweight on wheels, lb (N); and R 2%1.5%p.

R(2%1.5%p)WRW

RRfWRppW

yd^3 /h (m^3 /h)

16 WSLFE

P

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)